Switch to using lstat() instead of stat() to not match symlink targets.

The convenience function samefile() calls stat() and samestat(), but
this leads to treating a symlink and its target as the same which is
unlikely to be intentional here as that doesn't work well with venv.

Author: roubert

news/13156.bugfix.rst

@@ -0,0 +1 @@
+Show the correct path to the interpreter also when it's a symlink in a venv in the pip upgrade prompt.

src/pip/_internal/utils/entrypoints.py

@@ -77,7 +77,10 @@ def get_best_invocation_for_this_python() -> str:
 
     # Try to use the basename, if it's the first executable.
     found_executable = shutil.which(exe_name)
-    if found_executable and os.path.samefile(found_executable, exe):
+    # Virtual environments often symlink to their parent Python binaries, but we don't
+    # want to treat the Python binaries as equivalent when the environment's Python is
+    # not on PATH (not activated). Thus, we don't follow symlinks.
+    if found_executable and os.path.samestat(os.lstat(found_executable), os.lstat(exe)):
         return exe_name
 
     # Use the full executable name, because we couldn't find something simpler.