[linux] Listen to Enter key events on text inputs (#138)

Invokes TextInputAction.done on the platform channel when Enter is pressed.

Author: franciscojma86

library/linux/src/internal/text_input_plugin.cc

@@ -24,6 +24,10 @@ static constexpr char kHideMethod[] = "TextInput.hide";
 
 static constexpr char kUpdateEditingStateMethod[] =
     "TextInputClient.updateEditingState";
+static constexpr char kPerformActionMethod[] = "TextInputClient.performAction";
+
+static constexpr char kNewLineAction[] = "TextInputAction.newline";
+static constexpr char kDoneAction[] = "TextInputAction.done";
 
 static constexpr char kSelectionBaseKey[] = "selectionBase";
 static constexpr char kSelectionExtentKey[] = "selectionExtent";
@@ -85,6 +89,8 @@ void TextInputPlugin::KeyboardHook(GLFWwindow *window, int key, int scancode,
           SendStateUpdate(*active_model_);
         }
         break;
+      case GLFW_KEY_ENTER:
+        EnterPressed(*active_model_);
       default:
         break;
     }
@@ -170,4 +176,12 @@ void TextInputPlugin::SendStateUpdate(const TextInputModel &model) {
   InvokeMethod(kUpdateEditingStateMethod, model.GetState());
 }
 
+void TextInputPlugin::EnterPressed(const TextInputModel &model) {
+  Json::Value args = Json::arrayValue;
+  args.append(model.client_id());
+  args.append(kDoneAction);
+
+  InvokeMethod(kPerformActionMethod, args);
+}
+
 }  // namespace flutter_desktop_embedding

library/linux/src/internal/text_input_plugin.h

@@ -46,6 +46,9 @@ class TextInputPlugin : public KeyboardHookHandler, public JsonPlugin {
   // Sends the current state of the given model to the Flutter engine.
   void SendStateUpdate(const TextInputModel &model);
 
+  // Sends an action triggered by the Enter key to the Flutter engine.
+  void EnterPressed(const TextInputModel &model);
+
   // Mapping of client IDs to text input models.
   std::map<int, std::unique_ptr<TextInputModel>> input_models_;