Re: [PATCH] ci: avoid unnecessary builds

From: Jeff King <peff@peff.net>
Date: Nov 4, 2022, 03:20 UTC
Message-ID: <Y2SFGmQnx7CXtTEI@coredump.intra.peff.net>
In-Reply-To: <Y2R3vJf1A2KOZwA7@nand.local>

On Thu, Nov 03, 2022 at 10:23:56PM -0400, Taylor Blau wrote:

Show 10 quoted lines

> But I think you make a compelling point (which doesn't match my own
> workflow, but I can see the utility of nonetheless).
> 
> I was thinking that we could rely on something similar to the ci-config
> ref stuff from back in e76eec35540 (ci: allow per-branch config for
> GitHub Actions, 2020-05-07), but it looks like it'll be a little
> trickier than that, maybe impossible.
> 
> We need to know about the state of the ci-config branch before we set
> the concurrency bits. So I think you *could* do something like:

As an aside, I wish there was a way to interpret per-repo environment variables in the actual action config. The current ci-config stuff works, but it's pretty horrible because (if I understand correctly) it spins up a VM just to evaluate a glob and say "nope, no CI needed on this branch". So:

  1. It's wasteful of resources, compared to a system where the Actions
     parser can evaluate a variable.

  2. It makes the Actions results page for a repo ugly, because skipped
     branches clutter the output with "yes, I passed CI" even though all
     they passed was a trivial job to say "don't bother running more
     CI".

  3. The problem you mention: it happens too late to affect the overall
     Actions flow, and instead individual jobs have to take it into
     account.

When I wrote the original ci-config stuff I looked for an alternative. You _can_ set per-repo variables in the form of secrets, but I couldn't find a way to evaluate them at the top-level of the yaml file. But maybe that has improved in the meantime. I had looked against as recently as a month or two ago and didn't find anything, but I'm far from an expert on Actions.

-Peff