This patch fixes the access check for nested private C++ enums to look for the SWIFT_PRIVATE_FILEID of the enclosing C++ class, if any. Previously, the check was looking at for SWIFT_PRIVATE_FILEID on the enum decl itself (which is meaningless); that prevented nested private enum members from being accessible in Swift.
This patch also specializes the type signature of getPrivateFileIDAttrs to clarify the fact that SWIFT_PRIVATE_FILEID is not a meaningful annotation on anything other than CXXRecordDecl, because that is the only kind of decl that can assign access specifiers to its members.
rdar://148081340
This patch introduces an a C++ class annotation, SWIFT_PRIVATE_FILEID,
which will specify where Swift extensions of that class will be allowed
to access its non-public members, e.g.:
class SWIFT_PRIVATE_FILEID("MyModule/MyFile.swift") Foo { ... };
The goal of this feature is to help C++ developers incrementally migrate
the implementation of their C++ classes to Swift, without breaking
encapsulation and indiscriminately exposing those classes' private and
protected fields.
As an implementation detail of this feature, this patch introduces an
abstraction for file ID strings, FileIDStr, which represent a parsed pair
of module name/file name.
rdar://137764620
