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Tweak suggested lifetimes to modify return type instead of &self receiver

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Do not suggest constraining the `&self` param, but rather the return type.
If that is wrong (because it is not sufficient), a follow up error will tell the
user to fix it. This way we lower the chances of *over* constraining, but still
get the cake of "correctly" contrained in two steps.

This is a correct suggestion:

```
error: lifetime may not live long enough
  --> $DIR/ex3-both-anon-regions-return-type-is-anon.rs:9:9
   |
LL |     fn foo<'a>(&self, x: &i32) -> &i32 {
   |                -         - let's call the lifetime of this reference `'1`
   |                |
   |                let's call the lifetime of this reference `'2`
LL |         x
   |         ^ method was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
   |
help: consider introducing a named lifetime parameter and update trait if needed
   |
LL |     fn foo<'a>(&self, x: &'a i32) -> &'a i32 {
   |                           ++          ++
```

While this is incomplete because it should suggestino `&'a self`

```
error: lifetime may not live long enough
  --> $DIR/ex3-both-anon-regions-self-is-anon.rs:7:19
   |
LL |     fn foo<'a>(&self, x: &Foo) -> &Foo {
   |                -         - let's call the lifetime of this reference `'1`
   |                |
   |                let's call the lifetime of this reference `'2`
LL |         if true { x } else { self }
   |                   ^ method was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
   |
help: consider introducing a named lifetime parameter and update trait if needed
   |
LL |     fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
   |                           ++          ++
```

but the follow up error is

```
error: lifetime may not live long enough
 --> tests/ui/lifetimes/lifetime-errors/ex3-both-anon-regions-self-is-anon.rs:7:30
  |
6 |     fn foo<'a>(&self, x: &'a Foo) -> &'a Foo {
  |            --  - let's call the lifetime of this reference `'1`
  |            |
  |            lifetime `'a` defined here
7 |         if true { x } else { self }
  |                              ^^^^ method was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
  |
help: consider introducing a named lifetime parameter and update trait if needed
  |
6 |     fn foo<'a>(&'a self, x: &'a Foo) -> &'a Foo {
  |                 ++
```
This commit is contained in:
Esteban Küber 2024-05-07 19:54:16 +00:00
parent ee5a157b4a
commit 1775e7b93d
18 changed files with 111 additions and 105 deletions
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10
compiler/rustc_infer/src/errors/mod.rs
View file

@ -484,13 +484,19 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
suggestions: vec![],
suggestion_param_name: suggestion_param_name.clone(),
};
visitor.visit_ty(self.ty_sub);
visitor.visit_ty(self.ty_sup);
if let Some(fn_decl) = node.fn_decl()
&& let hir::FnRetTy::Return(ty) = fn_decl.output
{
visitor.visit_ty(ty);
}
if visitor.suggestions.is_empty() {
// Do not suggest constraining the `&self` param, but rather the return type.
// If that is wrong (because it is not sufficient), a follow up error will tell the
// user to fix it. This way we lower the chances of *over* constraining, but still
// get the cake of "correctly" contrained in two steps.
visitor.visit_ty(self.ty_sup);
}
visitor.visit_ty(self.ty_sub);
if visitor.suggestions.is_empty() {
return false;
}