Sema: Fix logic error in TypeReprCycleCheckWalker handling of 'Self.Foo' [5.10] #70831
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We don't want to throw out a witness if it has any mention of 'Self.Foo'; we must also check that 'Foo' is one of the associated types being inferred. Otherwise, it may be a protocol type alias, in which case we want to proceed with the witness. This fixes a regression from a recent change, a576984. Fixes rdar://problem/120743365.
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Jan 11, 2024
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Cherry-pick of #70830
Description: Fixes a regression where associated type inference did not consider any witness whose type contains
Self.Foo, whereFoois a member of a protocol (usually you can writeFooinstead ofSelf.Foo, but the latter is more explicit). The correct behavior is that such witnesses should only be discarded ifFoois one of the associated types being inferred.Scope of the issue: Anyone impacted would have to explicitly declare a type alias instead of letting the compiler infer it.
Origination: Regression from the second cherry-pick in Sema: Associated type inference fixes [5.10] #70696.
Radar: Fixes rdar://problem/120743365.
Tested: Reduced test case added from impacted project.
Risk: Sigh. Unfortunately this is the second follow-up PR fixing issues in the original change from November (Sema: Associated type inference skips witnesses that might trigger a request cycle [5.10] #69952), but I hope this particular change is safe since the new code path (ignoring a witness that "might cause a cycle") will now execute in strictly fewer situations than it did previously.
Reviewed by: @hborla