MAINT: simplify optional dependencies handling

Remove one layer of indirection to make code easier to follow. Extend
the tests to verify that the returned requirement strings are in the
correct format.

Author: dnicolodi

mesonpy/__init__.py

@@ -85,14 +85,6 @@
 _MESON_REQUIRED_VERSION = '0.63.3' # keep in sync with the version requirement in pyproject.toml
 
 
-class _depstr:
-    """Namespace that holds the requirement strings for dependencies we *might*
-    need at runtime. Having them in one place makes it easier to update.
-    """
-    patchelf = 'patchelf >= 0.11.0'
-    ninja = f'ninja >= {_NINJA_REQUIRED_VERSION}'
-
-
 def _init_colors() -> Dict[str, str]:
     """Detect if we should be using colors in the output. We will enable colors
     if running in a TTY, and no environment variable overrides it. Setting the
@@ -1017,12 +1009,13 @@ def wrapper(*args: P.args, **kwargs: P.kwargs) -> T:
 
 
 @_pyproject_hook
-def get_requires_for_build_sdist(
-    config_settings: Optional[Dict[str, str]] = None,
-) -> List[str]:
+def get_requires_for_build_sdist(config_settings: Optional[Dict[str, str]] = None) -> List[str]:
+    dependencies = []
+
     if os.environ.get('NINJA') is None and _env_ninja_command() is None:
-        return [_depstr.ninja]
-    return []
+        dependencies.append(f'ninja >= {_NINJA_REQUIRED_VERSION}')
+
+    return dependencies
 
 
 @_pyproject_hook
@@ -1042,10 +1035,10 @@ def get_requires_for_build_wheel(config_settings: Optional[Dict[str, str]] = Non
     dependencies = []
 
     if os.environ.get('NINJA') is None and _env_ninja_command() is None:
-        dependencies.append(_depstr.ninja)
+        dependencies.append(f'ninja >= {_NINJA_REQUIRED_VERSION}')
 
     if sys.platform.startswith('linux') and not shutil.which('patchelf'):
-        dependencies.append(_depstr.patchelf)
+        dependencies.append('patchelf >= 0.11.0')
 
     return dependencies
 

tests/test_pep517.py

@@ -8,6 +8,7 @@
 
 from typing import List
 
+import packaging.requirements
 import pytest
 
 import mesonpy
@@ -41,15 +42,18 @@ def run(cmd: List[str], *args: object, **kwargs: object) -> subprocess.Completed
 
     expected = set()
 
-    ninja_available = ninja is not None and [int(x) for x in ninja.split('.')] >= [1, 8, 2]
-
-    if not ninja_available:
-        expected |= {mesonpy._depstr.ninja}
+    if ninja is None or mesonpy._parse_version_string(ninja) < (1, 8, 2):
+        expected.add('ninja')
 
     if system_patchelf is None and sys.platform.startswith('linux'):
-        expected |= {mesonpy._depstr.patchelf}
+        expected.add('patchelf')
+
+    requirements = mesonpy.get_requires_for_build_wheel()
+
+    # Check that the requirement strings are in the correct format.
+    names = {packaging.requirements.Requirement(x).name for x in requirements}
 
-    assert set(mesonpy.get_requires_for_build_wheel()) == expected
+    assert names == expected
 
 
 def test_invalid_config_settings(capsys, package_pure, tmp_path_session):