if is_msvc and maintainer_mode
  error('Maintainer mode is not supported for Visual Studio builds.\nUse \'-Dmaintainer-mode=false\' to disable')
endif

Is it impossible or just difficult to install mm-common on Windows?
If it's at all possible to have a working mm-common-get command, it's not nice
to make it impossible for MSVC users to use mm-common-get. If you build from git
without letting mm-common-get copy files to the untracked/ directory, you can build
the libsigc++ library file and install it and the include files, but it will
be a limited build system. You can't build or install the documentation.
You can't create a tarball (ninja dist).

If it's possible to build sigc++-3 from git and have a working mm-common-get
command on Windows, I would suggest a less restricting test in meson.build.
Perhaps like so:

mm_common_get = find_program('mm-common-get', required: false)

if maintainer_mode and not mm_common_get.found()
  error('Maintainer mode requires the mm-common-get command.\nUse \'-Dmaintainer-mode=false\' or install the mm-common package, version 1.0.0 or higher.')
endif

I've tested mm-common on Windows. I just installed Meson and Ninja, but no compiler.
I could install mm-common, so the mm-common-get command was available. I tested
libsigc++-3 with very incomplete meson.build files, where I commented out a lot of stuff.

Result: Meson finds mm-common-get, if it's in the search PATH. In maintainer-mode
it copies the files it's supposed to copy to the untracked/ directory.

I recommend

mm_common_get = find_program('mm-common-get', required: false)
if maintainer_mode and not mm_common_get.found()
  error('Maintainer mode requires the mm-common-get command.\n' +
        'Use \'-Dmaintainer-mode=false\' or install the mm-common package, version 1.0.0 or higher.')
endif

I noticed a strange problem with MSVC_NMake/meson.build.

SyntaxError: (unicode error) 'unicodeescape' codes can't decode bytes in position 2-3: truncated \UXXXXXXXX escape

The error disappears if I change

'''.format(project_build_root / 'sigc++config.h', meson.current_build_dir())

to

'''.format(project_build_root / 'sigc++config.h', meson.current_build_dir() / '.')

meson.current_build_dir() uses backslash (\) as directory separator on Windows.
All backslashes are replaced by slashes (/) when / '.' is added.

I suppose you haven't noticed this. I've used Meson version 0.52.1 on Windows.

Hi @kjellahl,

Sorry for being quite late and inactive, as there were some things that I was caught up with. I made the changes that you suggested, and am looking at mm-common on how it can be built successfully on Visual Studio builds (disclaimer: please note the "builds", not "working").

Hmm, I was not able to re-produce the error you had in MSVC_NMake, even with Meson 0.52.1...

With blessings, thank you!

I have merged this PR to kjellahl/sigc3-meson, and then merged kjellahl/sigc3-meson
in PR #48 to master and removed the kjellahl/sigc3-meson branch.

Hmm, I was not able to re-produce the error you had in MSVC_NMake, even with Meson 0.52.1...

Probably it's no real error. Perhaps my Windows computer lacks some necessary program
or DLL or something. I don't use it for program development.