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Rollup merge of #87322 - chazkiker2:fix/suggestion-ref-sync-send, r=estebank

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fix: clarify suggestion that `&T` must refer to `T: Sync` for `&T: Send`

### Description

- [x] fix #86507
- [x] add UI test for relevant code from issue
- [x] change `rustc_trait_selection/src/traits/error_reporting/suggestions.rs` to include a more clear suggestion when `&T` fails to satisfy `Send` bounds due to the fact that `T` fails to implement `Sync`
- [x] update UI test in Clippy: `src/tools/tests/ui/future_not_send.stderr`
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Yuki Okushi 2021-07-24 04:31:11 +09:00 • committed by GitHub
commit 3fc79fde63
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4 changed files with 80 additions and 7 deletions
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35
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
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@ -1857,12 +1857,37 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
}
}
GeneratorInteriorOrUpvar::Upvar(upvar_span) => {
// `Some(ref_ty)` if `target_ty` is `&T` and `T` fails to impl `Sync`
let refers_to_non_sync = match target_ty.kind() {
ty::Ref(_, ref_ty, _) => match self.evaluate_obligation(&obligation) {
Ok(eval) if !eval.may_apply() => Some(ref_ty),
_ => None,
},
_ => None,
};
let (span_label, span_note) = match refers_to_non_sync {
// if `target_ty` is `&T` and `T` fails to impl `Sync`,
// include suggestions to make `T: Sync` so that `&T: Send`
Some(ref_ty) => (
format!(
"has type `{}` which {}, because `{}` is not `Sync`",
target_ty, trait_explanation, ref_ty
),
format!(
"captured value {} because `&` references cannot be sent unless their referent is `Sync`",
trait_explanation
),
),
None => (
format!("has type `{}` which {}", target_ty, trait_explanation),
format!("captured value {}", trait_explanation),
),
};
let mut span = MultiSpan::from_span(upvar_span);
span.push_span_label(
upvar_span,
format!("has type `{}` which {}", target_ty, trait_explanation),
);
err.span_note(span, &format!("captured value {}", trait_explanation));
span.push_span_label(upvar_span, span_label);
err.span_note(span, &span_note);
}
}