swift

c3fbc6e7 - Introduce a new Initializer subclass for the arguments of custom attributes

Introduce a new Initializer subclass for the arguments of custom attributes Since the introduction of custom attributes (as part of property wrappers), we've modeled the context of expressions within these attributes as PatternBindingInitializers. These PatternBindingInitializers would get wired in to the variable declarations they apply to, establishing the appropriate declaration context hierarchy. This worked because property wrappers only every applied to---you guessed it!---properties, so the PatternBindingInitializer would always get filled in. When custom attributes were extended to apply to anything for the purposes of macros, the use of PatternBindingInitializer became less appropriate. Specifically, the binding declaration would never get filled in (it's always NULL), so any place in the compiler that accesses the binding might have to deal with it being NULL, which is a new requirement. Few did, crashes ensued. Rather than continue to play whack-a-mole with the abused PatternBindingInitializer, introduce a new CustomAttributeInitializer to model the context of custom attribute arguments. When the attributes are assigned to a declaration that has a PatternBindingInitializer, we reparent this new initializer to the PatternBindingInitializer. This helps separate out the logic for custom attributes vs. actual initializers. Fixes https://github.com/swiftlang/swift/issues/76409 / rdar://136997841