[6.3] Fix a bug with binding parameters under a vanishing tuple AP #86094
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expansion component. Use this in emitPackTransform; this reorders a couple of projections, but that's fine, and the result is much cleaner and has better separation of concerns.
This only happens when binding parameters under an abstraction pattern and can therefore only currently happen with closures passed to functions that take variadic generic tuples (that happen to vanish). This is relatively straightforward using ExpandedTupleInputGenerator, and it cleans the code up a fair bit.
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@swift-ci Please test |
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This is the test case from #69028 (comment).
Explanation: Parameter binding usually doesn't have an abstraction pattern that's meaningfully different from the formal types of the parameters, but it can when we're emitting a closure in an abstracted type context. A tuple parameter with a type like
(repeat each T)is actually passed as a pack of elements. The binding logic handled some of the cases here, but because it was primarily type-matching on the substituted type rather than the AP, it was not properly handling the vanishing tuple case whereTis a singleton pack and therefore(repeat each T)is no longer a tuple.Original PR: #86078
Risk: Low; the new code re-uses a significant amount of the existing logic from reabstraction thunks, which is fairly well-tested.
Testing: New regression tests added
Reviewers: none as of yet