https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116827
--- Comment #3 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> --- I thought the dependence on -fmodule-header was indicative of an issue with the libstdc++ compatibility with the macOS SDK, but maybe I'm wrong. I've made it component == target. Looking at the macOS /usr/include/arm/_types.h header, in previous versions it was defining __darwin_ptrdiff_t as: ---- #if defined(__PTRDIFF_TYPE__) typedef __PTRDIFF_TYPE__ __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #elif defined(__LP64__) typedef long __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #else typedef int __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #endif /* __GNUC__ */ ---- and now it is: ---- #if USE_CLANG_TYPES typedef ptrdiff_t __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #elif defined(__PTRDIFF_TYPE__) typedef __PTRDIFF_TYPE__ __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #elif defined(__LP64__) typedef long __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #else typedef int __darwin_ptrdiff_t; /* ptr1 - ptr2 */ #endif /* __GNUC__ */ ---- where that new USE_CLANG_TYPES macro is defined at the top of the file: ---- #if defined(__has_feature) && __has_feature(modules) #define USE_CLANG_TYPES 1 #else #define USE_CLANG_TYPES 0 #endif #if USE_CLANG_TYPES #include <sys/_types/_ptrdiff_t.h> #include <sys/_types/_size_t.h> #include <sys/_types/_va_list.h> #include <sys/_types/_wchar_t.h> #endif ---- So -fmodule-header makes USE_CLANG_TYPES defined. Similarly, /usr/include/sys/_types/_ptrdiff_t.h used to be relatively straightforward: ---- #ifndef _PTRDIFF_T #define _PTRDIFF_T #include <machine/types.h> /* __darwin_ptrdiff_t */ typedef __darwin_ptrdiff_t ptrdiff_t; #endif /* _PTRDIFF_T */ ---- but now it has more complex logic: ---- #if defined(__has_feature) && __has_feature(modules) #define USE_CLANG_STDDEF 1 #else #define USE_CLANG_STDDEF 0 #endif #if USE_CLANG_STDDEF #ifndef __PTRDIFF_T #define __PTRDIFF_T #define __need_ptrdiff_t #include <stddef.h> #undef __need_ptrdiff_t #endif /* __PTRDIFF_T */ #else #ifndef _PTRDIFF_T #define _PTRDIFF_T #include <machine/types.h> /* __darwin_ptrdiff_t */ typedef __darwin_ptrdiff_t ptrdiff_t; #endif /* _PTRDIFF_T */ #endif ---- I'm thoroughly confused by this series of includes, especially as __need_ptrdiff_t is never used anywhere in the SDK.
