Added dartfmt fixer (#1683)

* Added dartfmt to Fixers
* Added dartfmt specific documentation

autoload/ale/fix/registry.vim

@@ -210,6 +210,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['qml'],
 \       'description': 'Fix QML files with qmlfmt.',
 \   },
+\   'dartfmt': {
+\       'function': 'ale#fixers#dartfmt#Fix',
+\       'suggested_filetypes': ['dart'],
+\       'description': 'Fix Dart files with dartfmt.',
+\   },
 \}
 
 " Reset the function registry to the default entries.

autoload/ale/fixers/dartfmt.vim

@@ -0,0 +1,18 @@
+" Author: reisub0 <reisub0@gmail.com>
+" Description: Integration of dartfmt with ALE.
+
+call ale#Set('dart_dartfmt_executable', 'dartfmt')
+call ale#Set('dart_dartfmt_options', '')
+
+function! ale#fixers#dartfmt#Fix(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'dart_dartfmt_executable')
+    let l:options = ale#Var(a:buffer, 'dart_dartfmt_options')
+
+    return {
+    \   'command': ale#Escape(l:executable)
+    \       . ' -w'
+    \       . (empty(l:options) ? '' : ' ' . l:options)
+    \       . ' %t',
+    \   'read_temporary_file': 1,
+    \}
+endfunction