Rollup merge of #108066 - compiler-errors:better-labels-for-bad-impl-trait, r=petrochenkov

Better names for illegal impl trait positions

Just some wording tweaks, no behavior changes.

9 files changed, 67 insertions, 42 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index cc523fe7d08..c4442b34fe4 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -139,13 +139,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::Cast(expr, ty) => {
                     let expr = self.lower_expr(expr);
                     let ty =
-                        self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                        self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Cast));
                     hir::ExprKind::Cast(expr, ty)
                 }
                 ExprKind::Type(expr, ty) => {
                     let expr = self.lower_expr(expr);
                     let ty =
-                        self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                        self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Cast));
                     hir::ExprKind::Type(expr, ty)
                 }
                 ExprKind::AddrOf(k, m, ohs) => {
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 2865082bd7a..6bafbfbc14c 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -378,8 +378,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                             )
                         });
 
-                        let lowered_ty = this
-                            .lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                        let lowered_ty = this.lower_ty(
+                            ty,
+                            &ImplTraitContext::Disallowed(ImplTraitPosition::ImplSelf),
+                        );
 
                         (trait_ref, lowered_ty)
                     });
@@ -458,7 +460,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         span: Span,
         body: Option<&Expr>,
     ) -> (&'hir hir::Ty<'hir>, hir::BodyId) {
-        let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+        let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
         (ty, self.lower_const_body(span, body))
     }
 
@@ -608,8 +610,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
                 }
                 ForeignItemKind::Static(t, m, _) => {
-                    let ty =
-                        self.lower_ty(t, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                    let ty = self
+                        .lower_ty(t, &ImplTraitContext::Disallowed(ImplTraitPosition::StaticTy));
                     hir::ForeignItemKind::Static(ty, *m)
                 }
                 ForeignItemKind::TyAlias(..) => hir::ForeignItemKind::Type,
@@ -679,11 +681,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 qself,
                 path,
                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
-                &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+                &ImplTraitContext::Disallowed(ImplTraitPosition::FieldTy),
             );
             self.arena.alloc(t)
         } else {
-            self.lower_ty(&f.ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
+            self.lower_ty(&f.ty, &ImplTraitContext::Disallowed(ImplTraitPosition::FieldTy))
         };
         let hir_id = self.lower_node_id(f.id);
         self.lower_attrs(hir_id, &f.attrs);
@@ -708,7 +710,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let (generics, kind, has_default) = match &i.kind {
             AssocItemKind::Const(_, ty, default) => {
-                let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                let ty =
+                    self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
                 let body = default.as_ref().map(|x| self.lower_const_body(i.span, Some(x)));
                 (hir::Generics::empty(), hir::TraitItemKind::Const(ty, body), body.is_some())
             }
@@ -746,7 +749,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     &ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
                     |this| {
                         let ty = ty.as_ref().map(|x| {
-                            this.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
+                            this.lower_ty(
+                                x,
+                                &ImplTraitContext::Disallowed(ImplTraitPosition::AssocTy),
+                            )
                         });
                         hir::TraitItemKind::Type(
                             this.lower_param_bounds(
@@ -805,7 +811,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
         let (generics, kind) = match &i.kind {
             AssocItemKind::Const(_, ty, expr) => {
-                let ty = self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                let ty =
+                    self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::ConstTy));
                 (
                     hir::Generics::empty(),
                     hir::ImplItemKind::Const(ty, self.lower_const_body(i.span, expr.as_deref())),
@@ -1441,7 +1448,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 hir_id: self.next_id(),
                 bound_generic_params: self.lower_generic_params(bound_generic_params),
                 bounded_ty: self
-                    .lower_ty(bounded_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type)),
+                    .lower_ty(bounded_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Bound)),
                 bounds: self.arena.alloc_from_iter(bounds.iter().map(|bound| {
                     self.lower_param_bound(
                         bound,
@@ -1465,9 +1472,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
             WherePredicate::EqPredicate(WhereEqPredicate { lhs_ty, rhs_ty, span }) => {
                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
                     lhs_ty: self
-                        .lower_ty(lhs_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type)),
+                        .lower_ty(lhs_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Bound)),
                     rhs_ty: self
-                        .lower_ty(rhs_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type)),
+                        .lower_ty(rhs_ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Bound)),
                     span: self.lower_span(*span),
                 })
             }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index a04a2595293..b543be3be50 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -253,7 +253,6 @@ enum ImplTraitContext {
 enum ImplTraitPosition {
     Path,
     Variable,
-    Type,
     Trait,
     AsyncBlock,
     Bound,
@@ -270,6 +269,13 @@ enum ImplTraitPosition {
     FnTraitReturn,
     TraitReturn,
     ImplReturn,
+    GenericDefault,
+    ConstTy,
+    StaticTy,
+    AssocTy,
+    FieldTy,
+    Cast,
+    ImplSelf,
 }
 
 impl std::fmt::Display for ImplTraitPosition {
@@ -277,7 +283,6 @@ impl std::fmt::Display for ImplTraitPosition {
         let name = match self {
             ImplTraitPosition::Path => "path",
             ImplTraitPosition::Variable => "variable binding",
-            ImplTraitPosition::Type => "type",
             ImplTraitPosition::Trait => "trait",
             ImplTraitPosition::AsyncBlock => "async block",
             ImplTraitPosition::Bound => "bound",
@@ -294,6 +299,13 @@ impl std::fmt::Display for ImplTraitPosition {
             ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
             ImplTraitPosition::TraitReturn => "trait method return",
             ImplTraitPosition::ImplReturn => "`impl` method return",
+            ImplTraitPosition::GenericDefault => "generic parameter default",
+            ImplTraitPosition::ConstTy => "const type",
+            ImplTraitPosition::StaticTy => "static type",
+            ImplTraitPosition::AssocTy => "associated type",
+            ImplTraitPosition::FieldTy => "field type",
+            ImplTraitPosition::Cast => "cast type",
+            ImplTraitPosition::ImplSelf => "impl header",
         };
 
         write!(f, "{name}")
@@ -2166,7 +2178,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             GenericParamKind::Type { default, .. } => {
                 let kind = hir::GenericParamKind::Type {
                     default: default.as_ref().map(|x| {
-                        self.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
+                        self.lower_ty(
+                            x,
+                            &ImplTraitContext::Disallowed(ImplTraitPosition::GenericDefault),
+                        )
                     }),
                     synthetic: false,
                 };
@@ -2174,7 +2189,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
             }
             GenericParamKind::Const { ty, kw_span: _, default } => {
-                let ty = self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
+                let ty = self.lower_ty(
+                    &ty,
+                    &ImplTraitContext::Disallowed(ImplTraitPosition::GenericDefault),
+                );
                 let default = default.as_ref().map(|def| self.lower_anon_const(def));
                 (
                     hir::ParamName::Plain(self.lower_ident(param.ident)),
diff --git a/tests/ui/associated-consts/issue-105330.stderr b/tests/ui/associated-consts/issue-105330.stderr
index 30c380152a5..08570d4a5d9 100644
--- a/tests/ui/associated-consts/issue-105330.stderr
+++ b/tests/ui/associated-consts/issue-105330.stderr
@@ -33,7 +33,7 @@ LL | fn main<A: TraitWAssocConst<A=32>>() {
    = note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
    = help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in impl header
   --> $DIR/issue-105330.rs:6:27
    |
 LL | impl TraitWAssocConst for impl Demo {
diff --git a/tests/ui/feature-gates/feature-gate-associated_type_bounds.stderr b/tests/ui/feature-gates/feature-gate-associated_type_bounds.stderr
index 5be1d97a059..6f2919b6c09 100644
--- a/tests/ui/feature-gates/feature-gate-associated_type_bounds.stderr
+++ b/tests/ui/feature-gates/feature-gate-associated_type_bounds.stderr
@@ -115,13 +115,13 @@ LL |     let _: impl Tr1<As1: Copy> = S1;
    = note: see issue #52662 <https://github.com/rust-lang/rust/issues/52662> for more information
    = help: add `#![feature(associated_type_bounds)]` to the crate attributes to enable
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in const type
   --> $DIR/feature-gate-associated_type_bounds.rs:58:14
    |
 LL | const _cdef: impl Tr1<As1: Copy> = S1;
    |              ^^^^^^^^^^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in const type
   --> $DIR/feature-gate-associated_type_bounds.rs:64:15
    |
 LL | static _sdef: impl Tr1<As1: Copy> = S1;
diff --git a/tests/ui/impl-trait/issues/issue-58956.stderr b/tests/ui/impl-trait/issues/issue-58956.stderr
index 123fb4df4b3..f591c07bcf5 100644
--- a/tests/ui/impl-trait/issues/issue-58956.stderr
+++ b/tests/ui/impl-trait/issues/issue-58956.stderr
@@ -1,4 +1,4 @@
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in const type
   --> $DIR/issue-58956.rs:7:11
    |
 LL | const _A: impl Lam = {
diff --git a/tests/ui/impl-trait/issues/issue-83929-impl-trait-in-generic-default.stderr b/tests/ui/impl-trait/issues/issue-83929-impl-trait-in-generic-default.stderr
index e635e554e23..a227f0ba7d1 100644
--- a/tests/ui/impl-trait/issues/issue-83929-impl-trait-in-generic-default.stderr
+++ b/tests/ui/impl-trait/issues/issue-83929-impl-trait-in-generic-default.stderr
@@ -1,10 +1,10 @@
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/issue-83929-impl-trait-in-generic-default.rs:1:16
    |
 LL | struct Foo<T = impl Copy>(T);
    |                ^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/issue-83929-impl-trait-in-generic-default.rs:4:20
    |
 LL | type Result<T, E = impl std::error::Error> = std::result::Result<T, E>;
diff --git a/tests/ui/impl-trait/issues/issue-86642.stderr b/tests/ui/impl-trait/issues/issue-86642.stderr
index 0ec118d5be8..a137777840b 100644
--- a/tests/ui/impl-trait/issues/issue-86642.stderr
+++ b/tests/ui/impl-trait/issues/issue-86642.stderr
@@ -1,4 +1,4 @@
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in const type
   --> $DIR/issue-86642.rs:1:11
    |
 LL | static x: impl Fn(&str) -> Result<&str, ()> = move |source| {
diff --git a/tests/ui/impl-trait/where-allowed.stderr b/tests/ui/impl-trait/where-allowed.stderr
index e3a9caa6460..201aba3adff 100644
--- a/tests/ui/impl-trait/where-allowed.stderr
+++ b/tests/ui/impl-trait/where-allowed.stderr
@@ -115,31 +115,31 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t
 LL | fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
    |                                        ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in field type
   --> $DIR/where-allowed.rs:81:32
    |
 LL | struct InBraceStructField { x: impl Debug }
    |                                ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in path
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in field type
   --> $DIR/where-allowed.rs:85:41
    |
 LL | struct InAdtInBraceStructField { x: Vec<impl Debug> }
    |                                         ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in field type
   --> $DIR/where-allowed.rs:89:27
    |
 LL | struct InTupleStructField(impl Debug);
    |                           ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in field type
   --> $DIR/where-allowed.rs:94:25
    |
 LL |     InBraceVariant { x: impl Debug },
    |                         ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in field type
   --> $DIR/where-allowed.rs:96:20
    |
 LL |     InTupleVariant(impl Debug),
@@ -187,31 +187,31 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t
 LL | impl PartialEq<impl Debug> for () {
    |                ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in impl header
   --> $DIR/where-allowed.rs:166:24
    |
 LL | impl PartialEq<()> for impl Debug {
    |                        ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in impl header
   --> $DIR/where-allowed.rs:171:6
    |
 LL | impl impl Debug {
    |      ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in impl header
   --> $DIR/where-allowed.rs:177:24
    |
 LL | impl InInherentImplAdt<impl Debug> {
    |                        ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in bound
   --> $DIR/where-allowed.rs:183:11
    |
 LL |     where impl Debug: Debug
    |           ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in bound
   --> $DIR/where-allowed.rs:190:15
    |
 LL |     where Vec<impl Debug>: Debug
@@ -235,37 +235,37 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t
 LL |     where T: Fn() -> impl Debug
    |                      ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/where-allowed.rs:217:40
    |
 LL | struct InStructGenericParamDefault<T = impl Debug>(T);
    |                                        ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/where-allowed.rs:221:36
    |
 LL | enum InEnumGenericParamDefault<T = impl Debug> { Variant(T) }
    |                                    ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/where-allowed.rs:225:38
    |
 LL | trait InTraitGenericParamDefault<T = impl Debug> {}
    |                                      ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/where-allowed.rs:229:41
    |
 LL | type InTypeAliasGenericParamDefault<T = impl Debug> = T;
    |                                         ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/where-allowed.rs:233:11
    |
 LL | impl <T = impl Debug> T {}
    |           ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type
+error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in generic parameter default
   --> $DIR/where-allowed.rs:240:40
    |
 LL | fn in_method_generic_param_default<T = impl Debug>(_: T) {}