Add 'scalafmt' fixer for Scala files

closes https://github.com/w0rp/ale/issues/1299

autoload/ale/fix/registry.vim

@@ -95,6 +95,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['ruby'],
 \       'description': 'Fix ruby files with rufo',
 \   },
+\   'scalafmt': {
+\       'function': 'ale#fixers#scalafmt#Fix',
+\       'suggested_filetypes': ['scala'],
+\       'description': 'Fix Scala files using scalafmt',
+\   },
 \   'standard': {
 \       'function': 'ale#fixers#standard#Fix',
 \       'suggested_filetypes': ['javascript'],

autoload/ale/fixers/scalafmt.vim

@@ -0,0 +1,26 @@
+" Author: Jeffrey Lau https://github.com/zoonfafer
+" Description: Integration of Scalafmt with ALE.
+
+call ale#Set('scala_scalafmt_executable', 'scalafmt')
+call ale#Set('scala_scalafmt_use_global', get(g:, 'ale_use_global_executables', 0))
+call ale#Set('scala_scalafmt_options', '')
+
+function! ale#fixers#scalafmt#GetCommand(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'scala_scalafmt_executable')
+    let l:options = ale#Var(a:buffer, 'scala_scalafmt_options')
+    let l:exec_args = l:executable =~? 'ng$'
+    \   ? ' scalafmt'
+    \   : ''
+
+    return ale#Escape(l:executable) . l:exec_args
+    \   . (empty(l:options) ? '' : ' ' . l:options)
+    \   . ' %t'
+
+endfunction
+
+function! ale#fixers#scalafmt#Fix(buffer) abort
+    return {
+    \   'command': ale#fixers#scalafmt#GetCommand(a:buffer),
+    \   'read_temporary_file': 1,
+    \}
+endfunction