bjoernager/rust
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Fix a error suggestion for E0121 when using placeholder _ as return types on function signature.

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Recommit after refactoring based on comment:
https://github.com/rust-lang/rust/pull/126017#issuecomment-2189149361

But when changing return type's lifetime to `ReError` will affect the subsequent borrow check process and cause test11 in typeck_type_placeholder_item.rs to lost E0515 message.
```rust
fn test11(x: &usize) -> &_ {
//~^ ERROR the placeholder `_` is not allowed within types on item signatures for return types
    &x //~ ERROR cannot return reference to function parameter(this E0515 msg will disappear)
}

```
This commit is contained in:
surechen 2024-06-29 14:23:33 +08:00
parent 4e63822fc4
commit 50edb32939
6 changed files with 127 additions and 11 deletions
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19
compiler/rustc_hir_analysis/src/collect.rs
View file

@ -1459,8 +1459,25 @@ fn infer_return_ty_for_fn_sig<'tcx>(
Some(ty) => {
let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
// Typeck doesn't expect erased regions to be returned from `type_of`.
// This is a heuristic approach. If the scope has region paramters,
// we should change fn_sig's lifetime from `ReErased` to `ReError`,
// otherwise to `ReStatic`.
let has_region_params = generics.params.iter().any(|param| match param.kind {
GenericParamKind::Lifetime { .. } => true,
_ => false,
});
let fn_sig = tcx.fold_regions(fn_sig, |r, _| match *r {
ty::ReErased => tcx.lifetimes.re_static,
ty::ReErased => {
if has_region_params {
ty::Region::new_error_with_message(
tcx,
DUMMY_SP,
"erased region is not allowed here in return type",
)
} else {
tcx.lifetimes.re_static
}
}
_ => r,
});