Add stylish-haskell as a fixer (#1837)

* Add stylish-haskell as a fixer

`stylish-haskell` is a common formatting tool for the haskell toolchain.
It is not as advanced as `brittany` or `hindent`, but it is commonly
used for formatting of imports and data declarations. This adds it as a
fixer in ALE.

6 files changed, 57 insertions, 2 deletions

diff --git a/README.md b/README.md
index 5bfe24ba..8c4f8138 100644
--- a/README.md
+++ b/README.md
@@ -129,7 +129,7 @@ formatting.
 | Hack | [hack](http://hacklang.org/), [hackfmt](https://github.com/facebook/hhvm/tree/master/hphp/hack/hackfmt), [hhast](https://github.com/hhvm/hhast) (disabled by default; see `:help ale-integration-hack`) |
 | Haml | [haml-lint](https://github.com/brigade/haml-lint) |
 | Handlebars | [ember-template-lint](https://github.com/rwjblue/ember-template-lint) |
-| Haskell | [brittany](https://github.com/lspitzner/brittany), [ghc](https://www.haskell.org/ghc/), [cabal-ghc](https://www.haskell.org/cabal/), [stack-ghc](https://haskellstack.org/), [stack-build](https://haskellstack.org/) !!, [ghc-mod](https://github.com/DanielG/ghc-mod), [stack-ghc-mod](https://github.com/DanielG/ghc-mod), [hlint](https://hackage.haskell.org/package/hlint), [hdevtools](https://hackage.haskell.org/package/hdevtools), [hfmt](https://github.com/danstiner/hfmt), [hie](https://github.com/haskell/haskell-ide-engine) |
+| Haskell | [brittany](https://github.com/lspitzner/brittany), [ghc](https://www.haskell.org/ghc/), [cabal-ghc](https://www.haskell.org/cabal/), [stylish-haskell](https://github.com/jaspervdj/stylish-haskell), [stack-ghc](https://haskellstack.org/), [stack-build](https://haskellstack.org/) !!, [ghc-mod](https://github.com/DanielG/ghc-mod), [stack-ghc-mod](https://github.com/DanielG/ghc-mod), [hlint](https://hackage.haskell.org/package/hlint), [hdevtools](https://hackage.haskell.org/package/hdevtools), [hfmt](https://github.com/danstiner/hfmt), [hie](https://github.com/haskell/haskell-ide-engine) |
 | HTML | [alex](https://github.com/wooorm/alex) !!, [HTMLHint](http://htmlhint.com/), [proselint](http://proselint.com/), [tidy](http://www.html-tidy.org/), [write-good](https://github.com/btford/write-good) |
 | Idris | [idris](http://www.idris-lang.org/) |
 | Java | [checkstyle](http://checkstyle.sourceforge.net), [javac](http://www.oracle.com/technetwork/java/javase/downloads/index.html), [google-java-format](https://github.com/google/google-java-format), [PMD](https://pmd.github.io/) |
diff --git a/autoload/ale/fix/registry.vim b/autoload/ale/fix/registry.vim
index ef287358..60de4a46 100644
--- a/autoload/ale/fix/registry.vim
+++ b/autoload/ale/fix/registry.vim
@@ -170,6 +170,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['haskell'],
 \       'description': 'Fix Haskell files with brittany.',
 \   },
+\   'stylish-haskell': {
+\       'function': 'ale#fixers#stylish_haskell#Fix',
+\       'suggested_filetypes': ['haskell'],
+\       'description': 'Refactor Haskell files with stylish-haskell.',
+\   },
 \   'refmt': {
 \       'function': 'ale#fixers#refmt#Fix',
 \       'suggested_filetypes': ['reason'],
diff --git a/autoload/ale/fixers/stylish_haskell.vim b/autoload/ale/fixers/stylish_haskell.vim
new file mode 100644
index 00000000..a352312f
--- /dev/null
+++ b/autoload/ale/fixers/stylish_haskell.vim
@@ -0,0 +1,15 @@
+" Author: eborden <evan@evan-borden.com>
+" Description: Integration of stylish-haskell formatting with ALE.
+"
+call ale#Set('haskell_stylish_haskell_executable', 'stylish-haskell')
+
+function! ale#fixers#stylish_haskell#Fix(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'haskell_stylish_haskell_executable')
+
+    return {
+    \   'command': ale#Escape(l:executable)
+    \       . ' --inplace'
+    \       . ' %t',
+    \   'read_temporary_file': 1,
+    \}
+endfunction
diff --git a/doc/ale-haskell.txt b/doc/ale-haskell.txt
index 379cd987..9bc9263a 100644
--- a/doc/ale-haskell.txt
+++ b/doc/ale-haskell.txt
@@ -78,6 +78,16 @@ g:ale_haskell_stack_build_options           *g:ale_haskell_stack_build_options*
   We default to using `'--fast'`. Since Stack generates binaries, your
   programs will be slower unless you separately rebuild them outside of ALE.
 
+===============================================================================
+stylish-haskell                                   *ale-haskell-stylish-haskell*
+
+g:ale_haskell_stylish_haskell_executable
+                                     *g:ale_haskell_stylish_haskell_executable*
+                                     *b:ale_haskell_stylish_haskell_executable*
+  Type: |String|
+  Default: `'stylish-haskell'`
+
+  This variable can be changed to use a different executable for stylish-haskell.
 
 ===============================================================================
 hie                                                           *ale-haskell-hie*
diff --git a/doc/ale.txt b/doc/ale.txt
index 416a48ff..2d3efa34 100644
--- a/doc/ale.txt
+++ b/doc/ale.txt
@@ -111,6 +111,7 @@ CONTENTS                                                         *ale-contents*
       hdevtools...........................|ale-haskell-hdevtools|
       hfmt................................|ale-haskell-hfmt|
       stack-build.........................|ale-haskell-stack-build|
+      stylish-haskell.....................|ale-haskell-stylish-haskell|
       hie.................................|ale-haskell-hie|
     html..................................|ale-html-options|
       htmlhint............................|ale-html-htmlhint|
@@ -380,7 +381,7 @@ Notes:
 * Hack: `hack`, `hackfmt`, `hhast`
 * Haml: `haml-lint`
 * Handlebars: `ember-template-lint`
-* Haskell: `brittany`, `ghc`, `cabal-ghc`, `stack-ghc`, `stack-build`!!, `ghc-mod`, `stack-ghc-mod`, `hlint`, `hdevtools`, `hfmt`, `hie`
+* Haskell: `brittany`, `ghc`, `cabal-ghc`, `stylish-haskell`, `stack-ghc`, `stack-build`!!, `ghc-mod`, `stack-ghc-mod`, `hlint`, `hdevtools`, `hfmt`, `hie`
 * HTML: `alex`!!, `HTMLHint`, `proselint`, `tidy`, `write-good`
 * Idris: `idris`
 * Java: `checkstyle`, `javac`, `google-java-format`, `PMD`
diff --git a/test/fixers/test_stylish_haskell_fixer_callback.vader b/test/fixers/test_stylish_haskell_fixer_callback.vader
new file mode 100644
index 00000000..755d3430
--- /dev/null
+++ b/test/fixers/test_stylish_haskell_fixer_callback.vader
@@ -0,0 +1,24 @@
+Before:
+  Save g:ale_haskell_stylish_haskell_executable
+
+  " Use an invalid global executable, so we don't match it.
+  let g:ale_haskell_stylish_haskell_executable = 'xxxinvalid'
+
+  call ale#test#SetDirectory('/testplugin/test/fixers')
+
+After:
+  Restore
+
+  call ale#test#RestoreDirectory()
+
+Execute(The stylish-haskell callback should return the correct default values):
+  call ale#test#SetFilename('../haskell_files/testfile.hs')
+
+  AssertEqual
+  \ {
+  \   'read_temporary_file': 1,
+  \   'command': ale#Escape('xxxinvalid')
+  \     . ' --inplace'
+  \     . ' %t',
+  \ },
+  \ ale#fixers#stylish_haskell#Fix(bufnr(''))