Close #2179 - Add support for gopls

test/command_callback/test_gopls_command_callback.vader

@@ -0,0 +1,46 @@
+Before:
+  call ale#assert#SetUpLinterTest('go', 'gopls')
+
+After:
+  Restore
+
+  if isdirectory(g:dir . '/.git')
+    call delete(g:dir . '/.git', 'd')
+  endif
+
+  unlet! b:ale_completion_enabled
+
+  call ale#assert#TearDownLinterTest()
+
+Execute(should set correct defaults):
+  AssertLinter 'gopls', ale#Escape('gopls') . ' --mode stdio'
+
+Execute(should configure gopls callback executable):
+  let b:ale_go_gopls_executable = 'boo'
+  let b:ale_go_gopls_options = ''
+
+  AssertLinter 'boo', ale#Escape('boo')
+
+Execute(should set gopls options):
+  call ale#test#SetFilename('go_paths/go1/prj1/file.go')
+  " let b:ale_completion_enabled = 1
+  let b:ale_go_gopls_options = ''
+
+  AssertLinter 'gopls',
+  \ ale#Escape('gopls') . ''
+
+  let b:ale_go_gopls_options = '--mode stdio --trace'
+
+  AssertLinter 'gopls',
+  \ ale#Escape('gopls') . ' --mode stdio --trace'
+
+Execute(Should return directory for 'go.mod' if found in parent directory):
+  call ale#test#SetFilename('../go_files/test.go')
+
+  AssertLSPProject ale#path#Simplify(g:dir . '/../go_files')
+
+Execute(Should return nearest directory with '.git' if found in parent directory):
+  call ale#test#SetFilename('test.go')
+  call mkdir(g:dir . '/.git')
+
+  AssertLSPProject g:dir