NC

Last year, I started to see a few common workflows that would create more work by those unaware or open yourself up to making annoying mistakes if you did, that I thought could be caught with just a little more automation.

This was typically when Dependabot would go and bump a dependency that would have other implications: for example, if you bump a npm dependency in a React Native project, it might change the Podfile.lock in the iOS portion of the codebase, or if you bump a dependency used by Appraisal, one of it’s generated files could change. It gets pretty annoying for everyone else if you merge in that seemingly okay Dependabot PR and then someone (even if it’s yourself) has to go and add another commit to add in the forgotten lock file change.

To try and tackle this, I’ve put together a GitHub Action called “diff-check”. It runs a command and fails if anything subsequently changes. For example, you might create a workflow that looks like this:

---
name: diff-check
on: [push]

jobs:
  demo:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: nickcharlton/diff-check@main
        with:
          command: echo "hello world" >> README.md

It would then fail because README.md changed and report on the summary page:

At its heart, it’s a fairly short shell script, that’s called by the action:

#!/bin/sh

set -e

if ! git diff-index --quiet HEAD; then
	printf 'These files changed when running the command:\n\n'

	git diff --name-only | while read -r n ; do
		echo "* $n"
	done

	exit 1
fi

But there’s enough logic in here that I really wanted some tests to make sure it was correct. I turned to Oli’s jet_black, which I’ve been meaning to try out for years and let me write some tests using RSpec. I’m pretty happy with how that turned out.

Trying to solve problems like these in such an abstract way is far harder than first solving a specific problem. I’d originally created the repo back in July of last year, and I really wanted the implementation to be able to suggest what needed to be done through a review suggestion, but this isn’t possible despite a long-standing feature request for it. In the end, this was the common thread through the situations I kept seeing. Hopefully it might help out some others too.