MAINT: put back mesonpy.__version__

The module constant has been used to check meson-python version in
other projects, see discussion on mesonbuild#691.  Add a test to ensure that the
version recorded in pyproject.toml and mesonpy/__init__.py are kept in
sync.

mesonpy/__init__.py

@@ -79,6 +79,9 @@ class InvalidLicenseExpression(Exception):  # type: ignore[no-redef]
     MesonArgs = Mapping[MesonArgsKeys, List[str]]
 
 
+__version__ = "0.18.0.dev0"
+
+
 _PYPROJECT_METADATA_VERSION = tuple(map(int, pyproject_metadata.__version__.split('.')[:2]))
 _SUPPORTED_DYNAMIC_FIELDS = {'version', } if _PYPROJECT_METADATA_VERSION < (0, 9) else {'version', 'license', 'license-files'}
 

tests/test_consistency.py

@@ -5,13 +5,21 @@
 import pathlib
 import sys
 
+import mesonpy
 
 if sys.version_info >= (3, 11):
     import tomllib
 else:
     import tomli as tomllib
 
 
+def test_version():
+    pyproject = pathlib.Path(__file__).parent.parent.joinpath('pyproject.toml')
+    with open(pyproject, 'rb') as f:
+        project_version = tomllib.load(f)['project']['version']
+    assert mesonpy.__version__ == project_version
+
+
 def test_pyproject_dependencies():
     pyproject = pathlib.Path(__file__).parent.parent.joinpath('pyproject.toml')
     with open(pyproject, 'rb') as f: