Split conformance isolation request to eliminate a reference cycle #81934
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DougGregor
commented
Jun 3, 2025
DougGregor
commented
- Explanation: Inference of conformance isolation needs to check whether all of the witnesses are nonisolated. However, witness checking looks at conformance isolation, causing a reference cycle in Swift 6 when inference of isolated conformances is enabled. This change breaks the reference cycle.
- Scope: Limited to the conformance checker when isolated conformance inference or default main actor are enabled.
- Issues: rdar://152461344
- Original PRs: Split conformance isolation request to eliminate a reference cycle #81933
- Risk: Low. Behavior only changes when one of the aforementioned upcoming features are enabled.
- Testing: CI, project demonstrating the issue.
- Reviewers:
Inference of conformance isolation needs to check whether all of the witnesses are nonisolated. However, witness checking looks at conformance isolation. To break this reference cycle, split the conformance isolation request into two requests: a "raw" request that looks at explicitly-specified isolation, and the existing one that also performs inference. The existing one builds on the "raw" one, as does a separate path for the conformance checker. Fixes rdar://152461344.
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@swift-ci please test |
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@swift-ci please test macOS |
slavapestov
approved these changes
Jun 4, 2025
| Bits.ProtocolConformance.IsComputedNonisolated = false; | ||
| } | ||
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| bool isRawConformanceInferred() const { |
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isRawIsolationInferred maybe?
| if (!rootNormal) | ||
| return ActorIsolation::forNonisolated(false); | ||
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| if (conformance != rootNormal) |
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It might be better to do this 'unwrapping' of specialized conformances before evaluating the request, to avoid polluting the cache with tons of duplicates that only differ by substitution map
hborla
approved these changes
Jun 4, 2025
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I'll address Slava's comments via a follow-up PR on main |
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