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Allow inference regions when relating consts #73225

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Jun 12, 2020
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Allow inference regions when relating consts #73225

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11 changes: 1 addition & 10 deletions src/librustc_middle/ty/relate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -508,16 +508,7 @@ pub fn super_relate_consts<R: TypeRelation<'tcx>>(
debug!("{}.super_relate_consts(a = {:?}, b = {:?})", relation.tag(), a, b);
let tcx = relation.tcx();

let eagerly_eval = |x: &'tcx ty::Const<'tcx>| {
// FIXME(eddyb) this doesn't account for lifetime inference variables
// being erased by `eval`, *nor* for the polymorphic aspect of `eval`.
// That is, we could always use `eval` and it will just return the
// old value back if it doesn't succeed.
if !x.val.needs_infer() {
return x.eval(tcx, relation.param_env()).val;
}
x.val
};
let eagerly_eval = |x: &'tcx ty::Const<'tcx>| x.eval(tcx, relation.param_env()).val;
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@eddyb eddyb Jun 18, 2020 •
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I think this makes sense. I left that FIXME comment (and the one below) while working on an unrelated PR #71049 (and glancing at code next to what I was touching). I should've probably filed issues.

At least I don't think this FIXME was a soundness problem, the overzealous check could only lead to types failing to equate (which could mean ICEs, clearly it happened here so it's possible).

This is reminiscent of #70773, where missing normalizations started showing up after we stopped ignoring generics in scope, in #70452.

I wonder if changing this one piece of code in relate makes the extra normalizations added to fix #70773 unnecessary.


// FIXME(eddyb) doesn't look like everything below checks that `a.ty == b.ty`.
// We could probably always assert it early, as `const` generic parameters
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12 changes: 12 additions & 0 deletions src/test/ui/async-await/issue-73050.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
// check-pass
// edition:2018

#[allow(unused)]
async fn foo<'a>() {
let _data = &mut [0u8; { 1 + 4 }];
bar().await
}
Comment on lines +5 to +8
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Weird that this would need async, presumably fn foo<'a: 'a> (forcing lifetime parameters aka "early-bound" as opposed to only the signature being lifetime-polymorphic aka "late-bound) would also work?

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I can't get it to ICE: playground

The ICE happened when unifying the generator witness with the generator type (IIRC?), so maybe there's something special about that operation.


async fn bar() {}

fn main() {}