swift

19419964 - [AutoDiff] Fix assert on missing struct decl on cross-file derivative search (#77183)

[AutoDiff] Fix assert on missing struct decl on cross-file derivative search (#77183) Consider: 1. File struct.swift defining `struct Struct` with `static func max` member 2. File derivatives.swift defining `extension Struct` with custom derivative of the `max` function 3. File error.swift defining a differentiable function which uses `Struct.max`. Previously, when passing error.swift as primary file and derivatives.swift as a secondary file to swift-frontend (and forgetting to pass struct.swift as a secondary file as well), an assertion failure was triggered. This patch fixes the issue by adding a check against `ErrorType` in `findAutoDiffOriginalFunctionDecl` before calling `lookupMember`. Co-authored-by: Anton Korobeynikov <anton@korobeynikov.info>