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kdmccormick merged 3 commits into from
Jan 28, 2026
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docs: Add learnings about _services.copy() fix to preview.py #37956

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docs: Add learnings about `_services.copy()` fix to preview.py
kdmccormick Jan 28, 2026
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kdmccormick Jan 28, 2026
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kdmccormick Jan 28, 2026
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11 changes: 11 additions & 0 deletions cms/djangoapps/contentstore/views/preview.py
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Expand Up @@ -200,6 +200,17 @@ def _prepare_runtime_for_preview(request, block):
# See the docstring of `DjangoXBlockUserService`.
deprecated_anonymous_user_id = anonymous_id_for_user(request.user, None)

# NOTE: As of Ulmo, these services only apply to the preview views. If you want a service to be present in all
# Studio ModuleStoreRuntimes, then add it to load_services_for_studio.
# HISTORICAL CONTEXT: Until Ulmo, the `block.runtime._services.update(service)` call below would
# actually update the services dictionary for all runtimes, as `_services` was aliased between them.
# This caused a grading bug, under certain conditions, so it was fixed
# in https://github.com/openedx/openedx-platform/pull/37825; now, every runtime gets a fresh,
# independent copy of `_services`. That's good, except that some Studio code had become dependent
# on the bugged behavior and thus expected the "preview" services below to be present in all Studio runtimes.
# We fixed the known instance of that bugged assumption here:
# https://github.com/openedx/openedx-platform/pull/37900.
# This comment is left here as a note for future devs investigating similar bugs.
services = {
"studio_user_permissions": StudioPermissionsService(request.user),
"i18n": XBlockI18nService,
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