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Rollup merge of #82165 - nellshamrell:nell/fix-80658-B, r=estebank

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Reword labels on E0308 involving async fn return type

Fix for #80658.

When someone writes code like this:

```rust
fn foo() -> u8 {
    async fn async_fn() -> () {}

    async_fn()
}
```

And they try to compile it, they will see an error that looks like this:

```bash
error[E0308]: mismatched types
 --> test.rs:4:5
  |
1 | fn foo() -> u8 {
  |             -- expected `u8` because of return type
2 |     async fn async_fn() -> () {}
  |                            -- checked the `Output` of this `async fn`, found opaque type
3 |
4 |     async_fn()
  |     ^^^^^^^^^^ expected `u8`, found opaque type
  |
  = note: while checking the return type of this `async fn`
  = note:     expected type `u8`
          found opaque type `impl Future`
```
This commit is contained in:
Guillaume Gomez 2021-02-26 15:52:30 +01:00 • committed by GitHub
commit a56bbb134f
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12 changed files with 49 additions and 22 deletions
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13
compiler/rustc_infer/src/infer/error_reporting/mod.rs
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@ -1484,13 +1484,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
for (key, values) in types.iter() {
let count = values.len();
let kind = key.descr();
let mut returned_async_output_error = false;
for sp in values {
err.span_label(
*sp,
format!(
"{}{}{} {}{}",
if sp.is_desugaring(DesugaringKind::Async) {
"the `Output` of this `async fn`'s "
if sp.is_desugaring(DesugaringKind::Async)
&& !returned_async_output_error
{
"checked the `Output` of this `async fn`, "
} else if count == 1 {
"the "
} else {
@ -1502,6 +1505,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
pluralize!(count),
),
);
if sp.is_desugaring(DesugaringKind::Async)
&& returned_async_output_error == false
{
err.note("while checking the return type of the `async fn`");
returned_async_output_error = true;
}
}
}
}