Revert "Do not append namespace packages to sys.path (#6405)"

ChangeLog

@@ -25,16 +25,6 @@ Release date: TBA
 
   Closes #4301
 
-* By default the similarity checker will now ignore imports and ignore function signatures when computing
-  duplication. If you want to keep the previous behaviour set ``ignore-imports`` and ``ignore-signatures`` to ``False``.
-
-* Improved recognition of namespace packages. They should no longer be added to ``sys.path``
-  which should prevent various issues with false positives.
-  Because of the difficulties with mirroring the python import mechanics we would gladly
-  hear feedback on this change.
-
-  Closes #5226, Closes #2648
-
 * ``BaseChecker`` classes now require the ``linter`` argument to be passed.
 
 * Fix a failure to respect inline disables for ``fixme`` occurring on the last line

doc/whatsnew/2.14.rst

@@ -129,13 +129,6 @@ Other Changes
 
   Closes #4301
 
-* Improved recognition of namespace packages. They should no longer be added to ``sys.path``
-  which should prevent various issues with false positives.
-  Because of the difficulties with mirroring the python import mechanics we would gladly
-  hear feedback on this change.
-
-  Closes #5226, Closes #2648
-
 * Update ``invalid-slots-object`` message to show bad object rather than its inferred value.
 
   Closes #6101

pylint/lint/utils.py

@@ -11,8 +11,6 @@
 from datetime import datetime
 from pathlib import Path
 
-from astroid import modutils
-
 from pylint.config import PYLINT_HOME
 from pylint.lint.expand_modules import get_python_path
 
@@ -73,29 +71,12 @@ def get_fatal_error_message(filepath: str, issue_template_path: Path) -> str:
     )
 
 
-def _is_part_of_namespace_package(filename: str) -> bool:
-    """Check if a file is part of a namespace package."""
-    try:
-        modname = modutils.modpath_from_file(filename)
-    except ImportError:
-        modname = [Path(filename).stem]
-
-    try:
-        spec = modutils.file_info_from_modpath(modname)
-    except ImportError:
-        return False
-
-    return modutils.is_namespace(spec)
-
-
 def _patch_sys_path(args: Sequence[str]) -> list[str]:
     original = list(sys.path)
     changes = []
     seen = set()
     for arg in args:
         path = get_python_path(arg)
-        if _is_part_of_namespace_package(path):
-            continue
         if path not in seen:
             changes.append(path)
             seen.add(path)

tests/lint/unittest_expand_modules.py

@@ -77,13 +77,6 @@ def test__is_in_ignore_list_re_match() -> None:
     "path": str(TEST_DIRECTORY / "lint/test_caching.py"),
 }
 
-test_namespace_packages = {
-    "basename": "lint",
-    "basepath": INIT_PATH,
-    "isarg": False,
-    "name": "lint.test_namespace_packages",
-    "path": str(TEST_DIRECTORY / "lint/test_namespace_packages.py"),
-}
 
 init_of_package = {
     "basename": "lint",
@@ -115,7 +108,6 @@ class Checker(BaseChecker):
                 [
                     init_of_package,
                     test_caching,
-                    test_namespace_packages,
                     test_pylinter,
                     test_utils,
                     this_file_from_init,