AST: Tweak a concrete-nested-type-of-archetype hack slightly [4.0] #10440
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When an archetype conforms to a protocol abstractly (ie, it is not class-constrained and we don't have any further information other than that it conforms), we can recover nested types, but we cannot recover the conformance of those nested types to protocols if those conformances are concrete (the nested type might be concrete, or it might be a class-constrained archetype). To work around this, we added a hack where if the conformance lookup in the SubstitutionMap fails, we fall back to the module. This is horrible and unprincipled, but has to remain in place until more infrastructure is plumbed through. Commit 620db5f made this workaround apply in fewer cases, so that we could still catch cases where the SubstitutionMap was constructed with missing conformances. Unfortunately this workaround didn't handle the case where the nested type was an archetype with a superclass constraint. This will all go away soon, but for now tweak the logic a bit, since I really want to keep the "narrow" workaround in place and not the general fallback, otherwise we run the risk of SubstitutionMap conformance lookup bitrotting completely. Fixes <https://bugs.swift.org/browse/SR-4088> and <rdar://problem/32773028>.
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@swift-ci Please test |
slavapestov
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Thanks @slavapestov and @DougGregor 🙌 👏 🎉 |
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What about 3.2? I am getting these all the time in a Swift 3.2 project on Xcode 9.0.1 and 9.1 beta 3. |
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@gistya This pull request went in to Xcode 9. Have you filed a bug for the issue you're seeing? |
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Description: There is a long-standing representational issue where SubstitutionMaps have a hard time dealing with associated types that are constrained to concrete types, but themselves have nested associated types. We put in a workaround in 3.1. In 4.0, I made the workaround slightly narrower so that we can test the conformance lookup logic better. Unfortunately I missed a case in 4.0 where we should have applied the workaround but didn't. This patch brings back the workaround in that specific case.
Scope of the issue: Affects an open source project in the source compatibility test suite (JSQDataSourcesKit).
Origination: Regression in 4.0.
Risk: Very low, this just performs a module-based lookup in one more case that wasn't being done before, and this should always work.
Tested: Reduced test case added.
Reviewed by: @DougGregor
Radar: rdar://problem/32773028