Add gopls format as a Go fixer

test/fixers/test_gopls_fixer_callback.vader

@@ -0,0 +1,57 @@
+Before:
+  Save g:ale_go_gopls_fix_executable
+  Save g:ale_go_gopls_fix_options
+  Save g:ale_go_go111module
+
+  " Use an invalid global executable, so we don't match it.
+  let g:ale_go_gopls_fix_executable = 'xxxinvalid'
+  let g:ale_go_gopls_fix_options = ''
+
+  call ale#test#SetDirectory('/testplugin/test/fixers')
+  call ale#test#SetFilename('../test-files/go/testfile.go')
+
+After:
+  Restore
+
+  unlet! b:ale_go_go111module
+
+  call ale#test#RestoreDirectory()
+
+Execute(The gopls callback should return 0 when the executable isn't executable):
+  AssertEqual
+  \ 0,
+  \ ale#fixers#gopls#Fix(bufnr(''))
+
+Execute(The gopls callback should the command when the executable test passes):
+  let g:ale_go_gopls_fix_executable = has('win32') ? 'cmd' : 'echo'
+
+  AssertEqual
+  \ {
+  \   'read_temporary_file': 1,
+  \   'command': ale#Escape(g:ale_go_gopls_fix_executable) . ' format -l -w %t'
+  \ },
+  \ ale#fixers#gopls#Fix(bufnr(''))
+
+Execute(The gopls callback should include extra options):
+  let g:ale_go_gopls_fix_executable = has('win32') ? 'cmd' : 'echo'
+  let g:ale_go_gopls_fix_options = '--xxx'
+
+  AssertEqual
+  \ {
+  \   'read_temporary_file': 1,
+  \   'command': ale#Escape(g:ale_go_gopls_fix_executable) . ' format --xxx -l -w %t'
+  \ },
+  \ ale#fixers#gopls#Fix(bufnr(''))
+
+Execute(The gopls callback should support Go environment variables):
+  let g:ale_go_gopls_fix_executable = has('win32') ? 'cmd' : 'echo'
+  let g:ale_go_go111module = 'on'
+
+  AssertEqual
+  \ {
+  \   'read_temporary_file': 1,
+  \   'command': ale#Env('GO111MODULE', 'on')
+  \     . ale#Escape(g:ale_go_gopls_fix_executable)
+  \     . ' format -l -w %t'
+  \ },
+  \ ale#fixers#gopls#Fix(bufnr(''))