This teaches ClangImporter to respect the `_Nonnull`/`_Nullable` arguments on templated function parameters.
Previously Swift would only import a non-annotated function overload. Using an overload that has either `_Nonnull` or `_Nullable` would result in a compiler error. The non-annotated overload would get imported with incorrect nullability: Swift would always assume non-null pointers, which was inconsistent with non-templated function parameters, which are mapped to implicitly unwrapped optionals.
With this change all three possible overloads are imported, and all of them get the correct nullability in Swift.
rdar://151939344
When instantiating templated functions with pointers to the templated
type, the ClangImporter does not strip type sugar. This strips type
sugar for bounds attributes, to make sure that they import the same
regardless of whether they are parsed or not.
rdar://151041990
Unfortunately, there is no common abstraction for initializers and
functions in SwiftSyntax, so this PR rolls our own. Alternatively, we
could probably achieve something similar with a new protocol, but we
only needed a handful of fields so this change keeps it simple.
rdar://152112660
Lookup into C++ namespaces uses a different path from C++ record declarations.
Augment the C++ namespace lookup path to also account for the auxiliary
declarations introduced by peer macro expansions.
When performing name lookup into a C++ record type, make sure that we
also walk through auxiliary declarations (i.e., declarations that can
come from peer macro expansions) to find results.
Fixes rdar://146833294.
