Switched to fourmolu, added a CI step to check formatting

Author: Soupstraw

.github/workflows/ci.yml

@@ -56,3 +56,28 @@ jobs:
     - name: Run tests
       run: |
         cabal test all
+
+  fourmolu:
+    runs-on: ubuntu-latest
+
+    defaults:
+      run:
+        shell: bash
+
+    strategy:
+      fail-fast: false
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Install fourmolu
+      run: |
+        FOURMOLU_VERSION="0.16.2.0"
+        mkdir -p "$HOME/.local/bin"
+        curl -sL "https://github.com/fourmolu/fourmolu/releases/download/v${FOURMOLU_VERSION}/fourmolu-${FOURMOLU_VERSION}-linux-x86_64" -o "$HOME/.local/bin/fourmolu"
+        chmod a+x "$HOME/.local/bin/fourmolu"
+        echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+    - name: Run fourmolu
+      run: ./scripts/fourmolize.sh
+

project.ncl

@@ -8,7 +8,7 @@ let shellFor = fun ghcver =>
   let hspkg = import_hs ghcver in {
     packages = {
       haskell-language-server = hspkg "haskell-language-server",
-      ormolu = hspkg "ormolu",
+      fourmolu = hspkg "fourmolu",
       ghc = organist.import_nix "nixpkgs#haskell.compiler.%{ghcver}",
       cabal-install = hspkg "cabal-install",
       cabal-fmt = hspkg "cabal-fmt",

scripts/fourmolize.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if [[ $# -gt 0 ]]; then
+  case "$1" in
+    --changes)
+      files=$(git diff --diff-filter=MA --name-only origin/master HEAD -- '*.hs')
+      if [[ -n "$files" ]]; then
+        # Run fourmolu on changes compared to `master`.
+        fourmolu -m inplace $(echo "$files" | grep -v Setup.hs)
+      fi
+      ;;
+    *)
+      echo "Invalid option: $1" >&2
+      exit 1
+      ;;
+  esac
+else
+  fourmolu -m inplace $(git ls-files -- '*.hs' | grep -v Setup.hs)
+fi
+
+git diff --exit-code