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Unexpected unsatisfied trait bound #115697

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benluelo opened this issue Sep 9, 2023 · 2 comments
Open

Unexpected unsatisfied trait bound #115697

benluelo opened this issue Sep 9, 2023 · 2 comments
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A-associated-items Area: Associated items (types, constants & functions) A-trait-system Area: Trait system C-bug Category: This is a bug. fixed-by-next-solver Fixed by the next-generation trait solver, `-Znext-solver`. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@benluelo
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benluelo commented Sep 9, 2023 •
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I tried this code:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=761c1cce2cdf196f23ef8eab2a59bf6d

There seems to be an issue when resolving a blanket impl through the GAT when an associated type of the T is used - the above code is as far as I could minimize it while keeping the error message the same.

Interesting to note is this line in the error:

help: the trait Unsatisfied<()> is implemented for GenericStruct<T>

Which is true(!) but the error states that:

the trait Unsatisfied<<GenericStruct<<Counterparty as HasAssoc>::Assoc> as Proto>::Proto> is not implemented for GenericStruct<<Counterparty as HasAssoc>::Assoc>

Which leads me to believe this is similar to #41756 or #24066? But I'm not sure honestly.

EDIT: I refactored the original (non-minimized) code to not use GATS and encountered this: #89910; perhaps the original issue is related?
@benluelo benluelo added the C-bug Category: This is a bug. label Sep 9, 2023
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Sep 9, 2023
@fmease fmease added A-trait-system Area: Trait system A-associated-items Area: Associated items (types, constants & functions) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. fixed-by-next-solver Fixed by the next-generation trait solver, `-Znext-solver`. and removed needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. labels Sep 19, 2023
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fmease commented Sep 19, 2023

(fixed by next solver: fail → pass)

@benluelo
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Another example, not sure if it's just a smaller example than the one I posted previously but it's also fixed by trait-solver=next: godbolt

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A-associated-items Area: Associated items (types, constants & functions) A-trait-system Area: Trait system C-bug Category: This is a bug. fixed-by-next-solver Fixed by the next-generation trait solver, `-Znext-solver`. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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