swift

38bc954e - [AutoDiff] Store original declaration in `DifferentiableAttr`. (#27985)

[AutoDiff] Store original declaration in `DifferentiableAttr`. (#27985) Store original `Decl *` in `DifferentiableAttr`. This is important for requestifying `DifferentiableAttr->getParameterIndices()`: we want the ability to resolve parameter indices without needing to pass the original `AbstractFunctionDecl` to `getParameterIndices`. Add round-trip `@differentiable` attribute AST serialization test. `@differentiable` attribute type-checking and serialization assert that the original declaration is set.