[widgets][assetwidget] Don't load invalid asset

Fixes #232

beat/editor/test/test_assetwidget.py

@@ -306,3 +306,26 @@ class TestAssetWidget:
         asset_widget.deleteAsset(asset.declaration_path)
         assert asset_widget.current_editor.asset_type == AssetType.UNKNOWN
         assert not os.path.exists(asset.declaration_path)
+
+    def test_load_empty_json(
+        self,
+        qtbot,
+        monkeypatch,
+        test_prefix,
+        beat_context,
+        asset_type,
+        asset_type_prefix_entry_map,
+    ):
+        asset_widget = AssetWidget()
+        qtbot.addWidget(asset_widget)
+        asset_widget.set_context(beat_context)
+        asset_name = asset_type_prefix_entry_map[asset_type][0]
+
+        monkeypatch.setattr(QMessageBox, "critical", lambda *args: QMessageBox.Ok)
+
+        asset = Asset(test_prefix, asset_type, asset_name)
+        with open(asset.declaration_path, "wt") as declaration_file:
+            declaration_file.write("")
+
+        asset = Asset(test_prefix, asset_type, asset_name)
+        asset_widget.loadAsset(asset)

beat/editor/widgets/assetwidget.py

@@ -355,12 +355,20 @@ class AssetWidget(QWidget):
 
         self.maybe_save()
 
-        self.current_asset = asset
-
         self.__clear_watcher()
-        self.watcher.addPath(self.current_asset.declaration_path)
 
-        self.__update_content()
+        is_valid, errors = asset.is_valid()
+        if not is_valid:
+            QMessageBox.critical(
+                self,
+                self.tr("Invalid asset"),
+                self.tr(f"The asset you are trying to load is invalid\n{errors}"),
+            )
+
+        else:
+            self.watcher.addPath(asset.declaration_path)
+            self.current_asset = asset
+            self.__update_content()
 
     @pyqtSlot()
     def saveJson(self):