[5.1] [runtime] Handle same-type constraints when resolving generic params #26032
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@swift-ci Please test |
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Note: I have further tests to run on other parts of the runtime, but I wanted to get this part in now. @swift-ci Please nominate |
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Explanation: Swift uses mangled names to encode references to types that can be resolved at run time. However, the runtime support for this wasn't doing so correctly when a nested generic context makes one of an outer context's generic parameters redundant with a same-type constraint. This patch fixes two ways in which that logic was incorrect: it wasn't following extensions back to the original type, and it wasn't looking at the innermost context to see if a type was redundant.
Scope: Affects how the runtime resolves generic parameters when referenced from the metadata of generic types.
Issue: rdar://problem/52364601
Risk: Medium. The scope is pretty broad here, even if working code shouldn't change behavior in practice. It's possible that an existing app is encountering this bug today but coincidentally "working" based on incorrect information, and that app could change behavior.
Testing: Added compiler regression tests.
Reviewed by: @jckarter, @DougGregor