Rollup merge of #126652 - Manishearth:anon-const-scope, r=bjorn3,Urgau

Clarify that anonymous consts still do introduce a new scope

See #120363 (comment)

This error message is misleading: it's trying to say that `const _ : () = ...` is a workaround for the lint, but by saying that anonymous constants are treated as being in the parent scope, it makes them appear useless for scope-hiding.

They *are* useful for scope-hiding, they are simply treated as part of the parent scope when it comes to this lint.

compiler/rustc_lint/messages.ftl

@@ -550,7 +550,7 @@ lint_non_local_definitions_impl = non-local `impl` definition, `impl` blocks sho
     .with_trait = an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
     .bounds = `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
     .doctest = make this doc-test a standalone test with its own `fn main() {"{"} ... {"}"}`
-    .exception = items in an anonymous const item (`const _: () = {"{"} ... {"}"}`) are treated as in the same scope as the anonymous const's declaration
+    .exception = items in an anonymous const item (`const _: () = {"{"} ... {"}"}`) are treated as in the same scope as the anonymous const's declaration for the purpose of this lint
     .const_anon = use a const-anon item to suppress this lint
     .macro_to_change = the {$macro_kind} `{$macro_to_change}` defines the non-local `impl`, and may need to be changed
 

tests/ui/lint/non-local-defs/cargo-update.stderr

@@ -12,7 +12,7 @@ LL | non_local_macro::non_local_impl!(LocalStruct);
    = note: the macro `non_local_macro::non_local_impl` may come from an old version of the `non_local_macro` crate, try updating your dependency with `cargo update -p non_local_macro`
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
-   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration
+   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration for the purpose of this lint
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
    = note: `#[warn(non_local_definitions)]` on by default
    = note: this warning originates in the macro `non_local_macro::non_local_impl` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/lint/non-local-defs/consts.stderr

@@ -15,7 +15,7 @@ LL |     impl Uto for &Test {}
    |
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
-   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration
+   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration for the purpose of this lint
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
    = note: `#[warn(non_local_definitions)]` on by default
 
@@ -32,7 +32,7 @@ LL |     impl Uto2 for Test {}
    |
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
-   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration
+   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration for the purpose of this lint
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
 
 warning: non-local `impl` definition, `impl` blocks should be written at the same level as their item
@@ -48,7 +48,7 @@ LL |     impl Uto3 for Test {}
    |
    = note: `impl` may be usable in bounds, etc. from outside the expression, which might e.g. make something constructible that previously wasn't, because it's still on a publicly-visible type
    = note: an `impl` is never scoped, even when it is nested inside an item, as it may impact type checking outside of that item, which can be the case if neither the trait or the self type are at the same nesting level as the `impl`
-   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration
+   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration for the purpose of this lint
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
 
 warning: non-local `impl` definition, `impl` blocks should be written at the same level as their item
@@ -94,7 +94,7 @@ LL |         impl Test {
    |              `Test` is not local
    |
    = note: methods and associated constants are still usable outside the current expression, only `impl Local` and `impl dyn Local` can ever be private, and only if the type is nested in the same item as the `impl`
-   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration
+   = note: items in an anonymous const item (`const _: () = { ... }`) are treated as in the same scope as the anonymous const's declaration for the purpose of this lint
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
 
 warning: non-local `impl` definition, `impl` blocks should be written at the same level as their item