Richard Wei 1a4ea67e2c [AutoDiff] Plumb witness derivative generic signatures through SILGen. ...

When SILGenWitnessTable creates a decl ref for the witness of a derivative function requirement, it is using the requirement's derivative generic signature in the resulting witness decl ref. This is wrong because the witness may have a different derivative generic signature than the requirement, leading to a crash. This bug was never discovered because GSB's dark magic made it "just work", until requirement machine.

The fix is to store the matched witness derivative generic signature in `Witness` during type checking, and during witness table generation, use the witness' generic signature to create a witness decl ref.

Resolves rdar://84716758, rdar://84213107 and rdar://84987079.

2021-11-05 10:28:33 -07:00

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