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Don't mention FromResidual on bad ? #137232

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Feb 19, 2025
Merged

Don't mention FromResidual on bad ? #137232

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8 changes: 8 additions & 0 deletions compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3293,6 +3293,14 @@ 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)
Comment on lines +3296 to +3297
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We could add a further check for whether the current compiler is nightly and the feature is disabled to still provide a note that the feature could be enabled.

{
// 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();
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1 change: 1 addition & 0 deletions tests/ui/traits/question-mark-result-err-mismatch.rs
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@@ -1,3 +1,4 @@
#![feature(try_trait_v2)]
fn foo() -> Result<String, String> { //~ NOTE expected `String` because of this
let test = String::from("one,two");
let x = test
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6 changes: 3 additions & 3 deletions tests/ui/traits/question-mark-result-err-mismatch.stderr
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@@ -1,5 +1,5 @@
error[E0277]: `?` couldn't convert the error to `String`
--> $DIR/question-mark-result-err-mismatch.rs:14:22
--> $DIR/question-mark-result-err-mismatch.rs:15:22
|
LL | fn foo() -> Result<String, String> {
| ---------------------- expected `String` because of this
Expand All @@ -17,7 +17,7 @@ LL | .map(|()| "")?;
= note: required for `Result<String, String>` to implement `FromResidual<Result<Infallible, ()>>`

error[E0277]: `?` couldn't convert the error to `String`
--> $DIR/question-mark-result-err-mismatch.rs:28:25
--> $DIR/question-mark-result-err-mismatch.rs:29:25
|
LL | fn bar() -> Result<(), String> {
| ------------------ expected `String` because of this
Expand All @@ -40,7 +40,7 @@ LL | .map_err(|_| ())?;
= note: required for `Result<(), String>` to implement `FromResidual<Result<Infallible, ()>>`

error[E0277]: `?` couldn't convert the error to `String`
--> $DIR/question-mark-result-err-mismatch.rs:48:11
--> $DIR/question-mark-result-err-mismatch.rs:49:11
|
LL | fn baz() -> Result<String, String> {
| ---------------------- expected `String` because of this
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1 change: 0 additions & 1 deletion tests/ui/try-block/try-block-bad-type.stderr
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Expand Up @@ -10,7 +10,6 @@ LL | Err("")?;
= help: the trait `From<&str>` is not implemented for `TryFromSliceError`
but trait `From<Infallible>` is implemented for it
= help: for that trait implementation, expected `Infallible`, found `&str`
= note: required for `Result<u32, TryFromSliceError>` to implement `FromResidual<Result<Infallible, &str>>`

error[E0271]: type mismatch resolving `<Result<i32, i32> as Try>::Output == &str`
--> $DIR/try-block-bad-type.rs:12:9
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1 change: 0 additions & 1 deletion tests/ui/try-trait/bad-interconversion.stderr
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Expand Up @@ -12,7 +12,6 @@ LL | Ok(Err(123_i32)?)
= help: the following other types implement trait `From<T>`:
`u8` implements `From<Char>`
`u8` implements `From<bool>`
= note: required for `Result<u64, u8>` to implement `FromResidual<Result<Infallible, i32>>`

error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
--> $DIR/bad-interconversion.rs:9:12
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1 change: 0 additions & 1 deletion tests/ui/try-trait/issue-32709.stderr
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Expand Up @@ -19,7 +19,6 @@ LL | Err(5)?;
`(T, T, T, T, T, T, T, T)` implements `From<[T; 8]>`
`(T, T, T, T, T, T, T, T, T)` implements `From<[T; 9]>`
and 4 others
= note: required for `Result<i32, ()>` to implement `FromResidual<Result<Infallible, {integer}>>`

error: aborting due to 1 previous error

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