interpreter: use python dunders instead of lock for unpicklability

This simplifies things for us, as we don't have to have threading
imported for no other reason, and we can remove the
`an_unpicklable_object` from the Interpreter and mesonlib, since there
was only one user of this.

mesonbuild/interpreter/interpreter.py

@@ -21,7 +21,7 @@ from .. import optinterpreter
 from .. import compilers
 from ..wrap import wrap, WrapMode
 from .. import mesonlib
-from ..mesonlib import HoldableObject, FileMode, MachineChoice, OptionKey, listify, extract_as_list, has_path_sep
+from ..mesonlib import MesonBugException, HoldableObject, FileMode, MachineChoice, OptionKey, listify, extract_as_list, has_path_sep
 from ..programs import ExternalProgram, NonExistingExternalProgram
 from ..dependencies import Dependency
 from ..depfile import DepFile
@@ -231,7 +231,6 @@ class Interpreter(InterpreterBase, HoldableObject):
                 is_translated: bool = False,
             ) -> None:
         super().__init__(_build.environment.get_source_dir(), subdir, subproject)
-        self.an_unpicklable_object = mesonlib.an_unpicklable_object
         self.build = _build
         self.environment = self.build.environment
         self.coredata = self.environment.get_coredata()
@@ -279,6 +278,9 @@ class Interpreter(InterpreterBase, HoldableObject):
             self.parse_project()
         self._redetect_machines()
 
+    def __getnewargs_ex__(self) -> T.Tuple[T.Tuple[object], T.Dict[str, object]]:
+        raise MesonBugException('This class is unpicklable')
+
     def _redetect_machines(self):
         # Re-initialize machine descriptions. We can do a better job now because we
         # have the compilers needed to gain more knowledge, so wipe out old

mesonbuild/mesonlib/universal.py

@@ -44,7 +44,6 @@ _U = T.TypeVar('_U')
 
 __all__ = [
     'GIT',
-    'an_unpicklable_object',
     'python_command',
     'project_meson_versions',
     'HoldableObject',
@@ -265,12 +264,6 @@ def check_direntry_issues(direntry_array: T.Union[T.List[T.Union[str, bytes]], s
                 not pure ASCII. This may cause problems.
                 '''), file=sys.stderr)
 
-
-# Put this in objects that should not get dumped to pickle files
-# by accident.
-import threading
-an_unpicklable_object = threading.Lock()
-
 class HoldableObject(metaclass=abc.ABCMeta):
     ''' Dummy base class for all objects that can be
         held by an interpreter.baseobjects.ObjectHolder '''

unittests/internaltests.py

@@ -1524,6 +1524,6 @@ class InternalTests(unittest.TestCase):
         build.environment = mock.Mock()
         build.environment.get_source_dir = mock.Mock(return_value='')
         with mock.patch('mesonbuild.interpreter.Interpreter._redetect_machines', mock.Mock()), \
-                self.assertRaises(Exception):
+                self.assertRaises(mesonbuild.mesonlib.MesonBugException):
             i = mesonbuild.interpreter.Interpreter(build, mock=True)
             pickle.dumps(i)