Fix error message when slicing with per-object setting errors

The message was generating a list of settings that had an error state by going through all extruder stacks and the global stack, but didn't bother to check the per-object stacks. I could've added it to the regular message but then the user would be confused because he can't find any errors either. So instead I opted to specify that it happened in per-model settings. It's not perfect, but should narrow down the user's search considerably.

Fixes #2427.

plugins/CuraEngineBackend/CuraEngineBackend.py

@@ -301,6 +301,26 @@ class CuraEngineBackend(QObject, Backend):
                 self.backendStateChange.emit(BackendState.NotStarted)
             return
 
+        elif job.getResult() == StartSliceJob.StartJobResult.ObjectSettingError:
+            errors = {}
+            for node in DepthFirstIterator(Application.getInstance().getController().getScene().getRoot()):
+                stack = node.callDecoration("getStack")
+                if not stack:
+                    continue
+                for key in stack.getErrorKeys():
+                    definition = self._global_container_stack.getBottom().findDefinitions(key = key)
+                    if not definition:
+                        Logger.log("e", "When checking settings for errors, unable to find definition for key {key} in per-object stack.".format(key = key))
+                        continue
+                    definition = definition[0]
+                    errors[key] = definition.label
+            error_labels = ", ".join(errors.values())
+            self._error_message = Message(catalog.i18nc("@info:status", "Unable to slice due to some per-model settings. The following settings have errors on one or more models: {error_labels}").format(error_labels = error_labels),
+                                          title = catalog.i18nc("@info:title", "Unable to slice"))
+            self._error_message.show()
+            self.backendStateChange.emit(BackendState.Error)
+            return
+
         if job.getResult() == StartSliceJob.StartJobResult.BuildPlateError:
             if Application.getInstance().platformActivity:
                 self._error_message = Message(catalog.i18nc("@info:status", "Unable to slice because the prime tower or prime position(s) are invalid."),

plugins/CuraEngineBackend/StartSliceJob.py

@@ -26,6 +26,7 @@ class StartJobResult(IntEnum):
     NothingToSlice = 4
     MaterialIncompatible = 5
     BuildPlateError = 6
+    ObjectSettingError = 7 #When an error occurs in per-object settings.
 
 
 ##  Formatter class that handles token expansion in start/end gcod
@@ -105,7 +106,7 @@ class StartSliceJob(Job):
                 continue
 
             if self._checkStackForErrors(node.callDecoration("getStack")):
-                self.setResult(StartJobResult.SettingError)
+                self.setResult(StartJobResult.ObjectSettingError)
                 return
 
         with self._scene.getSceneLock():