00251: Change user install location

Change the values of sysconfig's "posix_prefix" install scheme to /usr/local
when RPM build or venv/virtualenv is not detected,
to make pip, sysconfig and distutils install into an isolated location.

The original values are saved as an additional "rpm_prefix" install scheme.

The site module adds the /usr/local paths to sys.path when site packages are
enabled and RPM build is not detected.

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

Rewrote in Fedora 36+ to patch sysconfig instead of distutils,
see https://discuss.python.org/t/pep-632-deprecate-distutils-module/5134/104

Downstream only for now, waiting for https://bugs.python.org/issue43976

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>

Lib/site.py

@@ -380,8 +380,15 @@ 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.py

@@ -58,6 +58,25 @@
         },
     }
 
+# backup the original posix_prefix as rpm_prefix
+# RPM packages use it and we need to be able to read it even when changed
+_INSTALL_SCHEMES['rpm_prefix'] = _INSTALL_SCHEMES['posix_prefix']
+
+if (not (hasattr(sys, 'real_prefix') or
+    sys.prefix != sys.base_prefix) and
+    'RPM_BUILD_ROOT' not in os.environ):
+        _INSTALL_SCHEMES['posix_prefix'] = {
+            'stdlib': '{installed_base}/{platlibdir}/python{py_version_short}',
+            'platstdlib': '{platbase}/{platlibdir}/python{py_version_short}',
+            'purelib': '{base}/local/lib/python{py_version_short}/site-packages',
+            'platlib': '{platbase}/local/{platlibdir}/python{py_version_short}/site-packages',
+            'include':
+                '{installed_base}/include/python{py_version_short}{abiflags}',
+            'platinclude':
+                '{installed_platbase}/include/python{py_version_short}{abiflags}',
+            'scripts': '{base}/local/bin',
+            'data': '{base}/local',
+        }
 
 # NOTE: site.py has copy of this function.
 # Sync it when modify this function.

Lib/test/test_sysconfig.py

@@ -263,7 +263,7 @@ 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']
+        wanted = ['nt', 'posix_home', 'posix_prefix', 'rpm_prefix']
         if HAS_USER_BASE:
             wanted.extend(['nt_user', 'osx_framework_user', 'posix_user'])
         self.assertEqual(get_scheme_names(), tuple(sorted(wanted)))
@@ -274,6 +274,8 @@ 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