Have spackbot post a comment when pipeline is deferred?

[alalazo]

Currently, when a user submits a PR which is ahead of the current develop, we defer running pipelines according to the explanation here. To let user know what we do, the "Details" link of the Gitlab pipeline goes to the explanation above:

The issue that I have seen a few times already is that users rarely click on that link. Rather, they assume that having a seemingly stale yellow dot means something is wrong with syncronization - so they rebase their branch multiple times. The last example is:

• gromacs: add cufftmp variant to enable distributed PME when using CUDA spack#36552 (comment)

but I can find others. Would it be easy to have Spackbot post a comment when a pipeline is deferred, with some brief explanation and the link above? That would probably make our intent clearer.

[scottwittenburg]

That seems like a useful thing to do.

Spackbot already posts such a message when users ask it to run a pipeline for their PR, because it can check if that PR is deferred or the branch just hasn't been pushed yet. However, it only knows that by checking whether gitlab currently has the ref and whether or not the associated sha matches the one in the payload. And I don't see how we could be sure, when spackbot receives the event for an opened PR, whether the sync script has run or not. I would guess that most commonly spackbot receives the PR opened event, and then later the sync script runs to make the decision about whether to push a branch or defer.

So since it's the sync script that decides whether or not to defer pipelines (see here), we may need to add this feature there instead, unfortunately duplicating the message posting code in that repo. Unless you can think of some detail I'm forgetting that would make this possible here, I'll create an issue for this on spack-infrastructure and link to this one.

Thanks for the suggestion 😁