Abstract out get_python_lib() usages

src/pip/_internal/build_env.py

@@ -6,7 +6,6 @@ import os
 import sys
 import textwrap
 from collections import OrderedDict
-from distutils.sysconfig import get_python_lib
 from sysconfig import get_paths
 from types import TracebackType
 from typing import TYPE_CHECKING, Iterable, List, Optional, Set, Tuple, Type
@@ -15,6 +14,7 @@ from pip._vendor.pkg_resources import Requirement, VersionConflict, WorkingSet
 
 from pip import __file__ as pip_location
 from pip._internal.cli.spinners import open_spinner
+from pip._internal.locations import get_platlib, get_prefixed_libs, get_purelib
 from pip._internal.utils.subprocess import call_subprocess
 from pip._internal.utils.temp_dir import TempDirectory, tempdir_kinds
 
@@ -34,14 +34,7 @@ class _Prefix:
             'nt' if os.name == 'nt' else 'posix_prefix',
             vars={'base': path, 'platbase': path}
         )['scripts']
-        # Note: prefer distutils' sysconfig to get the
-        # library paths so PyPy is correctly supported.
-        purelib = get_python_lib(plat_specific=False, prefix=path)
-        platlib = get_python_lib(plat_specific=True, prefix=path)
-        if purelib == platlib:
-            self.lib_dirs = [purelib]
-        else:
-            self.lib_dirs = [purelib, platlib]
+        self.lib_dirs = get_prefixed_libs(path)
 
 
 class BuildEnvironment:
@@ -69,10 +62,7 @@ class BuildEnvironment:
         # - ensure .pth files are honored
         # - prevent access to system site packages
         system_sites = {
-            os.path.normcase(site) for site in (
-                get_python_lib(plat_specific=False),
-                get_python_lib(plat_specific=True),
-            )
+            os.path.normcase(site) for site in (get_purelib(), get_platlib())
         }
         self._site_dir = os.path.join(temp_dir.path, 'site')
         if not os.path.exists(self._site_dir):

src/pip/_internal/locations/__init__.py

@@ -1,7 +1,7 @@
 import logging
 import pathlib
 import sysconfig
-from typing import Optional
+from typing import List, Optional
 
 from pip._internal.models.scheme import SCHEME_KEYS, Scheme
 
@@ -19,6 +19,9 @@ __all__ = [
     "get_bin_prefix",
     "get_bin_user",
     "get_major_minor_version",
+    "get_platlib",
+    "get_prefixed_libs",
+    "get_purelib",
     "get_scheme",
     "get_src_prefix",
     "init_backend",
@@ -102,3 +105,33 @@ def get_bin_user():
     new = _sysconfig.get_bin_user()
     _warn_if_mismatch(pathlib.Path(old), pathlib.Path(new), key="bin_user")
     return old
+
+
+def get_purelib():
+    # type: () -> str
+    """Return the default pure-Python lib location."""
+    old = _distutils.get_purelib()
+    new = _sysconfig.get_purelib()
+    _warn_if_mismatch(pathlib.Path(old), pathlib.Path(new), key="purelib")
+    return old
+
+
+def get_platlib():
+    # type: () -> str
+    """Return the default platform-shared lib location."""
+    old = _distutils.get_platlib()
+    new = _sysconfig.get_platlib()
+    _warn_if_mismatch(pathlib.Path(old), pathlib.Path(new), key="platlib")
+    return old
+
+
+def get_prefixed_libs(prefix):
+    # type: (str) -> List[str]
+    """Return the lib locations under ``prefix``."""
+    old_pure, old_plat = _distutils.get_prefixed_libs(prefix)
+    new_pure, new_plat = _sysconfig.get_prefixed_libs(prefix)
+    _warn_if_mismatch(old_pure, new_pure, key="prefixed-purelib")
+    _warn_if_mismatch(old_plat, new_plat, key="prefixed-platlib")
+    if old_pure == old_plat:
+        return [old_pure]
+    return [old_pure, old_plat]

src/pip/_internal/locations/_distutils.py

@@ -9,7 +9,8 @@ import sys
 from distutils.cmd import Command as DistutilsCommand
 from distutils.command.install import SCHEME_KEYS
 from distutils.command.install import install as distutils_install_command
-from typing import Dict, List, Optional, Union, cast
+from distutils.sysconfig import get_python_lib
+from typing import Dict, List, Optional, Tuple, Union, cast
 
 from pip._internal.models.scheme import Scheme
 from pip._internal.utils.compat import WINDOWS
@@ -145,3 +146,21 @@ def get_bin_prefix():
 def get_bin_user():
     # type: () -> str
     return bin_user
+
+
+def get_purelib():
+    # type: () -> str
+    return get_python_lib(plat_specific=False)
+
+
+def get_platlib():
+    # type: () -> str
+    return get_python_lib(plat_specific=True)
+
+
+def get_prefixed_libs(prefix):
+    # type: (str) -> Tuple[str, str]
+    return (
+        get_python_lib(plat_specific=False, prefix=prefix),
+        get_python_lib(plat_specific=True, prefix=prefix),
+    )

src/pip/_internal/locations/_sysconfig.py

@@ -135,3 +135,19 @@ def get_bin_prefix():
 
 def get_bin_user():
     return sysconfig.get_path("scripts", scheme=_infer_scheme("user"))
+
+
+def get_purelib():
+    # type: () -> str
+    return sysconfig.get_path("purelib")
+
+
+def get_platlib():
+    # type: () -> str
+    return sysconfig.get_path("platlib")
+
+
+def get_prefixed_libs(prefix):
+    # type: (str) -> typing.Tuple[str, str]
+    paths = sysconfig.get_paths(vars={"base": prefix, "platbase": prefix})
+    return (paths["purelib"], paths["platlib"])