Add a test for the --vsenv meson setup option

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.

1 files changed, 15 insertions, 1 deletions

diff --git a/unittests/helpers.py b/unittests/helpers.py
index b759dba..bf06bdc 100644
--- a/unittests/helpers.py
+++ b/unittests/helpers.py
@@ -5,11 +5,13 @@ import unittest
 import functools
 import re
 import typing as T
+from pathlib import Path
 from contextlib import contextmanager
 
 from mesonbuild.compilers import detect_c_compiler, compiler_from_language
 from mesonbuild.mesonlib import (
-    MachineChoice, is_osx, is_cygwin, EnvironmentException, OptionKey, MachineChoice
+    MachineChoice, is_osx, is_cygwin, EnvironmentException, OptionKey, MachineChoice,
+    OrderedSet
 )
 from run_tests import get_fake_env
 
@@ -170,3 +172,15 @@ def get_rpath(fname: str) -> T.Optional[str]:
     # don't check for, so clear those
     final = ':'.join([e for e in raw.split(':') if not e.startswith('/nix')])
     return final
+
+def get_path_without_cmd(cmd: str, path: str) -> str:
+    pathsep = os.pathsep
+    paths = OrderedSet([Path(p).resolve() for p in path.split(pathsep)])
+    while True:
+        full_path = shutil.which(cmd, path=path)
+        if full_path is None:
+            break
+        dirname = Path(full_path).resolve().parent
+        paths.discard(dirname)
+        path = pathsep.join([str(p) for p in paths])
+    return path