fix: save env on plugins enable

Environment was not updated correctly on `tutor plugins enable ...`
because of a caching issue. To bypass this issue, we improve the caching
mechanism and introduce a new `lru_cache` decorator.

Close #989.

docs/reference/api/hooks/index.rst

@@ -23,6 +23,7 @@ Functions
 ---------
 
 .. autofunction:: tutor.core.hooks::clear_all
+.. autofunction:: tutor.hooks::lru_cache
 
 Priorities
 ----------

tests/test_plugins_v0.py

@@ -9,7 +9,7 @@ from tutor.plugins import v0 as plugins_v0
 from tutor.types import Config, get_typed
 
 
-class PluginsTests(PluginsTestCase):
+class PluginsV0Tests(PluginsTestCase):
     def test_iter_installed(self) -> None:
         self.assertEqual([], list(plugins.iter_installed()))
 

tutor/commands/plugins.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import os
-import sys
 import tempfile
 import typing as t
 

tutor/hooks/__init__.py

@@ -2,8 +2,35 @@
 __license__ = "Apache 2.0"
 
 import typing as t
+import functools
+
+from typing_extensions import ParamSpec
 
 # The imports that follow are the hooks API
 from tutor.core.hooks import clear_all, priorities
+from tutor.types import Config
 
 from .catalog import Actions, Contexts, Filters
+
+
+def lru_cache(func: t.Callable[..., t.Any]) -> t.Callable[..., t.Any]:
+    """
+    LRU cache decorator similar to `functools.lru_cache
+    <https://docs.python.org/3/library/functools.html#functools.lru_cache>`__ that is
+    automatically cleared whenever plugins are updated.
+
+    Use this to decorate functions that need to be called multiple times with a return
+    value that depends on which plugins are loaded. Typically: functions that depend on
+    the output of filters.
+    """
+    decorated = functools.lru_cache(func)
+
+    @Actions.PLUGIN_LOADED.add()
+    def _clear_func_cache_on_load(_plugin: str) -> None:
+        decorated.cache_clear()
+
+    @Actions.PLUGIN_UNLOADED.add()
+    def _clear_func_cache_on_unload(_plugin: str, _root: str, _config: Config) -> None:
+        decorated.cache_clear()
+
+    return decorated

tutor/plugins/__init__.py

@@ -3,6 +3,7 @@ Provide API for plugin features.
 """
 from __future__ import annotations
 
+import functools
 import typing as t
 from copy import deepcopy
 
@@ -12,38 +13,6 @@ from tutor.types import Config, get_typed
 # Import modules to trigger hook creation
 from . import openedx, v0, v1
 
-# Cache of plugin patches, for efficiency
-ENV_PATCHES_DICT: dict[str, list[str]] = {}
-
-
-@hooks.Actions.PLUGINS_LOADED.add()
-def _fill_patch_cache_on_load() -> None:
-    """
-    This action is run after plugins have been loaded.
-    """
-    _fill_patches_cache()
-
-
-@hooks.Actions.PLUGIN_UNLOADED.add()
-def _fill_patch_cache_on_unload(plugin: str, root: str, _config: Config) -> None:
-    """
-    This action is run after plugins have been unloaded.
-    """
-    _fill_patches_cache()
-
-
-def _fill_patches_cache() -> None:
-    """
-    Some patches are added as (name, content) tuples with the ENV_PATCHES
-    filter. We convert these patches to add them to ENV_PATCHES_DICT. This makes it
-    easier for end-user to declare patches, and it's more performant.
-    """
-    ENV_PATCHES_DICT.clear()
-    patches: t.Iterable[tuple[str, str]] = hooks.Filters.ENV_PATCHES.iterate()
-    for name, content in patches:
-        ENV_PATCHES_DICT.setdefault(name, [])
-        ENV_PATCHES_DICT[name].append(content)
-
 
 def is_installed(name: str) -> bool:
     """
@@ -127,7 +96,19 @@ def iter_patches(name: str) -> t.Iterator[str]:
     """
     Yields: patch (str)
     """
-    yield from ENV_PATCHES_DICT.get(name, [])
+    yield from _env_patches().get(name, [])
+
+
+@hooks.lru_cache
+def _env_patches() -> dict[str, list[str]]:
+    """
+    Dictionary of patches, implemented for performance reasons.
+    """
+    patches: dict[str, list[str]] = {}
+    for name, content in hooks.Filters.ENV_PATCHES.iterate():
+        patches.setdefault(name, [])
+        patches[name].append(content)
+    return patches
 
 
 def unload(plugin: str) -> None:

tutor/plugins/openedx.py

@@ -4,8 +4,7 @@ import os
 import re
 import typing as t
 
-from tutor import bindmount
-from tutor import hooks
+from tutor import bindmount, hooks
 from tutor.__about__ import __version_suffix__