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This commit is contained in:
Niko Matsakis 2021-04-08 10:56:03 -04:00
parent 1a14315975
commit c1dc0b7bbc
1 changed files with 23 additions and 1 deletions
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24
compiler/rustc_resolve/src/late/lifetimes.rs
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@ -2343,7 +2343,18 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
Scope::TraitRefBoundary { s, .. } => {
// We've exited nested poly trait refs; mark that we are no longer in nested trait refs.
// We don't increase the late depth because this isn't a `Binder` scope
// We don't increase the late depth because this isn't a `Binder` scope.
//
// This came up in #83737, which boiled down to a case like this:
//
// ```
// F: for<> Fn(&()) -> Box<dyn for<> Future<Output = ()> + Unpin>,
// // ^^^^^
// ```
//
// Here, as we traverse upwards from the `dyn for<>` binder, we want to reset `in_poly_trait_ref`
// to false, so that we avoid excess contaenation when we encounter the outer `for<>` binder.
in_poly_trait_ref = false;
scope = s;
}
@ -2369,6 +2380,17 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
// We've already seen a binder that is a poly trait ref and this one is too,
// that means that they are nested and we are concatenating the bound vars;
// don't increase the late depth.
//
// This happens specifically with associated trait bounds like the following:
//
// ```
// for<'a> T: Iterator<Item: for<'b> Foo<'a, 'b>>
// ```
//
// In this case, as we traverse `for<'b>`, we would increment `late_depth` but
// set `in_poly_trait_ref` to true. Then when we traverse `for<'a>`, we would
// not increment `late_depth` again. (NB: Niko thinks this logic is actually
// wrong.)
(true, true) => {}
// We've exited nested poly trait refs; add one to the late depth and mark
// that we are no longer in nested trait refs