add mingw_gcc_compiler config_setting to zlib.BUILD

[vvviktor]

Fixes #16024

Workaround to avoid bazel build failure using MinGW GCC toolchain under Windows. These changes suppress [-fpermissive] errors while compiling zlib external dependency with mingw-gcc toolchain.

[haberman]

It looks like -fpermissive will treat errors like warnings.

I don't think we want to do this. What errors are you getting in the mingw build?

[vvviktor]

@haberman

It looks like -fpermissive will treat errors like warnings.

I don't think we want to do this. What errors are you getting in the mingw build?

Thanks for reply. I'm getting these errors building protobuf with Bazel with mingw toolchain:

external/zlib~1.3.1/gzlib.c: In function 'gzFile_s* gz_open(const void*, int, const char*)':
external/zlib~1.3.1/gzlib.c:183:30: error: invalid conversion from 'const void*' to 'const wchar_t*' [-fpermissive]
  183 |         len = wcstombs(NULL, path, 0);
      |                              ^~~~
      |                              |
      |                              const void*
In file included from C:/msys64/ucrt64/include/c++/13.2.0/cstdlib:79,
                 from C:/msys64/ucrt64/include/c++/13.2.0/stdlib.h:36,
                 from external/zlib~1.3.1/gzguts.h:24,
                 from external/zlib~1.3.1/gzlib.c:6:
C:/msys64/ucrt64/include/stdlib.h:531:82: note:   initializing argument 2 of 'size_t wcstombs(char*, const wchar_t*, size_t)'
  531 |   size_t __cdecl wcstombs(char * __restrict__ _Dest,const wchar_t * __restrict__ _Source,size_t _MaxCount) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
      |                                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
external/zlib~1.3.1/gzlib.c:198:35: error: invalid conversion from 'const void*' to 'const wchar_t*' [-fpermissive]
  198 |             wcstombs(state->path, path, len + 1);
      |                                   ^~~~
      |                                   |
      |                                   const void*
C:/msys64/ucrt64/include/stdlib.h:531:82: note:   initializing argument 2 of 'size_t wcstombs(char*, const wchar_t*, size_t)'
  531 |   size_t __cdecl wcstombs(char * __restrict__ _Dest,const wchar_t * __restrict__ _Source,size_t _MaxCount) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
      |                                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
external/zlib~1.3.1/gzlib.c:233:27: error: invalid conversion from 'const void*' to 'const wchar_t*' [-fpermissive]
  233 |         fd == -2 ? _wopen(path, oflag, 0666) :
      |                           ^~~~
      |                           |
      |                           const void*
In file included from C:/msys64/ucrt64/include/fcntl.h:8,
                 from external/zlib~1.3.1/gzguts.h:31:
C:/msys64/ucrt64/include/io.h:316:45: note:   initializing argument 1 of 'int _wopen(const wchar_t*, int, ...)'
  316 |   _CRTIMP int __cdecl _wopen(const wchar_t *_Filename,int _OpenFlag,...) __MINGW_ATTRIB_DEPRECATED_SEC_WARN;
      |                              ~~~~~~~~~~~~~~~^~~~~~~~~

Full explanation is here: #16024

[vvviktor]

@haberman These default opts:

  copts = select({
        "@platforms//os:windows": [],
        "//conditions:default": [
            "-Wno-deprecated-non-prototype",
            "-Wno-unused-variable",
            "-Wno-implicit-function-declaration",
        ],
    }),

look more clang-specific. I use GCC, so -Wno-deprecated-non-prototype is unrecognized. May be some other options should be set specifically for GCC? Anyway, trick with -fpermissive works only after commenting -Werror in protobuf\build_defs\cpp_opts.bzl because -Werror somehow overrides options provided in protobuf\third_party\zlib.BUILD.

[vvviktor]

@haberman

If I add following flags :

        "-Wno-maybe-uninitialized",
        "-Wno-unused-parameter",
        "-Wno-missing-field-initializers",
        "-Wno-implicit-fallthrough",
        "-Wno-redundant-move",

to protobuf\build_defs\cpp_opts.bzl right after -Werror, protoc compiles successfully. But, anyway, I have to keep -fpermissive in protobuf\third_party\zlib.BUILD as external zlib won't compile without it.

[haberman]

I chatted with some people on the team, and I don't think we intended for user builds to get -Werror.

I think we'd prefer to remove -Werror from the build rather than add mingw-specific flags.

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