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Auto merge of #79689 - Vooblin:patch1, r=tmandry

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Update tests of "unused_lifetimes" lint for async functions and corresponding source code

Before this PR the following code would cause an error:
```
#![deny(unused_lifetimes)]
async fn f<'a>(_: &'a i32) {}
fn main() {}
```
It was happening because of the desugaring of return type in async functions. As a result of the desugaring, the return type contains all lifetimes involved in the function signature. And these lifetimes were interpreted separately from the same in the function scope => so they are unused.

Now, all lifetimes from the return type are interpreted as used. It is also not perfect, but at least this lint doesn't cause wrong errors now.

This PR connected to issues #78522, #77217
This commit is contained in:
bors 2021-01-14 17:27:15 +00:00
commit 4275ef6c9d
3 changed files with 58 additions and 57 deletions
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20
compiler/rustc_resolve/src/late/lifetimes.rs
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@ -644,17 +644,17 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
} else {
bug!();
};
if let hir::ParamName::Plain(param_name) = name {
if param_name.name == kw::UnderscoreLifetime {
// Pick the elided lifetime "definition" if one exists
// and use it to make an elision scope.
self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
elision = Some(reg);
} else {
lifetimes.insert(name, reg);
}
// We cannot predict what lifetimes are unused in opaque type.
self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
if let hir::ParamName::Plain(Ident {
name: kw::UnderscoreLifetime,
..
}) = name
{
// Pick the elided lifetime "definition" if one exists
// and use it to make an elision scope.
elision = Some(reg);
} else {
self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
lifetimes.insert(name, reg);
}
}