[CI] Add PR/Issue Auto Labeler

[DN6]

What does this PR do?

Addresses suggestions brought up in #13343 by adding scripts/workflows to auto labels issues and PRs .

For Issues:
Use Qwen/Qwen3.5-35B-A3B via Inference Providers to parse issues titles and content and assign appropriate labels from a fixed set.

For PRs:

• Add labels based on which files are changed
• Add labels in case tests are missing for new model additions and pipelines
• Adds a size label to PRs so it's easy for maintainers to prioritise reviews based on size.
  - S (<50 LOC diff)
  - M (<200 LOC diff)
  - L (>200 LOC diff)

Fixes # (issue)
#13343

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[yiyixuxu]

@claude are you here, can you do a review too?

[github-actions]

Claude finished @yiyixuxu's task in 1m 28s —— View job

---

PR Review

• Read PR diff and changed files
• Analyze changes and identify issues
• Post review feedback

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All 5 changed files in this PR are outside src/diffusers/ (they are in .github/ and utils/), which is the only directory within my configured review scope. There are no src/diffusers/ changes to report correctness issues on.

That said, here are a few observations worth noting on the utility scripts and CI files:

utils/label_issues.py

• [utils/label_issues.py:414] json.loads(response) will raise if the LLM returns non-JSON (e.g. thinking tokens or markdown fences). Qwen3 may emit <think>…</think> before JSON output — the bare except Exception: pass on line 425 silently swallows this and produces no labels. Consider stripping thinking tags or using response_format={"type":"json_object"} if the endpoint supports it. Fix this →

• [utils/label_issues.py:416] Variable name l shadows built-in l; minor but worth renaming to label for clarity.

• [utils/label_issues.py:421] any(model_name.lower() in name for name in existing) does substring matching. A model named "wan" would match a directory named "wanvideo" correctly, but a very short name like "flux" would also match "reflux" if such a directory existed. This is likely fine in practice, but worth being aware of.

utils/check_test_missing.py

• [utils/check_test_missing.py:276] The file is opened at f["filename"] (a repo-relative path). This only works if the script is run from the repository root. That's assumed by the workflow (it does actions/checkout first), so it's fine — but fragile if run locally from a different cwd.

• [utils/check_test_missing.py:283-287] Only added test files are checked, not modified ones. A PR that adds a new model class and extends an existing test file (rather than adding a new one) will incorrectly be labeled missing-tests. This could lead to false positives.

.github/workflows/issue_labeler.yml

• [.github/workflows/issue_labeler.yml:131-132] ISSUE_TITLE and ISSUE_BODY are passed as environment variables from github.event.issue.*. This is the safe pattern (avoids shell injection), so this is correct.

• [.github/workflows/issue_labeler.yml:143] The shell loop for label in $(echo "$LABELS" | python -c ...) will break on label names containing spaces. The current label set has no spaces, but it's a latent bug if labels are ever changed.

.github/workflows/pr_labeler.yml

• [.github/workflows/pr_labeler.yml:154] Uses pull_request_target with actions/checkout@v4 (default, checks out base branch). This is correct and safe — it does not check out the PR head in a privileged context.

• [.github/workflows/pr_labeler.yml:168] sync-labels: true on the labeler action means labels will be removed from PRs if the corresponding files are no longer changed. This is intentional but worth documenting so maintainers understand why labels disappear on synchronize events.

Overall the PR is well-structured. The main concern worth addressing before merge is the silent JSON parse failure in label_issues.py when Qwen3 produces thinking-token output.

[yiyixuxu]

this is awesome! thanks
I left one comment

[yiyixuxu]

I think we have a missing-info/ or missing-code-example label, cam we add it here too?

[DN6]

Reusing our existing needs-code-example label for that.
https://github.com/huggingface/diffusers/pull/13380/changes#diff-ed09b43f8018cb6694ae7bc3d686d34f5267f7bba506ca6b650d1ddb2b54a7b9R36

Did you also mean missing info like env details?

[yiyixuxu]

nice!

oh i just meant needs-code-example, but not sure if you want to re-use name. we can add one for missing env details too, but not as important I think!

Did you also mean missing info like env details?

[iwr-redmond]

A few suggestions:

• I agree with @claude that activating the structured output feature for the issues checker is a good idea
• You may wish to add the no-linked-issue rule for PRs
• It would be helpful to follow the lead of 🔒 Pin GitHub Actions to commit SHAs #13385 and pin the Github Actions to commit SHAs, as this will reduce exposure to supply chain risks

[yiyixuxu]

thanks for working on this!
super excited to see it in action

[yiyixuxu]

nice!

oh i just meant needs-code-example, but not sure if you want to re-use name. we can add one for missing env details too, but not as important I think!

Did you also mean missing info like env details?