[CI] fix docker image build by specifying merge-base commit id when downloading pre-compiled wheels

[Harry-Chen]

Purpose

Currently the docker image building stage in CI will try to download prebuilt wheels from the latest HEAD commit on the main branch:

vllm/setup.py

Lines 512 to 514 in 506ed87

	# In Docker build context, .git may be immutable or missing.
	if envs.VLLM_DOCKER_BUILD_CONTEXT:
	return upstream_main_commit

However, this might lead to 404 error when the main branch is too new (e.g. it taks ~30min to build a wheel), especially when PR author rebases it to the latest main.

Before PR #29838 (4b61266) was merged, the wheel downloading mechanism in setup.py will fallback to /nightly/ if 404 occurrs:

vllm/setup.py

Lines 674 to 680 in 7c1ed45

	try:
	with urlopen(wheel_url) as resp:
	if resp.status != 200:
	wheel_url = nightly_wheel_url
	except Exception as e:
	print(f"[warn] Falling back to nightly wheel: {e}")
	wheel_url = nightly_wheel_url

This was not safe, because /nightly/ might be newer than the merge-base of the current PR, and have native code changes, causing their .so files to change.

This PR passes the merge base commit to the Docker build process (and Python-only build test) in CI, so it could download the correct wheels. The VLLM_MERGE_BASE_COMMIT is provided by buildkite bootstrap script in vllm/ci-infra repo.

Test Plan

Tested by CI.

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request correctly addresses an issue with downloading pre-compiled wheels during CI builds by using the merge-base commit. The overall approach is sound. However, I've found a critical issue in one of the updated test scripts that will cause it to fail. Please see the detailed comment for the fix.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[khluu]

is this file not used anymore?

[Harry-Chen]

Yes, this file is replaced by .buildkite/scripts/generate_nightly_index.py