bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

Auto merge of #101437 - compiler-errors:erase-normalize-ordering, r=tmandry

Browse source 
Normalize before erasing late-bound regions in `equal_up_to_regions`

Normalize erasing regions **first**, before passing the type through a `BottomUpFolder` which erases late-bound regions too.

The root cause of this issue is due to 96d4137dee, which removes a `normalize_erasing_regions` that happens before this call to `equal_up_to_regions`. While reverting that commit might be a fix, I think it was suspicious to be erasing late-bound regions first _then_ normalizing types in the first place in `equal_up_to_regions`.

-----

I am tempted to ask the reviewer to review and `r+` this without a UI test, since the existing issues that I think this fixes are all incredibly difficult to minimize (anything hyper/warp related, given the nature of those libraries 😓) or impossible to reproduce locally (the miri test), namely:
* This recently reported issue with tokio + warp: #101430
* This issue from `@RalfJung` about Miri being broken: #101344
* This additional issue reported in a comment by `@tmandry` (issue with fuchsia + hyper): https://github.com/rust-lang/rust/issues/101344#issuecomment-1235974564

I have locally verified that the repro in #101430 is fixed with this PR, but after a couple of hours of attempting to minimize this error and either failing to actually repro the ICE, or being overwhelmed with the number of traits and functions I need to inline into a UI test, I have basically given up. Thoughts are appreciated on how best to handle this.

r? `@oli-obk` who is at the intersection of MIR and types-related stuff who may be able to give advice 😅
This commit is contained in:
bors 2022-09-08 19:01:39 +00:00
commit 1120c5e01d
1 changed files with 15 additions and 14 deletions
Download patch file Download diff file Expand all files Collapse all files

29
compiler/rustc_const_eval/src/transform/validate.rs
View file

@ -90,20 +90,21 @@ pub fn equal_up_to_regions<'tcx>(
// Normalize lifetimes away on both sides, then compare.
let normalize = |ty: Ty<'tcx>| {
let ty = ty.fold_with(&mut BottomUpFolder {
tcx,
// FIXME: We erase all late-bound lifetimes, but this is not fully correct.
// If you have a type like `<for<'a> fn(&'a u32) as SomeTrait>::Assoc`,
// 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,
// Leave consts and types unchanged.
ct_op: |ct| ct,
ty_op: |ty| ty,
});
tcx.try_normalize_erasing_regions(param_env, ty).unwrap_or(ty)
tcx.try_normalize_erasing_regions(param_env, ty).unwrap_or(ty).fold_with(
&mut BottomUpFolder {
tcx,
// FIXME: We erase all late-bound lifetimes, but this is not fully correct.
// If you have a type like `<for<'a> fn(&'a u32) as SomeTrait>::Assoc`,
// 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,
// Leave consts and types unchanged.
ct_op: |ct| ct,
ty_op: |ty| ty,
},
)
};
tcx.infer_ctxt().enter(|infcx| infcx.can_eq(param_env, normalize(src), normalize(dest)).is_ok())
}