Rollup merge of #108161 - WaffleLapkin:const_param_ty, r=BoxyUwU

Add `ConstParamTy` trait

This is a bit sketch, but idk.
r? `@BoxyUwU`

Yet to be done:
- [x] ~~Figure out if it's okay to implement `StructuralEq` for primitives / possibly remove their special casing~~ (it should be okay, but maybe not in this PR...)
- [ ] Maybe refactor the code a little bit
- [x] Use a macro to make impls a bit nicer

Future work:
- [ ] Actually™ use the trait when checking if a `const` generic type is allowed
- [ ] _Really_ refactor the surrounding code
- [ ] Refactor `marker.rs` into multiple modules for each "theme" of markers

compiler/rustc_hir/src/lang_items.rs

@@ -293,6 +293,8 @@ language_item_table! {
 
     PointerLike,             sym::pointer_like,        pointer_like,               Target::Trait,          GenericRequirement::Exact(0);
 
+    ConstParamTy,            sym::const_param_ty,      const_param_ty_trait,       Target::Trait,          GenericRequirement::Exact(0);
+
     Poll,                    sym::Poll,                poll,                       Target::Enum,           GenericRequirement::None;
     PollReady,               sym::Ready,               poll_ready_variant,         Target::Variant,        GenericRequirement::None;
     PollPending,             sym::Pending,             poll_pending_variant,       Target::Variant,        GenericRequirement::None;

compiler/rustc_hir_analysis/messages.ftl

@@ -35,6 +35,10 @@ hir_analysis_field_already_declared =
 
 hir_analysis_expected_used_symbol = expected `used`, `used(compiler)` or `used(linker)`
 
+hir_analysis_const_param_ty_impl_on_non_adt =
+    the trait `ConstParamTy` may not be implemented for this type
+    .label = type is not a structure or enumeration
+
 hir_analysis_ambiguous_lifetime_bound =
     ambiguous lifetime bound, explicit lifetime bound required
 

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -1,9 +1,11 @@
 //! Check properties that are required by built-in traits and set
 //! up data structures required by type-checking/codegen.
 
-use crate::errors::{CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem};
+use crate::errors::{
+    ConstParamTyImplOnNonAdt, CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem,
+};
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{struct_span_err, MultiSpan};
+use rustc_errors::{struct_span_err, ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
@@ -14,9 +16,11 @@ use rustc_infer::infer::{DefineOpaqueTypes, TyCtxtInferExt};
 use rustc_infer::traits::Obligation;
 use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
 use rustc_middle::ty::{self, suggest_constraining_type_params, Ty, TyCtxt, TypeVisitableExt};
+use rustc_span::Span;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::misc::{
-    type_allowed_to_implement_copy, CopyImplementationError, InfringingFieldsReason,
+    type_allowed_to_implement_const_param_ty, type_allowed_to_implement_copy,
+    ConstParamTyImplementationError, CopyImplementationError, InfringingFieldsReason,
 };
 use rustc_trait_selection::traits::ObligationCtxt;
 use rustc_trait_selection::traits::{self, ObligationCause};
@@ -27,6 +31,7 @@ pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) {
     Checker { tcx, trait_def_id }
         .check(lang_items.drop_trait(), visit_implementation_of_drop)
         .check(lang_items.copy_trait(), visit_implementation_of_copy)
+        .check(lang_items.const_param_ty_trait(), visit_implementation_of_const_param_ty)
         .check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized)
         .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn);
 }
@@ -83,110 +88,7 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
     match type_allowed_to_implement_copy(tcx, param_env, self_type, cause) {
         Ok(()) => {}
         Err(CopyImplementationError::InfringingFields(fields)) => {
-            let mut err = struct_span_err!(
+            infringing_fields_error(tcx, fields, LangItem::Copy, impl_did, span);
-                tcx.sess,
-                span,
-                E0204,
-                "the trait `Copy` cannot be implemented for this type"
-            );
-
-            // We'll try to suggest constraining type parameters to fulfill the requirements of
-            // their `Copy` implementation.
-            let mut errors: BTreeMap<_, Vec<_>> = Default::default();
-            let mut bounds = vec![];
-
-            let mut seen_tys = FxHashSet::default();
-
-            for (field, ty, reason) in fields {
-                // Only report an error once per type.
-                if !seen_tys.insert(ty) {
-                    continue;
-                }
-
-                let field_span = tcx.def_span(field.did);
-                err.span_label(field_span, "this field does not implement `Copy`");
-
-                match reason {
-                    InfringingFieldsReason::Fulfill(fulfillment_errors) => {
-                        for error in fulfillment_errors {
-                            let error_predicate = error.obligation.predicate;
-                            // Only note if it's not the root obligation, otherwise it's trivial and
-                            // should be self-explanatory (i.e. a field literally doesn't implement Copy).
-
-                            // FIXME: This error could be more descriptive, especially if the error_predicate
-                            // contains a foreign type or if it's a deeply nested type...
-                            if error_predicate != error.root_obligation.predicate {
-                                errors
-                                    .entry((ty.to_string(), error_predicate.to_string()))
-                                    .or_default()
-                                    .push(error.obligation.cause.span);
-                            }
-                            if let ty::PredicateKind::Clause(ty::Clause::Trait(
-                                ty::TraitPredicate {
-                                    trait_ref,
-                                    polarity: ty::ImplPolarity::Positive,
-                                    ..
-                                },
-                            )) = error_predicate.kind().skip_binder()
-                            {
-                                let ty = trait_ref.self_ty();
-                                if let ty::Param(_) = ty.kind() {
-                                    bounds.push((
-                                        format!("{ty}"),
-                                        trait_ref.print_only_trait_path().to_string(),
-                                        Some(trait_ref.def_id),
-                                    ));
-                                }
-                            }
-                        }
-                    }
-                    InfringingFieldsReason::Regions(region_errors) => {
-                        for error in region_errors {
-                            let ty = ty.to_string();
-                            match error {
-                                RegionResolutionError::ConcreteFailure(origin, a, b) => {
-                                    let predicate = format!("{b}: {a}");
-                                    errors
-                                        .entry((ty.clone(), predicate.clone()))
-                                        .or_default()
-                                        .push(origin.span());
-                                    if let ty::RegionKind::ReEarlyBound(ebr) = *b && ebr.has_name() {
-                                        bounds.push((b.to_string(), a.to_string(), None));
-                                    }
-                                }
-                                RegionResolutionError::GenericBoundFailure(origin, a, b) => {
-                                    let predicate = format!("{a}: {b}");
-                                    errors
-                                        .entry((ty.clone(), predicate.clone()))
-                                        .or_default()
-                                        .push(origin.span());
-                                    if let infer::region_constraints::GenericKind::Param(_) = a {
-                                        bounds.push((a.to_string(), b.to_string(), None));
-                                    }
-                                }
-                                _ => continue,
-                            }
-                        }
-                    }
-                }
-            }
-            for ((ty, error_predicate), spans) in errors {
-                let span: MultiSpan = spans.into();
-                err.span_note(
-                    span,
-                    &format!("the `Copy` impl for `{}` requires that `{}`", ty, error_predicate),
-                );
-            }
-            suggest_constraining_type_params(
-                tcx,
-                tcx.hir().get_generics(impl_did).expect("impls always have generics"),
-                &mut err,
-                bounds.iter().map(|(param, constraint, def_id)| {
-                    (param.as_str(), constraint.as_str(), *def_id)
-                }),
-                None,
-            );
-            err.emit();
         }
         Err(CopyImplementationError::NotAnAdt) => {
             tcx.sess.emit_err(CopyImplOnNonAdt { span });
@@ -197,6 +99,29 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
     }
 }
 
+fn visit_implementation_of_const_param_ty(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
+    let self_type = tcx.type_of(impl_did).subst_identity();
+    assert!(!self_type.has_escaping_bound_vars());
+
+    let param_env = tcx.param_env(impl_did);
+
+    let span = match tcx.hir().expect_item(impl_did).expect_impl() {
+        hir::Impl { polarity: hir::ImplPolarity::Negative(_), .. } => return,
+        impl_ => impl_.self_ty.span,
+    };
+
+    let cause = traits::ObligationCause::misc(span, impl_did);
+    match type_allowed_to_implement_const_param_ty(tcx, param_env, self_type, cause) {
+        Ok(()) => {}
+        Err(ConstParamTyImplementationError::InfrigingFields(fields)) => {
+            infringing_fields_error(tcx, fields, LangItem::ConstParamTy, impl_did, span);
+        }
+        Err(ConstParamTyImplementationError::NotAnAdtOrBuiltinAllowed) => {
+            tcx.sess.emit_err(ConstParamTyImplOnNonAdt { span });
+        }
+    }
+}
+
 fn visit_implementation_of_coerce_unsized(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
     debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did);
 
@@ -593,3 +518,119 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
 
     CoerceUnsizedInfo { custom_kind: kind }
 }
+
+fn infringing_fields_error(
+    tcx: TyCtxt<'_>,
+    fields: Vec<(&ty::FieldDef, Ty<'_>, InfringingFieldsReason<'_>)>,
+    lang_item: LangItem,
+    impl_did: LocalDefId,
+    impl_span: Span,
+) -> ErrorGuaranteed {
+    let trait_did = tcx.require_lang_item(lang_item, Some(impl_span));
+
+    let trait_name = tcx.def_path_str(trait_did);
+
+    let mut err = struct_span_err!(
+        tcx.sess,
+        impl_span,
+        E0204,
+        "the trait `{trait_name}` cannot be implemented for this type"
+    );
+
+    // We'll try to suggest constraining type parameters to fulfill the requirements of
+    // their `Copy` implementation.
+    let mut errors: BTreeMap<_, Vec<_>> = Default::default();
+    let mut bounds = vec![];
+
+    let mut seen_tys = FxHashSet::default();
+
+    for (field, ty, reason) in fields {
+        // Only report an error once per type.
+        if !seen_tys.insert(ty) {
+            continue;
+        }
+
+        let field_span = tcx.def_span(field.did);
+        err.span_label(field_span, format!("this field does not implement `{trait_name}`"));
+
+        match reason {
+            InfringingFieldsReason::Fulfill(fulfillment_errors) => {
+                for error in fulfillment_errors {
+                    let error_predicate = error.obligation.predicate;
+                    // Only note if it's not the root obligation, otherwise it's trivial and
+                    // should be self-explanatory (i.e. a field literally doesn't implement Copy).
+
+                    // FIXME: This error could be more descriptive, especially if the error_predicate
+                    // contains a foreign type or if it's a deeply nested type...
+                    if error_predicate != error.root_obligation.predicate {
+                        errors
+                            .entry((ty.to_string(), error_predicate.to_string()))
+                            .or_default()
+                            .push(error.obligation.cause.span);
+                    }
+                    if let ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
+                        trait_ref,
+                        polarity: ty::ImplPolarity::Positive,
+                        ..
+                    })) = error_predicate.kind().skip_binder()
+                    {
+                        let ty = trait_ref.self_ty();
+                        if let ty::Param(_) = ty.kind() {
+                            bounds.push((
+                                format!("{ty}"),
+                                trait_ref.print_only_trait_path().to_string(),
+                                Some(trait_ref.def_id),
+                            ));
+                        }
+                    }
+                }
+            }
+            InfringingFieldsReason::Regions(region_errors) => {
+                for error in region_errors {
+                    let ty = ty.to_string();
+                    match error {
+                        RegionResolutionError::ConcreteFailure(origin, a, b) => {
+                            let predicate = format!("{b}: {a}");
+                            errors
+                                .entry((ty.clone(), predicate.clone()))
+                                .or_default()
+                                .push(origin.span());
+                            if let ty::RegionKind::ReEarlyBound(ebr) = *b && ebr.has_name() {
+                                        bounds.push((b.to_string(), a.to_string(), None));
+                                    }
+                        }
+                        RegionResolutionError::GenericBoundFailure(origin, a, b) => {
+                            let predicate = format!("{a}: {b}");
+                            errors
+                                .entry((ty.clone(), predicate.clone()))
+                                .or_default()
+                                .push(origin.span());
+                            if let infer::region_constraints::GenericKind::Param(_) = a {
+                                bounds.push((a.to_string(), b.to_string(), None));
+                            }
+                        }
+                        _ => continue,
+                    }
+                }
+            }
+        }
+    }
+    for ((ty, error_predicate), spans) in errors {
+        let span: MultiSpan = spans.into();
+        err.span_note(
+            span,
+            format!("the `{trait_name}` impl for `{ty}` requires that `{error_predicate}`"),
+        );
+    }
+    suggest_constraining_type_params(
+        tcx,
+        tcx.hir().get_generics(impl_did).expect("impls always have generics"),
+        &mut err,
+        bounds
+            .iter()
+            .map(|(param, constraint, def_id)| (param.as_str(), constraint.as_str(), *def_id)),
+        None,
+    );
+
+    err.emit()
+}

compiler/rustc_hir_analysis/src/errors.rs

@@ -107,6 +107,14 @@ pub struct CopyImplOnNonAdt {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(hir_analysis_const_param_ty_impl_on_non_adt)]
+pub struct ConstParamTyImplOnNonAdt {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(hir_analysis_trait_object_declared_with_no_traits, code = "E0224")]
 pub struct TraitObjectDeclaredWithNoTraits {

compiler/rustc_span/src/symbol.rs

@@ -531,6 +531,7 @@ symbols! {
         const_mut_refs,
         const_panic,
         const_panic_fmt,
+        const_param_ty,
         const_precise_live_drops,
         const_raw_ptr_deref,
         const_raw_ptr_to_usize_cast,

compiler/rustc_trait_selection/src/traits/misc.rs

@@ -2,13 +2,14 @@
 
 use crate::traits::{self, ObligationCause, ObligationCtxt};
 
+use hir::LangItem;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_infer::infer::canonical::Canonical;
 use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::{infer::outlives::env::OutlivesEnvironment, traits::FulfillmentError};
-use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{self, AdtDef, GenericArg, List, ParamEnv, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::DUMMY_SP;
 
 use super::outlives_bounds::InferCtxtExt;
@@ -19,6 +20,11 @@ pub enum CopyImplementationError<'tcx> {
     HasDestructor,
 }
 
+pub enum ConstParamTyImplementationError<'tcx> {
+    InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>, InfringingFieldsReason<'tcx>)>),
+    NotAnAdtOrBuiltinAllowed,
+}
+
 pub enum InfringingFieldsReason<'tcx> {
     Fulfill(Vec<FulfillmentError<'tcx>>),
     Regions(Vec<RegionResolutionError<'tcx>>),
@@ -27,7 +33,10 @@ pub enum InfringingFieldsReason<'tcx> {
 /// Checks that the fields of the type (an ADT) all implement copy.
 ///
 /// If fields don't implement copy, return an error containing a list of
-/// those violating fields. If it's not an ADT, returns `Err(NotAnAdt)`.
+/// those violating fields.
+///
+/// If it's not an ADT, int ty, `bool`, float ty, `char`, raw pointer, `!`,
+/// a reference or an array returns `Err(NotAnAdt)`.
 pub fn type_allowed_to_implement_copy<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
@@ -47,12 +56,82 @@ pub fn type_allowed_to_implement_copy<'tcx>(
         | ty::Ref(_, _, hir::Mutability::Not)
         | ty::Array(..) => return Ok(()),
 
-        ty::Adt(adt, substs) => (adt, substs),
+        &ty::Adt(adt, substs) => (adt, substs),
 
         _ => return Err(CopyImplementationError::NotAnAdt),
     };
 
-    let copy_def_id = tcx.require_lang_item(hir::LangItem::Copy, Some(parent_cause.span));
+    all_fields_implement_trait(
+        tcx,
+        param_env,
+        self_type,
+        adt,
+        substs,
+        parent_cause,
+        hir::LangItem::Copy,
+    )
+    .map_err(CopyImplementationError::InfringingFields)?;
+
+    if adt.has_dtor(tcx) {
+        return Err(CopyImplementationError::HasDestructor);
+    }
+
+    Ok(())
+}
+
+/// Checks that the fields of the type (an ADT) all implement `ConstParamTy`.
+///
+/// If fields don't implement `ConstParamTy`, return an error containing a list of
+/// those violating fields.
+///
+/// If it's not an ADT, int ty, `bool` or `char`, returns `Err(NotAnAdtOrBuiltinAllowed)`.
+pub fn type_allowed_to_implement_const_param_ty<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    self_type: Ty<'tcx>,
+    parent_cause: ObligationCause<'tcx>,
+) -> Result<(), ConstParamTyImplementationError<'tcx>> {
+    let (adt, substs) = match self_type.kind() {
+        // `core` provides these impls.
+        ty::Uint(_)
+        | ty::Int(_)
+        | ty::Bool
+        | ty::Char
+        | ty::Str
+        | ty::Array(..)
+        | ty::Slice(_)
+        | ty::Ref(.., hir::Mutability::Not) => return Ok(()),
+
+        &ty::Adt(adt, substs) => (adt, substs),
+
+        _ => return Err(ConstParamTyImplementationError::NotAnAdtOrBuiltinAllowed),
+    };
+
+    all_fields_implement_trait(
+        tcx,
+        param_env,
+        self_type,
+        adt,
+        substs,
+        parent_cause,
+        hir::LangItem::ConstParamTy,
+    )
+    .map_err(ConstParamTyImplementationError::InfrigingFields)?;
+
+    Ok(())
+}
+
+/// Check that all fields of a given `adt` implement `lang_item` trait.
+pub fn all_fields_implement_trait<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    self_type: Ty<'tcx>,
+    adt: AdtDef<'tcx>,
+    substs: &'tcx List<GenericArg<'tcx>>,
+    parent_cause: ObligationCause<'tcx>,
+    lang_item: LangItem,
+) -> Result<(), Vec<(&'tcx ty::FieldDef, Ty<'tcx>, InfringingFieldsReason<'tcx>)>> {
+    let trait_def_id = tcx.require_lang_item(lang_item, Some(parent_cause.span));
 
     let mut infringing = Vec::new();
     for variant in adt.variants() {
@@ -93,7 +172,7 @@ pub fn type_allowed_to_implement_copy<'tcx>(
             // between expected and found const-generic types. Don't report an
             // additional copy error here, since it's not typically useful.
             if !normalization_errors.is_empty() || ty.references_error() {
-                tcx.sess.delay_span_bug(field_span, format!("couldn't normalize struct field `{unnormalized_ty}` when checking Copy implementation"));
+                tcx.sess.delay_span_bug(field_span, format!("couldn't normalize struct field `{unnormalized_ty}` when checking {tr} implementation", tr = tcx.def_path_str(trait_def_id)));
                 continue;
             }
 
@@ -101,7 +180,7 @@ pub fn type_allowed_to_implement_copy<'tcx>(
                 ObligationCause::dummy_with_span(field_ty_span),
                 param_env,
                 ty,
-                copy_def_id,
+                trait_def_id,
             );
             let errors = ocx.select_all_or_error();
             if !errors.is_empty() {
@@ -124,15 +203,7 @@ pub fn type_allowed_to_implement_copy<'tcx>(
         }
     }
 
-    if !infringing.is_empty() {
+    if infringing.is_empty() { Ok(()) } else { Err(infringing) }
-        return Err(CopyImplementationError::InfringingFields(infringing));
-    }
-
-    if adt.has_dtor(tcx) {
-        return Err(CopyImplementationError::HasDestructor);
-    }
-
-    Ok(())
 }
 
 pub fn check_tys_might_be_eq<'tcx>(

library/core/src/lib.rs

@@ -162,6 +162,7 @@
 #![feature(const_waker)]
 #![feature(core_panic)]
 #![feature(duration_consts_float)]
+#![feature(internal_impls_macro)]
 #![feature(ip)]
 #![feature(is_ascii_octdigit)]
 #![feature(maybe_uninit_uninit_array)]

library/core/src/marker.rs

@@ -12,6 +12,60 @@ use crate::fmt::Debug;
 use crate::hash::Hash;
 use crate::hash::Hasher;
 
+/// Implements a given marker trait for multiple types at the same time.
+///
+/// The basic syntax looks like this:
+/// ```ignore private macro
+/// marker_impls! { MarkerTrait for u8, i8 }
+/// ```
+/// You can also implement `unsafe` traits
+/// ```ignore private macro
+/// marker_impls! { unsafe MarkerTrait for u8, i8 }
+/// ```
+/// Add attributes to all impls:
+/// ```ignore private macro
+/// marker_impls! {
+///     #[allow(lint)]
+///     #[unstable(feature = "marker_trait", issue = "none")]
+///     MarkerTrait for u8, i8
+/// }
+/// ```
+/// And use generics:
+/// ```ignore private macro
+/// marker_impls! {
+///     MarkerTrait for
+///         u8, i8,
+///         {T: ?Sized} *const T,
+///         {T: ?Sized} *mut T,
+///         {T: MarkerTrait} PhantomData<T>,
+///         u32,
+/// }
+/// ```
+#[unstable(feature = "internal_impls_macro", issue = "none")]
+macro marker_impls {
+    ( $(#[$($meta:tt)*])* $Trait:ident for $( $({$($bounds:tt)*})? $T:ty ),+ $(,)?) => {
+        // This inner macro is needed because... idk macros are weird.
+        // It allows repeating `meta` on all impls.
+        #[unstable(feature = "internal_impls_macro", issue = "none")]
+        macro _impl {
+            ( $$({$$($$bounds_:tt)*})? $$T_:ty ) => {
+                $(#[$($meta)*])* impl<$$($$($$bounds_)*)?> $Trait for $$T_ {}
+            }
+        }
+        $( _impl! { $({$($bounds)*})? $T } )+
+    },
+    ( $(#[$($meta:tt)*])* unsafe $Trait:ident for $( $({$($bounds:tt)*})? $T:ty ),+ $(,)?) => {
+        #[unstable(feature = "internal_impls_macro", issue = "none")]
+        macro _impl {
+            ( $$({$$($$bounds_:tt)*})? $$T_:ty ) => {
+                $(#[$($meta)*])* unsafe impl<$$($$($$bounds_)*)?> $Trait for $$T_ {}
+            }
+        }
+
+        $( _impl! { $({$($bounds)*})? $T } )+
+    },
+}
+
 /// Types that can be transferred across thread boundaries.
 ///
 /// This trait is automatically implemented when the compiler determines it's
@@ -214,6 +268,20 @@ pub trait StructuralEq {
     // Empty.
 }
 
+// FIXME: Remove special cases of these types from the compiler pattern checking code and always check `T: StructuralEq` instead
+marker_impls! {
+    #[unstable(feature = "structural_match", issue = "31434")]
+    StructuralEq for
+        usize, u8, u16, u32, u64, u128,
+        isize, i8, i16, i32, i64, i128,
+        bool,
+        char,
+        str /* Technically requires `[u8]: StructuralEq` */,
+        {T, const N: usize} [T; N],
+        {T} [T],
+        {T: ?Sized} &T,
+}
+
 /// Types whose values can be duplicated simply by copying bits.
 ///
 /// By default, variable bindings have 'move semantics.' In other
@@ -401,6 +469,30 @@ pub macro Copy($item:item) {
     /* compiler built-in */
 }
 
+// Implementations of `Copy` for primitive types.
+//
+// Implementations that cannot be described in Rust
+// are implemented in `traits::SelectionContext::copy_clone_conditions()`
+// in `rustc_trait_selection`.
+marker_impls! {
+    #[stable(feature = "rust1", since = "1.0.0")]
+    Copy for
+        usize, u8, u16, u32, u64, u128,
+        isize, i8, i16, i32, i64, i128,
+        f32, f64,
+        bool, char,
+        {T: ?Sized} *const T,
+        {T: ?Sized} *mut T,
+
+}
+
+#[unstable(feature = "never_type", issue = "35121")]
+impl Copy for ! {}
+
+/// Shared references can be copied, but mutable references *cannot*!
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Copy for &T {}
+
 /// Types for which it is safe to share references between threads.
 ///
 /// This trait is automatically implemented when the compiler determines
@@ -778,11 +870,14 @@ pub trait DiscriminantKind {
 pub(crate) unsafe auto trait Freeze {}
 
 impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
-unsafe impl<T: ?Sized> Freeze for PhantomData<T> {}
+marker_impls! {
-unsafe impl<T: ?Sized> Freeze for *const T {}
+    unsafe Freeze for
-unsafe impl<T: ?Sized> Freeze for *mut T {}
+        {T: ?Sized} PhantomData<T>,
-unsafe impl<T: ?Sized> Freeze for &T {}
+        {T: ?Sized} *const T,
-unsafe impl<T: ?Sized> Freeze for &mut T {}
+        {T: ?Sized} *mut T,
+        {T: ?Sized} &T,
+        {T: ?Sized} &mut T,
+}
 
 /// Types that can be safely moved after being pinned.
 ///
@@ -843,17 +938,19 @@ pub struct PhantomPinned;
 #[stable(feature = "pin", since = "1.33.0")]
 impl !Unpin for PhantomPinned {}
 
-#[stable(feature = "pin", since = "1.33.0")]
+marker_impls! {
-impl<'a, T: ?Sized + 'a> Unpin for &'a T {}
+    #[stable(feature = "pin", since = "1.33.0")]
+    Unpin for
+        {T: ?Sized} &T,
+        {T: ?Sized} &mut T,
+}
 
-#[stable(feature = "pin", since = "1.33.0")]
+marker_impls! {
-impl<'a, T: ?Sized + 'a> Unpin for &'a mut T {}
+    #[stable(feature = "pin_raw", since = "1.38.0")]
-
+    Unpin for
-#[stable(feature = "pin_raw", since = "1.38.0")]
+        {T: ?Sized} *const T,
-impl<T: ?Sized> Unpin for *const T {}
+        {T: ?Sized} *mut T,
-
+}
-#[stable(feature = "pin_raw", since = "1.38.0")]
-impl<T: ?Sized> Unpin for *mut T {}
 
 /// A marker for types that can be dropped.
 ///
@@ -888,43 +985,25 @@ pub trait Tuple {}
 )]
 pub trait PointerLike {}
 
-/// Implementations of `Copy` for primitive types.
+/// A marker for types which can be used as types of `const` generic parameters.
-///
+#[cfg_attr(not(bootstrap), lang = "const_param_ty")]
-/// Implementations that cannot be described in Rust
+#[unstable(feature = "adt_const_params", issue = "95174")]
-/// are implemented in `traits::SelectionContext::copy_clone_conditions()`
+#[rustc_on_unimplemented(message = "`{Self}` can't be used as a const parameter type")]
-/// in `rustc_trait_selection`.
+pub trait ConstParamTy: StructuralEq {}
-mod copy_impls {
 
-    use super::Copy;
+// FIXME(generic_const_parameter_types): handle `ty::FnDef`/`ty::Closure`
-
+// FIXME(generic_const_parameter_types): handle `ty::Tuple`
-    macro_rules! impl_copy {
+marker_impls! {
-        ($($t:ty)*) => {
+    #[unstable(feature = "adt_const_params", issue = "95174")]
-            $(
+    ConstParamTy for
-                #[stable(feature = "rust1", since = "1.0.0")]
+        usize, u8, u16, u32, u64, u128,
-                impl Copy for $t {}
+        isize, i8, i16, i32, i64, i128,
-            )*
+        bool,
-        }
+        char,
-    }
+        str /* Technically requires `[u8]: ConstParamTy` */,
-
+        {T: ConstParamTy, const N: usize} [T; N],
-    impl_copy! {
+        {T: ConstParamTy} [T],
-        usize u8 u16 u32 u64 u128
+        {T: ?Sized + ConstParamTy} &T,
-        isize i8 i16 i32 i64 i128
-        f32 f64
-        bool char
-    }
-
-    #[unstable(feature = "never_type", issue = "35121")]
-    impl Copy for ! {}
-
-    #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Copy for *const T {}
-
-    #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Copy for *mut T {}
-
-    /// Shared references can be copied, but mutable references *cannot*!
-    #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Copy for &T {}
 }
 
 /// A common trait implemented by all function pointers.

src/tools/compiletest/src/runtest.rs

@@ -1385,7 +1385,9 @@ impl<'test> TestCx<'test> {
         let actual_errors = json::parse_output(&diagnostic_file_name, &proc_res.stderr, proc_res);
         let mut unexpected = Vec::new();
         let mut found = vec![false; expected_errors.len()];
-        for actual_error in &actual_errors {
+        for mut actual_error in actual_errors {
+            actual_error.msg = self.normalize_output(&actual_error.msg, &[]);
+
             let opt_index =
                 expected_errors.iter().enumerate().position(|(index, expected_error)| {
                     !found[index]
@@ -1404,7 +1406,8 @@ impl<'test> TestCx<'test> {
 
                 None => {
                     // If the test is a known bug, don't require that the error is annotated
-                    if self.is_unexpected_compiler_message(actual_error, expect_help, expect_note) {
+                    if self.is_unexpected_compiler_message(&actual_error, expect_help, expect_note)
+                    {
                         self.error(&format!(
                             "{}:{}: unexpected {}: '{}'",
                             file_name,

tests/ui/const-generics/adt_const_params/const_param_ty_bad.rs

@@ -0,0 +1,13 @@
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+
+fn check(_: impl std::marker::ConstParamTy) {}
+
+fn main() {
+    check(main);               //~ error: `fn() {main}` can't be used as a const parameter type
+    check(|| {});              //~ error: `[closure@$DIR/const_param_ty_bad.rs:8:11: 8:13]` can't be used as a const parameter type
+    check(main as fn());       //~ error: `fn()` can't be used as a const parameter type
+    check(&mut ());            //~ error: `&mut ()` can't be used as a const parameter type
+    check(&mut () as *mut ()); //~ error: `*mut ()` can't be used as a const parameter type
+    check(&() as *const ());   //~ error: `*const ()` can't be used as a const parameter type
+}

tests/ui/const-generics/adt_const_params/const_param_ty_bad.stderr

@@ -0,0 +1,87 @@
+error[E0277]: `fn() {main}` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad.rs:7:11
+   |
+LL |     check(main);
+   |     ----- ^^^^ the trait `ConstParamTy` is not implemented for fn item `fn() {main}`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad.rs:4:18
+   |
+LL | fn check(_: impl std::marker::ConstParamTy) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `[closure@$DIR/const_param_ty_bad.rs:8:11: 8:13]` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad.rs:8:11
+   |
+LL |     check(|| {});
+   |     ----- ^^^^^ the trait `ConstParamTy` is not implemented for closure `[closure@$DIR/const_param_ty_bad.rs:8:11: 8:13]`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad.rs:4:18
+   |
+LL | fn check(_: impl std::marker::ConstParamTy) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `fn()` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad.rs:9:11
+   |
+LL |     check(main as fn());
+   |     ----- ^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `fn()`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad.rs:4:18
+   |
+LL | fn check(_: impl std::marker::ConstParamTy) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `&mut ()` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad.rs:10:11
+   |
+LL |     check(&mut ());
+   |     ----- ^^^^^^^ the trait `ConstParamTy` is not implemented for `&mut ()`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad.rs:4:18
+   |
+LL | fn check(_: impl std::marker::ConstParamTy) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `*mut ()` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad.rs:11:11
+   |
+LL |     check(&mut () as *mut ());
+   |     ----- ^^^^^^^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `*mut ()`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad.rs:4:18
+   |
+LL | fn check(_: impl std::marker::ConstParamTy) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `*const ()` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad.rs:12:11
+   |
+LL |     check(&() as *const ());
+   |     ----- ^^^^^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `*const ()`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad.rs:4:18
+   |
+LL | fn check(_: impl std::marker::ConstParamTy) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/const-generics/adt_const_params/const_param_ty_bad_empty_array.rs

@@ -0,0 +1,12 @@
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+
+#[derive(PartialEq, Eq)]
+struct NotParam;
+
+fn check<T: std::marker::ConstParamTy>() {}
+
+fn main() {
+    check::<[NotParam; 0]>();
+    //~^ error: `NotParam` can't be used as a const parameter type
+}

tests/ui/const-generics/adt_const_params/const_param_ty_bad_empty_array.stderr

@@ -0,0 +1,16 @@
+error[E0277]: `NotParam` can't be used as a const parameter type
+  --> $DIR/const_param_ty_bad_empty_array.rs:10:13
+   |
+LL |     check::<[NotParam; 0]>();
+   |             ^^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `NotParam`
+   |
+   = note: required for `[NotParam; 0]` to implement `ConstParamTy`
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_bad_empty_array.rs:7:13
+   |
+LL | fn check<T: std::marker::ConstParamTy>() {}
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/const-generics/adt_const_params/const_param_ty_generic_bounds_do_not_hold.rs

@@ -0,0 +1,13 @@
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+
+#[derive(PartialEq, Eq)]
+struct NotParam;
+
+fn check<T: std::marker::ConstParamTy + ?Sized>() {}
+
+fn main() {
+    check::<&NotParam>();      //~ error: `NotParam` can't be used as a const parameter type
+    check::<[NotParam]>();     //~ error: `NotParam` can't be used as a const parameter type
+    check::<[NotParam; 17]>(); //~ error: `NotParam` can't be used as a const parameter type
+}

tests/ui/const-generics/adt_const_params/const_param_ty_generic_bounds_do_not_hold.stderr

@@ -0,0 +1,42 @@
+error[E0277]: `NotParam` can't be used as a const parameter type
+  --> $DIR/const_param_ty_generic_bounds_do_not_hold.rs:10:13
+   |
+LL |     check::<&NotParam>();
+   |             ^^^^^^^^^ the trait `ConstParamTy` is not implemented for `NotParam`
+   |
+   = note: required for `&NotParam` to implement `ConstParamTy`
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_generic_bounds_do_not_hold.rs:7:13
+   |
+LL | fn check<T: std::marker::ConstParamTy + ?Sized>() {}
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `NotParam` can't be used as a const parameter type
+  --> $DIR/const_param_ty_generic_bounds_do_not_hold.rs:11:13
+   |
+LL |     check::<[NotParam]>();
+   |             ^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `NotParam`
+   |
+   = note: required for `[NotParam]` to implement `ConstParamTy`
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_generic_bounds_do_not_hold.rs:7:13
+   |
+LL | fn check<T: std::marker::ConstParamTy + ?Sized>() {}
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error[E0277]: `NotParam` can't be used as a const parameter type
+  --> $DIR/const_param_ty_generic_bounds_do_not_hold.rs:12:13
+   |
+LL |     check::<[NotParam; 17]>();
+   |             ^^^^^^^^^^^^^^ the trait `ConstParamTy` is not implemented for `NotParam`
+   |
+   = note: required for `[NotParam; 17]` to implement `ConstParamTy`
+note: required by a bound in `check`
+  --> $DIR/const_param_ty_generic_bounds_do_not_hold.rs:7:13
+   |
+LL | fn check<T: std::marker::ConstParamTy + ?Sized>() {}
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `check`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/const-generics/adt_const_params/const_param_ty_good.rs

@@ -0,0 +1,43 @@
+// check-pass
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+use std::marker::ConstParamTy;
+
+#[derive(PartialEq, Eq)]
+struct S<T> {
+    field: u8,
+    gen: T,
+}
+
+impl<T: ConstParamTy> ConstParamTy for S<T> {}
+
+fn check<T: ConstParamTy + ?Sized>() {}
+
+fn main() {
+    check::<u8>();
+    check::<u16>();
+    check::<u32>();
+    check::<u64>();
+    check::<u128>();
+
+    check::<i8>();
+    check::<i16>();
+    check::<i32>();
+    check::<i64>();
+    check::<i128>();
+
+    check::<char>();
+    check::<bool>();
+    check::<str>();
+
+    check::<&u8>();
+    check::<&str>();
+    check::<[usize]>();
+    check::<[u16; 0]>();
+    check::<[u8; 42]>();
+
+    check::<S<u8>>();
+    check::<S<[&[bool]; 8]>>();
+
+    // FIXME: test tuples
+}

tests/ui/const-generics/adt_const_params/const_param_ty_impl_bad_field.rs

@@ -0,0 +1,13 @@
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+
+#[derive(PartialEq, Eq)]
+struct NotParam;
+
+#[derive(PartialEq, Eq)]
+struct CantParam(NotParam);
+
+impl std::marker::ConstParamTy for CantParam {}
+//~^ error: the trait `ConstParamTy` cannot be implemented for this type
+
+fn main() {}

tests/ui/const-generics/adt_const_params/const_param_ty_impl_bad_field.stderr

@@ -0,0 +1,12 @@
+error[E0204]: the trait `ConstParamTy` cannot be implemented for this type
+  --> $DIR/const_param_ty_impl_bad_field.rs:10:36
+   |
+LL | struct CantParam(NotParam);
+   |                  -------- this field does not implement `ConstParamTy`
+LL |
+LL | impl std::marker::ConstParamTy for CantParam {}
+   |                                    ^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0204`.

tests/ui/const-generics/adt_const_params/const_param_ty_impl_no_structural_eq.rs

@@ -0,0 +1,17 @@
+#![allow(incomplete_features)]
+#![feature(adt_const_params)]
+
+#[derive(PartialEq, Eq)]
+struct ImplementsConstParamTy;
+impl std::marker::ConstParamTy for ImplementsConstParamTy {}
+
+struct CantParam(ImplementsConstParamTy);
+
+impl std::marker::ConstParamTy for CantParam {}
+//~^ error: the type `CantParam` does not `#[derive(Eq)]`
+
+fn check<T: std::marker::ConstParamTy>() {}
+
+fn main() {
+    check::<ImplementsConstParamTy>();
+}

tests/ui/const-generics/adt_const_params/const_param_ty_impl_no_structural_eq.stderr

@@ -0,0 +1,12 @@
+error[E0277]: the type `CantParam` does not `#[derive(Eq)]`
+  --> $DIR/const_param_ty_impl_no_structural_eq.rs:10:36
+   |
+LL | impl std::marker::ConstParamTy for CantParam {}
+   |                                    ^^^^^^^^^ the trait `StructuralEq` is not implemented for `CantParam`
+   |
+note: required by a bound in `ConstParamTy`
+  --> $SRC_DIR/core/src/marker.rs:LL:COL
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/const-generics/nested-type.rs

@@ -3,7 +3,7 @@
 #![cfg_attr(full, feature(adt_const_params))]
 #![cfg_attr(full, allow(incomplete_features))]
 
-struct Foo<const N: [u8; { //[min]~ ERROR `[u8; _]` is forbidden
+struct Foo<const N: [u8; {
     struct Foo<const N: usize>;
 
     impl<const N: usize> Foo<N> {
@@ -15,5 +15,9 @@ struct Foo<const N: [u8; { //[min]~ ERROR `[u8; _]` is forbidden
     Foo::<17>::value()
     //~^ ERROR cannot call non-const fn
 }]>;
+//[min]~^^^^^^^^^^^^ ERROR `[u8; {
+
+// N.B. it is important that the comment above is not inside the array length,
+//      otherwise it may check for itself, instead of the actual error
 
 fn main() {}

tests/ui/fmt/format-string-error.rs

@@ -17,7 +17,7 @@ fn main() {
     let _ = format!("}");
     //~^ ERROR invalid format string: unmatched `}` found
     let _ = format!("{\\}");
-    //~^ ERROR invalid format string: expected `'}'`, found `'\\'`
+    //~^ ERROR invalid format string: expected `'}'`, found `'\'`
     let _ = format!("\n\n\n{\n\n\n");
     //~^ ERROR invalid format string
     let _ = format!(r###"

tests/ui/parser/issues/issue-62913.rs

@@ -1,4 +1,4 @@
 "\u\\"
 //~^ ERROR incorrect unicode escape sequence
 //~| ERROR invalid trailing slash in literal
-//~| ERROR expected item, found `"\u\\"`
+//~| ERROR expected item, found `"\u\"`