gofmt fixer for Go (#970)

Add a gofmt fixer for golang.

autoload/ale/fix/registry.vim

@@ -92,6 +92,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['c', 'cpp'],
 \       'description': 'Fix C/C++ files with clang-format.',
 \   },
+\   'gofmt': {
+\       'function': 'ale#fixers#gofmt#Fix',
+\       'suggested_filetypes': ['go'],
+\       'description': 'Fix Go files with go fmt.',
+\   },
 \}
 
 " Reset the function registry to the default entries.

autoload/ale/fixers/gofmt.vim

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