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improve fixme

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This commit is contained in:
Bastian Kauschke 2020-11-06 19:21:17 +01:00
parent cc19df627e
commit e06785b676
1 changed files with 6 additions and 3 deletions
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9
compiler/rustc_mir/src/transform/validate.rs
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@ -85,9 +85,12 @@ pub fn equal_up_to_regions(
param_env, param_env,
ty.fold_with(&mut BottomUpFolder { ty.fold_with(&mut BottomUpFolder {
tcx, tcx,
// We just erase all late-bound lifetimes, but this is not fully correct (FIXME): // FIXME: We erase all late-bound lifetimes, but this is not fully correct.
// lifetimes in invariant positions could matter (e.g. through associated types). // If you have a type like `<for<'a> fn(&'a u32) as SomeTrait>::Assoc`,
// We rely on the fact that layout was confirmed to be equal above. // this is not necessarily equivalent to `<fn(&'static u32) as SomeTrait>::Assoc`,
// since one may have an `impl SomeTrait for fn(&32)` and
// `impl SomeTrait for fn(&'static u32)` at the same time which
// specify distinct values for Assoc. (See also #56105)
lt_op: |_| tcx.lifetimes.re_erased, lt_op: |_| tcx.lifetimes.re_erased,
// Leave consts and types unchanged. // Leave consts and types unchanged.
ct_op: |ct| ct, ct_op: |ct| ct,