Rollup merge of #135044 - compiler-errors:better-infer-suggestions-in-const, r=oli-obk

Improve infer (`_`) suggestions in `const`s and `static`s

Fixes https://github.com/rust-lang/rust/issues/135010.

This PR does a few things to (imo) greatly improve the error message when users write something like `static FOO: [i32; _] = [1, 2, 3]`.

Firstly, it adapts the recovery code for when we encounter `_` in a const/static to work a bit more like `fn foo() -> _`, and removes the somewhat redundant query `diagnostic_only_typeck`.

Secondly, it changes the lowering for `[T; _]` to always lower under the `feature(generic_arg_infer)` logic to `ConstArgKind::Infer`. We still issue the feature error, so it's not doing anything *observable* on the good path, but it does mean that we no longer erroneously interpret `[T; _]`'s array length as a `_` **wildcard expression** (à la destructuring assignment, like `(_, y) = expr`).

Lastly it makes the suggestions verbose and fixes (well, suppresses) a bug with stashing and suggestions.

r? oli-obk

1 files changed, 0 insertions, 3 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 7e7b602c560..b6934495e44 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1100,9 +1100,6 @@ rustc_queries! {
         desc { |tcx| "type-checking `{}`", tcx.def_path_str(key) }
         cache_on_disk_if(tcx) { !tcx.is_typeck_child(key.to_def_id()) }
     }
-    query diagnostic_only_typeck(key: LocalDefId) -> &'tcx ty::TypeckResults<'tcx> {
-        desc { |tcx| "type-checking `{}`", tcx.def_path_str(key) }
-    }
 
     query used_trait_imports(key: LocalDefId) -> &'tcx UnordSet<LocalDefId> {
         desc { |tcx| "finding used_trait_imports `{}`", tcx.def_path_str(key) }