Swap plugin cache to pickle-able values when done (#7640)

When the dictionary has served its purpose (making plugin loading
pre-and-post init a consistent behaviour), we swap it for bools
indicating whether or not a module was loaded.
We don't currently use the bools, but it seemed a sensible choice.
The main idea is to make the dictionary fully pickle-able, so that when
dill pickles the linter for multiprocessing, it doesn't crash horribly.

Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>
Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/pylint/lint/pylinter.py b/pylint/lint/pylinter.py
index 12726e278..d337fd32c 100644
--- a/pylint/lint/pylinter.py
+++ b/pylint/lint/pylinter.py
@@ -296,7 +296,7 @@ class PyLinter(
             str, list[checkers.BaseChecker]
         ] = collections.defaultdict(list)
         """Dictionary of registered and initialized checkers."""
-        self._dynamic_plugins: dict[str, ModuleType | ModuleNotFoundError] = {}
+        self._dynamic_plugins: dict[str, ModuleType | ModuleNotFoundError | bool] = {}
         """Set of loaded plugin names."""
 
         # Attributes related to registering messages and their handling
@@ -402,7 +402,15 @@ class PyLinter(
                     "bad-plugin-value", args=(modname, module_or_error), line=0
                 )
             elif hasattr(module_or_error, "load_configuration"):
-                module_or_error.load_configuration(self)
+                module_or_error.load_configuration(self)  # type: ignore[union-attr]
+
+        # We re-set all the dictionary values to True here to make sure the dict
+        # is pickle-able. This is only a problem in multiprocessing/parallel mode.
+        # (e.g. invoking pylint -j 2)
+        self._dynamic_plugins = {
+            modname: not isinstance(val, ModuleNotFoundError)
+            for modname, val in self._dynamic_plugins.items()
+        }
 
     def _load_reporters(self, reporter_names: str) -> None:
         """Load the reporters if they are available on _reporters."""