fix: stringify plugin definitions so they can be pickled during caching

pelican/__init__.py

@@ -23,7 +23,7 @@ from pelican.plugins import signals
 from pelican.plugins._utils import load_plugins
 from pelican.readers import Readers
 from pelican.server import ComplexHTTPRequestHandler, RootedHTTPServer
-from pelican.settings import coerce_overrides, read_settings
+from pelican.settings import coerce_overrides, read_settings, stringify_plugins
 from pelican.utils import (FileSystemWatcher, clean_output_dir, maybe_pluralize)
 from pelican.writers import Writer
 
@@ -73,6 +73,7 @@ class Pelican:
             except Exception as e:
                 logger.error('Cannot register plugin `%s`\n%s',
                              plugin.__name__, e)
+        stringify_plugins(self.settings)
 
     def run(self):
         """Run the generators and return"""

pelican/settings.py

@@ -681,3 +681,15 @@ def coerce_overrides(overrides):
                              'load as json', k, v)
                 coerced[k] = json.loads(v)
     return coerced
+
+
+def stringify_plugins(settings):
+    """
+    Plugins can be passed as module objects, however this breaks caching as
+    module objects cannot be pickled. To work around this, we stringify all
+    plugin definitions post-initialization.
+    """
+    if 'PLUGINS' in settings and settings['PLUGINS'] is not None:
+        settings['PLUGINS'] = [str(p) for p in settings['PLUGINS']]
+
+    return settings

pelican/tests/support.py

@@ -193,6 +193,11 @@ def get_context(settings=None, **kwargs):
     return context
 
 
+class NoopPlugin:
+    def register(self):
+        pass
+
+
 class LogCountHandler(BufferingHandler):
     """Capturing and counting logged messages."""
 

pelican/tests/test_settings.py

@@ -8,8 +8,9 @@ from sys import platform
 from pelican.settings import (DEFAULT_CONFIG, DEFAULT_THEME,
                               _printf_s_to_format_field,
                               coerce_overrides, configure_settings,
-                              handle_deprecated_settings, read_settings)
-from pelican.tests.support import unittest
+                              handle_deprecated_settings, read_settings,
+                              stringify_plugins)
+from pelican.tests.support import NoopPlugin, unittest
 
 
 class TestSettingsConfiguration(unittest.TestCase):
@@ -319,3 +320,11 @@ class TestSettingsConfiguration(unittest.TestCase):
             'THEME_STATIC_DIR': 'theme',
         }
         self.assertDictEqual(overrides, expected)
+
+    def test_stringify_plugins(self):
+        settings = {
+            'PLUGINS': ['string_plugin', NoopPlugin]
+        }
+        stringify_plugins(settings)
+        # Plugins are converted to string references
+        self.assertTrue(all(str(p) == p for p in settings['PLUGINS']))