Fix 3371 - Add terraform-ls support

test/command_callback/test_terraform_ls_command_callback.vader

@@ -0,0 +1,61 @@
+Before:
+  call ale#assert#SetUpLinterTest('terraform', 'terraform_ls')
+
+After:
+  if isdirectory(g:dir . '/.terraform')
+    call delete(g:dir . '/.terraform', 'd')
+  endif
+
+  unlet! b:ale_terraform_terraform_executable
+  unlet! b:ale_terraform_ls_executable
+  unlet! b:ale_terraform_ls_options
+
+  call ale#assert#TearDownLinterTest()
+
+Execute(Should send correct LSP language):
+  AssertLSPLanguage 'terraform'
+
+Execute(Should load default executable):
+  AssertLinter 'terraform-ls',
+  \ ale#Escape('terraform-ls') . ' serve'
+
+Execute(Should configure custom executable):
+  let b:ale_terraform_ls_executable = 'foo'
+  AssertLinter 'foo',
+  \ ale#Escape('foo') . ' serve'
+
+Execute(Should ignore non-absolute custom terraform executable):
+  let b:ale_terraform_terraform_executable = 'terraform'
+  AssertLinter 'terraform-ls',
+  \ ale#Escape('terraform-ls') . ' serve'
+
+Execute(Should set absolute custom terraform executable):
+  let b:ale_terraform_terraform_executable = '/bin/terraform'
+  AssertLinter 'terraform-ls',
+  \ ale#Escape('terraform-ls') . ' serve -tf-exec /bin/terraform'
+
+Execute(Should set custom options):
+  let b:ale_terraform_ls_options = '--bar'
+
+  AssertLinter 'terraform-ls',
+  \ ale#Escape('terraform-ls') . ' serve --bar'
+
+Execute(Should return current directory if it contains .terraform directory):
+  call mkdir(g:dir . '/.terraform')
+  AssertLSPProject g:dir
+
+Execute(Should return nearest directory with .terraform if found in parent directory):
+  call ale#test#SetFilename('../terraform_files/main.tf')
+
+  let b:parent_dir = ale#path#Simplify(g:dir . '/..')
+  let b:tf_dir = b:parent_dir . '/.terraform'
+
+  if !isdirectory(b:tf_dir)
+    call mkdir(b:tf_dir)
+  endif
+
+  AssertLSPProject b:parent_dir
+
+  call delete(b:tf_dir, 'd')
+  unlet!b:parent_dir
+  unlet!b:tf_dir