env: override default scheme for Apple Python venv

Author: layday

src/build/env.py

@@ -246,20 +246,22 @@ def _find_executable_and_scripts(path):  # type: (str) -> Tuple[str, str, str]
         """
         config_vars = sysconfig.get_config_vars().copy()  # globally cached, copy before altering it
         config_vars['base'] = path
-        env_scripts = sysconfig.get_path('scripts', vars=config_vars)
-        if not env_scripts:
-            raise RuntimeError("Couldn't get environment scripts path")
-        exe = 'pypy3' if platform.python_implementation() == 'PyPy' else 'python'
-        if os.name == 'nt':
-            exe = '{}.exe'.format(exe)
-        executable = os.path.join(env_scripts, exe)
+        # The Python that ships with the macOS developer tools varies the
+        # default scheme depending on whether the ``sys.prefix`` is part of a framework.
+        # The framework "osx_framework_library" scheme
+        # can't be used to expand the paths in a venv, which
+        # can happen if build itself is not installed in a venv.
+        # If the Apple-custom "osx_framework_library" scheme is available
+        # we enforce "posix_prefix", the venv scheme, for isolated envs.
+        if 'osx_framework_library' in sysconfig.get_scheme_names():
+            paths = sysconfig.get_paths(scheme='posix_prefix', vars=config_vars)
+        else:
+            paths = sysconfig.get_paths(vars=config_vars)
+        executable = os.path.join(paths['scripts'], 'python.exe' if os.name == 'nt' else 'python')
         if not os.path.exists(executable):
             raise RuntimeError('Virtual environment creation failed, executable {} missing'.format(executable))
 
-        purelib = sysconfig.get_path('purelib', vars=config_vars)
-        if not purelib:
-            raise RuntimeError("Couldn't get environment purelib folder")
-        return executable, env_scripts, purelib
+        return executable, paths['scripts'], paths['purelib']
 
 
 __all__ = (

tests/test_env.py

@@ -51,21 +51,32 @@ def test_isolated_environment_install(mocker):
         ]
 
 
+@pytest.mark.skipif(IS_PY2, reason='venv module used on Python 3 only')
+@pytest.mark.skipif(IS_PYPY3, reason='PyPy3 uses get path to create and provision venv')
+@pytest.mark.skipif(sys.platform != 'darwin', reason='workaround for Apple Python')
+def test_can_get_venv_paths_with_conflicting_default_scheme(mocker):
+    mocker.patch.object(build.env, 'virtualenv', None)
+    get_scheme_names = mocker.patch('sysconfig.get_scheme_names', return_value=('osx_framework_library',))
+    with build.env.IsolatedEnvBuilder():
+        pass
+    assert get_scheme_names.call_count == 1
+
+
 @pytest.mark.skipif(IS_PY2, reason='venv module used on Python 3 only')
 @pytest.mark.skipif(IS_PYPY3, reason='PyPy3 uses get path to create and provision venv')
 def test_executable_missing_post_creation(mocker):
     mocker.patch.object(build.env, 'virtualenv', None)
-    original_get_path = sysconfig.get_path
+    original_get_paths = sysconfig.get_paths
 
-    def _get_path(name, vars):  # noqa
+    def _get_paths(vars):  # noqa
         shutil.rmtree(vars['base'])
-        return original_get_path(name, vars=vars)
+        return original_get_paths(vars=vars)
 
-    get_path = mocker.patch('sysconfig.get_path', side_effect=_get_path)
+    get_paths = mocker.patch('sysconfig.get_paths', side_effect=_get_paths)
     with pytest.raises(RuntimeError, match='Virtual environment creation failed, executable .* missing'):
         with build.env.IsolatedEnvBuilder():
             pass
-    assert get_path.call_count == 1
+    assert get_paths.call_count == 1
 
 
 def test_isolated_env_abstract():