refactor: slash-and-burn Poll BuiltIn XBlock

[irfanuddinahmad]

Summary

Removes the built-in Poll XBlock and all associated assets. The extracted xblocks_contrib.poll.PollBlock has been the default since USE_EXTRACTED_POLL_QUESTION_BLOCK was set to True, so the built-in implementation is now dead code.

Step 1 of 8 in the Slash-n-Burn Built-In XBlocks epic.

Closes openedx/public-engineering#533

Changes

• Remove USE_EXTRACTED_POLL_QUESTION_BLOCK toggle from openedx/envs/common.py
• Remove conflicting built-in poll_question entrypoint from pyproject.toml (the xblocks-contrib entrypoint remains active)
• Delete xmodule/poll_block.py (built-in class + shim)
• Delete xmodule/js/src/poll/ (JS assets)
• Delete lms/templates/poll.html
• Delete xmodule/static/css-builtin-blocks/PollBlockDisplay.css
• Remove PollBlockDisplay / PollBlockEditor webpack entries from webpack.builtinblocks.config.js and webpack.common.config.js
• Delete xmodule/tests/test_poll.py (covered by xblocks-contrib tests)

Epic Step 1: Post-extraction commit review

Reviewed commits to xmodule/poll_block.py after USE_EXTRACTED_POLL_QUESTION_BLOCK was set to True (2025-12-16 · 24cb3cf9f5). All 3 post-toggle commits were cosmetic: deprecation markers (#38174), import sorting, and lint-amnesty removal. No functional bug fixes or features to port.

Test plan

Testing scope: The xblocks-contrib implementation's behavioral correctness was fully validated during the extraction phase (when USE_EXTRACTED_* was set to True). These slash-n-burn PRs only delete dead built-in code — no behavioral change is possible. The only regression risk is that an entrypoint, webpack bundle, or import path is broken, which surfaces as a block failing to load. Basic load verification across LMS, CMS course, and CMS library is sufficient.

Smoke tests require a live Tutor environment and cannot be pre-checked in CI. Please verify during staging.

• Block loads and renders in LMS (student view)
• Block loads and renders in CMS course unit
• Block loads and renders in CMS V2 Library

Automated checks (CI):

• Run xmodule unit tests: pytest xmodule/tests/
• Confirm webpack build succeeds: npm run build

⚠️ Scope of the checks above, and why merging should wait on xblocks-core#274:

• The LMS and CMS course unit checks confirm rendering only, via content authored through raw OLX import — the normal "Add Component → Edit" flow for this block doesn't work at all, for anyone, in courses or libraries. xblocks_contrib.poll.PollBlock has no studio_view (unlike every other extracted block).
• CMS V2 Library is unchecked, and not just because it's untested: any Poll block created directly in a library (the standard, empty-first creation flow) becomes permanently unloadable — confirmed by reproducing the crash against the real block class. It's not a matter of testing harder; that flow is broken.

Both issues predate this PR (they're gaps in the xblocks-contrib extraction), but this PR removes the last working fallback (the built-in block's editor) for them. Recommend holding merge until xblocks-core#274 is resolved — same pattern as the Word Cloud PR being gated on xblocks-core#273.

Screenshots on sandbox

CMS

LMS

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[irfanuddinahmad]

Found two real blockers to merging this while testing poll_question in the sandbox — full detail and reproduction steps tracked in openedx/xblocks-core#274:

1. No Studio editing view. xblocks_contrib.poll.PollBlock only defines student_view — no studio_view, unlike every other extracted block (Video/Annotatable/Word Cloud/HTML/LTI/Discussion all have one). Opening "Edit" on a poll_question block fails client-side (edit_xblock.js: xblockElement is empty or not defined).

2. Empty Poll blocks are permanently unloadable in Content Libraries v2. definition_from_xml hard-fails if there are zero <answer> tags. That check is meant to run once at course-import time, but under Content Libraries v2's Learning Core runtime it re-runs on every load — so any Poll created via the normal "Add Component" flow (always empty at first) can never be loaded again, by anyone, for any reason. Confirmed by reproducing against the real block class in a local devstack.

This PR shouldn't merge until both are resolved in xblocks-core.

Updated the test plan checkboxes above with a note on what the LMS/CMS checks actually cover (rendering, via an OLX-import workaround, since the normal editor is broken) and why CMS V2 Library stays unchecked — it's not a matter of testing harder, that flow is broken for any Poll created directly in a library.