Add elm-format as a new fixer (#916)

* Add elm-format as a new fixer

autoload/ale/fix/registry.vim

@@ -27,6 +27,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['javascript', 'typescript'],
 \       'description': 'Apply eslint --fix to a file.',
 \   },
+\   'format': {
+\       'function': 'ale#fixers#format#Fix',
+\       'suggested_filetypes': ['elm'],
+\       'description': 'Apply elm-format to a file.',
+\   },
 \   'isort': {
 \       'function': 'ale#fixers#isort#Fix',
 \       'suggested_filetypes': ['python'],

autoload/ale/fixers/format.vim

@@ -0,0 +1,23 @@
+" Author: soywod <clement.douin@gmail.com>
+" Description: Integration of elm-format with ALE.
+
+call ale#Set('elm_format_executable', 'elm-format')
+call ale#Set('elm_format_use_global', 0)
+call ale#Set('elm_format_options', '--yes')
+
+function! ale#fixers#format#GetExecutable(buffer) abort
+    return ale#node#FindExecutable(a:buffer, 'elm_format', [
+    \   'node_modules/.bin/elm-format',
+    \])
+endfunction
+
+function! ale#fixers#format#Fix(buffer) abort
+    let l:options = ale#Var(a:buffer, 'elm_format_options')
+
+    return {
+    \   'command': ale#Escape(ale#fixers#format#GetExecutable(a:buffer))
+    \       . ' %t'
+    \       . (empty(l:options) ? '' : ' ' . l:options),
+    \   'read_temporary_file': 1,
+    \}
+endfunction