Should we stop supporting building with Visual Studio?

I'm not sure if that was mentioned, but Ninja could potentially be used inside Visual Studio with a Makefile project type [1].
We're already doing this to compile with Fastbuild inside Visual Studio.

You generate `cmake -G"Visual Studio 15 2017 Win64" ...` in such way that, in Project Properties / General / Project Defaults, "Configuration Type" would be set to "Makefile" for all generated .vcxproj.
For example:

  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='FastBuild Debug|x64'" Label="Configuration">

Now a "NMake" section replaces all the previous sections in "Project Properties". This is where any batch command(s) can be called for building/rebuild/clean. In this case, we would probably use `ninja -C build_release` for example:

  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='FastBuild Debug|x64'">
    <NMakeBuildCommandLine>ninja -C build_debug</NMakeBuildCommandLine>
    <NMakeReBuildCommandLine> ninja -t rebuild -C build_debug</NMakeReBuildCommandLine>
    <NMakeCleanCommandLine>ninja -t clean -C build_debug</NMakeCleanCommandLine>

To avoid calling ninja many times for each vcxproj, we also disable the "Build" checkbox in the "Configuration Manager" for all projects but one (say for ALL_BUILD).

The only quirk I see would be for the NMake batch to first call `cmake -G Ninja" with the parameters initially passed to `cmake -G"Visual Studio 15 2017".

This overall scheme would retain the different targets in Visual Studio (Debug, Release, RelWithDebInfo, etc.) by passing a different CMAKE_BUILD_TYPE to the above NMake batch file.

The only thing you're loosing with this is the ability to compile as single .cpp (Ctrl-F7). However, you can get around that by installing the "Clang Power Tools" extension and bind a key for that purpose.