Tell people to report sysconfig issues to Apple

src/pip/_internal/locations/__init__.py

@@ -435,13 +435,40 @@ def _deduplicated(v1: str, v2: str) -> List[str]:
  return [v1, v2]
 
 
+def _looks_like_apple_library(path: str) -> bool:
+ """Apple patches sysconfig to *always* look under */Library/Python*."""
+ if sys.platform[:6] != "darwin":
+ return False
+ return path == f"/Library/Python/{get_major_minor_version()}/site-packages"
+
+
 def get_prefixed_libs(prefix: str) -> List[str]:
  """Return the lib locations under ``prefix``."""
  new_pure, new_plat = _sysconfig.get_prefixed_libs(prefix)
  if _USE_SYSCONFIG:
  return _deduplicated(new_pure, new_plat)
 
  old_pure, old_plat = _distutils.get_prefixed_libs(prefix)
+ old_lib_paths = _deduplicated(old_pure, old_plat)
+
+ # Apple's Python (shipped with Xcode and Command Line Tools) hard-code
+ # platlib and purelib to '/Library/Python/X.Y/site-packages'. This will
+ # cause serious build isolation bugs when Apple starts shipping 3.10 because
+ # pip will install build backends to the wrong location. This tells users
+ # who is at fault so Apple may notice it and fix the issue in time.
+ if all(_looks_like_apple_library(p) for p in old_lib_paths):
+ deprecated(
+ reason=(
+ "Python distributed by Apple's Command Line Tools incorrectly "
+ "patches sysconfig to always point to '/Library/Python'. This "
+ "will cause build isolation to operate incorrectly on Python "
+ "3.10 or later. Please help report this to Apple so they can "
+ "fix this. https://developer.apple.com/bug-reporting/"
+ ),
+ replacement=None,
+ gone_in=None,
+ )
+ return old_lib_paths
 
  warned = [
  _warn_if_mismatch(
@@ -458,4 +485,4 @@ def get_prefixed_libs(prefix: str) -> List[str]:
  if any(warned):
  _log_context(prefix=prefix)
 
- return _deduplicated(old_pure, old_plat)
+ return old_lib_paths