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temporarily revert "ice on ambguity in mir typeck" #118736

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merged 1 commit into from
Dec 9, 2023
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temporarily revert "ice on ambguity in mir typeck" #118736

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temporarily revert "ice on ambguity in mir typeck" 
Reverts #116530
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@aliemjay
aliemjay committed Dec 8, 2023
commit 5fdb648fc3a672140f3fc8f98ee3268ed3fe5389
16 changes: 4 additions & 12 deletions compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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24 changes: 24 additions & 0 deletions tests/ui/wf/unnormalized-projection-guides-inference.rs
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Original file line number Diff line number Diff line change
@@ -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.
}
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