The tests and the unittests both unconditionally call setup_vsenv()
because all tests are run using the backend commands directly: ninja,
msbuild, etc.
There's no way to undo this vs env setup, so the only way to test that
--vsenv works is by:
1. Removing all paths in PATH that provide ninja
2. Changing setup_vsenv(force=True) to forcibly set-up a new vsenv
when MESON_FORCE_VSENV_FOR_UNITTEST is set
3. Mock-patching build_command, test_command, install_command to use
`meson` instead of `ninja`
4. Asserting that 'Activating VS' is in the output for all commands
5. Ensure that compilation works because ninja is picked up from the
vs env.
I manually checked that this test actually does fail when the previous
commit is reverted.
Visual Studio Express does not come with the
'Microsoft.VisualStudio.Component.VC.Tools.x86.x64' workload.
This adds a check for the 'Microsoft.VisualStudio.Workload.WDExpress'
workload. Non-express versions take precedence over express versions
when activating.
NamedTemporaryFile can't be opened by name on Windows.
For Windows the created temporary bat file is now closed before
passing to a subprocess, prevented from removal automatically upon
close and deleted explicitly upon finish.
The `except` line was missing its `as e` clause.
As a result, when erroring out, after not finding a compiler, Meson
gives an error ending:
```
File "C:\Users\Matthew\AppData\Roaming\Python\Python39\site-packages\mesonbuild\mesonlib\vsenv.py",
line 100, in setup_vsenv
mlog.warning('Failed to activate VS environment:', str(e))
```
Eli Schwartz