Prefer the resolved base executable for exec_prefix discovery

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Author: itamaro

Lib/test/test_getpath.py

@@ -542,6 +542,41 @@ def test_venv_symlink_to_separate_exec_prefix_posix(self):
         actual = getpath(ns, expected)
         self.assertEqual(expected, actual)
 
+    def test_venv_separate_exec_prefix_with_misleading_home_posix(self):
+        "Test that a stale lib-dynload near home does not override the base executable."
+        ns = MockPosixNamespace(
+            argv0="/venv/bin/python",
+            PREFIX="/stdlib",
+            EXEC_PREFIX="/build/exec",
+        )
+        ns.add_known_xfile("/exec/bin/python")
+        ns.add_known_xfile("/public/bin/python")
+        ns.add_known_link("/public/bin/python", "/exec/bin/python")
+        ns.add_known_xfile("/venv/bin/python")
+        ns.add_known_link("/venv/bin/python", "/public/bin/python")
+        ns.add_known_file("/stdlib/lib/python9.8/os.py")
+        ns.add_known_dir("/exec/lib/python9.8/lib-dynload")
+        # An empty directory near the symlink must not win.
+        ns.add_known_dir("/public/lib/python9.8/lib-dynload")
+        ns.add_known_file("/venv/pyvenv.cfg", [
+            "home = /public/bin",
+        ])
+        expected = dict(
+            executable="/venv/bin/python",
+            prefix="/venv",
+            exec_prefix="/venv",
+            base_executable="/exec/bin/python",
+            base_prefix="/stdlib",
+            base_exec_prefix="/exec",
+            module_search_paths_set=1,
+            module_search_paths=[
+                "/stdlib/lib/python98.zip",
+                "/stdlib/lib/python9.8",
+                "/exec/lib/python9.8/lib-dynload",
+            ],
+        )
+        actual = getpath(ns, expected)
+        self.assertEqual(expected, actual)
     def test_venv_non_installed_zip_path_posix(self):
         "Test a venv created from non-installed python has correct zip path."""
         ns = MockPosixNamespace(

Modules/getpath.py

@@ -633,13 +633,13 @@ def search_up(prefix, *landmarks, test=isfile):
             exec_prefix = prefix
         if not exec_prefix and prefix and isdir(joinpath(prefix, PLATSTDLIB_LANDMARK)):
             exec_prefix = prefix
-        if not exec_prefix and executable_dir:
-            exec_prefix = search_up(executable_dir, PLATSTDLIB_LANDMARK, test=isdir)
         if not exec_prefix and base_executable_dir and base_executable_dir != executable_dir:
             # The venv's resolved base executable may live under a separate
             # exec_prefix (e.g. ./configure --exec-prefix) even when the
             # stdlib was found from 'home'.
             exec_prefix = search_up(base_executable_dir, PLATSTDLIB_LANDMARK, test=isdir)
+        if not exec_prefix and executable_dir:
+            exec_prefix = search_up(executable_dir, PLATSTDLIB_LANDMARK, test=isdir
         if not exec_prefix and EXEC_PREFIX:
             exec_prefix = EXEC_PREFIX
         if not exec_prefix or not isdir(joinpath(exec_prefix, PLATSTDLIB_LANDMARK)):