coalals.langserver: Add support for showMessageRequest

Add support for window/showMessageRequest so that
coala-ls can interact with server when it requires.

coalals/langserver.py

@@ -332,3 +332,40 @@ def send_diagnostics(self, path, diagnostics):
         self._endpoint.notify(
             'textDocument/publishDiagnostics',
             params=params)
+
+    def send_show_message_req(self, message_type, message, actions):
+        """
+        Send a showMessage request to the editor, this
+        can be useful for showing a dialog and getting
+        some user choice or action back.
+        (https://bit.ly/2J7TjX9)
+
+        :param message_type:
+            The type of message/severity of the dialog
+            in question. It can range from 1 - 4. Refer
+            to the LS docs for more detail.
+        :param message:
+            The message to display while providing the
+            choice.
+        :param actions:
+            A list/iterable of strings containing the
+            the various options to choose from.
+        :return:
+            Returns a Future that will be resolved with
+            error or result when the user chooses an
+            action or cancels it.
+        """
+        if message_type > 4 or message_type < 1:
+            message_type = 4
+
+        params = {
+            'type': int(message_type),
+            'message': message,
+            'actions': list(map(lambda l: {'title': l, }, actions)),
+        }
+
+        req_future = self._endpoint.request(
+                        'window/showMessageRequest',
+                        params=params)
+
+        return req_future

tests/tests_coalals/test_langserver.py

@@ -136,6 +136,37 @@ def test_send_diagnostics(file_langserver, verify_publish_respone):
     verify_publish_respone(file, langserver, 0)
 
 
+@pytest.mark.parametrize('msg_type', [1, 5])
+def test_send_show_message_req(file_langserver, verify_response, msg_type):
+    file, langserver = file_langserver
+
+    future = langserver.send_show_message_req(
+                msg_type,
+                'This is not a message.',
+                ('Okay', 'Yo!'))
+
+    def _responder(file, request, passed, **kargs):
+        msg_id = request['id']
+
+        langserver._endpoint.consume({
+            'id': msg_id,
+            'result': 'Yo!',
+            'jsonrpc': '2.0',
+        })
+
+        # now wait for the future to be resolved with
+        # the result of the selection
+        result = future.result()
+
+        assert result is not None
+        assert result == 'Yo!'
+
+        file.close()
+        passed[0] = True
+
+    verify_response(file, langserver, _responder)
+
+
 def test_lanserver_shutdown(file_langserver):
     file, langserver = file_langserver
     langserver.m_shutdown()