There are two main scenarios when printing a compatibility header that
references a @cdecl enum defined in Swift code. (1) When defined in the
same module as it's used we can print the definition normally and then
reference it. (2) When used in a different mode we need to print a
forward declaration before we can reference it.
This change adds printing the forward declaration and fix an issue where
the compiler would instead print an @include of the Swift module. The
import of the Swift module would work only in a local scenario where a
compatibility header and module would be generated under the same name.
However for a distributed frameworks we do not distribute the
compatibility header so this strategy doesn't work. Relying on a forward
declaration should be more reliable in all cases but clients may need to
import the other compatibility header explicitly.
Print @cdecl enums in the C section of the compatibility header. Use and
extend the macros to support C compiler clients.
The macro is adapted to the features supported by the client compiler.
It uses an Objective-C style macro with raw type when available and
fallbacks to a simple typedef for C compatibility.
This macro applies always_inline in addition to inline. It also applies artificial, which lets debugger know that this is an artificial function. The used attribute is added in debug builds to ensure that the symbol is emitted in the binary so that LLDB can invoke it.
apple/swift#59072 accidentally changed the SWIFT_CLASS_NAMED macro to use `__attribute` when it previously used `__attribute__` (note the trailing underscores). While both keywords have the same semantics in clang, they are technically different tokens, so clang refuses to merge macro definitions that use one instead of the other; instead it would diagnose an ambiguity when a generated header from a new compiler imported a generated header from an old compiler. Change back to the old token to avoid this problem.
Fixes rdar://104252758.
