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Don't return definite guidance if we find one solution and then flounder #331
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Original file line number | Diff line number | Diff line change |
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@@ -96,6 +96,63 @@ fn flounder() { | |
} | ||
} | ||
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/// Don't return definite guidance if we flounder after finding one solution. | ||
#[test] | ||
fn flounder_ambiguous() { | ||
test! { | ||
program { | ||
trait IntoIterator { } | ||
#[non_enumerable] | ||
trait OtherTrait { } | ||
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struct Ref<T> { } | ||
struct A { } | ||
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impl IntoIterator for Ref<A> { } | ||
impl<T> IntoIterator for Ref<T> where T: OtherTrait { } | ||
} | ||
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goal { | ||
exists<T> { Ref<T>: IntoIterator } | ||
} yields { | ||
"Ambiguous; no inference guidance" | ||
} | ||
} | ||
} | ||
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/// Don't return definite guidance if we are able to merge two solutions and the | ||
/// third one matches that as well (the fourth may not). | ||
#[test] | ||
fn normalize_ambiguous() { | ||
test! { | ||
program { | ||
trait IntoIterator { type Item; } | ||
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struct Ref<T> { } | ||
struct A { } | ||
struct B { } | ||
struct C { } | ||
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struct D { } | ||
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impl IntoIterator for Ref<A> { type Item = Ref<A>; } | ||
impl IntoIterator for Ref<B> { type Item = Ref<B>; } | ||
impl IntoIterator for Ref<C> { type Item = Ref<C>; } | ||
impl IntoIterator for Ref<D> { type Item = D; } | ||
} | ||
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goal { | ||
exists<T, U> { | ||
Normalize(<Ref<T> as IntoIterator>::Item -> U) | ||
} | ||
} yields { | ||
// FIXME: this is wrong! | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. We should probably create a FIXME policy of creating open issues to track these... |
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"Ambiguous; definite substitution" | ||
// "Ambiguous; no inference guidance" | ||
} | ||
} | ||
} | ||
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// Test that, when solving `?T: Sized`, we only wind up pulling a few | ||
// answers before we stop. | ||
// Also tests that we search breadth-first. | ||
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Does this test have anything to do with floundering?
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I don't think so (except that this test only reproduces the problem with the fix for the other problem, I think because it calls
peek_answer
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I see, curious.