BUG: ensure build options are preserved

Using `pip install -Cbuild-dir=<existing-dir>` used to overwrite
the `buildtype` instead of reusing it from the build directory.

Now, we don't provide default options if the directory exist.

Author: Alvaro-Kothe

mesonpy/__init__.py

@@ -899,23 +899,33 @@ def _run(self, cmd: Sequence[str]) -> None:
 
     def _configure(self, reconfigure: bool = False) -> None:
         """Configure Meson project."""
-        setup_args = [
+        setup_cmd = self._meson + ['setup']
+
+        if reconfigure:
+            setup_cmd.append('--reconfigure')
+
+        setup_cmd += [
             os.fspath(self._source_dir),
             os.fspath(self._build_dir),
-            # default build options
-            '-Dbuildtype=release',
-            '-Db_ndebug=if-release',
-            '-Db_vscrt=md',
-            # user build options
-            *self._meson_args['setup'],
-            # pass native file last to have it override the python
-            # interpreter path that may have been specified in user
-            # provided native files
-            f'--native-file={os.fspath(self._meson_native_file)}',
         ]
-        if reconfigure:
-            setup_args.insert(0, '--reconfigure')
-        self._run(self._meson + ['setup', *setup_args])
+
+        if not reconfigure:
+            # default build options
+            setup_cmd += [
+                '-Dbuildtype=release',
+                '-Db_ndebug=if-release',
+                '-Db_vscrt=md',
+            ]
+
+        # user build options
+        setup_cmd += self._meson_args['setup']
+
+        # pass native file last to have it override the python
+        # interpreter path that may have been specified in user
+        # provided native files
+        setup_cmd.append(f'--native-file={os.fspath(self._meson_native_file)}')
+
+        self._run(setup_cmd)
 
     @property
     def _build_command(self) -> List[str]:

tests/test_project.py

@@ -332,6 +332,27 @@ def test_invalid_build_dir(package_pure, tmp_path, mocker):
     assert '--reconfigure' not in meson.call_args_list[0].args[1]
     project.build()
 
+def test_reconfigure_preserves_config(package_simple, tmp_path):
+    # initial configuration
+    project = mesonpy.Project(package_simple, tmp_path, meson_args={
+        'setup': ['-Dbuildtype=debug', '-Dwarning_level=2'],
+    })
+
+    initial_options = {opt['name']: opt['value'] for opt in project._info('intro-buildoptions')}
+
+    # reconfiguration with a new option
+    project = mesonpy.Project(package_simple, tmp_path, meson_args={
+        'setup': ['-Doptimization=2'],
+    })
+
+    reconfigure_options = {opt['name']: opt['value'] for opt in project._info('intro-buildoptions')}
+
+    assert initial_options != reconfigure_options
+
+    initial_options['optimization'] = '2'
+    assert initial_options == reconfigure_options
+
+
 
 @pytest.mark.skipif(not os.getenv('CI') or sys.platform != 'win32', reason='requires MSVC')
 def test_compiler(venv, package_detect_compiler, tmp_path):