Add Haskell Language Server check to CI #27

	name: "Haskell Language Server works"
	on:
	pull_request:
	push:
	branches:
	- main

	permissions:
	contents: read

	jobs:
	test-hls-works:
	runs-on: ubuntu-latest
	steps:
	- name: Check out repo
	uses: actions/checkout@v4
	- name: Install Nix with good defaults
	uses: input-output-hk/install-nix-action@v20
	with:
	extra_nix_config: \|
	trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
	substituters = https://cache.iog.io/ https://cache.nixos.org/
	nix_path: nixpkgs=channel:nixos-unstable
	- name: Open nix environment
	uses: rrbutani/use-nix-shell-action@v1
	- name: Update dependencies
	run: cabal update; cabal freeze
	- name: Obtain GHC version
	run: \|
	echo "VERSION=$(ghc --numeric-version)" >> $GITHUB_OUTPUT
	id: ghc
	- name: HLS caching
	uses: actions/cache@v4
	with:
	path: \|
	/home/runner/.cache/hie-bios
	/home/runner/.cache/ghcide
	/home/runner/.cache/cabal
	dist-newstyle
	key: hls-cache-${{ env.CABAL_CACHE_VERSION }}-${{ runner.os }}-${{ steps.ghc.outputs.VERSION }}-${{ hashFiles('/cabal.project.freeze') }}-${{ hashFiles('/.cabal', '*/cabal.project') }}
	restore-keys: \|
	hls-cache-${{ env.CABAL_CACHE_VERSION }}-${{ runner.os }}-${{ steps.ghc.outputs.VERSION }}-${{ hashFiles('**/cabal.project.freeze') }}-
	- name: Snapshot file list
	run: \|
	find / > /tmp/before.txt
	- name: Test HLS works
	run: haskell-language-server
	- name: Check files modified
	run: \|
	find / > /tmp/after.txt
	diff /tmp/before.txt /tmp/after.txt

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