Allow clear_cache() to load brain plugins

ChangeLog

@@ -13,6 +13,8 @@ Release date: TBA
 
   Closes #1512
 
+* Allowed ``AstroidManager.clear_cache`` to reload necessary brain plugins.
+
 * Rename ``ModuleSpec`` -> ``module_type`` constructor parameter to match attribute
   name and improve typing. Use ``type`` instead.
 

astroid/manager.py

@@ -10,6 +10,7 @@
 import os
 import types
 import zipimport
+from importlib.util import find_spec, module_from_spec
 from typing import TYPE_CHECKING, ClassVar, List, Optional
 
 from astroid.exceptions import AstroidBuildingError, AstroidImportError
@@ -362,5 +363,17 @@ def bootstrap(self):
 
     def clear_cache(self):
         """Clear the underlying cache. Also bootstraps the builtins module."""
+        # import here because of cyclic imports
+        # pylint: disable=import-outside-toplevel
+
+        from astroid import BRAIN_MODULES_DIRECTORY
+
         self.astroid_cache.clear()
         self.bootstrap()
+
+        # Load brain plugins: currently done in astroid.__init__.py
+        for module in BRAIN_MODULES_DIRECTORY.iterdir():
+            if module.suffix == ".py":
+                spec = find_spec(f"astroid.brain.{module.stem}")
+                module_object = module_from_spec(spec)
+                spec.loader.exec_module(module_object)

tests/unittest_manager.py

@@ -16,6 +16,7 @@
 from astroid import manager, test_utils
 from astroid.const import IS_JYTHON
 from astroid.exceptions import AstroidBuildingError, AstroidImportError
+from astroid.nodes import Const
 
 from . import resources
 
@@ -315,5 +316,13 @@ def test_borg(self) -> None:
         self.assertIs(built, second_built)
 
 
+class ClearCacheTest(unittest.TestCase, resources.AstroidCacheSetupMixin):
+    def test_brain_plugins_reloaded_after_clearing_cache(self) -> None:
+        astroid.MANAGER.clear_cache()
+        format_call = astroid.extract_node("''.format()")
+        inferred = next(format_call.infer())
+        self.assertIsInstance(inferred, Const)
+
+
 if __name__ == "__main__":
     unittest.main()