ENH: detect missing version information in meson.build when required

When pyproject.toml does not contain a "project" section, or when the
"version" field is declared as dynamic, the package version is
retrieved from the one specified in the project() call in meson.build.
However, providing a version in meson.build is optional. Detect when
the version is missing and report an appropriate error.

mesonpy/__init__.py

@@ -734,10 +734,18 @@ def __init__(  # noqa: C901
             self._metadata = Metadata.from_pyproject(pyproject, self._source_dir)
             # set version from meson.build if version is declared as dynamic
             if 'version' in self._metadata.dynamic:
-                self._metadata.version = packaging.version.Version(self._meson_version)
+                version = self._meson_version
+                if version == 'undefined':
+                    raise pyproject_metadata.ConfigurationError(
+                        'Field "version" declared as dynamic but version is not defined in meson.build')
+                self._metadata.version = packaging.version.Version(version)
         else:
             # if project section is missing, use minimal metdata from meson.build
-            self._metadata = Metadata(name=self._meson_name, version=packaging.version.Version(self._meson_version))
+            name, version = self._meson_name, self._meson_version
+            if version == 'undefined':
+                raise pyproject_metadata.ConfigurationError(
+                    'Section "project" missing in pyproject.toml and version is not defined in meson.build')
+            self._metadata = Metadata(name=name, version=packaging.version.Version(version))
 
         # verify that we are running on a supported interpreter
         if self._metadata.requires_python:

tests/packages/missing-dynamic-version/meson.build

@@ -0,0 +1,5 @@
+# SPDX-FileCopyrightText: 2023 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+project('missing-dynamic-version')

tests/packages/missing-dynamic-version/pyproject.toml

@@ -0,0 +1,11 @@
+# SPDX-FileCopyrightText: 2023 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+[build-system]
+build-backend = 'mesonpy'
+requires = ['meson-python']
+
+[project]
+name = 'missing-dynamic-version'
+dynamic = ['version']

tests/packages/missing-meson-version/meson.build

@@ -0,0 +1,5 @@
+# SPDX-FileCopyrightText: 2023 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+project('missing-meson-version')

tests/packages/missing-meson-version/pyproject.toml

@@ -0,0 +1,7 @@
+# SPDX-FileCopyrightText: 2023 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+[build-system]
+build-backend = 'mesonpy'
+requires = ['meson-python']

tests/test_project.py

@@ -64,6 +64,19 @@ def test_missing_version(package_missing_version):
         with mesonpy.Project.with_temp_working_dir():
             pass
 
+
+def test_missing_meson_version(package_missing_meson_version):
+    with pytest.raises(pyproject_metadata.ConfigurationError, match='Section "project" missing in pyproject.toml'):
+        with mesonpy.Project.with_temp_working_dir():
+            pass
+
+
+def test_missing_dynamic_version(package_missing_dynamic_version):
+    with pytest.raises(pyproject_metadata.ConfigurationError, match='Field "version" declared as dynamic but'):
+        with mesonpy.Project.with_temp_working_dir():
+            pass
+
+
 def test_user_args(package_user_args, tmp_path, monkeypatch):
     project_run = mesonpy.Project._run
     cmds = []