modules/python: Allow use of the native file

Currently this just allows setting a "python" variable that always
overrides, probably we want to have the option for "python2" and
"python3" as well.

mesonbuild/modules/python.py

@@ -480,7 +480,9 @@ class PythonModule(ExtensionModule):
         if len(args) > 1:
             raise InvalidArguments('find_installation takes zero or one positional argument.')
 
-        if args:
+        if 'python' in state.environment.config_info.binaries:
+            name_or_path = state.environment.config_info.binaries['python']
+        elif args:
             name_or_path = args[0]
             if not isinstance(name_or_path, str):
                 raise InvalidArguments('find_installation argument must be a string.')

run_unittests.py

@@ -4557,6 +4557,14 @@ class NativeFileTests(BasePlatformTests):
     def test_python3_module(self):
         self._simple_test('python3', 'python3')
 
+    def test_python_module(self):
+        if is_windows():
+            # Bat adds extra crap to stdout, so the version check logic in the
+            # python module breaks. This is fine on other OSes because they
+            # don't need the extra indirection.
+            raise unittest.SkipTest('bat indirection breaks internal sanity checks.')
+        self._simple_test('python', 'python')
+
 
 def unset_envs():
     # For unit tests we must fully control all command lines

test cases/unit/46 native file binary/meson.build

@@ -14,4 +14,8 @@ elif case == 'python3'
   prog = import('python3').find_python()
   result = run_command(prog, ['--version'])
   assert(result.stdout().strip().endswith('12345'), 'Didn\'t load python3 from config file')
+elif case == 'python'
+  prog = import('python').find_installation()
+  result = run_command(prog, ['--version'])
+  assert(result.stdout().strip().endswith('12345'), 'Didn\'t load python from config file')
 endif

test cases/unit/46 native file binary/meson_options.txt

@@ -1,5 +1,5 @@
 option(
   'case',
   type : 'combo',
-  choices : ['find_program', 'config_dep', 'python3']
+  choices : ['find_program', 'config_dep', 'python3', 'python']
 )