Rollup merge of #132388 - frank-king:feature/where-cfg, r=petrochenkov

Implement `#[cfg]` in `where` clauses This PR implements #115590, which supports `#[cfg]` attributes in `where` clauses. The biggest change is, that it adds `AttrsVec` and `NodeId` to the `ast::WherePredicate` and `HirId` to the `hir::WherePredicate`.
2025-03-03 10:40:56 +01:00 · 2025-03-03 10:40:56 +01:00 · 2344a34241
commit 2344a34241
parent 81d8edc200 42f51d4fd4
38 changed files with 3296 additions and 88 deletions
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@ -417,9 +417,11 @@ impl WhereClause {
 /// A single predicate in a where-clause.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WherePredicate {
+    pub attrs: AttrVec,
    pub kind: WherePredicateKind,
    pub id: NodeId,
    pub span: Span,
+    pub is_placeholder: bool,
 }

 /// Predicate kind in where-clause.
--- a/compiler/rustc_ast/src/ast_traits.rs
+++ b/compiler/rustc_ast/src/ast_traits.rs
@ -11,7 +11,7 @@ use crate::tokenstream::LazyAttrTokenStream;
 use crate::{
    Arm, AssocItem, AttrItem, AttrKind, AttrVec, Attribute, Block, Crate, Expr, ExprField,
    FieldDef, ForeignItem, GenericParam, Item, NodeId, Param, Pat, PatField, Path, Stmt, StmtKind,
-    Ty, Variant, Visibility,
+    Ty, Variant, Visibility, WherePredicate,
 };

 /// A utility trait to reduce boilerplate.
@ -79,6 +79,7 @@ impl_has_node_id!(
    Stmt,
    Ty,
    Variant,
+    WherePredicate,
 );

 impl<T: AstDeref<Target: HasNodeId>> HasNodeId for T {
@ -127,7 +128,16 @@ macro_rules! impl_has_tokens_none {
 }

 impl_has_tokens!(AssocItem, AttrItem, Block, Expr, ForeignItem, Item, Pat, Path, Ty, Visibility);
-impl_has_tokens_none!(Arm, ExprField, FieldDef, GenericParam, Param, PatField, Variant);
+impl_has_tokens_none!(
+    Arm,
+    ExprField,
+    FieldDef,
+    GenericParam,
+    Param,
+    PatField,
+    Variant,
+    WherePredicate
+);

 impl<T: AstDeref<Target: HasTokens>> HasTokens for T {
    fn tokens(&self) -> Option<&LazyAttrTokenStream> {
@ -279,6 +289,7 @@ impl_has_attrs!(
    Param,
    PatField,
    Variant,
+    WherePredicate,
 );
 impl_has_attrs_none!(Attribute, AttrItem, Block, Pat, Path, Ty, Visibility);

--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@ -338,8 +338,11 @@ pub trait MutVisitor: Sized {
        walk_where_clause(self, where_clause);
    }

-    fn visit_where_predicate(&mut self, where_predicate: &mut WherePredicate) {
-        walk_where_predicate(self, where_predicate)
+    fn flat_map_where_predicate(
+        &mut self,
+        where_predicate: WherePredicate,
+    ) -> SmallVec<[WherePredicate; 1]> {
+        walk_flat_map_where_predicate(self, where_predicate)
    }

    fn visit_where_predicate_kind(&mut self, kind: &mut WherePredicateKind) {
@ -1097,15 +1100,20 @@ fn walk_ty_alias_where_clauses<T: MutVisitor>(vis: &mut T, tawcs: &mut TyAliasWh

 fn walk_where_clause<T: MutVisitor>(vis: &mut T, wc: &mut WhereClause) {
    let WhereClause { has_where_token: _, predicates, span } = wc;
-    visit_thin_vec(predicates, |predicate| vis.visit_where_predicate(predicate));
+    predicates.flat_map_in_place(|predicate| vis.flat_map_where_predicate(predicate));
    vis.visit_span(span);
 }

-pub fn walk_where_predicate<T: MutVisitor>(vis: &mut T, pred: &mut WherePredicate) {
-    let WherePredicate { kind, id, span } = pred;
+pub fn walk_flat_map_where_predicate<T: MutVisitor>(
+    vis: &mut T,
+    mut pred: WherePredicate,
+) -> SmallVec<[WherePredicate; 1]> {
+    let WherePredicate { attrs, kind, id, span, is_placeholder: _ } = &mut pred;
    vis.visit_id(id);
+    visit_attrs(vis, attrs);
    vis.visit_where_predicate_kind(kind);
    vis.visit_span(span);
+    smallvec![pred]
 }

 pub fn walk_where_predicate_kind<T: MutVisitor>(vis: &mut T, kind: &mut WherePredicateKind) {
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@ -833,7 +833,8 @@ pub fn walk_where_predicate<'a, V: Visitor<'a>>(
    visitor: &mut V,
    predicate: &'a WherePredicate,
 ) -> V::Result {
-    let WherePredicate { kind, id: _, span: _ } = predicate;
+    let WherePredicate { attrs, kind, id: _, span: _, is_placeholder: _ } = predicate;
+    walk_list!(visitor, visit_attribute, attrs);
    visitor.visit_where_predicate_kind(kind)
 }

--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@ -1728,6 +1728,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
    fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate<'hir> {
        let hir_id = self.lower_node_id(pred.id);
        let span = self.lower_span(pred.span);
+        self.lower_attrs(hir_id, &pred.attrs, span);
        let kind = self.arena.alloc(match &pred.kind {
            WherePredicateKind::BoundPredicate(WhereBoundPredicate {
                bound_generic_params,
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@ -503,6 +503,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
    gate_all!(unsafe_binders, "unsafe binder types are experimental");
    gate_all!(contracts, "contracts are incomplete");
    gate_all!(contracts_internals, "contract internal machinery is for internal use only");
+    gate_all!(where_clause_attrs, "attributes in `where` clause are unstable");

    if !visitor.features.never_patterns() {
        if let Some(spans) = spans.get(&sym::never_patterns) {
--- a/compiler/rustc_ast_pretty/src/pprust/state/item.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
@ -735,7 +735,8 @@ impl<'a> State<'a> {
    }

    pub fn print_where_predicate(&mut self, predicate: &ast::WherePredicate) {
-        let ast::WherePredicate { kind, id: _, span: _ } = predicate;
+        let ast::WherePredicate { attrs, kind, id: _, span: _, is_placeholder: _ } = predicate;
+        self.print_outer_attributes(attrs);
        match kind {
            ast::WherePredicateKind::BoundPredicate(where_bound_predicate) => {
                self.print_where_bound_predicate(where_bound_predicate);
--- a/compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs
@ -300,13 +300,16 @@ pub(crate) fn expand_deriving_coerce_pointee(
                to_ty: &s_ty,
                rewritten: false,
            };
-            let mut predicate = ast::WherePredicate {
-                kind: ast::WherePredicateKind::BoundPredicate(bound.clone()),
+            let mut kind = ast::WherePredicateKind::BoundPredicate(bound.clone());
+            substitution.visit_where_predicate_kind(&mut kind);
+            if substitution.rewritten {
+                let predicate = ast::WherePredicate {
+                    attrs: predicate.attrs.clone(),
+                    kind,
                    span: predicate.span,
                    id: ast::DUMMY_NODE_ID,
+                    is_placeholder: false,
                };
-            substitution.visit_where_predicate(&mut predicate);
-            if substitution.rewritten {
                impl_generics.where_clause.predicates.push(predicate);
            }
        }
@ -388,8 +391,8 @@ impl<'a> ast::mut_visit::MutVisitor for TypeSubstitution<'a> {
        }
    }

-    fn visit_where_predicate(&mut self, where_predicate: &mut ast::WherePredicate) {
-        match &mut where_predicate.kind {
+    fn visit_where_predicate_kind(&mut self, kind: &mut ast::WherePredicateKind) {
+        match kind {
            rustc_ast::WherePredicateKind::BoundPredicate(bound) => {
                bound
                    .bound_generic_params
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@ -687,9 +687,11 @@ impl<'a> TraitDef<'a> {
        // and similarly for where clauses
        where_clause.predicates.extend(generics.where_clause.predicates.iter().map(|clause| {
            ast::WherePredicate {
+                attrs: clause.attrs.clone(),
                kind: clause.kind.clone(),
                id: ast::DUMMY_NODE_ID,
                span: clause.span.with_ctxt(ctxt),
+                is_placeholder: false,
            }
        }));

@ -744,8 +746,13 @@ impl<'a> TraitDef<'a> {
                        };

                        let kind = ast::WherePredicateKind::BoundPredicate(predicate);
-                        let predicate =
-                            ast::WherePredicate { kind, id: ast::DUMMY_NODE_ID, span: self.span };
+                        let predicate = ast::WherePredicate {
+                            attrs: ThinVec::new(),
+                            kind,
+                            id: ast::DUMMY_NODE_ID,
+                            span: self.span,
+                            is_placeholder: false,
+                        };
                        where_clause.predicates.push(predicate);
                    }
                }
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@ -53,6 +53,7 @@ pub enum Annotatable {
    Param(ast::Param),
    FieldDef(ast::FieldDef),
    Variant(ast::Variant),
+    WherePredicate(ast::WherePredicate),
    Crate(ast::Crate),
 }

@ -71,6 +72,7 @@ impl Annotatable {
            Annotatable::Param(p) => p.span,
            Annotatable::FieldDef(sf) => sf.span,
            Annotatable::Variant(v) => v.span,
+            Annotatable::WherePredicate(wp) => wp.span,
            Annotatable::Crate(c) => c.spans.inner_span,
        }
    }
@ -89,6 +91,7 @@ impl Annotatable {
            Annotatable::Param(p) => p.visit_attrs(f),
            Annotatable::FieldDef(sf) => sf.visit_attrs(f),
            Annotatable::Variant(v) => v.visit_attrs(f),
+            Annotatable::WherePredicate(wp) => wp.visit_attrs(f),
            Annotatable::Crate(c) => c.visit_attrs(f),
        }
    }
@ -107,6 +110,7 @@ impl Annotatable {
            Annotatable::Param(p) => visitor.visit_param(p),
            Annotatable::FieldDef(sf) => visitor.visit_field_def(sf),
            Annotatable::Variant(v) => visitor.visit_variant(v),
+            Annotatable::WherePredicate(wp) => visitor.visit_where_predicate(wp),
            Annotatable::Crate(c) => visitor.visit_crate(c),
        }
    }
@ -128,6 +132,7 @@ impl Annotatable {
            | Annotatable::Param(..)
            | Annotatable::FieldDef(..)
            | Annotatable::Variant(..)
+            | Annotatable::WherePredicate(..)
            | Annotatable::Crate(..) => panic!("unexpected annotatable"),
        }
    }
@ -223,6 +228,13 @@ impl Annotatable {
        }
    }

+    pub fn expect_where_predicate(self) -> ast::WherePredicate {
+        match self {
+            Annotatable::WherePredicate(wp) => wp,
+            _ => panic!("expected where predicate"),
+        }
+    }
+
    pub fn expect_crate(self) -> ast::Crate {
        match self {
            Annotatable::Crate(krate) => krate,
@ -446,6 +458,10 @@ pub trait MacResult {
        None
    }

+    fn make_where_predicates(self: Box<Self>) -> Option<SmallVec<[ast::WherePredicate; 1]>> {
+        None
+    }
+
    fn make_crate(self: Box<Self>) -> Option<ast::Crate> {
        // Fn-like macros cannot produce a crate.
        unreachable!()
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@ -227,6 +227,12 @@ ast_fragments! {
    Variants(SmallVec<[ast::Variant; 1]>) {
        "variant"; many fn flat_map_variant; fn visit_variant(); fn make_variants;
    }
+    WherePredicates(SmallVec<[ast::WherePredicate; 1]>) {
+        "where predicate";
+        many fn flat_map_where_predicate;
+        fn visit_where_predicate();
+        fn make_where_predicates;
+     }
    Crate(ast::Crate) { "crate"; one fn visit_crate; fn visit_crate; fn make_crate; }
 }

@ -259,7 +265,8 @@ impl AstFragmentKind {
            | AstFragmentKind::GenericParams
            | AstFragmentKind::Params
            | AstFragmentKind::FieldDefs
-            | AstFragmentKind::Variants => SupportsMacroExpansion::No,
+            | AstFragmentKind::Variants
+            | AstFragmentKind::WherePredicates => SupportsMacroExpansion::No,
        }
    }

@ -290,6 +297,9 @@ impl AstFragmentKind {
            AstFragmentKind::Variants => {
                AstFragment::Variants(items.map(Annotatable::expect_variant).collect())
            }
+            AstFragmentKind::WherePredicates => AstFragment::WherePredicates(
+                items.map(Annotatable::expect_where_predicate).collect(),
+            ),
            AstFragmentKind::Items => {
                AstFragment::Items(items.map(Annotatable::expect_item).collect())
            }
@ -865,7 +875,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
            | Annotatable::GenericParam(..)
            | Annotatable::Param(..)
            | Annotatable::FieldDef(..)
-            | Annotatable::Variant(..) => panic!("unexpected annotatable"),
+            | Annotatable::Variant(..)
+            | Annotatable::WherePredicate(..) => panic!("unexpected annotatable"),
        };
        if self.cx.ecfg.features.proc_macro_hygiene() {
            return;
@ -1002,7 +1013,8 @@ pub fn parse_ast_fragment<'a>(
        | AstFragmentKind::GenericParams
        | AstFragmentKind::Params
        | AstFragmentKind::FieldDefs
-        | AstFragmentKind::Variants => panic!("unexpected AST fragment kind"),
+        | AstFragmentKind::Variants
+        | AstFragmentKind::WherePredicates => panic!("unexpected AST fragment kind"),
    })
 }

@ -1414,6 +1426,19 @@ impl InvocationCollectorNode for ast::Variant {
    }
 }

+impl InvocationCollectorNode for ast::WherePredicate {
+    const KIND: AstFragmentKind = AstFragmentKind::WherePredicates;
+    fn to_annotatable(self) -> Annotatable {
+        Annotatable::WherePredicate(self)
+    }
+    fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
+        fragment.make_where_predicates()
+    }
+    fn walk_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
+        walk_flat_map_where_predicate(visitor, self)
+    }
+}
+
 impl InvocationCollectorNode for ast::FieldDef {
    const KIND: AstFragmentKind = AstFragmentKind::FieldDefs;
    fn to_annotatable(self) -> Annotatable {
@ -2116,6 +2141,13 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
        self.flat_map_node(node)
    }

+    fn flat_map_where_predicate(
+        &mut self,
+        node: ast::WherePredicate,
+    ) -> SmallVec<[ast::WherePredicate; 1]> {
+        self.flat_map_node(node)
+    }
+
    fn flat_map_field_def(&mut self, node: ast::FieldDef) -> SmallVec<[ast::FieldDef; 1]> {
        self.flat_map_node(node)
    }
--- a/compiler/rustc_expand/src/placeholders.rs
+++ b/compiler/rustc_expand/src/placeholders.rs
@ -188,6 +188,19 @@ pub(crate) fn placeholder(
            vis,
            is_placeholder: true,
        }]),
+        AstFragmentKind::WherePredicates => {
+            AstFragment::WherePredicates(smallvec![ast::WherePredicate {
+                attrs: Default::default(),
+                id,
+                span,
+                kind: ast::WherePredicateKind::BoundPredicate(ast::WhereBoundPredicate {
+                    bound_generic_params: Default::default(),
+                    bounded_ty: ty(),
+                    bounds: Default::default(),
+                }),
+                is_placeholder: true,
+            }])
+        }
    }
 }

@ -267,6 +280,17 @@ impl MutVisitor for PlaceholderExpander {
        }
    }

+    fn flat_map_where_predicate(
+        &mut self,
+        predicate: ast::WherePredicate,
+    ) -> SmallVec<[ast::WherePredicate; 1]> {
+        if predicate.is_placeholder {
+            self.remove(predicate.id).make_where_predicates()
+        } else {
+            walk_flat_map_where_predicate(self, predicate)
+        }
+    }
+
    fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
        match item.kind {
            ast::ItemKind::MacCall(_) => self.remove(item.id).make_items(),
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@ -661,6 +661,8 @@ declare_features! (
    (unstable, unsized_tuple_coercion, "1.20.0", Some(42877)),
    /// Allows using the `#[used(linker)]` (or `#[used(compiler)]`) attribute.
    (unstable, used_with_arg, "1.60.0", Some(93798)),
+    /// Allows use of attributes in `where` clauses.
+    (unstable, where_clause_attrs, "CURRENT_RUSTC_VERSION", Some(115590)),
    /// Allows use of x86 `AMX` target-feature attributes and intrinsics
    (unstable, x86_amx_intrinsics, "1.81.0", Some(126622)),
    /// Allows use of the `xop` target-feature
--- a/compiler/rustc_hir/src/target.rs
+++ b/compiler/rustc_hir/src/target.rs
@ -56,6 +56,7 @@ pub enum Target {
    Param,
    PatField,
    ExprField,
+    WherePredicate,
 }

 impl Display for Target {
@ -96,7 +97,8 @@ impl Target {
            | Target::MacroDef
            | Target::Param
            | Target::PatField
-            | Target::ExprField => false,
+            | Target::ExprField
+            | Target::WherePredicate => false,
        }
    }

@ -217,6 +219,7 @@ impl Target {
            Target::Param => "function param",
            Target::PatField => "pattern field",
            Target::ExprField => "struct field",
+            Target::WherePredicate => "where predicate",
        }
    }
 }
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@ -2386,6 +2386,7 @@ impl<'a> State<'a> {
    }

    fn print_where_predicate(&mut self, predicate: &hir::WherePredicate<'_>) {
+        self.print_attrs_as_outer(self.attrs(predicate.hir_id));
        match *predicate.kind {
            hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate {
                bound_generic_params,
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@ -367,34 +367,47 @@ impl<'a> Parser<'a> {

        loop {
            let where_sp = where_lo.to(self.prev_token.span);
+            let attrs = self.parse_outer_attributes()?;
            let pred_lo = self.token.span;
-            let kind = if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
-                let lifetime = self.expect_lifetime();
+            let predicate = self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
+                for attr in &attrs {
+                    self.psess.gated_spans.gate(sym::where_clause_attrs, attr.span);
+                }
+                let kind = if this.check_lifetime() && this.look_ahead(1, |t| !t.is_like_plus()) {
+                    let lifetime = this.expect_lifetime();
                    // Bounds starting with a colon are mandatory, but possibly empty.
-                self.expect(exp!(Colon))?;
-                let bounds = self.parse_lt_param_bounds();
-                ast::WherePredicateKind::RegionPredicate(ast::WhereRegionPredicate {
+                    this.expect(exp!(Colon))?;
+                    let bounds = this.parse_lt_param_bounds();
+                    Some(ast::WherePredicateKind::RegionPredicate(ast::WhereRegionPredicate {
                        lifetime,
                        bounds,
-                })
-            } else if self.check_type() {
-                match self.parse_ty_where_predicate_kind_or_recover_tuple_struct_body(
+                    }))
+                } else if this.check_type() {
+                    match this.parse_ty_where_predicate_kind_or_recover_tuple_struct_body(
                        struct_, pred_lo, where_sp,
                    )? {
-                    PredicateKindOrStructBody::PredicateKind(kind) => kind,
+                        PredicateKindOrStructBody::PredicateKind(kind) => Some(kind),
                        PredicateKindOrStructBody::StructBody(body) => {
                            tuple_struct_body = Some(body);
-                        break;
+                            None
                        }
                    }
                } else {
-                break;
+                    None
                };
-            where_clause.predicates.push(ast::WherePredicate {
+                let predicate = kind.map(|kind| ast::WherePredicate {
+                    attrs,
                    kind,
                    id: DUMMY_NODE_ID,
-                span: pred_lo.to(self.prev_token.span),
+                    span: pred_lo.to(this.prev_token.span),
+                    is_placeholder: false,
                });
+                Ok((predicate, Trailing::No, UsePreAttrPos::No))
+            })?;
+            match predicate {
+                Some(predicate) => where_clause.predicates.push(predicate),
+                None => break,
+            }

            let prev_token = self.prev_token.span;
            let ate_comma = self.eat(exp!(Comma));
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@ -779,6 +779,10 @@ passes_unstable_attr_for_already_stable_feature =
    .item = the stability attribute annotates this item
    .help = consider removing the attribute

+passes_unsupported_attributes_in_where =
+    most attributes are not supported in `where` clauses
+    .help = only `#[cfg]` and `#[cfg_attr]` are supported
+
 passes_unused =
    unused attribute
    .suggestion = remove this attribute
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@ -919,7 +919,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
            | Target::Arm
            | Target::ForeignMod
            | Target::Closure
-            | Target::Impl => Some(target.name()),
+            | Target::Impl
+            | Target::WherePredicate => Some(target.name()),
            Target::ExternCrate
            | Target::Use
            | Target::Static
@ -2614,6 +2615,32 @@ impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
        intravisit::walk_item(self, item)
    }

+    fn visit_where_predicate(&mut self, where_predicate: &'tcx hir::WherePredicate<'tcx>) {
+        // FIXME(where_clause_attrs): Currently, as the following check shows,
+        // only `#[cfg]` and `#[cfg_attr]` are allowed, but it should be removed
+        // if we allow more attributes (e.g., tool attributes and `allow/deny/warn`)
+        // in where clauses. After that, only `self.check_attributes` should be enough.
+        const ATTRS_ALLOWED: &[Symbol] = &[sym::cfg, sym::cfg_attr];
+        let spans = self
+            .tcx
+            .hir()
+            .attrs(where_predicate.hir_id)
+            .iter()
+            .filter(|attr| !ATTRS_ALLOWED.iter().any(|&sym| attr.has_name(sym)))
+            .map(|attr| attr.span())
+            .collect::<Vec<_>>();
+        if !spans.is_empty() {
+            self.tcx.dcx().emit_err(errors::UnsupportedAttributesInWhere { span: spans.into() });
+        }
+        self.check_attributes(
+            where_predicate.hir_id,
+            where_predicate.span,
+            Target::WherePredicate,
+            None,
+        );
+        intravisit::walk_where_predicate(self, where_predicate)
+    }
+
    fn visit_generic_param(&mut self, generic_param: &'tcx hir::GenericParam<'tcx>) {
        let target = Target::from_generic_param(generic_param);
        self.check_attributes(generic_param.hir_id, generic_param.span, target, None);
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@ -1909,3 +1909,11 @@ pub(crate) struct RustcConstStableIndirectPairing {
    #[primary_span]
    pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(passes_unsupported_attributes_in_where)]
+#[help]
+pub(crate) struct UnsupportedAttributesInWhere {
+    #[primary_span]
+    pub span: MultiSpan,
+}
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@ -1529,6 +1529,14 @@ impl<'a, 'ra, 'tcx> Visitor<'a> for BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
        visit::walk_variant(self, variant);
    }

+    fn visit_where_predicate(&mut self, p: &'a ast::WherePredicate) {
+        if p.is_placeholder {
+            self.visit_invoc(p.id);
+        } else {
+            visit::walk_where_predicate(self, p);
+        }
+    }
+
    fn visit_crate(&mut self, krate: &'a ast::Crate) {
        if krate.is_placeholder {
            self.visit_invoc_in_module(krate.id);
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@ -285,6 +285,14 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
        });
    }

+    fn visit_where_predicate(&mut self, pred: &'a WherePredicate) {
+        if pred.is_placeholder {
+            self.visit_macro_invoc(pred.id)
+        } else {
+            visit::walk_where_predicate(self, pred)
+        }
+    }
+
    fn visit_variant_data(&mut self, data: &'a VariantData) {
        // The assumption here is that non-`cfg` macro expansion cannot change field indices.
        // It currently holds because only inert attributes are accepted on fields,
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@ -2234,6 +2234,7 @@ symbols! {
        wasm_abi,
        wasm_import_module,
        wasm_target_feature,
+        where_clause_attrs,
        while_let,
        windows,
        windows_subsystem,
--- a/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
+++ b/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
@ -682,7 +682,8 @@ pub fn eq_generics(l: &Generics, r: &Generics) -> bool {

 pub fn eq_where_predicate(l: &WherePredicate, r: &WherePredicate) -> bool {
    use WherePredicateKind::*;
-    match (&l.kind, &r.kind) {
+    over(&l.attrs, &r.attrs, eq_attr) 
+        && match (&l.kind, &r.kind) {
            (BoundPredicate(l), BoundPredicate(r)) => {
                over(&l.bound_generic_params, &r.bound_generic_params, |l, r| {
                    eq_generic_param(l, r)
--- a/src/tools/rustfmt/src/spanned.rs
+++ b/src/tools/rustfmt/src/spanned.rs
@ -58,6 +58,7 @@ implement_spanned!(ast::ExprField);
 implement_spanned!(ast::ForeignItem);
 implement_spanned!(ast::Item);
 implement_spanned!(ast::Local);
+implement_spanned!(ast::WherePredicate);

 impl Spanned for ast::Stmt {
    fn span(&self) -> Span {
@ -149,12 +150,6 @@ impl Spanned for ast::FieldDef {
    }
 }

-impl Spanned for ast::WherePredicate {
-    fn span(&self) -> Span {
-        self.span
-    }
-}
-
 impl Spanned for ast::FnRetTy {
    fn span(&self) -> Span {
        match *self {
--- a/src/tools/rustfmt/src/types.rs
+++ b/src/tools/rustfmt/src/types.rs
@ -463,8 +463,9 @@ impl Rewrite for ast::WherePredicate {
    }

    fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
+        let attrs_str = self.attrs.rewrite_result(context, shape)?;
        // FIXME: dead spans?
-        let result = match self.kind {
+        let pred_str = &match self.kind {
            ast::WherePredicateKind::BoundPredicate(ast::WhereBoundPredicate {
                ref bound_generic_params,
                ref bounded_ty,
@ -499,6 +500,38 @@ impl Rewrite for ast::WherePredicate {
            }
        };

+        let mut result = String::with_capacity(attrs_str.len() + pred_str.len() + 1);
+        result.push_str(&attrs_str);
+        let pred_start = self.span.lo();
+        let line_len = last_line_width(&attrs_str) + 1 + first_line_width(&pred_str);
+        if let Some(last_attr) = self.attrs.last().filter(|last_attr| {
+            contains_comment(context.snippet(mk_sp(last_attr.span.hi(), pred_start)))
+        }) {
+            result = combine_strs_with_missing_comments(
+                context,
+                &result,
+                &pred_str,
+                mk_sp(last_attr.span.hi(), pred_start),
+                Shape {
+                    width: shape.width.min(context.config.inline_attribute_width()),
+                    ..shape
+                },
+                !last_attr.is_doc_comment(),
+            )?;
+        } else {
+            if !self.attrs.is_empty() {
+                if context.config.inline_attribute_width() < line_len
+                    || self.attrs.len() > 1
+                    || self.attrs.last().is_some_and(|a| a.is_doc_comment())
+                {
+                    result.push_str(&shape.indent.to_string_with_newline(context.config));
+                } else {
+                    result.push(' ');
+                }
+            }
+            result.push_str(&pred_str);
+        }
+
        Ok(result)
    }
 }
--- a/src/tools/rustfmt/tests/target/cfg_attribute_in_where.rs
+++ b/src/tools/rustfmt/tests/target/cfg_attribute_in_where.rs
@ -0,0 +1,116 @@
+// rustfmt-inline_attribute_width: 40
+
+#![crate_type = "lib"]
+#![feature(cfg_attribute_in_where)]
+use std::marker::PhantomData;
+
+#[cfg(a)]
+trait TraitA {}
+
+#[cfg(b)]
+trait TraitB {}
+
+trait A<T>
+where
+    #[cfg = a_very_long_attribute_name]
+    T: TraitA,
+    #[cfg = another_very_long_attribute_name]
+    T: TraitB,
+{
+    type B<U>
+    where
+        #[cfg = a]
+        // line comment after the attribute
+        U: TraitA,
+        #[cfg = b]
+        /* block comment after the attribute */
+        U: TraitB,
+        #[cfg = a] // short
+        U: TraitA,
+        #[cfg = b] /* short */ U: TraitB;
+
+    fn foo<U>(&self)
+    where
+        /// line doc comment before the attribute
+        U: TraitA,
+        /** line doc block comment before the attribute */
+        U: TraitB;
+}
+
+impl<T> A<T> for T
+where
+    #[doc = "line doc before the attribute"]
+    T: TraitA,
+    /** short doc */
+    T: TraitB,
+{
+    type B<U>
+        = ()
+    where
+        #[doc = "short"] U: TraitA,
+        #[doc = "short"]
+        #[cfg = a]
+        U: TraitB;
+
+    fn foo<U>(&self)
+    where
+        #[cfg = a]
+        #[cfg = b]
+        U: TraitA,
+        /// line doc
+        #[cfg = c]
+        U: TraitB,
+    {
+    }
+}
+
+struct C<T>
+where
+    #[cfg = a] T: TraitA,
+    #[cfg = b] T: TraitB,
+{
+    _t: PhantomData<T>,
+}
+
+union D<T>
+where
+    #[cfg = a] T: TraitA,
+    #[cfg = b] T: TraitB,
+{
+    _t: PhantomData<T>,
+}
+
+enum E<T>
+where
+    #[cfg = a] T: TraitA,
+    #[cfg = b] T: TraitB,
+{
+    E(PhantomData<T>),
+}
+
+#[allow(type_alias_bounds)]
+type F<T>
+where
+    #[cfg = a] T: TraitA,
+    #[cfg = b] T: TraitB,
+= T;
+
+impl<T> C<T>
+where
+    #[cfg = a] T: TraitA,
+    #[cfg = b] T: TraitB,
+{
+    fn new<U>()
+    where
+        #[cfg = a] U: TraitA,
+        #[cfg = b] U: TraitB,
+    {
+    }
+}
+
+fn foo<T>()
+where
+    #[cfg = a] T: TraitA,
+    #[cfg = b] T: TraitB,
+{
+}
--- a/tests/ui/feature-gates/feature-gate-where_clause_attrs.a.stderr
+++ b/tests/ui/feature-gates/feature-gate-where_clause_attrs.a.stderr
@ -0,0 +1,883 @@
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:33:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:34:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:35:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:36:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:37:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:38:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:39:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:40:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:44:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:45:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:46:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:47:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:48:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:49:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:50:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:51:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:55:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:56:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:57:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:58:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:59:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:60:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:61:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:62:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:67:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:68:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:69:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:70:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:71:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:72:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:73:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:74:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:77:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:78:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:79:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:80:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:81:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:82:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:83:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:84:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:88:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:89:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:90:9
+   |
+LL |         #[cfg(all())] T: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:91:9
+   |
+LL |         #[cfg(any())] T: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:92:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:93:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:94:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:95:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:101:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:102:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:103:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:104:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:105:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:106:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:107:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:108:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:115:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:116:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:117:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:118:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:119:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:120:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:121:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:122:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:130:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:131:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:132:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:133:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:134:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:135:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:136:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:137:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:143:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:144:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:145:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:146:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:147:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:148:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:149:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:150:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:153:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:154:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:155:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:156:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:157:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:158:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:159:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:160:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 88 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
--- a/tests/ui/feature-gates/feature-gate-where_clause_attrs.b.stderr
+++ b/tests/ui/feature-gates/feature-gate-where_clause_attrs.b.stderr
@ -0,0 +1,883 @@
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:33:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:34:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:35:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:36:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:37:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:38:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:39:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:40:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:44:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:45:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:46:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:47:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:48:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:49:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:50:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:51:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:55:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:56:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:57:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:58:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:59:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:60:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:61:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:62:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:67:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:68:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:69:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:70:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:71:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:72:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:73:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:74:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:77:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:78:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:79:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:80:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:81:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:82:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:83:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:84:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:88:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:89:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:90:9
+   |
+LL |         #[cfg(all())] T: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:91:9
+   |
+LL |         #[cfg(any())] T: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:92:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:93:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:94:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:95:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:101:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:102:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:103:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:104:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:105:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:106:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:107:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:108:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:115:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:116:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:117:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:118:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:119:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:120:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:121:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:122:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:130:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:131:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:132:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:133:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:134:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:135:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:136:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:137:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:143:5
+   |
+LL |     #[cfg(a)] T: TraitA,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:144:5
+   |
+LL |     #[cfg(b)] T: TraitB,
+   |     ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:145:5
+   |
+LL |     #[cfg(all())] T: TraitAll,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:146:5
+   |
+LL |     #[cfg(any())] T: TraitAny,
+   |     ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:147:5
+   |
+LL |     #[cfg_attr(a, cfg(a))] T: TraitAA,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:148:5
+   |
+LL |     #[cfg_attr(b, cfg(b))] T: TraitBB,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:149:5
+   |
+LL |     #[cfg_attr(all(), cfg(all()))] T: TraitAllAll,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:150:5
+   |
+LL |     #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:153:9
+   |
+LL |         #[cfg(a)] U: TraitA,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:154:9
+   |
+LL |         #[cfg(b)] U: TraitB,
+   |         ^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:155:9
+   |
+LL |         #[cfg(all())] U: TraitAll,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:156:9
+   |
+LL |         #[cfg(any())] U: TraitAny,
+   |         ^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:157:9
+   |
+LL |         #[cfg_attr(a, cfg(a))] U: TraitAA,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:158:9
+   |
+LL |         #[cfg_attr(b, cfg(b))] U: TraitBB,
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:159:9
+   |
+LL |         #[cfg_attr(all(), cfg(all()))] U: TraitAllAll,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: attributes in `where` clause are unstable
+  --> $DIR/feature-gate-where_clause_attrs.rs:160:9
+   |
+LL |         #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #115590 <https://github.com/rust-lang/rust/issues/115590> for more information
+   = help: add `#![feature(where_clause_attrs)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 88 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
--- a/tests/ui/feature-gates/feature-gate-where_clause_attrs.rs
+++ b/tests/ui/feature-gates/feature-gate-where_clause_attrs.rs
@ -0,0 +1,162 @@
+//@ revisions: a b
+
+#![crate_type = "lib"]
+use std::marker::PhantomData;
+
+#[cfg(a)]
+trait TraitA {}
+
+#[cfg(b)]
+trait TraitB {}
+
+#[cfg_attr(a, cfg(a))]
+trait TraitAA {}
+
+#[cfg_attr(b, cfg(b))]
+trait TraitBB {}
+
+#[cfg(all())]
+trait TraitAll {}
+
+#[cfg(any())]
+trait TraitAny {}
+
+#[cfg_attr(all(), cfg(all()))]
+trait TraitAllAll {}
+
+#[cfg_attr(any(), cfg(any()))]
+trait TraitAnyAny {}
+
+
+trait A<T>
+where
+    #[cfg(a)] T: TraitA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(b)] T: TraitB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(a, cfg(a))] T: TraitAA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(b, cfg(b))] T: TraitBB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+{
+    type B<U>
+    where
+        #[cfg(a)] U: TraitA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(b)] U: TraitB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(all())] U: TraitAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(any())] U: TraitAny, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(a, cfg(a))] U: TraitAA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(b, cfg(b))] U: TraitBB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(all(), cfg(all()))] U: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny; //~ ERROR attributes in `where` clause are unstable
+
+    fn foo<U>(&self)
+    where
+        #[cfg(a)] U: TraitA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(b)] U: TraitB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(all())] U: TraitAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(any())] U: TraitAny, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(a, cfg(a))] U: TraitAA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(b, cfg(b))] U: TraitBB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(all(), cfg(all()))] U: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny; //~ ERROR attributes in `where` clause are unstable
+}
+
+impl<T> A<T> for T
+where
+    #[cfg(a)] T: TraitA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(b)] T: TraitB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(a, cfg(a))] T: TraitAA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(b, cfg(b))] T: TraitBB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+{
+    type B<U> = () where
+        #[cfg(a)] U: TraitA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(b)] U: TraitB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(all())] U: TraitAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(any())] U: TraitAny, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(a, cfg(a))] U: TraitAA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(b, cfg(b))] U: TraitBB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(all(), cfg(all()))] U: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny; //~ ERROR attributes in `where` clause are unstable
+
+    fn foo<U>(&self)
+    where
+        #[cfg(a)] U: TraitA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(b)] U: TraitB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(a, cfg(a))] U: TraitAA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(b, cfg(b))] U: TraitBB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+    {}
+}
+
+struct C<T>
+where
+    #[cfg(a)] T: TraitA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(b)] T: TraitB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(a, cfg(a))] T: TraitAA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(b, cfg(b))] T: TraitBB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+{
+    _t: PhantomData<T>,
+}
+
+union D<T>
+where
+    #[cfg(a)] T: TraitA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(b)] T: TraitB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(a, cfg(a))] T: TraitAA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(b, cfg(b))] T: TraitBB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+{
+
+    _t: PhantomData<T>,
+}
+
+enum E<T>
+where
+    #[cfg(a)] T: TraitA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(b)] T: TraitB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(a, cfg(a))] T: TraitAA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(b, cfg(b))] T: TraitBB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+{
+    E(PhantomData<T>),
+}
+
+impl<T> C<T> where
+    #[cfg(a)] T: TraitA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(b)] T: TraitB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(all())] T: TraitAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg(any())] T: TraitAny, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(a, cfg(a))] T: TraitAA, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(b, cfg(b))] T: TraitBB, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(all(), cfg(all()))] T: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+    #[cfg_attr(any(), cfg(any()))] T: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+{
+    fn new<U>() where
+        #[cfg(a)] U: TraitA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(b)] U: TraitB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(all())] U: TraitAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg(any())] U: TraitAny, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(a, cfg(a))] U: TraitAA, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(b, cfg(b))] U: TraitBB, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(all(), cfg(all()))] U: TraitAllAll, //~ ERROR attributes in `where` clause are unstable
+        #[cfg_attr(any(), cfg(any()))] U: TraitAnyAny, //~ ERROR attributes in `where` clause are unstable
+    {}
+}
--- a/tests/ui/parser/bounds-lifetime-where.rs
+++ b/tests/ui/parser/bounds-lifetime-where.rs
@ -5,6 +5,6 @@ type A where 'a:, = u8; // OK
 type A where 'a: 'b + 'c = u8; // OK
 type A where = u8; // OK
 type A where 'a: 'b + = u8; // OK
-type A where , = u8; //~ ERROR expected one of `;`, `=`, `where`, lifetime, or type, found `,`
+type A where , = u8; //~ ERROR expected one of `#`, `;`, `=`, `where`, lifetime, or type, found `,`

 fn main() {}
--- a/tests/ui/parser/bounds-lifetime-where.stderr
+++ b/tests/ui/parser/bounds-lifetime-where.stderr
@ -1,8 +1,8 @@
-error: expected one of `;`, `=`, `where`, lifetime, or type, found `,`
+error: expected one of `#`, `;`, `=`, `where`, lifetime, or type, found `,`
  --> $DIR/bounds-lifetime-where.rs:8:14
   |
 LL | type A where , = u8;
-   |              ^ expected one of `;`, `=`, `where`, lifetime, or type
+   |              ^ expected one of `#`, `;`, `=`, `where`, lifetime, or type

 error: aborting due to 1 previous error

--- a/tests/ui/parser/issues/misplaced-return-type-where-in-next-line-issue-126311.stderr
+++ b/tests/ui/parser/issues/misplaced-return-type-where-in-next-line-issue-126311.stderr
@ -2,7 +2,7 @@ error: return type should be specified after the function parameters
  --> $DIR/misplaced-return-type-where-in-next-line-issue-126311.rs:5:15
   |
 LL |     K: Clone, -> Result<u8, String>
-   |               ^^ expected one of `{`, lifetime, or type
+   |               ^^ expected one of `#`, `{`, lifetime, or type
   |
 help: place the return type after the function parameters
   |
--- a/tests/ui/stats/input-stats.stderr
+++ b/tests/ui/stats/input-stats.stderr
@ -8,8 +8,8 @@ ast-stats-1 ExprField                 48 ( 0.7%)             1            48
 ast-stats-1 Attribute                 64 ( 1.0%)             2            32
 ast-stats-1 - DocComment                32 ( 0.5%)             1
 ast-stats-1 - Normal                    32 ( 0.5%)             1
-ast-stats-1 WherePredicate            64 ( 1.0%)             1            64
-ast-stats-1 - BoundPredicate            64 ( 1.0%)             1
+ast-stats-1 WherePredicate            72 ( 1.1%)             1            72
+ast-stats-1 - BoundPredicate            72 ( 1.1%)             1
 ast-stats-1 Local                     80 ( 1.2%)             1            80
 ast-stats-1 ForeignItem               88 ( 1.3%)             1            88
 ast-stats-1 - Fn                        88 ( 1.3%)             1
@ -37,14 +37,14 @@ ast-stats-1 Expr                     576 ( 8.6%)             8            72
 ast-stats-1 - Match                     72 ( 1.1%)             1
 ast-stats-1 - Path                      72 ( 1.1%)             1
 ast-stats-1 - Struct                    72 ( 1.1%)             1
-ast-stats-1 - Lit                      144 ( 2.2%)             2
+ast-stats-1 - Lit                      144 ( 2.1%)             2
 ast-stats-1 - Block                    216 ( 3.2%)             3
 ast-stats-1 PathSegment              744 (11.1%)            31            24
 ast-stats-1 Ty                       896 (13.4%)            14            64
 ast-stats-1 - Ptr                       64 ( 1.0%)             1
 ast-stats-1 - Ref                       64 ( 1.0%)             1
 ast-stats-1 - ImplicitSelf             128 ( 1.9%)             2
-ast-stats-1 - Path                     640 ( 9.6%)            10
+ast-stats-1 - Path                     640 ( 9.5%)            10
 ast-stats-1 Item                   1_224 (18.3%)             9           136
 ast-stats-1 - Enum                     136 ( 2.0%)             1
 ast-stats-1 - ForeignMod               136 ( 2.0%)             1
@ -53,7 +53,7 @@ ast-stats-1 - Trait                    136 ( 2.0%)             1
 ast-stats-1 - Fn                       272 ( 4.1%)             2
 ast-stats-1 - Use                      408 ( 6.1%)             3
 ast-stats-1 ----------------------------------------------------------------
-ast-stats-1 Total                  6_696                   116
+ast-stats-1 Total                  6_704                   116
 ast-stats-1
 ast-stats-2 POST EXPANSION AST STATS
 ast-stats-2 Name                Accumulated Size         Count     Item Size
@ -62,8 +62,8 @@ ast-stats-2 Crate                     40 ( 0.5%)             1            40
 ast-stats-2 GenericArgs               40 ( 0.5%)             1            40
 ast-stats-2 - AngleBracketed            40 ( 0.5%)             1
 ast-stats-2 ExprField                 48 ( 0.7%)             1            48
-ast-stats-2 WherePredicate            64 ( 0.9%)             1            64
-ast-stats-2 - BoundPredicate            64 ( 0.9%)             1
+ast-stats-2 WherePredicate            72 ( 1.0%)             1            72
+ast-stats-2 - BoundPredicate            72 ( 1.0%)             1
 ast-stats-2 Local                     80 ( 1.1%)             1            80
 ast-stats-2 ForeignItem               88 ( 1.2%)             1            88
 ast-stats-2 - Fn                        88 ( 1.2%)             1
@ -104,16 +104,16 @@ ast-stats-2 - Ptr                       64 ( 0.9%)             1
 ast-stats-2 - Ref                       64 ( 0.9%)             1
 ast-stats-2 - ImplicitSelf             128 ( 1.7%)             2
 ast-stats-2 - Path                     640 ( 8.7%)            10
-ast-stats-2 Item                   1_496 (20.4%)            11           136
-ast-stats-2 - Enum                     136 ( 1.9%)             1
-ast-stats-2 - ExternCrate              136 ( 1.9%)             1
-ast-stats-2 - ForeignMod               136 ( 1.9%)             1
-ast-stats-2 - Impl                     136 ( 1.9%)             1
-ast-stats-2 - Trait                    136 ( 1.9%)             1
+ast-stats-2 Item                   1_496 (20.3%)            11           136
+ast-stats-2 - Enum                     136 ( 1.8%)             1
+ast-stats-2 - ExternCrate              136 ( 1.8%)             1
+ast-stats-2 - ForeignMod               136 ( 1.8%)             1
+ast-stats-2 - Impl                     136 ( 1.8%)             1
+ast-stats-2 - Trait                    136 ( 1.8%)             1
 ast-stats-2 - Fn                       272 ( 3.7%)             2
 ast-stats-2 - Use                      544 ( 7.4%)             4
 ast-stats-2 ----------------------------------------------------------------
-ast-stats-2 Total                  7_344                   127
+ast-stats-2 Total                  7_352                   127
 ast-stats-2
 hir-stats HIR STATS
 hir-stats Name                Accumulated Size         Count     Item Size
--- a/tests/ui/where-clauses/cfg_attribute.a.stderr
+++ b/tests/ui/where-clauses/cfg_attribute.a.stderr
@ -0,0 +1,288 @@
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:32:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:43:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:54:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:66:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:76:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:87:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:100:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:114:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:129:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:144:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:155:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:165:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:178:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:32:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:35:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:66:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:69:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:100:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:103:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:114:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:117:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:129:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:132:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:144:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:147:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:155:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:158:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:178:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:181:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:43:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:46:9
+   |
+LL |         #[rustfmt::skip] ():;
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:54:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:57:9
+   |
+LL |         #[rustfmt::skip] ():;
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:76:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:79:9
+   |
+LL |         #[rustfmt::skip] ():;
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:87:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:90:9
+   |
+LL |         #[rustfmt::skip] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:165:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:168:9
+   |
+LL |         #[rustfmt::skip] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: aborting due to 39 previous errors
+
--- a/tests/ui/where-clauses/cfg_attribute.b.stderr
+++ b/tests/ui/where-clauses/cfg_attribute.b.stderr
@ -0,0 +1,288 @@
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:32:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:43:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:54:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:66:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:76:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:87:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:100:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:114:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:129:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:144:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:155:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:165:11
+   |
+LL |         #[derive(Clone)] ():,
+   |           ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/cfg_attribute.rs:178:7
+   |
+LL |     #[derive(Clone)] ():,
+   |       ^^^^^^ not a non-macro attribute
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:32:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:35:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:66:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:69:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:100:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:103:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:114:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:117:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:129:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:132:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:144:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:147:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:155:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:158:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:178:5
+   |
+LL |     #[derive(Clone)] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:181:5
+   |
+LL |     #[rustfmt::skip] ():,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:43:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:46:9
+   |
+LL |         #[rustfmt::skip] ():;
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:54:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:57:9
+   |
+LL |         #[rustfmt::skip] ():;
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:76:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:79:9
+   |
+LL |         #[rustfmt::skip] ():;
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:87:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:90:9
+   |
+LL |         #[rustfmt::skip] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:165:9
+   |
+LL |         #[derive(Clone)] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/cfg_attribute.rs:168:9
+   |
+LL |         #[rustfmt::skip] ():,
+   |         ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: aborting due to 39 previous errors
+
--- a/tests/ui/where-clauses/cfg_attribute.rs
+++ b/tests/ui/where-clauses/cfg_attribute.rs
@ -0,0 +1,183 @@
+//@ revisions: a b
+
+#![crate_type = "lib"]
+#![feature(alloc_error_handler)]
+#![feature(cfg_accessible)]
+#![feature(cfg_eval)]
+#![feature(custom_test_frameworks)]
+#![feature(derive_const)]
+#![feature(where_clause_attrs)]
+#![allow(soft_unstable)]
+
+use std::marker::PhantomData;
+
+#[cfg(a)]
+trait TraitA {}
+
+#[cfg(b)]
+trait TraitB {}
+
+#[cfg_attr(a, cfg(a))]
+trait TraitAA {}
+
+#[cfg_attr(b, cfg(b))]
+trait TraitBB {}
+
+trait A<T>
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+    type B<U>
+    where
+        #[cfg(a)] U: TraitA,
+        #[cfg(b)] U: TraitB,
+        #[cfg_attr(a, cfg(a))] U: TraitAA,
+        #[cfg_attr(b, cfg(b))] U: TraitBB,
+        #[derive(Clone)] ():,
+        //~^ ERROR most attributes are not supported in `where` clauses
+        //~| ERROR expected non-macro attribute, found attribute macro `derive`
+        #[rustfmt::skip] ():; //~ ERROR most attributes are not supported in `where` clauses
+
+    fn foo<U>(&self)
+    where
+        #[cfg(a)] U: TraitA,
+        #[cfg(b)] U: TraitB,
+        #[cfg_attr(a, cfg(a))] U: TraitAA,
+        #[cfg_attr(b, cfg(b))] U: TraitBB,
+        #[derive(Clone)] ():,
+        //~^ ERROR most attributes are not supported in `where` clauses
+        //~| ERROR expected non-macro attribute, found attribute macro `derive`
+        #[rustfmt::skip] ():; //~ ERROR most attributes are not supported in `where` clauses
+}
+
+impl<T> A<T> for T
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+    type B<U> = () where
+        #[cfg(a)] U: TraitA,
+        #[cfg(b)] U: TraitB,
+        #[cfg_attr(a, cfg(a))] U: TraitAA,
+        #[cfg_attr(b, cfg(b))] U: TraitBB,
+        #[derive(Clone)] ():,
+        //~^ ERROR most attributes are not supported in `where` clauses
+        //~| ERROR expected non-macro attribute, found attribute macro `derive`
+        #[rustfmt::skip] ():; //~ ERROR most attributes are not supported in `where` clauses
+
+    fn foo<U>(&self)
+    where
+        #[cfg(a)] U: TraitA,
+        #[cfg(b)] U: TraitB,
+        #[cfg_attr(a, cfg(a))] U: TraitAA,
+        #[cfg_attr(b, cfg(b))] U: TraitBB,
+        #[derive(Clone)] ():,
+        //~^ ERROR most attributes are not supported in `where` clauses
+        //~| ERROR expected non-macro attribute, found attribute macro `derive`
+        #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+    {}
+}
+
+struct C<T>
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+    _t: PhantomData<T>,
+}
+
+union D<T>
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+
+    _t: PhantomData<T>,
+}
+
+enum E<T>
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+    E(PhantomData<T>),
+}
+
+#[allow(type_alias_bounds)]
+type F<T>
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+= T;
+
+impl<T> C<T> where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+    fn new<U>() where
+        #[cfg(a)] U: TraitA,
+        #[cfg(b)] U: TraitB,
+        #[cfg_attr(a, cfg(a))] U: TraitAA,
+        #[cfg_attr(b, cfg(b))] U: TraitBB,
+        #[derive(Clone)] ():,
+        //~^ ERROR most attributes are not supported in `where` clauses
+        //~| ERROR expected non-macro attribute, found attribute macro `derive`
+        #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+    {}
+}
+
+fn foo<T>()
+where
+    #[cfg(a)] T: TraitA,
+    #[cfg(b)] T: TraitB,
+    #[cfg_attr(a, cfg(a))] T: TraitAA,
+    #[cfg_attr(b, cfg(b))] T: TraitBB,
+    #[derive(Clone)] ():,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] ():, //~ ERROR most attributes are not supported in `where` clauses
+{
+}
--- a/tests/ui/where-clauses/unsupported_attribute.rs
+++ b/tests/ui/where-clauses/unsupported_attribute.rs
@ -0,0 +1,36 @@
+#![crate_type = "lib"]
+#![feature(alloc_error_handler)]
+#![feature(cfg_accessible)]
+#![feature(cfg_eval)]
+#![feature(custom_test_frameworks)]
+#![feature(derive_const)]
+#![feature(where_clause_attrs)]
+#![allow(soft_unstable)]
+
+trait Trait {}
+
+fn foo<'a, T>()
+where
+    #[doc = "doc"] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[doc = "doc"] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[ignore] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[ignore] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[should_panic] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[should_panic] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[macro_use] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[macro_use] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[allow(unused)] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[allow(unused)] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[deprecated] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[deprecated] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[automatically_derived] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[automatically_derived] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+    #[derive(Clone)] T: Trait,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[derive(Clone)] 'a: 'static,
+    //~^ ERROR most attributes are not supported in `where` clauses
+    //~| ERROR expected non-macro attribute, found attribute macro `derive`
+    #[rustfmt::skip] T: Trait, //~ ERROR most attributes are not supported in `where` clauses
+    #[rustfmt::skip] 'a: 'static, //~ ERROR most attributes are not supported in `where` clauses
+{}
--- a/tests/ui/where-clauses/unsupported_attribute.stderr
+++ b/tests/ui/where-clauses/unsupported_attribute.stderr
@ -0,0 +1,158 @@
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/unsupported_attribute.rs:28:7
+   |
+LL |     #[derive(Clone)] T: Trait,
+   |       ^^^^^^ not a non-macro attribute
+
+error: expected non-macro attribute, found attribute macro `derive`
+  --> $DIR/unsupported_attribute.rs:31:7
+   |
+LL |     #[derive(Clone)] 'a: 'static,
+   |       ^^^^^^ not a non-macro attribute
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:14:5
+   |
+LL |     #[doc = "doc"] T: Trait,
+   |     ^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:15:5
+   |
+LL |     #[doc = "doc"] 'a: 'static,
+   |     ^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:16:5
+   |
+LL |     #[ignore] T: Trait,
+   |     ^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:17:5
+   |
+LL |     #[ignore] 'a: 'static,
+   |     ^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:18:5
+   |
+LL |     #[should_panic] T: Trait,
+   |     ^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:19:5
+   |
+LL |     #[should_panic] 'a: 'static,
+   |     ^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:20:5
+   |
+LL |     #[macro_use] T: Trait,
+   |     ^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:21:5
+   |
+LL |     #[macro_use] 'a: 'static,
+   |     ^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:22:5
+   |
+LL |     #[allow(unused)] T: Trait,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:23:5
+   |
+LL |     #[allow(unused)] 'a: 'static,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:24:5
+   |
+LL |     #[deprecated] T: Trait,
+   |     ^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:25:5
+   |
+LL |     #[deprecated] 'a: 'static,
+   |     ^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:26:5
+   |
+LL |     #[automatically_derived] T: Trait,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:27:5
+   |
+LL |     #[automatically_derived] 'a: 'static,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:28:5
+   |
+LL |     #[derive(Clone)] T: Trait,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:31:5
+   |
+LL |     #[derive(Clone)] 'a: 'static,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:34:5
+   |
+LL |     #[rustfmt::skip] T: Trait,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/unsupported_attribute.rs:35:5
+   |
+LL |     #[rustfmt::skip] 'a: 'static,
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: aborting due to 20 previous errors
+