[6.3] SILGen: Fix assert when emitting re-abstraction thunk in edge case involving opaque return type #86159
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…volving opaque return type If we can see the underlying type of an opaque return type, and this underlying type does not depend on the opaque return type's generic signature, then we can end up in a situation where the lowered type of a re-abstraction thunk is not generic, but the formal type is. This would trigger an assertion failure. Check both the lowered type and formal type for type parameters to cope with this. - Fixes swiftlang#86118.
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@swift-ci Please test |
jckarter
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Dec 20, 2025
slavapestov
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@swift-ci Please test Windows |
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6.3 cherry-pick of #86131
Description: If we can see the underlying type of an opaque return type, and this underlying type does not depend on the opaque return type's generic signature, then we can end up in a situation where the lowered type of a re-abstraction thunk is not generic, but the formal type is. This would trigger an assertion failure. Check both the lowered type and formal type for type parameters to cope with this.
Issue: Fixes SILGen assertion failure with ForEach(Array(enumerated())) in SwiftUI View #86118.
Risk: Extremely low, because dropping the generic signature here is an optimization, so making it more conservative should generally be safe.
Reviewed by: @jckarter