fix: plugin enable/disable/enable

changelog.d/20250109_184104_regis_plugin_unload.md

@@ -0,0 +1 @@
+- [Bugfix] Properly reload a plugin module on enable/disable/enable. This is an edge case that should not have affected anyone. (by @regisb)

tutor/plugins/v1.py

@@ -1,10 +1,12 @@
 import importlib.util
 import os
 from glob import glob
+import sys
 
 import importlib_metadata
 
 from tutor import hooks
+from tutor.types import Config
 
 from .base import PLUGINS_ROOT
 
@@ -71,8 +73,34 @@ def discover_package(entrypoint: importlib_metadata.EntryPoint) -> None:
     dist_version = entrypoint.dist.version if entrypoint.dist else "Unknown"
     hooks.Filters.PLUGINS_INFO.add_item((name, dist_version))
 
-    # Import module on enable
     @hooks.Actions.PLUGIN_LOADED.add()
     def load(plugin_name: str) -> None:
+        """
+        Import module on enable.
+        """
         if name == plugin_name:
             importlib.import_module(entrypoint.value)
+
+    # Remove module from cache on disable
+    @hooks.Actions.PLUGIN_UNLOADED.add()
+    def unload(plugin_name: str, _root: str, _config: Config) -> None:
+        """
+        Remove plugin module from import cache on disable.
+
+        This is necessary in one particular use case: when a plugin is enabled,
+        disabled, and enabled again -- all within the same call to Tutor. In such a
+        case, the following happens:
+
+        1. plugin enabled: the plugin module is imported. It is automatically added by
+           Python to the import cache.
+        2. plugin disabled: action and filter callbacks are removed, but the module
+           remains in the import cache.
+        3. plugin enabled again: the plugin module is imported. But because it's in the
+           import cache, the module instructions are not executed again.
+
+        This is not supposed to happen when we run Tutor normally from the CLI. But when
+        running a long-lived process, such as a web app, where a plugin might be enabled
+        and disabled multiple times, this becomes an issue.
+        """
+        if name == plugin_name and entrypoint.value in sys.modules:
+            sys.modules.pop(entrypoint.value)