Assert that Ormolu is formatted with current version of Ormolu

.circleci/config.yml

@@ -29,6 +29,11 @@ jobs:
       - run:
           name: Build the package (includes running the tests)
           command: nix-build --keep-going
+      - run:
+          name: Check formatting
+          command: |
+            ./format.sh
+            git diff --exit-code --color=always
       - run:
           name: Generate Haddocks
           command: nix-build --attr ormolu.doc

CONTRIBUTING.md

@@ -55,5 +55,10 @@ User settings -> Account integrations -> Refresh permissions
 
 in Circle CI app.
 
+## Formatting
+
+Use `format.sh` script to format Ormolu with current version of Ormolu. If
+Ormolu is not formatted like this, the CI will fail.
+
 [issues]: https://github.com/tweag/ormolu/issues
 [bugs]: https://github.com/tweag/ormolu/issues?q=is%3Aissue+is%3Aopen+label%3Abug

default.nix

@@ -41,6 +41,7 @@ let
     }) haskellPackages;
 in {
   ormolu = haskellPackages.ormolu;
+  locales = pkgs.glibcLocales;
   ormoluShell = haskellPackages.shellFor {
     packages = ps: [ ps.ormolu ];
     buildInputs = [ haskellPackages.cabal-install haskellPackages.ghcid ];

format.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+#
+# Format Ormolu using current version of Ormolu.
+
+set -e
+
+export LANG="en_US.UTF-8"
+
+nix run -f default.nix ormolu locales -c ormolu --mode inplace $(find src -type f \( -name "*.hs" -o -name "*.hs-boot" \))
+nix run -f default.nix ormolu locales -c ormolu --mode inplace $(find tests -type f -name "*.hs")