swift

658b7f7d - [AutoDiff] Support derivative registration for more declaration kinds. (#28468)

[AutoDiff] Support derivative registration for more declaration kinds. (#28468) Make `@differentiating` and `@transposing` attributes support more original declaration kinds: computed properties, subscripts, and initializers. - Change `DifferentiatingAttr` and `TransposingAttr` to store an `AbstractFunctionDecl` representing the original declaration, instead of a `FuncDecl`. - Change attribute parsing to support initializer/subscript `DeclName`s. - Make `TypeChecker::lookupFuncDecl` a static function in TypeCheckAttr.cpp. - Assorted parsing and type-checking gardening. `@differentiating` now has feature parity with `@differentiable(jvp: ..., vjp: ...)` for derivative registration. This is a necessary step towards making `@differentiating` and `@transposing` the canonical mechanism for registering derivative/transpose functions. Registering non-`func` declaration derivatives with `@differentiable` attribute `jvp:`/`vjp:` labels is now explicitly rejected. Resolves TF-281. Todos: - TF-997: support `@transposing` attribute with initializer original declarations. - TF-988: do not reuse `@differentiable` attribute type-checking diagnostics for `@differentiating`/`@transposing` attribute type-checking.