Add fixer for Go modules (#1873)

* Add fixer for Go modules

autoload/ale/fix/registry.vim

@@ -145,6 +145,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['go'],
 \       'description': 'Fix Go files imports with goimports.',
 \   },
+\   'gomod': {
+\       'function': 'ale#fixers#gomod#Fix',
+\       'suggested_filetypes': ['gomod'],
+\       'description': 'Fix Go module files with go mod edit -fmt.',
+\   },
 \   'tslint': {
 \       'function': 'ale#fixers#tslint#Fix',
 \       'suggested_filetypes': ['typescript'],

autoload/ale/fixers/gomod.vim

@@ -0,0 +1,10 @@
+call ale#Set('go_go_executable', 'go')
+
+function! ale#fixers#gomod#Fix(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'go_go_executable')
+
+    return {
+    \   'command': ale#Escape(l:executable) . ' mod edit -fmt %t',
+    \   'read_temporary_file': 1,
+    \}
+endfunction