windows: usage of deprecated std:wstring_convert #32361

1. 
   fanquake commented at 9:47 am on April 28, 2025: member

   std:wstring_convert was deprecated in C++17 & is removed in C++26. Cross-compiling for Windows with GCC 15.1.0 is warning about this:

    0../../src/common/system.cpp: In function 'void runCommand(const std::string&)':
    1../../src/common/system.cpp:52:32: warning: 'template<class _Codecvt, class _Elem, class _Wide_alloc, class _Byte_alloc> class std::__cxx11::wstring_convert' is deprecated [-Wdeprecated-declarations]
    2   52 |     int nErr = ::_wsystem(std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>,wchar_t>().from_bytes(strCommand).c_str());
    3      |                                ^~~~~~~~~~~~~~~
    4In file included from /opt/homebrew/Cellar/mingw-w64/12.0.0_3/toolchain-x86_64/x86_64-w64-mingw32/include/c++/15.1.0/locale:47,
    5                 from ../../src/util/string.h:13,
    6                 from ../../src/tinyformat.h:149,
    7                 from ../../src/logging.h:10,
    8                 from ../../src/common/system.cpp:10:
    9/opt/homebrew/Cellar/mingw-w64/12.0.0_3/toolchain-x86_64/x86_64-w64-mingw32/include/c++/15.1.0/bits/locale_conv.h:262:33: note: declared here
   10  262 |     class _GLIBCXX17_DEPRECATED wstring_convert
   11      |                                 ^~~~~~~~~~~~~~~
   

2. hebasto added the label Windows on Apr 28, 2025
3. 
   laanwj commented at 11:16 am on April 28, 2025: member

   Apparently there is no direct replacement in the standard library.

   i hope we can replace runCommand with use of the subprocess library soon, to unify the “launch subprocess” path.

4. 
   fanquake commented at 11:55 am on April 28, 2025: member

   with use of the subprocess library soon

   Note that subprocess.h is also using wstring_convert: https://github.com/bitcoin/bitcoin/blob/d62c2d82e14d27307d8790fd9d921b740b784668/src/util/subprocess.h#L1071.

5. 
   laanwj commented at 10:29 am on April 29, 2025: member

   Note that subprocess.h is also using wstring_convert:

   Ugh. Well at least it’s an upstream issue for them, too, then.

6. 
   laanwj commented at 10:32 am on April 29, 2025: member

   So in principle modern Windows can use UTF-8 on the 8-bit APIs, removing need for any conversion, but i’m not sure starting from when, and this relies on setting a specific code page globally at startup. Edit: according to Microsoft this is since Windows Version 1903 (May 2019 Update). This requires providing a “Fusion manifest for an unpackaged Win32 app”, whatever that means, if we can even do this with mingw32.

   Alternatively we could borrow these (windows specific) functions from our leveldb patch:

    0  // Converts a Windows wide multi-byte UTF-16 string to a UTF-8 string.
    1  // See http://utf8everywhere.org/#windows
    2  std::string toUtf8(const std::wstring& wstr) {
    3    if (wstr.empty()) return std::string();
    4    int size_needed = WideCharToMultiByte(
    5        CP_UTF8, 0, &wstr[0], (int)wstr.size(), NULL, 0, NULL, NULL);
    6    std::string strTo(size_needed, 0);
    7    WideCharToMultiByte(CP_UTF8, 0, &wstr[0], (int)wstr.size(), &strTo[0],
    8                        size_needed, NULL, NULL);
    9    return strTo;
   10  }
   11
   12  // Converts a UTF-8 string to a Windows UTF-16 multi-byte wide character
   13  // string.
   14  // See http://utf8everywhere.org/#windows
   15  std::wstring toUtf16(const std::string& str) {
   16    if (str.empty()) return std::wstring();
   17    int size_needed =
   18        MultiByteToWideChar(CP_UTF8, 0, &str[0], (int)str.size(), NULL, 0);
   19    std::wstring strTo(size_needed, 0);
   20    MultiByteToWideChar(CP_UTF8, 0, &str[0], (int)str.size(), &strTo[0],
   21                        size_needed);
   22    return strTo;
   23  }
   

7. 
   hebasto commented at 12:16 pm on April 29, 2025: member

   This requires providing a “Fusion manifest for an unpackaged Win32 app”, whatever that means, if we can even do this with mingw32.

   I believe we can use an approach similar to the one described at https://stackoverflow.com/questions/33000158/embed-manifest-file-to-require-administrator-execution-level-with-mingw32.

8. 
   laanwj commented at 1:39 pm on April 29, 2025: member

   Great, good to know that’s possible. i guess by the time we switch to C++26 and this becomes a blocking issue, it will be fine to require a 2019 windows version, and we can simplify things by using the “ASCII” Windows APIs everywhere and provide strings as-is. This would also allow dropping the leveldb patch.
9. 
   hebasto commented at 4:56 pm on April 29, 2025: member

   Great, good to know that’s possible. i guess by the time we switch to C++26 and this becomes a blocking issue, it will be fine to require a 2019 windows version, and we can simplify things by using the “ASCII” Windows APIs everywhere and provide strings as-is. This would also allow dropping the leveldb patch.

   A proof of concept is available in #32380.

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fanquake laanwj hebasto

Labels
Windows