Strip back pipeline to Rubocop linting only #2337

	name: Linting

	# Trigger each time HEAD branch is updated in a pull request
	# see https://github.com/orgs/community/discussions/26366
	on:
	pull_request:
	types: [synchronize]

	jobs:

	rubocop:
	name: RuboCop
	runs-on: ubuntu-latest
	steps:
	- name: 'Checkout PR branch (with test merge-commit)'
	uses: actions/checkout@v3
	with:
	fetch-depth: 2 # to also fetch parent of PR

	# Adapted from this great comment [1]. Git diff adapted from [2].
	# "\|\| test $? = 1;" is used to ignore the exit code of grep when no files
	# are found matching the pattern. For the "three dots" ... syntax, see [3].
	- name: Get changed files
	run: \|
	files=$(git diff --name-only --diff-filter=ACMR -r HEAD^1...HEAD \| grep '\.rb$' \|\| test $? = 1;)
	printf "🎴 Changed ruby files: \n$files"
	echo "CHANGED_FILES=\"$(echo ${files} \| xargs)\"" >> $GITHUB_ENV

	- name: Set up Ruby 3
	uses: ruby/setup-ruby@v1
	with:
	ruby-version: 3.1.4
	bundler-cache: true

	- name: Run RuboCop
	if: env.CHANGED_FILES != ''
	run: \|
	echo "Changed files: $CHANGED_FILES"
	bundle exec rubocop $CHANGED_FILES


	# Useful resources
	# [1] https://github.com/actions/checkout/issues/520#issuecomment-1167205721
	# [2] https://robertfaldo.medium.com/commands-to-run-rubocop-and-specs-you-changed-in-your-branch-e6d2f2e4110b
	# [3] https://community.atlassian.com/t5/Bitbucket-questions/Git-diff-show-different-files-than-PR-Pull-Request/qaq-p/2331786

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