c-interop: teach @c to handle ObjC type metatype Class. rdar://179401427#90608
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ClangImporter imports C 'Class' as AnyClass, but declaring a C-interop function that takes/returns it via @c or @_extern(c) was rejected. Support it across three layers: Sema: make AnyClass (an ExistentialMetatypeType of AnyObject) representable in ForeignLanguage::C, gated on ObjC interop since 'Class' is an ObjC runtime type. Reuse getObjCObjectRepresentable so C and ObjC agree on the kind. SILGen: a @c/@_extern(c) function is emitted directly as its C entry point (no separate native thunk), so bridge the metatype at that boundary in place: objc_to_thick_metatype on a 'Class' parameter in the prolog, and thick_to_objc_metatype on an AnyClass result in the epilog. Both are no-ops unless the native and foreign SIL types differ. PrintAsClang: keep the @c declaration in the plain-C section and emit '#include <objc/objc.h>' there when a @c decl uses 'Class', so the generated header stays usable from plain C.
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| // ClangImporter imports C 'Class' as AnyClass. Restrict to the AnyObject | ||
| // class metatype and gate on ObjC interop, since 'Class' is an ObjC runtime | ||
| // type. Reuse the ObjC path's result so bridging stays consistent. | ||
| if (language == ForeignLanguage::C && |
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Could you elaborate on the motivation here? Why do we want to support this with @c as opposed to @objc?
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Sure! It's basically because the original issue that the originator reported was about using @_extern(c) on a global function taking Class as a parameter.
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I see. I was just wondering if this is something we wanted to support as opposed to asking the originator to use @objc.
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ClangImporter imports C 'Class' as AnyClass, but declaring a C-interop function that takes/returns it via @c or @_extern(c) was rejected. Support it across three layers:
Sema: make AnyClass (an ExistentialMetatypeType of AnyObject) representable in ForeignLanguage::C, gated on ObjC interop since 'Class' is an ObjC runtime type. Reuse getObjCObjectRepresentable so C and ObjC agree on the kind.
SILGen: a @c/@_extern(c) function is emitted directly as its C entry point (no separate native thunk), so bridge the metatype at that boundary in place: objc_to_thick_metatype on a 'Class' parameter in the prolog, and thick_to_objc_metatype on an AnyClass result in the epilog. Both are no-ops unless the native and foreign SIL types differ.
PrintAsClang: keep the @c declaration in the plain-C section and emit '#include <objc/objc.h>' there when a @c decl uses 'Class', so the generated header stays usable from plain C.