00251: Change user install location

Set values of base and platbase in sysconfig from /usr
to /usr/local when RPM build is not detected
to make pip and similar tools install into separate location.

Fedora Change: https://fedoraproject.org/wiki/Changes/Making_sudo_pip_safe
Downstream only.

We've tried to rework in Fedora 36/Python 3.10 to follow https://bugs.python.org/issue43976
but we have identified serious problems with that approach,
see https://bugzilla.redhat.com/2026979 or https://bugzilla.redhat.com/2097183

pypa/distutils integration: pypa/distutils#70

Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Miro Hrončok <miro@hroncok.cz>
Co-authored-by: Michal Cyprian <m.cyprian@gmail.com>
Co-authored-by: Lumír Balhar <frenzy.madness@gmail.com>

Lib/site.py

@@ -406,8 +406,15 @@ def getsitepackages(prefixes=None):
     return sitepackages
 
 def addsitepackages(known_paths, prefixes=None):
-    """Add site-packages to sys.path"""
+    """Add site-packages to sys.path
+
+    '/usr/local' is included in PREFIXES if RPM build is not detected
+    to make packages installed into this location visible.
+
+    """
     _trace("Processing global site-packages")
+    if ENABLE_USER_SITE and 'RPM_BUILD_ROOT' not in os.environ:
+        PREFIXES.insert(0, "/usr/local")
     for sitedir in getsitepackages(prefixes):
         if os.path.isdir(sitedir):
             addsitedir(sitedir, known_paths)

Lib/sysconfig/__init__.py

@@ -106,6 +106,12 @@
 else:
     _INSTALL_SCHEMES['venv'] = _INSTALL_SCHEMES['posix_venv']
 
+# For a brief period of time in the Fedora 36 life cycle,
+# this installation scheme existed and was documented in the release notes.
+# For backwards compatibility, we keep it here (at least on 3.10 and 3.11).
+_INSTALL_SCHEMES['rpm_prefix'] = _INSTALL_SCHEMES['posix_prefix']
+
+
 def _get_implementation():
     return 'Python'
 
@@ -167,6 +173,19 @@ def joinuser(*args):
             },
     }
 
+# This is used by distutils.command.install in the stdlib
+# as well as pypa/distutils (e.g. bundled in setuptools).
+# The self.prefix value is set to sys.prefix + /local/
+# if neither RPM build nor virtual environment is
+# detected to make distutils install packages
+# into the separate location.
+# https://fedoraproject.org/wiki/Changes/Making_sudo_pip_safe
+if (not (hasattr(sys, 'real_prefix') or
+    sys.prefix != sys.base_prefix) and
+    'RPM_BUILD_ROOT' not in os.environ):
+    _prefix_addition = '/local'
+
+
 _SCHEME_KEYS = ('stdlib', 'platstdlib', 'purelib', 'platlib', 'include',
                 'scripts', 'data')
 
@@ -261,11 +280,40 @@ def _extend_dict(target_dict, other_dict):
         target_dict[key] = value
 
 
+_CONFIG_VARS_LOCAL = None
+
+
+def _config_vars_local():
+    # This function returns the config vars with prefixes amended to /usr/local
+    # https://fedoraproject.org/wiki/Changes/Making_sudo_pip_safe
+    global _CONFIG_VARS_LOCAL
+    if _CONFIG_VARS_LOCAL is None:
+        _CONFIG_VARS_LOCAL = dict(get_config_vars())
+        _CONFIG_VARS_LOCAL['base'] = '/usr/local'
+        _CONFIG_VARS_LOCAL['platbase'] = '/usr/local'
+    return _CONFIG_VARS_LOCAL
+
+
 def _expand_vars(scheme, vars):
     res = {}
     if vars is None:
         vars = {}
-    _extend_dict(vars, get_config_vars())
+
+    # when we are not in a virtual environment or an RPM build
+    # we change '/usr' to '/usr/local'
+    # to avoid surprises, we explicitly check for the /usr/ prefix
+    # Python virtual environments have different prefixes
+    # we only do this for posix_prefix, not to mangle the venv scheme
+    # posix_prefix is used by sudo pip install
+    # we only change the defaults here, so explicit --prefix will take precedence
+    # https://fedoraproject.org/wiki/Changes/Making_sudo_pip_safe
+    if (scheme == 'posix_prefix' and
+        _PREFIX == '/usr' and
+        'RPM_BUILD_ROOT' not in os.environ):
+            _extend_dict(vars, _config_vars_local())
+    else:
+        _extend_dict(vars, get_config_vars())
+
     if os.name == 'nt':
         # On Windows we want to substitute 'lib' for schemes rather
         # than the native value (without modifying vars, in case it

Lib/test/test_sysconfig.py

@@ -121,8 +121,19 @@ def test_get_path(self):
         for scheme in _INSTALL_SCHEMES:
             for name in _INSTALL_SCHEMES[scheme]:
                 expected = _INSTALL_SCHEMES[scheme][name].format(**config_vars)
+                tested = get_path(name, scheme)
+                # https://fedoraproject.org/wiki/Changes/Making_sudo_pip_safe
+                if tested.startswith('/usr/local'):
+                    # /usr/local should only be used in posix_prefix
+                    self.assertEqual(scheme, 'posix_prefix')
+                    # Fedora CI runs tests for venv and virtualenv that check for other prefixes
+                    self.assertEqual(sys.prefix, '/usr')
+                    # When building the RPM of Python, %check runs this with RPM_BUILD_ROOT set
+                    # Fedora CI runs this with RPM_BUILD_ROOT unset
+                    self.assertNotIn('RPM_BUILD_ROOT', os.environ)
+                    tested = tested.replace('/usr/local', '/usr')
                 self.assertEqual(
-                    os.path.normpath(get_path(name, scheme)),
+                    os.path.normpath(tested),
                     os.path.normpath(expected),
                 )
 
@@ -377,7 +388,7 @@ def test_get_config_h_filename(self):
         self.assertTrue(os.path.isfile(config_h), config_h)
 
     def test_get_scheme_names(self):
-        wanted = ['nt', 'posix_home', 'posix_prefix', 'posix_venv', 'nt_venv', 'venv']
+        wanted = ['nt', 'posix_home', 'posix_prefix', 'posix_venv', 'nt_venv', 'venv', 'rpm_prefix']
         if HAS_USER_BASE:
             wanted.extend(['nt_user', 'osx_framework_user', 'posix_user'])
         self.assertEqual(get_scheme_names(), tuple(sorted(wanted)))
@@ -389,6 +400,8 @@ def test_symlink(self): # Issue 7880
             cmd = "-c", "import sysconfig; print(sysconfig.get_platform())"
             self.assertEqual(py.call_real(*cmd), py.call_link(*cmd))
 
+    @unittest.skipIf('RPM_BUILD_ROOT' not in os.environ,
+                     "Test doesn't expect Fedora's paths")
     def test_user_similar(self):
         # Issue #8759: make sure the posix scheme for the users
         # is similar to the global posix_prefix one