runpython: make it work for -c as well

In commit 4e4f97edb3 we added support for
runpython to accept `-c 'code to execute'` in addition to just script
files. However, doing so would mangle the sys.argv in the executed code
-- which assumes, as python itself does, that argv is the stuff after
the code to execute. We correctly handled this for script files, but the
original addition of -c support pushed this handling into a script-file
specific block.

mesonbuild/mesonmain.py

@@ -139,11 +139,11 @@ class CommandLineParser:
         parser.add_argument('script_args', nargs=argparse.REMAINDER)
 
     def run_runpython_command(self, options):
-        import runpy
+        sys.argv[1:] = options.script_args
         if options.eval_arg:
             exec(options.script_file)
         else:
-            sys.argv[1:] = options.script_args
+            import runpy
             sys.path.insert(0, os.path.dirname(options.script_file))
             runpy.run_path(options.script_file, run_name='__main__')
         return 0

run_meson_command_tests.py

@@ -84,7 +84,7 @@ class CommandTests(unittest.TestCase):
         os.chdir(str(self.orig_dir))
         super().tearDown()
 
-    def _run(self, command, workdir=None):
+    def _run(self, command, workdir=None, env=None):
         '''
         Run a command while printing the stdout, and also return a copy of it
         '''
@@ -92,7 +92,7 @@ class CommandTests(unittest.TestCase):
         # between CI issue and test bug in that case. Set timeout and fail loud
         # instead.
         p = subprocess.run(command, stdout=subprocess.PIPE,
-                           env=os.environ.copy(), text=True,
+                           env=env, text=True,
                            cwd=workdir, timeout=60 * 5)
         print(p.stdout)
         if p.returncode != 0:
@@ -210,6 +210,21 @@ class CommandTests(unittest.TestCase):
         self._run([script.as_posix(), source, '--outfile', target, '--interpreter', python_command[0]])
         self._run([target.as_posix(), '--help'])
 
+    def test_meson_runpython(self):
+        meson_command = str(self.src_root / 'meson.py')
+        script_file = str(self.src_root / 'foo.py')
+        test_command = 'import sys; print(sys.argv[1])'
+        env = os.environ.copy()
+        del env['MESON_COMMAND_TESTS']
+        with open(script_file, 'w') as f:
+            f.write('#!/usr/bin/env python3\n\n')
+            f.write(f'{test_command}\n')
+
+        for cmd in [['-c', test_command, 'fake argument'], [script_file, 'fake argument']]:
+            pyout = self._run(python_command + cmd)
+            mesonout = self._run(python_command + [meson_command, 'runpython'] + cmd, env=env)
+            self.assertEqual(pyout, mesonout)
+
 
 if __name__ == '__main__':
     print('Meson build system', meson_version, 'Command Tests')