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Rollup merge of #90933 - compiler-errors:master, r=estebank

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Fix await suggestion on non-future type

Remove a match block that would suggest to add `.await` in the case where the expected type's `Future::Output` equals the found type. We only want to suggest `.await`ing in the opposite case (the found type's `Future::Output` equals the expected type).

The code sample is here: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=6ba6b83d4dddda263553b79dca9f6bcb

Before:
```
➜  ~ rustc --edition=2021 --crate-type=lib test.rs
error[E0308]: `match` arms have incompatible types
 --> test.rs:4:14
  |
2 |       let x = match 1 {
  |  _____________-
3 | |         1 => other(),
  | |              ------- this is found to be of type `impl Future`
4 | |         2 => other().await,
  | |              ^^^^^^^^^^^^^ expected opaque type, found enum `Result`
5 | |     };
  | |_____- `match` arms have incompatible types
  |
  = note: expected type `impl Future`
             found enum `Result<(), ()>`
help: consider `await`ing on the `Future`
  |
4 |         2 => other().await.await,
  |                           ++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
```

After:
```
➜  ~ rustc +stage1 --edition=2021 --crate-type=lib test.rs
error[E0308]: `match` arms have incompatible types
 --> test.rs:4:14
  |
2 |       let x = match 1 {
  |  _____________-
3 | |         1 => other(),
  | |              ------- this is found to be of type `impl Future`
4 | |         2 => other().await,
  | |              ^^^^^^^^^^^^^ expected opaque type, found enum `Result`
5 | |     };
  | |_____- `match` arms have incompatible types
  |
  = note: expected type `impl Future`
             found enum `Result<(), ()>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
```

Fixes #90931
This commit is contained in:
Matthias Krüger 2021-11-16 23:58:24 +01:00 • committed by GitHub
commit eb9859f00d
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3 changed files with 123 additions and 20 deletions
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45
compiler/rustc_infer/src/infer/error_reporting/mod.rs
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@ -1794,31 +1794,38 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
}
},
(_, Some(ty)) if ty::TyS::same_type(exp_found.expected, ty) => {
let span = match cause.code {
// scrutinee's span
ObligationCauseCode::Pattern { span: Some(span), .. } => span,
_ => exp_span,
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
(Some(ty), _) if ty::TyS::same_type(ty, exp_found.found) => {
let span = match cause.code {
// scrutinee's span
ObligationCauseCode::Pattern { span: Some(span), .. } => span,
_ => exp_span,
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
exp_span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
(Some(ty), _) if ty::TyS::same_type(ty, exp_found.found) => match cause.code {
ObligationCauseCode::Pattern { span: Some(span), .. }
| ObligationCauseCode::IfExpression(box IfExpressionCause { then: span, .. }) => {
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
ref prior_arms,
..
}) => {
diag.multipart_suggestion_verbose(
"consider `await`ing on the `Future`",
prior_arms
.iter()
.map(|arm| (arm.shrink_to_hi(), ".await".to_string()))
.collect(),
Applicability::MaybeIncorrect,
);
}
_ => {}
},
_ => {}
}
}