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Rollup merge of #118736 - aliemjay:revert-ice-on-ambig, r=compiler-errors

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temporarily revert "ice on ambguity in mir typeck"

Reverts #116530 as a temporary measure to fix #117577. That issue should be ultimately fixed by checking WF of type annotations prior to normalization, which is implemented in #104098 but this PR is intended to be backported to beta.

r? ``@compiler-errors`` (the reviewer of the reverted PR)
This commit is contained in:
Matthias Krüger 2023-12-08 23:15:14 +01:00 committed by GitHub
commit a255b52525
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2 changed files with 28 additions and 12 deletions
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16
compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
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@ -157,18 +157,10 @@ where
}
let mut region_constraints = QueryRegionConstraints::default();
let (output, error_info, mut obligations) =
Q::fully_perform_into(self, infcx, &mut region_constraints)
.map_err(|_| {
infcx.tcx.sess.span_delayed_bug(span, format!("error performing {self:?}"))
})
.and_then(|(output, error_info, obligations, certainty)| match certainty {
Certainty::Proven => Ok((output, error_info, obligations)),
Certainty::Ambiguous => Err(infcx
.tcx
.sess
.span_delayed_bug(span, format!("ambiguity performing {self:?}"))),
})?;
let (output, error_info, mut obligations, _) =
Q::fully_perform_into(self, infcx, &mut region_constraints).map_err(|_| {
infcx.tcx.sess.span_delayed_bug(span, format!("error performing {self:?}"))
})?;
// Typically, instantiating NLL query results does not
// create obligations. However, in some cases there

24
tests/ui/wf/unnormalized-projection-guides-inference.rs Normal file
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@ -0,0 +1,24 @@
// The WF requirements of the *unnormalized* form of type annotations
// can guide inference.
// check-pass
pub trait EqualTo {
type Ty;
}
impl<X> EqualTo for X {
type Ty = X;
}
trait MyTrait<U: EqualTo<Ty = Self>> {
type Out;
}
impl<T, U: EqualTo<Ty = T>> MyTrait<U> for T {
type Out = ();
}
fn main() {
let _: <_ as MyTrait<u8>>::Out;
// We shoud be able to infer a value for the inference variable above.
// The WF of the unnormalized projection requires `u8: EqualTo<Ty = _>`,
// which is sufficient to guide inference.
}