When @compatibility_alias is used with an ObjC generic class, this ends up importing as a generic typealias. PrintAsObjC previously didn’t handle declarations involving these types correctly; it would fail an assertion in asserts compilers, and potentially print an incorrect compatibility header in non-asserts compilers.
This PR makes it so that PrintAsObjC can now correctly use generic typealiases imported from Objective-C modules. It is, of course, still not possible to declare a generic typealias in Swift that will be printed into the Objective-C header.
Fixes rdar://67256866.
The initial pass through a type’s members to forward-declare or import anything needed by them did not account for _ObjectiveCBridgeable conformances; instead, it would examine the Swift type being bridged from, either tripping an assertion or just failing to do anything. Treat these as references to the bridged type instead.
Fixes rdar://67263753.
The assertion here is too strict. The TypeAliasDecl will inherit a
generic signature from the outer context even if it does not have
generic parameters of its own. Instead, let's just assert that the
TypeAliasDecl does not have its own generic parameters.
Fixes <rdar://problem/63188938>.
Structurally prevent a number of common anti-patterns involving generic
signatures by separating the interface into GenericSignature and the
implementation into GenericSignatureBase. In particular, this allows
the comparison operators to be deleted which forces callers to
canonicalize the signature or ask to compare pointers explicitly.
The top-level PrintAsObjC now just covers import printing and the
near-literal prologue/epilogue text, while the decl printing (and
import collecting) is in its own file. No functionality change.
