We do not need the python module's find_installation() for this, as this
does various things to set up building and installing python modules
(pure python and C-API). This functionality is already tested in the
python tests.
Elsewhere, when we just need an interpreter capable of running python
scripts in order to guarantee a useful scripting language for custom
commands, it suffices to use find_program(), which does not run an
introspection script or do module imports, and is thus faster and
a bit cleaner.
Either way, both methods are guaranteed to find the python3 interpreter,
deferring to mesonlib.python_command for that guarantee.
test "71 summary" can sometimes return the python command with the
".exe" part all uppercased for mysterious Windows reasons. Smooth this
over with ExternalProgram.
Fixes the following error in the testcase:
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/ninjabackend.py", line 548, in generate
self.generate_tests()
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/ninjabackend.py", line 1093, in generate_tests
self.serialize_tests()
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/backends.py", line 567, in serialize_tests
self.write_test_file(datafile)
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/backends.py", line 943, in write_test_file
self.write_test_serialisation(self.build.get_tests(), datafile)
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/backends.py", line 1017, in write_test_serialisation
pickle.dump(self.create_test_serialisation(tests), datafile)
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/backends.py", line 1002, in create_test_serialisation
cmd_args.append(self.construct_target_rel_path(a, t.workdir))
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/backends.py", line 1021, in construct_target_rel_path
return self.get_target_filename(a)
File "/usr/lib/python3.10/site-packages/mesonbuild/backend/backends.py", line 253, in get_target_filename
assert(isinstance(t, build.BuildTarget))