CI: use preinstalled Stack; fix caching #25

	name: Stack CI

	on:
	push:
	branches: [ "main", "dev-minor" ]
	pull_request:
	branches: [ "main", "dev-minor" ]

	permissions:
	contents: read

	jobs:
	build:
	runs-on: ubuntu-latest

	steps:
	- name: Checkout code
	uses: actions/checkout@v4

	- name: Install required libraries
	run: >-
	sudo apt install
	z3

	# Use preinstalled Stack. Should Stack fail to be installed, use the setup action:
	# - name: Setup Haskell
	# uses: haskell-actions/setup@v2
	# with:
	# enable-stack: true
	# stack-no-global: true

	- name: Restore Stack build artifacts (user + project)
	uses: actions/cache/restore@v4
	id: cache
	with:
	path: \|
	~/.stack
	.stack-work
	# Write a fresh cache each time
	key: ${{ runner.os }}-stack-${{ github.sha }}
	restore-keys: \|
	${{ runner.os }}-stack

	- name: Setup Stack
	run: stack setup

	- name: Build dependencies
	run: stack test --only-dependencies

	# This step only consumes an extra minute without gains.
	# - name: Build w/o tests
	# run: stack build

	- name: Build w/ tests
	run: stack test --no-run-tests

	- name: Run tests
	run: stack test

	# Always cache dependencies.
	# This makes esp. sense now that some tests are broken.
	- name: Cache Stack build artifacts (user + project)
	uses: actions/cache/save@v4
	if: always() && steps.cache.outputs.cache-hit != 'true'
	with:
	path: \|
	~/.stack
	.stack-work
	key: ${{ steps.cache.outputs.cache-primary-key }}

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