Add a Compact mode #48

	name: Linting on PR, with stricter rules on new code

	on: [pull_request]

	jobs:
	lint:

	runs-on: ubuntu-latest

	strategy:
	fail-fast: false
	matrix:
	python-version: [3.7, 3.8, 3.9, '3.10', '3.11']

	steps:
	- name: Checkout PR merge commit
	uses: actions/checkout@v3

	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v4
	with:
	python-version: ${{ matrix.python-version }}

	- name: Install dependencies
	run: \|
	python -m pip install --upgrade pip
	python -m pip install flake8 flake8-docstrings

	- name: Fetch pull request target branch
	run: git fetch origin ${{ github.base_ref }}

	- name: Lint with standard ignores on modified files
	shell: bash
	run: \|
	flake8 . --count --show-source --statistics \| sed -r 'h;s/^(\S+):([0-9]+):([0-9]+): /::error file=\1,line=\2,col=\3::/p;g'

	- name: Lint changes with flake8
	shell: bash
	# Reduced list of ignores, applied on the changed lines only
	run: \|
	git diff -z --name-only FETCH_HEAD -- '**.py' \| xargs -r0 flake8 --exit-zero --ignore=D107,D200,D210,D413,E251,E302,E303,W504 > errors
	git diff FETCH_HEAD -U0 -- '*.py' \| sed -rn -e '/^\+\+\+ /{s,^\+\+\+ ./,,;h}' -e '/^@@ /{G;s/^@@ -[0-9,]+ \+([0-9,]+) @@.\n(.*)/\2,\1/p}' \| (
	while IFS=, read file start lines; do for (( l = start ; l < $start + ${lines:-1}; ++l )); do echo "^$file:$l:"; done; done
	) > changed_lines
	# Invert return value, i.e. error iff matches
	! grep -f changed_lines errors \| sed -r 'h;s/^(\S+):([0-9]+):([0-9]+): /::error file=\1,line=\2,col=\3::/p;g'

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