gh-158540: Resolve symlinks when adding the script directory to sys.path

``python script.py`` resolves symlinks when computing ``sys.path[0]``, so
a script reached through a symlink (``link.py -> sub/where.py``) imports
modules from the real script's directory.  Apply ``os.path.realpath()``
before taking the directory name, and make sure the result is placed at
the front of ``sys.path`` even if it was already listed.

Add a regression test for a symlinked script.

Author: hetaozdh

Lib/profiling/sampling/_sync_coordinator.py

@@ -168,10 +168,14 @@ def _execute_script(script_path: str, script_args: List[str], cwd: str) -> None:
     if not os.path.isfile(script_path):
         raise TargetError(f"Script not found: {script_path}")
 
-    # Put directory containing the script (not the current working directory) on sys.path so that modules next to it can be imported. Similar to ``python script.py``
-    script_dir = os.path.dirname(script_path)
-    if script_dir not in sys.path:
-        sys.path.insert(0, script_dir)
+    # Put the directory containing the script (not the current working
+    # directory) on sys.path so that modules next to it can be imported,
+    # like ``python script.py`` does.  Resolve symlinks first so that
+    # modules next to the real script (not next to the link) are found.
+    script_dir = os.path.dirname(os.path.realpath(script_path))
+    if script_dir in sys.path:
+        sys.path.remove(script_dir)
+    sys.path.insert(0, script_dir)
 
     # Replace sys.argv to match original script call
     sys.argv = [script_path] + script_args

Lib/test/test_profiling/test_sampling_profiler/test_sync_coordinator.py

@@ -7,7 +7,7 @@
 import tempfile
 import unittest
 
-from test.support import SHORT_TIMEOUT, requires_subprocess
+from test.support import SHORT_TIMEOUT, os_helper, requires_subprocess
 
 
 @requires_subprocess()
@@ -79,6 +79,35 @@ def test_script_directory_on_sys_path(self):
         self.assertIn("HELPER: helper imported", stdout)
         self.assertIn(f"PATH0: {os.path.realpath(script_dir)}", stdout)
 
+    @os_helper.skip_unless_symlink
+    def test_symlinked_script_uses_real_directory(self):
+        # gh-158540: ``python script.py`` resolves symlinks when computing
+        # sys.path[0], so a symlinked script must import modules next to the
+        # real script, not next to the link.
+        with tempfile.TemporaryDirectory() as tmpdir:
+            script_dir = os.path.join(tmpdir, "sub")
+            os.mkdir(script_dir)
+            with open(os.path.join(script_dir, "helper.py"), "w") as f:
+                f.write("message = 'helper imported'\n")
+            with open(os.path.join(script_dir, "where.py"), "w") as f:
+                f.write(
+                    "import os\n"
+                    "import sys\n"
+                    "print('PATH0:', os.path.realpath(sys.path[0]))\n"
+                    "import helper\n"
+                    "print('HELPER:', helper.message)\n"
+                )
+            os.symlink(
+                os.path.join("sub", "where.py"),
+                os.path.join(tmpdir, "link.py"),
+            )
+
+            stdout, stderr = self.run_coordinator(tmpdir, "link.py")
+
+        self.assertNotIn("ModuleNotFoundError", stderr)
+        self.assertIn("HELPER: helper imported", stdout)
+        self.assertIn(f"PATH0: {os.path.realpath(script_dir)}", stdout)
+
 
 if __name__ == "__main__":
     unittest.main()