fix: fall back to block type when XBlock plugin is missing

openedx/core/djangoapps/content_staging/serializers.py

@@ -2,6 +2,7 @@
 Serializers for the content libraries REST API
 """
 from rest_framework import serializers
+from xblock.plugin import PluginMissingError
 
 from common.djangoapps.student.auth import has_studio_read_access
 from xmodule.modulestore.django import modulestore
@@ -36,7 +37,15 @@ def get_block_type_display(self, obj):
         """ Get the friendly name for this XBlock/component type """
         from cms.djangoapps.contentstore.helpers import xblock_type_display_name
 
-        return xblock_type_display_name(obj.block_type)
+        try:
+            return xblock_type_display_name(obj.block_type)
+        except PluginMissingError:
+            # The clipboard holds a *copy* of a block, so the XBlock may no longer be installed (e.g. its
+            # plugin was removed from the platform after the content was copied).  Fall back to the raw block
+            # type instead of raising, so that one stale clipboard cannot break unrelated requests (the
+            # clipboard is embedded in the course index response for every course).  This mirrors
+            # openedx.core.djangoapps.xblock.api.xblock_type_display_name, which already does this.
+            return obj.block_type
 
 
 class UserClipboardSerializer(serializers.Serializer):

openedx/core/djangoapps/content_staging/tests/test_clipboard.py

@@ -13,6 +13,7 @@
 from common.djangoapps.student.tests.factories import UserFactory
 from openedx.core.djangoapps.authz.tests.mixins import CourseAuthoringAuthzTestMixin
 from openedx.core.djangoapps.content_staging import api as python_api
+from openedx.core.djangoapps.content_staging.models import StagedContent
 from xmodule.contentstore.django import contentstore
 from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase, upload_file_to_course
 from xmodule.modulestore.tests.factories import BlockFactory, CourseFactory, ToyCourseFactory
@@ -133,6 +134,34 @@ def test_copy_video_python_get(self) -> None:
         assert olx_data is not None
         self.assertXmlEqual(olx_data, SAMPLE_VIDEO_OLX)
 
+    def test_uninstalled_xblock_in_clipboard(self) -> None:
+        """
+        A clipboard may hold a *copy* of a block whose XBlock plugin is no longer installed.  Reading the
+        clipboard must still work (it is embedded in the course index response for every course), falling
+        back to the raw block type for the display name.
+        """
+        course_key, client = self._setup_course()
+
+        # Copy the video to the clipboard:
+        video_key = course_key.make_usage_key("video", "sample_video")
+        response = client.post(CLIPBOARD_ENDPOINT, {"usage_key": str(video_key)}, format="json")
+        assert response.status_code == 200
+        staged_content_id = response.json()["content"]["id"]
+        assert response.json()["content"]["block_type_display"] == "Video"
+
+        # Pretend the plugin for this block type was uninstalled after the content was copied:
+        StagedContent.objects.filter(pk=staged_content_id).update(block_type="an_uninstalled_xblock")
+
+        # The REST API should answer 200, using the raw block type as the display name:
+        response = client.get(CLIPBOARD_ENDPOINT)
+        assert response.status_code == 200
+        response_data = response.json()
+        assert response_data["content"]["block_type"] == "an_uninstalled_xblock"
+        assert response_data["content"]["block_type_display"] == "an_uninstalled_xblock"
+
+        # ...and so should the python API, which is what the course index response uses:
+        assert python_api.get_user_clipboard_json(self.user.id, response.wsgi_request) == response_data
+
     def test_copy_html(self) -> None:
         """
         Test copying an HTML XBlock from the course