0a035de removed main from meson.py breaking the call from __main__.py.
This causes zipapps to fail, since the call to meson.main() fails.
Copying the invocation from meson.py fixes this issue.
Additionally, add a test to run_meson_command_tests.py that
builds a zipapp from the source and attempts executing this
zipapp with --help to ensure that the resulting zipapp is
properly executable.
Instead of using fragile guessing to figure out how to invoke meson,
set the value when meson is run. Also rework how we pass of
meson_script_launcher to regenchecker.py -- it wasn't even being used
With this change, we only need to guess the meson path when running
the tests, and in that case:
1. If MESON_EXE is set in the env, we know how to run meson
for project tests.
2. MESON_EXE is not set, which means we run the configure in-process
for project tests and need to guess what meson to run, so either
- meson.py is found next to run_tests.py, or
- meson, meson.py, or meson.exe is in PATH
Otherwise, you can invoke meson in the following ways:
1. meson is installed, and mesonbuild is available in PYTHONPATH:
- meson, meson.py, meson.exe from PATH
- python3 -m mesonbuild.mesonmain
- python3 /path/to/meson.py
- meson is a shell wrapper to meson.real
2. meson is not installed, and is run from git:
- Absolute path to meson.py
- Relative path to meson.py
- Symlink to meson.py
All these are tested in test_meson_commands.py, except meson.exe since
that involves building the meson msi and installing it.