Bundled mingw-w64-headers issues: #include windows.foundation.h from a C++ file

[past-due]

We'd previously been using llvm-mingw 18.1.8, but since attempting to jump to llvm-mingw 20250402 with LLVM 20.1.2 we're seeing errors in the mingw-w64-headers (windows.foundation.h):

In file included from C:/llvm-mingw/include/dispatcherqueue.h:10:
In file included from C:/llvm-mingw/include/windows.system.h:276:
C:/llvm-mingw/include/windows.foundation.h:13904:13: error: redefinition of 'IReference<unsigned char>'
 13904 |             IReference<boolean > : IReference_impl<boolean >
       |             ^~~~~~~~~~~~~~~~~~~~
C:/llvm-mingw/include/windows.foundation.h:12196:13: note: previous definition is here
 12196 |             IReference<BYTE > : IReference_impl<BYTE >
       |             ^
C:/llvm-mingw/include/windows.foundation.h:13912:1: error: redefinition of '__mingw_uuidof_s<ABI::Windows::Foundation::IReference<BYTE>>'
 13912 | __CRT_UUID_DECL(__FIReference_1_boolean, 0x3c00fd60, 0x2950, 0x5939, 0xa2,0x1a, 0x2d,0x12,0xc5,0xa0,0x1b,0x8a)
       | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:/llvm-mingw/include/_mingw.h:558:23: note: expanded from macro '__CRT_UUID_DECL'
  558 |     template<> struct __mingw_uuidof_s<type> {                   \
      |                       ^~~~~~~~~~~~~~~~~~~~~~
C:/llvm-mingw/include/windows.foundation.h:12204:1: note: previous definition is here
 12204 | __CRT_UUID_DECL(__FIReference_1_BYTE, 0xe5198cc8, 0x2873, 0x55f5, 0xb0,0xa1, 0x84,0xff,0x9e,0x4a,0xad,0x62)
       | ^
C:/llvm-mingw/include/_mingw.h:558:23: note: expanded from macro '__CRT_UUID_DECL'
  558 |     template<> struct __mingw_uuidof_s<type> {                   \
      |                       ^

[...]

In file included from C:/llvm-mingw/include/dispatcherqueue.h:10:
In file included from C:/llvm-mingw/include/windows.system.h:276:
C:/llvm-mingw/include/windows.foundation.h:13912:1: error: redefinition of '__mingw_uuidof<ABI::Windows::Foundation::IReference<BYTE>>'
 13912 | __CRT_UUID_DECL(__FIReference_1_boolean, 0x3c00fd60, 0x2950, 0x5939, 0xa2,0x1a, 0x2d,0x12,0xc5,0xa0,0x1b,0x8a)
       | ^
C:/llvm-mingw/include/_mingw.h:563:38: note: expanded from macro '__CRT_UUID_DECL'
  563 |     template<> constexpr const GUID &__mingw_uuidof<type>() {    \
      |                                      ^
C:/llvm-mingw/include/windows.foundation.h:12204:1: note: previous definition is here
 12204 | __CRT_UUID_DECL(__FIReference_1_BYTE, 0xe5198cc8, 0x2873, 0x55f5, 0xb0,0xa1, 0x84,0xff,0x9e,0x4a,0xad,0x62)
       | ^
C:/llvm-mingw/include/_mingw.h:563:38: note: expanded from macro '__CRT_UUID_DECL'
  563 |     template<> constexpr const GUID &__mingw_uuidof<type>() {    \
      |                                      ^

[...]

In file included from C:/llvm-mingw/include/dispatcherqueue.h:10:
In file included from C:/llvm-mingw/include/windows.system.h:276:
C:/llvm-mingw/include/windows.foundation.h:13912:1: error: redefinition of '__mingw_uuidof<ABI::Windows::Foundation::IReference<BYTE> *>'
 13912 | __CRT_UUID_DECL(__FIReference_1_boolean, 0x3c00fd60, 0x2950, 0x5939, 0xa2,0x1a, 0x2d,0x12,0xc5,0xa0,0x1b,0x8a)
       | ^
C:/llvm-mingw/include/_mingw.h:566:38: note: expanded from macro '__CRT_UUID_DECL'
  566 |     template<> constexpr const GUID &__mingw_uuidof<type*>() {   \
      |                                      ^
C:/llvm-mingw/include/windows.foundation.h:12204:1: note: previous definition is here
 12204 | __CRT_UUID_DECL(__FIReference_1_BYTE, 0xe5198cc8, 0x2873, 0x55f5, 0xb0,0xa1, 0x84,0xff,0x9e,0x4a,0xad,0x62)
       | ^
C:/llvm-mingw/include/_mingw.h:566:38: note: expanded from macro '__CRT_UUID_DECL'
  566 |     template<> constexpr const GUID &__mingw_uuidof<type*>() {   \
      |                                      ^
4 errors generated.

(For reference, it appears the IReference<boolean > (etc) bits were added in mingw-w64/mingw-w64@77eaa95)

[mstorsjo]

Please report such issues directly to mingw-w64; this issue doesn't sound like it would be specific to the llvm-mingw packaging.

[past-due]

mingw-w64/mingw-w64#88

For reference, minimal repro (must compile as C++):

#ifndef __cplusplus
  #error "Must compile as C++ to repro"
#endif

#include <windows.foundation.h>

int main() {
  return 0;
}

[lhmouse]

msys2/MINGW-packages#22160

[past-due]

msys2/MINGW-packages#22160

Very interesting. The issue seems to break compiling quite a bit. 🫤

Might be worth applying the same patch here? https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-headers-git/0001-remove-ireference-boolean.patch

[lhmouse]

These files are copied from Wine. Therefore, unless it's fixed in Wine, any changes will be overwritten.

[past-due]

Yes, although a patch could be applied just like msys2/MINGW-packages#22403 - presumably in /build-mingw-w64.sh - to ensure that the llvm-mingw distribution & builds don’t ship with broken headers.

(This was apparently reported on the Wine side 5 months ago, but I haven’t found any indication of progress on that end of things. There was some talk / contemplation about whether it should be fixed in widl or in the .idl files... but in the interim, this is a major breakage in the headers. I think it’s worth considering the same workaround as msys2 for now.)