The goal of this PR is to provide a native Windows build of Sage using MSVC (using the new Meson build system).

Instructions on how to test are under the Windows tab at https://doc-pr-38872--sagemath.netlify.app/html/en/installation/meson.
Afterwards, you should be able to import some sage modules in a normal python install (but most modules actually don't properly import due to various errors that will be fixed peu a peu in follow-up PRs)

State of Windows support of dependencies

• m4rie: upstream (https://github.com/malb/m4rie) doesn't provide win build
• ec: not sure if upstream (https://github.com/JohnCremona/eclib) provide win build
• ecm: upstream (https://gitlab.inria.fr/zimmerma/ecm) doesn't provide native win build (only Cygwin)
• ntl: upstream provides win build (kind of), but it's not yet available on conda (Build for windows with CMake conda-forge/ntl-feedstock#16)
• maxima/ecl: upstream provides win build, but it's not yet available on conda (Windows build conda-forge/maxima-feedstock#38)
• GAP: only cygiwn build exists Thoughts for a native (well, mingw) Window version of GAP gap-system/gap#4157
• pari: now available on conda (Windows version conda-forge/pari-feedstock#45)
• cypari2: no windows support yet merge cypari and cypari2 cypari2#19
• lrcalc
• pplpy
• primecountpy
• fpylll
• rw
• cliquer
• lcalc
• ecl
• braiding
• gc
• homfly
• iml
• brial_groebner

Conda Issues:

• Meson cannot find libraries without pkg-config files.
  • Workaround: Check that set LIB includes the conda env (e.g. ...\.conda\envs\sage-dev\Library\lib). If not, run conda deactivate followed by conda activate sage-dev and then check again.
  • Alternatively, set LIB=%CONDA_PREFIX%\Library\lib;%LIB%
  • Possible upstream improvement: the compilers conda package should set LIB
• If you don't have the debug version of Python installed, you may get "LINK : fatal error LNK1104: cannot open file 'python311_d.lib'"
  • Workaround: meson setup builddir -Dbuildtype=release
  • Alternatively, in <path to conda>\sage-dev\include\pyconfig.h uncomment: //# define Py_DEBUG and change python311_d.lib to python311.lib
  • Possible upstream improvement: conda should either ship a debug version of python or a correct pyconfig.h
• pkgconfig is wrong conda-forge/gsl-feedstock#63
  • Workaround: Fallback to find_library in meson and/or change the gsl.pc to match:

    prefix=C:/Users/Tobia/.conda/envs/sage-dev/Library
    exec_prefix=C:/Users/Tobia/.conda/envs/sage-dev/Library
    libdir=C:/Users/Tobia/.conda/envs/sage-dev/Library/lib
    sharedlibdir=C:/Users/Tobia/.conda/envs/sage-dev/Library/lib
    includedir=C:/Users/Tobia/.conda/envs/sage-dev/Library/include
    GSL_CBLAS_LIB=-lgslcblas
    
    Name: GSL
    Description: GNU Scientific Library
    Version: 2.7
    Libs: -L${libdir} -lgsl ${GSL_CBLAS_LIB}  
    Cflags: -I${includedir}
    

• When installingc-compiler on Windows, VS 2022 Build Tools init file is not installed conda-forge/compilers-feedstock#66
  • Workaround: Run everything in "VS x64 Native Tools Command Prompt" (for 64bit) or "Developer Command Prompt for VS2022 (or 2019)" (for 32bit)
• Doesn't include a pkg-config file (on Windows) conda-forge/libgd-feedstock#55
  • Workaround: Fallback to find_library in meson
• Linker issue LNK2019: unresolved external symbol on Windows conda-forge/m4ri-feedstock#15
  • Workaround: Don't try to use m4ri on windows
• winpthreads-related issue when compiling against flint conda-forge/libflint-feedstock#38
  • Workaround: Don't try to use flint on windows

Upstream issues

Singular

• Improve symbol exports on Windows Singular/Singular#1245
• Use dynamic arrays when the have non-constant length Singular/Singular#1246
• Add NOMINMAX for Windows compatibility Singular/Singular#1247

Flint:

• Fix name conflicts with small macro from rpcndr flintlib/flint#2100
• Using winpthreads with python leads to confliciting pid_t mingw-w64/mingw-w64#65 (indirectly since pthread is flint dependency). Would be fixed by winpthreads-related issue when compiling against flint conda-forge/libflint-feedstock#38.
  -> Workaround: Change typedef __int64 pid_t; to typedef int pid_t; in .conda\envs\sage-dev\Library\include\pthread_compat.h
• Replace inline assembly with function prototypes in sanity check flintlib/flint#2101:
  -> Workaround: disable compilation of fraction_field_FpT for now

Cysignals:

• Fix compilation on Windows cysignals#207
• Update build system to use Meson cysignals#206

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies