...rather than replacing particular macros with an 'annotate'
attribute and then looking for that. This isn't /really/ any
particular win except maybe ever-so-slightly faster module imports
(with one fewer attribute being added to each declaration in a
mixed-source header).
This doesn't remove the SWIFT_CLASS_EXTRA, SWIFT_PROTOCOL_EXTRA, or
SWIFT_ENUM_EXTRA macros from PrintAsObjC (note that
SWIFT_EXTENSION_EXTRA was never used). They're not exactly needed
anymore, but they're not doing any harm if someone else is using them.
Still to do: test and fix up the use of multiple enum_extensibility
annotations, possibly with API notes. This is important because the
definition of NS/CF_ENUM /includes/ enum_extensibility(open) as of
Xcode 9.0; there should be a convenient out people can use to declare
exhaustive enums in C that's backwards-compatible.
This would fail later down the line anyway, meaning this does not
change the ultimate behavior of the importer, but since I added an
assertion that we're expecting a definition here in 2c68f8d49d, we
need to avoid even asking the question.
Also fix up a few other places where we aren't sure we'll have a
definition when calling these functions.
rdar://problem/33784466
These new Clang attributes identify whether an enum is intended to
represent an option set or not, and whether the set of cases listed in
the enum declaration is exhaustive. (Swift doesn't currently have a
closed/open distinction for enums, so treat any C enum with
enum_extensibility as a proper closed Swift enum, like we do with
NS_ENUM.)
Enums with neither attribute will continue to be imported as unique
types.
rdar://problem/28476618
