TST: enable fatal meson warnings for all tests, unless explicitly disabled

This uses a pytest ``autouse`` fixture to monkeypatch the function
that validates the ``pyproject.toml`` meson-python configuration to
add ``--fatal-meson-warnings`` to the ``meson setup`` arguments,
unless ``--no-fatal-meson-warnings`` is specified by the package.

Author: dnicolodi

tests/conftest.py

@@ -2,6 +2,7 @@
 #
 # SPDX-License-Identifier: MIT
 
+import argparse
 import contextlib
 import importlib.metadata
 import os
@@ -192,3 +193,31 @@ def cleanenv():
     # $MACOSX_DEPLOYMENT_TARGET affects the computation of the platform tag on macOS.
     yield mpatch.delenv('MACOSX_DEPLOYMENT_TARGET', raising=False)
     mpatch.undo()
+
+
+@pytest.fixture(autouse=True, scope='session')
+def meson_fatal_warnings():
+    # Cannot use the 'monkeypatch' fixture because of scope mismatch.
+    mpatch = pytest.MonkeyPatch()
+    mesonpy_validate_pyproject_config = mesonpy._validate_pyproject_config
+
+    def _validate_pyproject_config(pyproject):
+        pyproject_config = mesonpy_validate_pyproject_config(pyproject)
+
+        meson_args = pyproject_config.setdefault('args', {})
+        meson_setup_args = meson_args.get('setup', [])
+
+        # Add ``--fatal-meson-warnings`` to the ``meson setup`` arguments
+        # unless the project specifies ``--no-fatal-meson-warnings`` in
+        # ``tool.meson-build.args.setup``.
+        parser = argparse.ArgumentParser(add_help=False)
+        parser.add_argument('--no-fatal-meson-warnings', action='store_true')
+        meson_setup_args = meson_args.get('setup', [])
+        args, meson_setup_args = parser.parse_known_args(meson_setup_args)
+        if not args.no_fatal_meson_warnings:
+            meson_setup_args.append('--fatal-meson-warnings')
+        meson_args['setup'] = meson_setup_args
+
+        return pyproject_config
+
+    mpatch.setattr(mesonpy, '_validate_pyproject_config', _validate_pyproject_config)

tests/test_project.py

@@ -399,7 +399,7 @@ def test_ios_project(package_simple, monkeypatch, multiarch, tmp_path):
     project = mesonpy.Project(source_dir=package_simple, build_dir=tmp_path)
 
     # Meson configuration points at the cross file
-    assert project._meson_args['setup'] == ['--cross-file', os.fspath(tmp_path / 'meson-python-cross-file.ini')]
+    assert project._meson_args['setup'][-2:] == ['--cross-file', os.fspath(tmp_path / 'meson-python-cross-file.ini')]
 
     # Meson config files exist, and have some relevant keys
     assert (tmp_path / 'meson-python-native-file.ini').exists()