When importing a C header in the C++ language mode, Clang/Swift treat C structs as C++ structs.
Currently Swift synthesizes a default initializer that zero-initializes the backing memory of the struct for C structs, but not for C++ structs.
This is causing issues in existing projects that use C libraries and rely on having the default initializer available in Swift. This change enables the synthesis of a default initializer for C++ structs. Since many C++ structs are not designed to be initialized this way, the initializer is marked as deprecated in Swift.
rdar://109727620
This patch to the Clang Importer avoids an assert by detecting when an
IndirectField belongs to an anonymous union that is not importable. How
it does this is by determining if an IndirectFieldDecl's anonymous
parent field is non-importable (based on isCxxRecordImportable) and if
so skips importing the IndirectFieldDecl.
This avoids the mentioned assert because makeIndirectFieldAccessors
expects a FieldDecl of __Unnamed_union___Anonymous_field that is only
populated when the top-level union is imported from an
IndirectFieldDecl's parent. IndirectFieldDecls for the members of an
anonymous union are dependent on their parent and should not be imported
if their parent can not also be imported.
This corner case can happen in cases when an anonymous union contains an
ARC pointer, which results in a non-trivial but also inaccessible dtor.
