Make ImplTraitPosition display more descriptive

Author: compiler-errors

compiler/rustc_ast_lowering/src/lib.rs

@@ -329,24 +329,24 @@ impl std::fmt::Display for ImplTraitPosition {
             ImplTraitPosition::AsyncBlock => "async blocks",
             ImplTraitPosition::Bound => "bounds",
             ImplTraitPosition::Generic => "generics",
-            ImplTraitPosition::ExternFnParam => "`extern fn` params",
-            ImplTraitPosition::ClosureParam => "closure params",
-            ImplTraitPosition::PointerParam => "`fn` pointer params",
-            ImplTraitPosition::FnTraitParam => "`Fn` trait params",
-            ImplTraitPosition::TraitParam => "trait method params",
-            ImplTraitPosition::ImplParam => "`impl` method params",
+            ImplTraitPosition::ExternFnParam => "`extern fn` parameters",
+            ImplTraitPosition::ClosureParam => "closure parameters",
+            ImplTraitPosition::PointerParam => "`fn` pointer parameters",
+            ImplTraitPosition::FnTraitParam => "the parameters of `Fn` trait bounds",
+            ImplTraitPosition::TraitParam => "trait method parameters",
+            ImplTraitPosition::ImplParam => "`impl` method parameters",
             ImplTraitPosition::ExternFnReturn => "`extern fn` return types",
             ImplTraitPosition::ClosureReturn => "closure return types",
             ImplTraitPosition::PointerReturn => "`fn` pointer return types",
-            ImplTraitPosition::FnTraitReturn => "`Fn` trait return types",
+            ImplTraitPosition::FnTraitReturn => "the return types of `Fn` trait bounds",
             ImplTraitPosition::GenericDefault => "generic parameter defaults",
             ImplTraitPosition::ConstTy => "const types",
             ImplTraitPosition::StaticTy => "static types",
             ImplTraitPosition::AssocTy => "associated types",
             ImplTraitPosition::FieldTy => "field types",
-            ImplTraitPosition::Cast => "cast types",
+            ImplTraitPosition::Cast => "cast expression types",
             ImplTraitPosition::ImplSelf => "impl headers",
-            ImplTraitPosition::OffsetOf => "`offset_of!` params",
+            ImplTraitPosition::OffsetOf => "`offset_of!` parameters",
         };
 
         write!(f, "{name}")

tests/ui/feature-gates/feature-gate-impl_trait_in_fn_trait_return.rs

@@ -1,6 +1,6 @@
 fn f() -> impl Fn() -> impl Sized { || () }
-//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return
+//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
 fn g() -> &'static dyn Fn() -> impl Sized { &|| () }
-//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return
+//~^ ERROR `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
 
 fn main() {}

tests/ui/feature-gates/feature-gate-impl_trait_in_fn_trait_return.stderr

@@ -1,4 +1,4 @@
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
   --> $DIR/feature-gate-impl_trait_in_fn_trait_return.rs:1:24
    |
 LL | fn f() -> impl Fn() -> impl Sized { || () }
@@ -7,7 +7,7 @@ LL | fn f() -> impl Fn() -> impl Sized { || () }
    = note: see issue #99697 <https://github.com/rust-lang/rust/issues/99697> for more information
    = help: add `#![feature(impl_trait_in_fn_trait_return)]` to the crate attributes to enable
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
   --> $DIR/feature-gate-impl_trait_in_fn_trait_return.rs:3:32
    |
 LL | fn g() -> &'static dyn Fn() -> impl Sized { &|| () }

tests/ui/impl-trait/where-allowed.stderr

@@ -43,7 +43,7 @@ LL | type InReturnInTypeAlias<R> = fn() -> impl Debug;
    = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
    = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer parameters
   --> $DIR/where-allowed.rs:18:40
    |
 LL | fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
@@ -55,7 +55,7 @@ error[E0562]: `impl Trait` only allowed in function and inherent method argument
 LL | fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() }
    |                                          ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `fn` pointer parameters
   --> $DIR/where-allowed.rs:26:38
    |
 LL | fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() }
@@ -67,49 +67,49 @@ error[E0562]: `impl Trait` only allowed in function and inherent method argument
 LL | fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() }
    |                                        ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the parameters of `Fn` trait bounds
   --> $DIR/where-allowed.rs:34:49
    |
 LL | fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() }
    |                                                 ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
   --> $DIR/where-allowed.rs:38:51
    |
 LL | fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() }
    |                                                   ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the parameters of `Fn` trait bounds
   --> $DIR/where-allowed.rs:42:55
    |
 LL | fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() }
    |                                                       ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the parameters of `Fn` trait bounds
   --> $DIR/where-allowed.rs:49:51
    |
 LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
    |                                                   ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
   --> $DIR/where-allowed.rs:54:53
    |
 LL | fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
    |                                                     ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the parameters of `Fn` trait bounds
   --> $DIR/where-allowed.rs:58:57
    |
 LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
    |                                                         ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the parameters of `Fn` trait bounds
   --> $DIR/where-allowed.rs:66:38
    |
 LL | fn in_Fn_parameter_in_generics<F: Fn(impl Debug)> (_: F) { panic!() }
    |                                      ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
   --> $DIR/where-allowed.rs:70:40
    |
 LL | fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
@@ -145,7 +145,7 @@ error[E0562]: `impl Trait` only allowed in function and inherent method argument
 LL |     InTupleVariant(impl Debug),
    |                    ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `extern fn` params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `extern fn` parameters
   --> $DIR/where-allowed.rs:138:33
    |
 LL |     fn in_foreign_parameters(_: impl Debug);
@@ -205,13 +205,13 @@ error[E0562]: `impl Trait` only allowed in function and inherent method argument
 LL |     where T: PartialEq<impl Debug>
    |                        ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait params
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the parameters of `Fn` trait bounds
   --> $DIR/where-allowed.rs:205:17
    |
 LL |     where T: Fn(impl Debug)
    |                 ^^^^^^^^^^
 
-error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in `Fn` trait return types
+error[E0562]: `impl Trait` only allowed in function and inherent method argument and return types, not in the return types of `Fn` trait bounds
   --> $DIR/where-allowed.rs:212:22
    |
 LL |     where T: Fn() -> impl Debug