Rollup merge of #133589 - voidc:remove-array-len, r=boxyuwu

Remove `hir::ArrayLen`

This refactoring removes `hir::ArrayLen`, replacing it with `hir::ConstArg`. To represent inferred array lengths (previously `hir::ArrayLen::Infer`), a new variant `ConstArgKind::Infer` is added.

r? `@BoxyUwU`

compiler/rustc_ast_lowering/src/expr.rs

@@ -116,7 +116,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 }
                 ExprKind::Repeat(expr, count) => {
                     let expr = self.lower_expr(expr);
-                    let count = self.lower_array_length(count);
+                    let count = self.lower_array_length_to_const_arg(count);
                     hir::ExprKind::Repeat(expr, count)
                 }
                 ExprKind::Tup(elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),

compiler/rustc_ast_lowering/src/index.rs

@@ -235,8 +235,7 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
     }
 
     fn visit_anon_const(&mut self, constant: &'hir AnonConst) {
-        // FIXME: use real span?
+        self.insert(constant.span, constant.hir_id, Node::AnonConst(constant));
-        self.insert(DUMMY_SP, constant.hir_id, Node::AnonConst(constant));
 
         self.with_parent(constant.hir_id, |this| {
             intravisit::walk_anon_const(this, constant);
@@ -252,8 +251,7 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
     }
 
     fn visit_const_arg(&mut self, const_arg: &'hir ConstArg<'hir>) {
-        // FIXME: use real span?
+        self.insert(const_arg.span(), const_arg.hir_id, Node::ConstArg(const_arg));
-        self.insert(DUMMY_SP, const_arg.hir_id, Node::ConstArg(const_arg));
 
         self.with_parent(const_arg.hir_id, |this| {
             intravisit::walk_const_arg(this, const_arg);
@@ -387,13 +385,6 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         });
     }
 
-    fn visit_array_length(&mut self, len: &'hir ArrayLen<'hir>) {
-        match len {
-            ArrayLen::Infer(inf) => self.insert(inf.span, inf.hir_id, Node::ArrayLenInfer(inf)),
-            ArrayLen::Body(..) => intravisit::walk_array_len(self, len),
-        }
-    }
-
     fn visit_pattern_type_pattern(&mut self, p: &'hir hir::Pat<'hir>) {
         self.visit_pat(p)
     }

compiler/rustc_ast_lowering/src/lib.rs

@@ -1257,9 +1257,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     }),
                 ))
             }
-            TyKind::Array(ty, length) => {
+            TyKind::Array(ty, length) => hir::TyKind::Array(
-                hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
+                self.lower_ty(ty, itctx),
-            }
+                self.lower_array_length_to_const_arg(length),
+            ),
             TyKind::Typeof(expr) => hir::TyKind::Typeof(self.lower_anon_const_to_anon_const(expr)),
             TyKind::TraitObject(bounds, kind) => {
                 let mut lifetime_bound = None;
@@ -2007,14 +2008,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.expr_block(block)
     }
 
-    fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen<'hir> {
+    fn lower_array_length_to_const_arg(&mut self, c: &AnonConst) -> &'hir hir::ConstArg<'hir> {
         match c.value.kind {
             ExprKind::Underscore => {
                 if self.tcx.features().generic_arg_infer() {
-                    hir::ArrayLen::Infer(hir::InferArg {
+                    let ct_kind = hir::ConstArgKind::Infer(self.lower_span(c.value.span));
-                        hir_id: self.lower_node_id(c.id),
+                    self.arena.alloc(hir::ConstArg { hir_id: self.next_id(), kind: ct_kind })
-                        span: self.lower_span(c.value.span),
-                    })
                 } else {
                     feature_err(
                         &self.tcx.sess,
@@ -2023,10 +2022,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         fluent_generated::ast_lowering_underscore_array_length_unstable,
                     )
                     .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
-                    hir::ArrayLen::Body(self.lower_anon_const_to_const_arg(c))
+                    self.lower_anon_const_to_const_arg(c)
                 }
             }
-            _ => hir::ArrayLen::Body(self.lower_anon_const_to_const_arg(c)),
+            _ => self.lower_anon_const_to_const_arg(c),
         }
     }
 

compiler/rustc_hir/src/hir.rs

@@ -275,6 +275,7 @@ impl<'hir> ConstArg<'hir> {
         match self.kind {
             ConstArgKind::Path(path) => path.span(),
             ConstArgKind::Anon(anon) => anon.span,
+            ConstArgKind::Infer(span) => span,
         }
     }
 }
@@ -289,6 +290,11 @@ pub enum ConstArgKind<'hir> {
     /// However, in the future, we'll be using it for all of those.
     Path(QPath<'hir>),
     Anon(&'hir AnonConst),
+    /// **Note:** Not all inferred consts are represented as
+    /// `ConstArgKind::Infer`. In cases where it is ambiguous whether
+    /// a generic arg is a type or a const, inference variables are
+    /// represented as `GenericArg::Infer` instead.
+    Infer(Span),
 }
 
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
@@ -308,6 +314,10 @@ pub enum GenericArg<'hir> {
     Lifetime(&'hir Lifetime),
     Type(&'hir Ty<'hir>),
     Const(&'hir ConstArg<'hir>),
+    /// **Note:** Inference variables are only represented as
+    /// `GenericArg::Infer` in cases where it is ambiguous whether
+    /// a generic arg is a type or a const. Otherwise, inference variables
+    /// are represented as `TyKind::Infer` or `ConstArgKind::Infer`.
     Infer(InferArg),
 }
 
@@ -1645,29 +1655,6 @@ impl fmt::Display for ConstContext {
 /// A literal.
 pub type Lit = Spanned<LitKind>;
 
-#[derive(Copy, Clone, Debug, HashStable_Generic)]
-pub enum ArrayLen<'hir> {
-    Infer(InferArg),
-    Body(&'hir ConstArg<'hir>),
-}
-
-impl ArrayLen<'_> {
-    pub fn span(self) -> Span {
-        match self {
-            ArrayLen::Infer(arg) => arg.span,
-            ArrayLen::Body(body) => body.span(),
-        }
-    }
-
-    pub fn hir_id(self) -> HirId {
-        match self {
-            ArrayLen::Infer(InferArg { hir_id, .. }) | ArrayLen::Body(&ConstArg { hir_id, .. }) => {
-                hir_id
-            }
-        }
-    }
-}
-
 /// A constant (expression) that's not an item or associated item,
 /// but needs its own `DefId` for type-checking, const-eval, etc.
 /// These are usually found nested inside types (e.g., array lengths)
@@ -2115,7 +2102,7 @@ pub enum ExprKind<'hir> {
     ///
     /// E.g., `[1; 5]`. The first expression is the element
     /// to be repeated; the second is the number of times to repeat it.
-    Repeat(&'hir Expr<'hir>, ArrayLen<'hir>),
+    Repeat(&'hir Expr<'hir>, &'hir ConstArg<'hir>),
 
     /// A suspension point for coroutines (i.e., `yield <expr>`).
     Yield(&'hir Expr<'hir>, YieldSource),
@@ -2625,7 +2612,7 @@ impl<'hir> Ty<'hir> {
             TyKind::Infer => true,
             TyKind::Slice(ty) => ty.is_suggestable_infer_ty(),
             TyKind::Array(ty, length) => {
-                ty.is_suggestable_infer_ty() || matches!(length, ArrayLen::Infer(..))
+                ty.is_suggestable_infer_ty() || matches!(length.kind, ConstArgKind::Infer(..))
             }
             TyKind::Tup(tys) => tys.iter().any(Self::is_suggestable_infer_ty),
             TyKind::Ptr(mut_ty) | TyKind::Ref(_, mut_ty) => mut_ty.ty.is_suggestable_infer_ty(),
@@ -2834,7 +2821,7 @@ pub enum TyKind<'hir> {
     /// A variable length slice (i.e., `[T]`).
     Slice(&'hir Ty<'hir>),
     /// A fixed length array (i.e., `[T; n]`).
-    Array(&'hir Ty<'hir>, ArrayLen<'hir>),
+    Array(&'hir Ty<'hir>, &'hir ConstArg<'hir>),
     /// A raw pointer (i.e., `*const T` or `*mut T`).
     Ptr(MutTy<'hir>),
     /// A reference (i.e., `&'a T` or `&'a mut T`).
@@ -2861,6 +2848,11 @@ pub enum TyKind<'hir> {
     Typeof(&'hir AnonConst),
     /// `TyKind::Infer` means the type should be inferred instead of it having been
     /// specified. This can appear anywhere in a type.
+    ///
+    /// **Note:** Not all inferred types are represented as
+    /// `TyKind::Infer`. In cases where it is ambiguous whether
+    /// a generic arg is a type or a const, inference variables are
+    /// represented as `GenericArg::Infer` instead.
     Infer,
     /// Placeholder for a type that has failed to be defined.
     Err(rustc_span::ErrorGuaranteed),
@@ -3801,8 +3793,6 @@ pub enum Node<'hir> {
     Crate(&'hir Mod<'hir>),
     Infer(&'hir InferArg),
     WherePredicate(&'hir WherePredicate<'hir>),
-    // FIXME: Merge into `Node::Infer`.
-    ArrayLenInfer(&'hir InferArg),
     PreciseCapturingNonLifetimeArg(&'hir PreciseCapturingNonLifetimeArg),
     // Created by query feeding
     Synthetic,
@@ -3856,7 +3846,6 @@ impl<'hir> Node<'hir> {
             | Node::OpaqueTy(..)
             | Node::Infer(..)
             | Node::WherePredicate(..)
-            | Node::ArrayLenInfer(..)
             | Node::Synthetic
             | Node::Err(..) => None,
         }

compiler/rustc_hir/src/intravisit.rs

@@ -343,9 +343,6 @@ pub trait Visitor<'v>: Sized {
     fn visit_pat_field(&mut self, f: &'v PatField<'v>) -> Self::Result {
         walk_pat_field(self, f)
     }
-    fn visit_array_length(&mut self, len: &'v ArrayLen<'v>) -> Self::Result {
-        walk_array_len(self, len)
-    }
     fn visit_anon_const(&mut self, c: &'v AnonConst) -> Self::Result {
         walk_anon_const(self, c)
     }
@@ -710,14 +707,6 @@ pub fn walk_pat_field<'v, V: Visitor<'v>>(visitor: &mut V, field: &'v PatField<'
     visitor.visit_pat(field.pat)
 }
 
-pub fn walk_array_len<'v, V: Visitor<'v>>(visitor: &mut V, len: &'v ArrayLen<'v>) -> V::Result {
-    match len {
-        // FIXME: Use `visit_infer` here.
-        ArrayLen::Infer(InferArg { hir_id, span: _ }) => visitor.visit_id(*hir_id),
-        ArrayLen::Body(c) => visitor.visit_const_arg(c),
-    }
-}
-
 pub fn walk_anon_const<'v, V: Visitor<'v>>(visitor: &mut V, constant: &'v AnonConst) -> V::Result {
     try_visit!(visitor.visit_id(constant.hir_id));
     visitor.visit_nested_body(constant.body)
@@ -739,6 +728,7 @@ pub fn walk_const_arg<'v, V: Visitor<'v>>(
     match &const_arg.kind {
         ConstArgKind::Path(qpath) => visitor.visit_qpath(qpath, const_arg.hir_id, qpath.span()),
         ConstArgKind::Anon(anon) => visitor.visit_anon_const(*anon),
+        ConstArgKind::Infer(..) => V::Result::output(),
     }
 }
 
@@ -753,7 +743,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
         }
         ExprKind::Repeat(ref element, ref count) => {
             try_visit!(visitor.visit_expr(element));
-            try_visit!(visitor.visit_array_length(count));
+            try_visit!(visitor.visit_const_arg(count));
         }
         ExprKind::Struct(ref qpath, fields, ref optional_base) => {
             try_visit!(visitor.visit_qpath(qpath, expression.hir_id, expression.span));
@@ -901,7 +891,7 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) -> V::Resul
         }
         TyKind::Array(ref ty, ref length) => {
             try_visit!(visitor.visit_ty(ty));
-            try_visit!(visitor.visit_array_length(length));
+            try_visit!(visitor.visit_const_arg(length));
         }
         TyKind::TraitObject(bounds, ref lifetime, _syntax) => {
             for bound in bounds {

compiler/rustc_hir_analysis/src/collect.rs

@@ -151,11 +151,11 @@ impl<'v> Visitor<'v> for HirPlaceholderCollector {
             _ => {}
         }
     }
-    fn visit_array_length(&mut self, length: &'v hir::ArrayLen<'v>) {
+    fn visit_const_arg(&mut self, const_arg: &'v hir::ConstArg<'v>) {
-        if let hir::ArrayLen::Infer(inf) = length {
+        if let hir::ConstArgKind::Infer(span) = const_arg.kind {
-            self.0.push(inf.span);
+            self.0.push(span);
         }
-        intravisit::walk_array_len(self, length)
+        intravisit::walk_const_arg(self, const_arg)
     }
 }
 

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -181,7 +181,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                     // expressions' count (i.e. `N` in `[x; N]`), and explicit
                     // `enum` discriminants (i.e. `D` in `enum Foo { Bar = D }`),
                     // as they shouldn't be able to cause query cycle errors.
-                    Node::Expr(Expr { kind: ExprKind::Repeat(_, ArrayLen::Body(ct)), .. })
+                    Node::Expr(Expr { kind: ExprKind::Repeat(_, ct), .. })
                         if ct.anon_const_hir_id() == Some(hir_id) =>
                     {
                         Some(parent_did)

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -145,7 +145,7 @@ fn const_arg_anon_type_of<'tcx>(tcx: TyCtxt<'tcx>, arg_hir_id: HirId, span: Span
         // Easy case: arrays repeat expressions.
         Node::Ty(&hir::Ty { kind: TyKind::Array(_, ref constant), .. })
         | Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
-            if constant.hir_id() == arg_hir_id =>
+            if constant.hir_id == arg_hir_id =>
         {
             return tcx.types.usize;
         }
@@ -579,8 +579,6 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_
             x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
         },
 
-        Node::ArrayLenInfer(_) => tcx.types.usize,
-
         x => {
             bug!("unexpected sort of node in type_of(): {:?}", x);
         }

compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs

@@ -104,7 +104,7 @@ fn generic_arg_mismatch_err(
             GenericArg::Type(hir::Ty { kind: hir::TyKind::Array(_, len), .. }),
             GenericParamDefKind::Const { .. },
         ) if tcx.type_of(param.def_id).skip_binder() == tcx.types.usize => {
-            let snippet = sess.source_map().span_to_snippet(tcx.hir().span(len.hir_id()));
+            let snippet = sess.source_map().span_to_snippet(tcx.hir().span(len.hir_id));
             if let Ok(snippet) = snippet {
                 err.span_suggestion(
                     arg.span(),

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2090,6 +2090,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 format!("Const::lower_const_arg: invalid qpath {qpath:?}"),
             ),
             hir::ConstArgKind::Anon(anon) => Const::from_anon_const(tcx, anon.def_id),
+            hir::ConstArgKind::Infer(span) => self.ct_infer(None, span),
         }
     }
 
@@ -2310,13 +2311,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 tcx.at(span).type_of(def_id).instantiate(tcx, args)
             }
             hir::TyKind::Array(ty, length) => {
-                let length = match length {
+                let length = self.lower_const_arg(length, FeedConstTy::No);
-                    hir::ArrayLen::Infer(inf) => self.ct_infer(None, inf.span),
-                    hir::ArrayLen::Body(constant) => {
-                        self.lower_const_arg(constant, FeedConstTy::No)
-                    }
-                };
-
                 Ty::new_array_with_const_len(tcx, self.lower_ty(ty), length)
             }
             hir::TyKind::Typeof(e) => tcx.type_of(e.def_id).instantiate_identity(),

compiler/rustc_hir_pretty/src/lib.rs

@@ -118,7 +118,6 @@ impl<'a> State<'a> {
             Node::LetStmt(a) => self.print_local_decl(a),
             Node::Crate(..) => panic!("cannot print Crate"),
             Node::WherePredicate(pred) => self.print_where_predicate(pred),
-            Node::ArrayLenInfer(_) => self.word("_"),
             Node::Synthetic => unreachable!(),
             Node::Err(_) => self.word("/*ERROR*/"),
         }
@@ -315,7 +314,7 @@ impl<'a> State<'a> {
                 self.word("[");
                 self.print_type(ty);
                 self.word("; ");
-                self.print_array_length(length);
+                self.print_const_arg(length);
                 self.word("]");
             }
             hir::TyKind::Typeof(ref e) => {
@@ -986,13 +985,6 @@ impl<'a> State<'a> {
         self.print_else(elseopt)
     }
 
-    fn print_array_length(&mut self, len: &hir::ArrayLen<'_>) {
-        match len {
-            hir::ArrayLen::Infer(..) => self.word("_"),
-            hir::ArrayLen::Body(ct) => self.print_const_arg(ct),
-        }
-    }
-
     fn print_anon_const(&mut self, constant: &hir::AnonConst) {
         self.ann.nested(self, Nested::Body(constant.body))
     }
@@ -1001,6 +993,7 @@ impl<'a> State<'a> {
         match &const_arg.kind {
             ConstArgKind::Path(qpath) => self.print_qpath(qpath, true),
             ConstArgKind::Anon(anon) => self.print_anon_const(anon),
+            ConstArgKind::Infer(..) => self.word("_"),
         }
     }
 
@@ -1073,12 +1066,12 @@ impl<'a> State<'a> {
         self.end()
     }
 
-    fn print_expr_repeat(&mut self, element: &hir::Expr<'_>, count: &hir::ArrayLen<'_>) {
+    fn print_expr_repeat(&mut self, element: &hir::Expr<'_>, count: &hir::ConstArg<'_>) {
         self.ibox(INDENT_UNIT);
         self.word("[");
         self.print_expr(element);
         self.word_space(";");
-        self.print_array_length(count);
+        self.print_const_arg(count);
         self.word("]");
         self.end()
     }

compiler/rustc_hir_typeck/src/expr.rs

@@ -19,7 +19,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{ExprKind, HirId, QPath};
-use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer as _;
+use rustc_hir_analysis::hir_ty_lowering::{FeedConstTy, HirTyLowerer as _};
 use rustc_infer::infer;
 use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_infer::traits::ObligationCause;
@@ -425,7 +425,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             | hir::Node::Crate(_)
             | hir::Node::Infer(_)
             | hir::Node::WherePredicate(_)
-            | hir::Node::ArrayLenInfer(_)
             | hir::Node::PreciseCapturingNonLifetimeArg(_)
             | hir::Node::OpaqueTy(_) => {
                 unreachable!("no sub-expr expected for {parent_node:?}")
@@ -1673,9 +1672,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         else {
             return;
         };
-        if let hir::TyKind::Array(_, length) = ty.peel_refs().kind
+        if let hir::TyKind::Array(_, ct) = ty.peel_refs().kind {
-            && let hir::ArrayLen::Body(ct) = length
-        {
             let span = ct.span();
             self.dcx().try_steal_modify_and_emit_err(
                 span,
@@ -1713,13 +1710,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     fn check_expr_repeat(
         &self,
         element: &'tcx hir::Expr<'tcx>,
-        count: &'tcx hir::ArrayLen<'tcx>,
+        count: &'tcx hir::ConstArg<'tcx>,
         expected: Expectation<'tcx>,
         expr: &'tcx hir::Expr<'tcx>,
     ) -> Ty<'tcx> {
         let tcx = self.tcx;
         let count_span = count.span();
-        let count = self.try_structurally_resolve_const(count_span, self.lower_array_length(count));
+        let count = self.try_structurally_resolve_const(
+            count_span,
+            self.normalize(count_span, self.lower_const_arg(count, FeedConstTy::No)),
+        );
 
         if let Some(count) = count.try_to_target_usize(tcx) {
             self.suggest_array_len(expr, count);

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -487,24 +487,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    pub(crate) fn lower_array_length(&self, length: &hir::ArrayLen<'tcx>) -> ty::Const<'tcx> {
-        match length {
-            hir::ArrayLen::Infer(inf) => self.ct_infer(None, inf.span),
-            hir::ArrayLen::Body(const_arg) => {
-                let span = const_arg.span();
-                let c = self.lowerer().lower_const_arg(const_arg, FeedConstTy::No);
-                self.register_wf_obligation(c.into(), span, ObligationCauseCode::WellFormed(None));
-                self.normalize(span, c)
-            }
-        }
-    }
-
     pub(crate) fn lower_const_arg(
         &self,
         const_arg: &'tcx hir::ConstArg<'tcx>,
-        param_def_id: DefId,
+        feed: FeedConstTy,
     ) -> ty::Const<'tcx> {
-        let ct = self.lowerer().lower_const_arg(const_arg, FeedConstTy::Param(param_def_id));
+        let ct = self.lowerer().lower_const_arg(const_arg, feed);
         self.register_wf_obligation(
             ct.into(),
             self.tcx.hir().span(const_arg.hir_id),
@@ -1279,7 +1267,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.fcx.lower_ty(ty).raw.into()
                     }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
-                        self.fcx.lower_const_arg(ct, param.def_id).into()
+                        self.fcx.lower_const_arg(ct, FeedConstTy::Param(param.def_id)).into()
                     }
                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
                         self.fcx.ty_infer(Some(param), inf.span).into()

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -7,7 +7,7 @@ use rustc_hir_analysis::hir_ty_lowering::generics::{
     check_generic_arg_count_for_call, lower_generic_args,
 };
 use rustc_hir_analysis::hir_ty_lowering::{
-    GenericArgsLowerer, HirTyLowerer, IsMethodCall, RegionInferReason,
+    FeedConstTy, GenericArgsLowerer, HirTyLowerer, IsMethodCall, RegionInferReason,
 };
 use rustc_infer::infer::{self, DefineOpaqueTypes, InferOk};
 use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext};
@@ -429,7 +429,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                         self.cfcx.lower_ty(ty).raw.into()
                     }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
-                        self.cfcx.lower_const_arg(ct, param.def_id).into()
+                        self.cfcx.lower_const_arg(ct, FeedConstTy::Param(param.def_id)).into()
                     }
                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
                         self.cfcx.ty_infer(Some(param), inf.span).into()

compiler/rustc_middle/src/hir/map/mod.rs

@@ -948,7 +948,6 @@ impl<'hir> Map<'hir> {
             Node::LetStmt(local) => local.span,
             Node::Crate(item) => item.spans.inner_span,
             Node::WherePredicate(pred) => pred.span,
-            Node::ArrayLenInfer(inf) => inf.span,
             Node::PreciseCapturingNonLifetimeArg(param) => param.ident.span,
             Node::Synthetic => unreachable!(),
             Node::Err(span) => span,
@@ -1226,7 +1225,6 @@ fn hir_id_to_string(map: Map<'_>, id: HirId) -> String {
         }
         Node::Crate(..) => String::from("(root_crate)"),
         Node::WherePredicate(_) => node_str("where predicate"),
-        Node::ArrayLenInfer(_) => node_str("array len infer"),
         Node::Synthetic => unreachable!(),
         Node::Err(_) => node_str("error"),
         Node::PreciseCapturingNonLifetimeArg(_param) => node_str("parameter"),

compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs

@@ -1837,11 +1837,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         };
         if let Some(tykind) = tykind
             && let hir::TyKind::Array(_, length) = tykind
-            && let hir::ArrayLen::Body(ct) = length
             && let Some((scalar, ty)) = sz.found.try_to_scalar()
             && ty == self.tcx.types.usize
         {
-            let span = ct.span();
+            let span = length.span();
             Some(TypeErrorAdditionalDiags::ConsiderSpecifyingLength {
                 span,
                 length: scalar.to_target_usize(&self.tcx).unwrap(),

src/librustdoc/clean/mod.rs

@@ -290,6 +290,7 @@ pub(crate) fn clean_const<'tcx>(
             ConstantKind::Path { path: qpath_to_string(qpath).into() }
         }
         hir::ConstArgKind::Anon(anon) => ConstantKind::Anonymous { body: anon.body },
+        hir::ConstArgKind::Infer(..) => ConstantKind::Infer,
     }
 }
 
@@ -1803,10 +1804,7 @@ pub(crate) fn clean_ty<'tcx>(ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> T
         }
         TyKind::Slice(ty) => Slice(Box::new(clean_ty(ty, cx))),
         TyKind::Pat(ty, pat) => Type::Pat(Box::new(clean_ty(ty, cx)), format!("{pat:?}").into()),
-        TyKind::Array(ty, ref length) => {
+        TyKind::Array(ty, ref const_arg) => {
-            let length = match length {
-                hir::ArrayLen::Infer(..) => "_".to_string(),
-                hir::ArrayLen::Body(const_arg) => {
             // NOTE(min_const_generics): We can't use `const_eval_poly` for constants
             // as we currently do not supply the parent generics to anonymous constants
             // but do allow `ConstKind::Param`.
@@ -1814,19 +1812,19 @@ pub(crate) fn clean_ty<'tcx>(ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> T
             // `const_eval_poly` tries to first substitute generic parameters which
             // results in an ICE while manually constructing the constant and using `eval`
             // does nothing for `ConstKind::Param`.
+            let length = match const_arg.kind {
+                hir::ConstArgKind::Infer(..) => "_".to_string(),
+                hir::ConstArgKind::Anon(hir::AnonConst { def_id, .. }) => {
                     let ct = lower_const_arg_for_rustdoc(cx.tcx, const_arg, FeedConstTy::No);
-                    let ct = if let hir::ConstArgKind::Anon(hir::AnonConst { def_id, .. }) =
-                        const_arg.kind
-                    {
                     let typing_env = ty::TypingEnv::post_analysis(cx.tcx, *def_id);
-                        cx.tcx.normalize_erasing_regions(typing_env, ct)
+                    let ct = cx.tcx.normalize_erasing_regions(typing_env, ct);
-                    } else {
+                    print_const(cx, ct)
-                        ct
+                }
-                    };
+                hir::ConstArgKind::Path(..) => {
+                    let ct = lower_const_arg_for_rustdoc(cx.tcx, const_arg, FeedConstTy::No);
                     print_const(cx, ct)
                 }
             };
-
             Array(Box::new(clean_ty(ty, cx)), length.into())
         }
         TyKind::Tup(tys) => Tuple(tys.iter().map(|ty| clean_ty(ty, cx)).collect()),

src/librustdoc/clean/types.rs

@@ -2399,6 +2399,8 @@ pub(crate) enum ConstantKind {
     Extern { def_id: DefId },
     /// `const FOO: u32 = ...;`
     Local { def_id: DefId, body: BodyId },
+    /// An inferred constant as in `[10u8; _]`.
+    Infer,
 }
 
 impl Constant {
@@ -2424,6 +2426,7 @@ impl ConstantKind {
             ConstantKind::Local { body, .. } | ConstantKind::Anonymous { body } => {
                 rendered_const(tcx, tcx.hir().body(body), tcx.hir().body_owner_def_id(body))
             }
+            ConstantKind::Infer { .. } => "_".to_string(),
         }
     }
 
@@ -2431,7 +2434,8 @@ impl ConstantKind {
         match *self {
             ConstantKind::TyConst { .. }
             | ConstantKind::Path { .. }
-            | ConstantKind::Anonymous { .. } => None,
+            | ConstantKind::Anonymous { .. }
+            | ConstantKind::Infer => None,
             ConstantKind::Extern { def_id } | ConstantKind::Local { def_id, .. } => {
                 print_evaluated_const(tcx, def_id, true, true)
             }
@@ -2442,7 +2446,8 @@ impl ConstantKind {
         match *self {
             ConstantKind::TyConst { .. }
             | ConstantKind::Extern { .. }
-            | ConstantKind::Path { .. } => false,
+            | ConstantKind::Path { .. }
+            | ConstantKind::Infer => false,
             ConstantKind::Local { body, .. } | ConstantKind::Anonymous { body } => {
                 is_literal_expr(tcx, body.hir_id)
             }

src/tools/clippy/clippy_lints/src/large_stack_arrays.rs

@@ -5,7 +5,7 @@ use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::is_from_proc_macro;
 use clippy_utils::macros::macro_backtrace;
 use clippy_utils::source::snippet;
-use rustc_hir::{ArrayLen, Expr, ExprKind, Item, ItemKind, Node};
+use rustc_hir::{Expr, ExprKind, Item, ItemKind, Node};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, ConstKind};
@@ -118,13 +118,13 @@ impl<'tcx> LateLintPass<'tcx> for LargeStackArrays {
 
 /// Only giving help messages if the expr does not contains macro expanded codes.
 fn might_be_expanded<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> bool {
-    /// Check if the span of `ArrayLen` of a repeat expression is within the expr's span,
+    /// Check if the span of `ConstArg` of a repeat expression is within the expr's span,
     /// if not, meaning this repeat expr is definitely from some proc-macro.
     ///
     /// This is a fail-safe to a case where even the `is_from_proc_macro` is unable to determain the
     /// correct result.
     fn repeat_expr_might_be_expanded(expr: &Expr<'_>) -> bool {
-        let ExprKind::Repeat(_, ArrayLen::Body(len_ct)) = expr.kind else {
+        let ExprKind::Repeat(_, len_ct) = expr.kind else {
             return false;
         };
         !expr.span.contains(len_ct.span())

src/tools/clippy/clippy_lints/src/utils/author.rs

@@ -3,7 +3,7 @@ use rustc_ast::LitIntType;
 use rustc_ast::ast::{LitFloatType, LitKind};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::{
-    self as hir, ArrayLen, BindingMode, CaptureBy, Closure, ClosureKind, ConstArg, ConstArgKind, CoroutineKind,
+    self as hir, BindingMode, CaptureBy, Closure, ClosureKind, ConstArg, ConstArgKind, CoroutineKind,
     ExprKind, FnRetTy, HirId, Lit, PatKind, QPath, StmtKind, TyKind,
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
@@ -278,6 +278,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 chain!(self, "let ConstArgKind::Anon({anon_const}) = {const_arg}.kind");
                 self.body(field!(anon_const.body));
             },
+            ConstArgKind::Infer(..) => chain!(self, "let ConstArgKind::Infer(..) = {const_arg}.kind"),
         }
     }
 
@@ -611,14 +612,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 bind!(self, value, length);
                 kind!("Repeat({value}, {length})");
                 self.expr(value);
-                match length.value {
+                self.const_arg(length);
-                    ArrayLen::Infer(..) => chain!(self, "let ArrayLen::Infer(..) = length"),
-                    ArrayLen::Body(const_arg) => {
-                        bind!(self, const_arg);
-                        chain!(self, "let ArrayLen::Body({const_arg}) = {length}");
-                        self.const_arg(const_arg);
-                    },
-                }
             },
             ExprKind::Err(_) => kind!("Err(_)"),
             ExprKind::DropTemps(expr) => {

src/tools/clippy/clippy_lints/src/zero_repeat_side_effects.rs

@@ -5,7 +5,7 @@ use clippy_utils::visitors::for_each_expr_without_closures;
 use rustc_ast::LitKind;
 use rustc_data_structures::packed::Pu128;
 use rustc_errors::Applicability;
-use rustc_hir::{ArrayLen, ConstArgKind, ExprKind, Node};
+use rustc_hir::{ConstArgKind, ExprKind, Node};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::Ty;
 use rustc_session::declare_lint_pass;
@@ -60,8 +60,7 @@ impl LateLintPass<'_> for ZeroRepeatSideEffects {
         // doesn't seem as confusing as `[f(); 0]`. It would also have false positives when eg.
         // the const item depends on `#[cfg]s` and has different values in different compilation
         // sessions).
-        else if let ExprKind::Repeat(inner_expr, length) = expr.kind
+        else if let ExprKind::Repeat(inner_expr, const_arg) = expr.kind
-            && let ArrayLen::Body(const_arg) = length
             && let ConstArgKind::Anon(anon_const) = const_arg.kind
             && let length_expr = hir_map.body(anon_const.body).value
             && !length_expr.span.from_expansion()

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -7,7 +7,7 @@ use rustc_data_structures::fx::FxHasher;
 use rustc_hir::MatchSource::TryDesugar;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{
-    ArrayLen, AssocItemConstraint, BinOpKind, BindingMode, Block, BodyId, Closure, ConstArg, ConstArgKind, Expr,
+    AssocItemConstraint, BinOpKind, BindingMode, Block, BodyId, Closure, ConstArg, ConstArgKind, Expr,
     ExprField, ExprKind, FnRetTy, GenericArg, GenericArgs, HirId, HirIdMap, InlineAsmOperand, LetExpr, Lifetime,
     LifetimeName, Pat, PatField, PatKind, Path, PathSegment, PrimTy, QPath, Stmt, StmtKind, TraitBoundModifiers, Ty,
     TyKind,
@@ -266,14 +266,6 @@ impl HirEqInterExpr<'_, '_, '_> {
         })
     }
 
-    pub fn eq_array_length(&mut self, left: ArrayLen<'_>, right: ArrayLen<'_>) -> bool {
-        match (left, right) {
-            (ArrayLen::Infer(..), ArrayLen::Infer(..)) => true,
-            (ArrayLen::Body(l_ct), ArrayLen::Body(r_ct)) => self.eq_const_arg(l_ct, r_ct),
-            (_, _) => false,
-        }
-    }
-
     pub fn eq_body(&mut self, left: BodyId, right: BodyId) -> bool {
         // swap out TypeckResults when hashing a body
         let old_maybe_typeck_results = self.inner.maybe_typeck_results.replace((
@@ -383,7 +375,7 @@ impl HirEqInterExpr<'_, '_, '_> {
             },
             (ExprKind::Path(l), ExprKind::Path(r)) => self.eq_qpath(l, r),
             (&ExprKind::Repeat(le, ll), &ExprKind::Repeat(re, rl)) => {
-                self.eq_expr(le, re) && self.eq_array_length(ll, rl)
+                self.eq_expr(le, re) && self.eq_const_arg(ll, rl)
             },
             (ExprKind::Ret(l), ExprKind::Ret(r)) => both(l.as_ref(), r.as_ref(), |l, r| self.eq_expr(l, r)),
             (&ExprKind::Struct(l_path, lf, ref lo), &ExprKind::Struct(r_path, rf, ref ro)) => {
@@ -469,8 +461,10 @@ impl HirEqInterExpr<'_, '_, '_> {
         match (&left.kind, &right.kind) {
             (ConstArgKind::Path(l_p), ConstArgKind::Path(r_p)) => self.eq_qpath(l_p, r_p),
             (ConstArgKind::Anon(l_an), ConstArgKind::Anon(r_an)) => self.eq_body(l_an.body, r_an.body),
+            (ConstArgKind::Infer(..), ConstArgKind::Infer(..)) => true,
             // Use explicit match for now since ConstArg is undergoing flux.
-            (ConstArgKind::Path(..), ConstArgKind::Anon(..)) | (ConstArgKind::Anon(..), ConstArgKind::Path(..)) => {
+            (ConstArgKind::Path(..), ConstArgKind::Anon(..)) | (ConstArgKind::Anon(..), ConstArgKind::Path(..))
+            | (ConstArgKind::Infer(..), _) | (_, ConstArgKind::Infer(..)) => {
                 false
             },
         }
@@ -589,7 +583,7 @@ impl HirEqInterExpr<'_, '_, '_> {
     pub fn eq_ty(&mut self, left: &Ty<'_>, right: &Ty<'_>) -> bool {
         match (&left.kind, &right.kind) {
             (&TyKind::Slice(l_vec), &TyKind::Slice(r_vec)) => self.eq_ty(l_vec, r_vec),
-            (&TyKind::Array(lt, ll), &TyKind::Array(rt, rl)) => self.eq_ty(lt, rt) && self.eq_array_length(ll, rl),
+            (&TyKind::Array(lt, ll), &TyKind::Array(rt, rl)) => self.eq_ty(lt, rt) && self.eq_const_arg(ll, rl),
             (TyKind::Ptr(l_mut), TyKind::Ptr(r_mut)) => l_mut.mutbl == r_mut.mutbl && self.eq_ty(l_mut.ty, r_mut.ty),
             (TyKind::Ref(_, l_rmut), TyKind::Ref(_, r_rmut)) => {
                 l_rmut.mutbl == r_rmut.mutbl && self.eq_ty(l_rmut.ty, r_rmut.ty)
@@ -1008,7 +1002,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
             },
             ExprKind::Repeat(e, len) => {
                 self.hash_expr(e);
-                self.hash_array_length(len);
+                self.hash_const_arg(len);
             },
             ExprKind::Ret(ref e) => {
                 if let Some(e) = *e {
@@ -1201,7 +1195,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
             },
             &TyKind::Array(ty, len) => {
                 self.hash_ty(ty);
-                self.hash_array_length(len);
+                self.hash_const_arg(len);
             },
             TyKind::Pat(ty, pat) => {
                 self.hash_ty(ty);
@@ -1252,13 +1246,6 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
         }
     }
 
-    pub fn hash_array_length(&mut self, length: ArrayLen<'_>) {
-        match length {
-            ArrayLen::Infer(..) => {},
-            ArrayLen::Body(ct) => self.hash_const_arg(ct),
-        }
-    }
-
     pub fn hash_body(&mut self, body_id: BodyId) {
         // swap out TypeckResults when hashing a body
         let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body_id));
@@ -1270,6 +1257,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
         match &const_arg.kind {
             ConstArgKind::Path(path) => self.hash_qpath(path),
             ConstArgKind::Anon(anon) => self.hash_body(anon.body),
+            ConstArgKind::Infer(..) => {},
         }
     }
 

src/tools/clippy/clippy_utils/src/lib.rs

@@ -103,7 +103,7 @@ use rustc_hir::definitions::{DefPath, DefPathData};
 use rustc_hir::hir_id::{HirIdMap, HirIdSet};
 use rustc_hir::intravisit::{FnKind, Visitor, walk_expr};
 use rustc_hir::{
-    self as hir, Arm, ArrayLen, BindingMode, Block, BlockCheckMode, Body, ByRef, Closure, ConstArgKind, ConstContext,
+    self as hir, Arm, BindingMode, Block, BlockCheckMode, Body, ByRef, Closure, ConstArgKind, ConstContext,
     Destination, Expr, ExprField, ExprKind, FnDecl, FnRetTy, GenericArgs, HirId, Impl, ImplItem, ImplItemKind,
     ImplItemRef, Item, ItemKind, LangItem, LetStmt, MatchSource, Mutability, Node, OwnerId, OwnerNode, Param, Pat,
     PatKind, Path, PathSegment, PrimTy, QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitItemRef, TraitRef,
@@ -910,7 +910,7 @@ pub fn is_default_equivalent(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
             _ => false,
         },
         ExprKind::Tup(items) | ExprKind::Array(items) => items.iter().all(|x| is_default_equivalent(cx, x)),
-        ExprKind::Repeat(x, ArrayLen::Body(len)) => {
+        ExprKind::Repeat(x, len) => {
             if let ConstArgKind::Anon(anon_const) = len.kind
                 && let ExprKind::Lit(const_lit) = cx.tcx.hir().body(anon_const.body).value.kind
                 && let LitKind::Int(v, _) = const_lit.node
@@ -940,7 +940,7 @@ fn is_default_equivalent_from(cx: &LateContext<'_>, from_func: &Expr<'_>, arg: &
                 ..
             }) => return sym.is_empty() && is_path_lang_item(cx, ty, LangItem::String),
             ExprKind::Array([]) => return is_path_diagnostic_item(cx, ty, sym::Vec),
-            ExprKind::Repeat(_, ArrayLen::Body(len)) => {
+            ExprKind::Repeat(_, len) => {
                 if let ConstArgKind::Anon(anon_const) = len.kind
                     && let ExprKind::Lit(const_lit) = cx.tcx.hir().body(anon_const.body).value.kind
                     && let LitKind::Int(v, _) = const_lit.node

src/tools/clippy/tests/ui/author/repeat.stdout

@@ -1,8 +1,7 @@
 if let ExprKind::Repeat(value, length) = expr.kind
     && let ExprKind::Lit(ref lit) = value.kind
     && let LitKind::Int(1, LitIntType::Unsigned(UintTy::U8)) = lit.node
-    && let ArrayLen::Body(const_arg) = length
+    && let ConstArgKind::Anon(anon_const) = length.kind
-    && let ConstArgKind::Anon(anon_const) = const_arg.kind
     && expr1 = &cx.tcx.hir().body(anon_const.body).value
     && let ExprKind::Lit(ref lit1) = expr1.kind
     && let LitKind::Int(5, LitIntType::Unsuffixed) = lit1.node