Add a pre commit hook for code formatting

.gitignore

@@ -30,3 +30,6 @@ test/testdata/**/hie.yaml
 
 # shake build folder (used in benchmark suite)
 .shake/
+
+# pre-commit-hook.nix
+.pre-commit-config.yaml

.stylish-haskell.yaml

@@ -0,0 +1,63 @@
+# See https://github.com/jaspervdj/stylish-haskell/blob/main/data/stylish-haskell.yaml
+# for reference.
+
+steps:
+  # - unicode_syntax:
+  #     add_language_pragma: true
+
+  # - module_header:
+  #     indent: 4
+  #     sort: true
+  #     separate_lists: true
+
+  # - records:
+  #     equals: "indent 2"
+  #     first_field: "indent 2"
+  #     field_comment: 2
+  #     deriving: 2
+  #     via: "indent 2"
+  #     sort_deriving: true
+  #     break_enums: false
+  #     break_single_constructors: true
+  #     curried_context: false
+
+  - simple_align:
+      cases: always
+      top_level_patterns: always
+      records: always
+      multi_way_if: always
+
+  - imports:
+      align: global
+      list_align: after_alias
+      pad_module_names: true
+      long_list_align: inline
+      empty_list_align: inherit
+      list_padding: 4
+      separate_lists: true
+      space_surround: false
+      ghc_lib_parser: false
+
+  - language_pragmas:
+      style: vertical
+      align: true
+      remove_redundant: true
+      language_prefix: LANGUAGE
+
+  # - tabs:
+  #     spaces: 8
+
+  - trailing_whitespace: {}
+
+  # - squash: {}
+
+columns: 80
+
+newline: native
+
+language_extensions:
+  - DataKinds
+  - OverloadedStrings
+  - TypeOperators
+
+cabal: true

CONTRIBUTING.md

@@ -1,5 +1,40 @@
 # Contributors Guide
 
+## Pre-commit hook
+We are using [pre-commit-hook.nix](https://github.com/cachix/pre-commit-hooks.nix) to configure git pre-commit hook for formatting. Although it is possible to run formatting manually, we recommend you to use it to set pre-commit hook as our CI checks pre-commit hook is applied or not.
+
+You can configure the pre-commit-hook by running
+
+``` bash
+nix-shell
+```
+
+If you don't want to use [nix](https://nixos.org/guides/install-nix.html), you can instead use [pre-commit](https://pre-commit.com) with the following config.
+
+```json
+{
+  "repos": [
+    {
+      "hooks": [
+        {
+          "entry": "stylish-haskell -i ",
+          "exclude": "(/test/testdata/*)",
+          "files": "\\.l?hs$",
+          "id": "stylish-haskell",
+          "language": "system",
+          "name": "stylish-haskell",
+          "pass_filenames": true,
+          "types": [
+            "file"
+          ]
+        }
+      ],
+      "repo": "local"
+    }
+  ]
+}
+```
+
 ## Testing
 
 The tests make use of the [Tasty](https://github.com/feuerbach/tasty) test framework.

ghcide/.stylish-haskell.yaml

@@ -0,0 +1,74 @@
+# See https://github.com/jaspervdj/stylish-haskell/blob/main/data/stylish-haskell.yaml
+# for reference.
+
+steps:
+  # - unicode_syntax:
+  #     add_language_pragma: true
+
+  # - module_header:
+  #     indent: 4
+  #     sort: true
+  #     separate_lists: true
+
+  # - records:
+  #     equals: "indent 2"
+  #     first_field: "indent 2"
+  #     field_comment: 2
+  #     deriving: 2
+  #     via: "indent 2"
+  #     sort_deriving: true
+  #     break_enums: false
+  #     break_single_constructors: true
+  #     curried_context: false
+
+  - simple_align:
+      cases: always
+      top_level_patterns: always
+      records: always
+      multi_way_if: always
+
+  - imports:
+      align: global
+      list_align: after_alias
+      pad_module_names: true
+      long_list_align: inline
+      empty_list_align: inherit
+      list_padding: 4
+      separate_lists: true
+      space_surround: false
+      ghc_lib_parser: false
+
+  - language_pragmas:
+      style: vertical
+      align: true
+      remove_redundant: true
+      language_prefix: LANGUAGE
+
+  # - tabs:
+  #     spaces: 8
+
+  - trailing_whitespace: {}
+
+  # - squash: {}
+
+columns: 80
+
+newline: native
+
+language_extensions:
+  - BangPatterns
+  - DeriveFunctor
+  - DeriveGeneric
+  - FlexibleContexts
+  - GeneralizedNewtypeDeriving
+  - LambdaCase
+  - NamedFieldPuns
+  - OverloadedStrings
+  - RecordWildCards
+  - ScopedTypeVariables
+  - StandaloneDeriving
+  - TupleSections
+  - TypeApplications
+  - ViewPatterns
+
+cabal: true

hls-plugin-api/.stylish-haskell.yaml

@@ -0,0 +1,63 @@
+# See https://github.com/jaspervdj/stylish-haskell/blob/main/data/stylish-haskell.yaml
+# for reference.
+
+steps:
+  # - unicode_syntax:
+  #     add_language_pragma: true
+
+  # - module_header:
+  #     indent: 4
+  #     sort: true
+  #     separate_lists: true
+
+  # - records:
+  #     equals: "indent 2"
+  #     first_field: "indent 2"
+  #     field_comment: 2
+  #     deriving: 2
+  #     via: "indent 2"
+  #     sort_deriving: true
+  #     break_enums: false
+  #     break_single_constructors: true
+  #     curried_context: false
+
+  - simple_align:
+      cases: always
+      top_level_patterns: always
+      records: always
+      multi_way_if: always
+
+  - imports:
+      align: global
+      list_align: after_alias
+      pad_module_names: true
+      long_list_align: inline
+      empty_list_align: inherit
+      list_padding: 4
+      separate_lists: true
+      space_surround: false
+      ghc_lib_parser: false
+
+  - language_pragmas:
+      style: vertical
+      align: true
+      remove_redundant: true
+      language_prefix: LANGUAGE
+
+  # - tabs:
+  #     spaces: 8
+
+  - trailing_whitespace: {}
+
+  # - squash: {}
+
+columns: 80
+
+newline: native
+
+language_extensions:
+  - DataKinds
+  - KindSignatures
+  - TypeOperators
+
+cabal: true

nix/default.nix

@@ -1,5 +1,6 @@
 { sources ? import ./sources.nix }:
 let
+  nix-pre-commit-hooks = import (builtins.fetchTarball "https://github.com/cachix/pre-commit-hooks.nix/tarball/master");
   overlay = _self: pkgs:
     let sharedOverrides = {
         overrides = _self: super: {
@@ -42,5 +43,18 @@ let
         };
         };
 
-in import sources.nixpkgs
-{ overlays = [ overlay ] ; config = {allowBroken = true;}; }
+in (import sources.nixpkgs
+  {
+    overlays = [ overlay ];
+    config = {allowBroken = true;};
+  }) // {
+    pre-commit-check = nix-pre-commit-hooks.run {
+      src = ./.;
+      # If your hooks are intrusive, avoid running on each commit with a default_states like this:
+      # default_stages = ["manual" "push"];
+      hooks = {
+        stylish-haskell.enable = true;
+        stylish-haskell.excludes = [ "/test/testdata/*" "/hie-compat/*" ];
+      };
+    };
+  }

shell.nix

@@ -64,5 +64,6 @@ haskellPackagesForProject.shellFor {
     export LD_LIBRARY_PATH=${gmp}/lib:${zlib}/lib:${ncurses}/lib:${capstone}/lib
     export DYLD_LIBRARY_PATH=${gmp}/lib:${zlib}/lib:${ncurses}/lib:${capstone}/lib
     export PATH=$PATH:$HOME/.local/bin
+    ${pre-commit-check.shellHook}
   '';
 }