'function': different 'const' qualifiers when compiling on Visual Studio 2019 / MSVC 14

[indygreg]

Attempting to upgrade python-zstandard from 1.5.2 to 1.5.4. My Windows CI environment is still using GitHub's Windows 2019 runners with Visual Studio 2019 / MSVC 14.

Using the single file library with zstd.h + legacy support. I get the following error:

"C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\bin\HostX86\x64\cl.exe" /c /nologo /O2 /W3 /GL /DNDEBUG /MD -Ic-ext -Izstd -IC:\hostedtoolcache\windows\Python\3.11.2\x64\include -IC:\hostedtoolcache\windows\Python\3.11.2\x64\Include "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\ATLMFC\include" "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include" "-IC:\Program Files (x86)\Windows Kits\NETFXSDK\4.8\include\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\shared" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\winrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.22621.0\cppwinrt" /Tcc-ext\backend_c.c /Fobuild\temp.win-amd64-cpython-311\Release\c-ext\backend_c.obj -DZSTD_SINGLE_FILE -DZSTDLIB_VISIBLE= -DZDICTLIB_VISIBLE= -DZSTDERRORLIB_VISIBLE= /WX
backend_c.c
zstd\zstd.c(36246): error C2220: the following warning is treated as an error
zstd\zstd.c(36246): warning C4090: 'function': different 'const' qualifiers
zstd\zstd.c(36329): warning C4090: 'function': different 'const' qualifiers
zstd\zstd.c(37026): warning C4090: 'function': different 'const' qualifiers
zstd\zstd.c(37149): warning C4090: 'function': different 'const' qualifiers
error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise\\VC\\Tools\\MSVC\\14.29.30133\\bin\\HostX86\\x64\\cl.exe' failed with exit code 2

See also https://github.com/indygreg/python-zstandard/actions/runs/4214186727/jobs/7314474490.

Here are direct links to the failing lines:

• https://github.com/indygreg/python-zstandard/blob/54472b013aaf46fa7089de24f6c543f5b77abf44/zstd/zstd.c#L36246
• https://github.com/indygreg/python-zstandard/blob/54472b013aaf46fa7089de24f6c543f5b77abf44/zstd/zstd.c#L36329
• https://github.com/indygreg/python-zstandard/blob/54472b013aaf46fa7089de24f6c543f5b77abf44/zstd/zstd.c#L37026
• https://github.com/indygreg/python-zstandard/blob/54472b013aaf46fa7089de24f6c543f5b77abf44/zstd/zstd.c#L37149

AFAICT all of these are the common pattern:

typedef struct {
    BYTE const* ip[4];
    ...
} HUF_DecompressFastArgs;

BYTE const* ip[4];
...
ZSTD_memcpy(&ip, &args->ip, sizeof(ip));

[embg]

Thanks for the report! This was fixed in #3495, which will be included in the next zstd release (1.5.5). That PR also fixes a couple Visual Studio 2022 warnings -- just want to make you aware in case you upgrade and run into them.