Do not append namespace packages to sys.path

Author: DanielNoord

namespace_pkg/existing/__init__.py

@@ -0,0 +1,7 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
+# Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt
+
+from existing import my_func  # type: ignore[attr-defined]
+
+my_func()

namespace_pkg/something_else/__init__.py

@@ -5,12 +5,16 @@
 from __future__ import annotations
 
 import contextlib
+import os
 import sys
 import traceback
 from collections.abc import Iterator, Sequence
 from datetime import datetime
 from pathlib import Path
 
+from astroid import modutils
+from astroid.interpreter._import.spec import ModuleType, find_spec
+
 from pylint.config import PYLINT_HOME
 from pylint.lint.expand_modules import get_python_path
 
@@ -77,6 +81,12 @@ def _patch_sys_path(args: Sequence[str]) -> list[str]:
     seen = set()
     for arg in args:
         path = get_python_path(arg)
+        try:
+            spec = find_spec(modutils.modpath_from_file(arg))
+            if spec.type == ModuleType.PY_NAMESPACE:
+                continue
+        except ImportError:
+            pass
         if path not in seen:
             changes.append(path)
             seen.add(path)

pylint/lint/utils.py

@@ -9,6 +9,7 @@
 import argparse
 import os
 import re
+import subprocess
 import sys
 import tempfile
 from collections.abc import Iterable, Iterator
@@ -170,6 +171,16 @@ def test_more_args(fake_path, case):
         assert sys.path == fake_path
 
 
+def test_namespace_package_sys_path() -> None:
+    """Test that we do not append namespace packages to sys.path."""
+    result = subprocess.run(
+        [sys.executable, "-m", "pylint", "namespace_pkg/"],
+        check=False,
+        stdout=subprocess.PIPE,
+    )
+    assert "Module import itself" not in result.stdout.decode("utf-8")
+
+
 @pytest.fixture(scope="module")
 def disable():
     return ["I"]