Allow PR refs for jax or xla

[terrykong]

We already allow standard git-refs to be configurable in the build for xla and jax.

This change makes it possible to specify a PR git-ref so we can test an experimental change.

[yhtang]

Could you please provide an example of how PRs are specified for a build?

[terrykong]

Sure. So for this PR: https://github.com/openxla/xla/pull/4044/files

You'd specify it in the CI workflow as https://github.com/openxla/xla.git#pull/4044/head

[yhtang]

We can make it more intuitive. pull/<ID>/heads feels a bit magical here, and users would have to guess the correct format from the git refs.

Given that a PR is referenced in GitHub Flavored Markdown by user/repo#<PR_ID>, which coincides with that ci.yaml currently accepts, how about we determine if the content after # is a PR if it is:

• purely numeric
• decimal

There is a small chance of conflict if a branch is named by a decimal integer, which is extremely rare in practice. The chance that it collides with a commit hash is also negligible.

Moreover, this job might be a better place to host such logic. The idea is to keep the Dockerfile clean and independent of the CI workflow. We can detect if the content after # is a PR, then convert it to the corresponding git ref and pass it into subsequent reusable workflows/Dockerfiles.

[terrykong]

GitHub Flavored Markdown by user/repo#<PR_ID>

That's cool! I didn't realize that was that syntax in GH markdown.

Moreover, this job might be a better place to host such logic. The idea is to keep the Dockerfile clean and independent of the CI workflow. We can detect if the content after # is a PR, then convert it to the corresponding git ref and pass it into subsequent reusable workflows/Dockerfiles.

We can definitely move the logic that converts integers to PR git-refs 1320 -> pull/1320/head in that job. But, I'm not sure of a better way to reference the PR other than what's already in the Dockerfile. It is a bit magical that that's the git-ref, but it is what is documented in the GH's docs

I can make the change to accept a decimal instead.

[terrykong]

Closing this as it complicates the dockerfile. Better ways of handling this were discussed offline like potentially moving the logic of fetching github git refs outside of the dockerfile