This is more of rdar://problem/24869070; StringRefs are leaking out of
importFullName still, in a DenseMap that can get deallocated. When we
cache this data, put them in "permanent" (Swift ASTContext) storage.
ns_error_domain can now be used to communicate with the ClangImporter
when an enum has an associated error domain string. In this case, when
we import it as a Swift enum, we can also synthesize a conformance to
_BridgedNSError.
This allows the creation of something like NS_ERROR_ENUM, in which the
developer can declare an enum for the purposes of error handling. Adds
Sema and executable tests demonstrating this funcionality.
In order for the imported ns_error_domain bridging to work, we have to
at some point forcibly pull in a _BridgedNSError conformance, as one
will not be pulled in normally. This is a problem, and is explicitly
signaled in the provided test case
Introduces new class, EnumInfo, just for the implementation of the
ClangImporter to encapsulate various computed information about the
enum we're importing.
This helps refactor some functionality, aids clarity, and also
prevents us from repeating calculations multiple times, as we were
doing with classifyEnum's macro-expansion tracking. Provides a base
where we can add more heavy lifting in classifyEnum in the future.
