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Rollup merge of #137232 - estebank:from-residual-note, r=petrochenkov

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Don't mention `FromResidual` on bad `?`

Unless `try_trait_v2` is enabled, don't mention that `FromResidual` isn't implemented for a specific type when the implicit `From` conversion of a `?` fails. For the end user on stable, `?` might as well be a compiler intrinsic, so we remove that note to avoid further confusion and allowing other parts of the error to be more prominent.

```
error[E0277]: `?` couldn't convert the error to `u8`
  --> $DIR/bad-interconversion.rs:4:20
   |
LL | fn result_to_result() -> Result<u64, u8> {
   |                          --------------- expected `u8` because of this
LL |     Ok(Err(123_i32)?)
   |        ------------^ the trait `From<i32>` is not implemented for `u8`
   |        |
   |        this can't be annotated with `?` because it has type `Result<_, i32>`
   |
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
   = help: the following other types implement trait `From<T>`:
             `u8` implements `From<Char>`
             `u8` implements `From<bool>`
```
This commit is contained in:
Matthias Krüger 2025-02-19 18:52:08 +01:00 • committed by GitHub
commit dd60b6ca27
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6 changed files with 12 additions and 6 deletions
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8
compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
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@ -3289,6 +3289,14 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
let mut parent_trait_pred =
self.resolve_vars_if_possible(data.derived.parent_trait_pred);
let parent_def_id = parent_trait_pred.def_id();
if tcx.is_diagnostic_item(sym::FromResidual, parent_def_id)
&& !tcx.features().enabled(sym::try_trait_v2)
{
// If `#![feature(try_trait_v2)]` is not enabled, then there's no point on
// talking about `FromResidual<Result<A, B>>`, as the end user has nothing they
// can do about it. As far as they are concerned, `?` is compiler magic.
return;
}
let self_ty_str =
tcx.short_string(parent_trait_pred.skip_binder().self_ty(), err.long_ty_path());
let trait_name = parent_trait_pred.print_modifiers_and_trait_path().to_string();