Allow equivalent distutils and sysconfig locations

news/9838.bugfix.rst

@@ -0,0 +1 @@
+Fix compatibility between distutils and sysconfig when the project name is unknown outside of a virtual environment.

news/9839.bugfix.rst

@@ -0,0 +1 @@
+Fix compatibility between distutils and sysconfig when the returned location is a symbolic link.

src/pip/_internal/locations/__init__.py

@@ -1,3 +1,4 @@
+import contextlib
 import logging
 import pathlib
 import sys
@@ -45,6 +46,9 @@ def _default_base(*, user: bool) -> str:
 def _warn_if_mismatch(old: pathlib.Path, new: pathlib.Path, *, key: str) -> bool:
     if old == new:
         return False
+    with contextlib.suppress(OSError):
+        if old.samefile(new):
+            return False
     issue_url = "https://github.com/pypa/pip/issues/9617"
     message = (
         "Value for %s does not match. Please report this to <%s>"

src/pip/_internal/locations/_sysconfig.py

@@ -128,13 +128,16 @@ def get_scheme(
     paths = sysconfig.get_paths(scheme=scheme_name, vars=variables)
 
     # Pip historically uses a special header path in virtual environments.
+    # Logic here is very arbitrary, we're doing it for compatibility, don't ask.
     if running_under_virtualenv():
         if user:
             base = variables.get("userbase", sys.prefix)
         else:
             base = variables.get("base", sys.prefix)
         python_xy = f"python{get_major_minor_version()}"
         paths["include"] = os.path.join(base, "include", "site", python_xy)
+    elif not dist_name:
+        dist_name = "UNKNOWN"
 
     scheme = Scheme(
         platlib=paths["platlib"],