Fixing up logic around selecting/deselecting nested labels

src/examples/nested_labels/config.xml

@@ -0,0 +1,24 @@
+<View>
+  <Choices name="has_math_choice" toName="interaction" choice="single" showInLine="true">
+    <Choice value="This thread has math"/>
+    <Choice value="This thread does not have math"/>
+  </Choices>
+
+  <View style="top: 0; position: sticky; z-index: 5; background: white" visibleWhen="choice-selected" whenTagName="has_math_choice" whenChoiceValue="This thread has math">
+    <Labels name="interaction_correctness" toName="interaction">
+      <Label value="Correct" hotkey="c" hint="This statement is accurate and pedagogically sound" granularity="div" background="green"/>
+      <Label value="Incorrect: Khanmigo" hotkey="k" granularity="div" background="red"/>
+      <Label value="Incorrect: Student" hotkey="s" granularity="div" background="orange"/>
+    </Labels>
+  </View>
+
+  <View style="position: sticky; top: 32px; z-index: 5; background: white" visibleWhen="region-selected" whenTagName="interaction_correctness" whenLabelValue="Incorrect: Khanmigo">
+    <Labels name="khanmigo_incorrect_type" toName="interaction">
+      <Label alias="type-incorrect" value="Wrong calculation" hotkey="w" hint="Khanmigo calculates incorrectly, e.g. 2+2=5"  granularity="div" background="pink"/>
+      <Label alias="type-process" value="Wrong process" hotkey="p" hint="Khanmigo suggests a bad method, e.g. 'to find 2+2 you must divide'" granularity="div" background="purple"/>
+      <Label alias="type-other" value="Other" hotkey="o" hint="Use this label for any noteworthy issue that is not addressed by other labels; elaborate in Labeler Notes" granularity="div" background="blue"/>
+    </Labels>
+  </View>
+
+  <TableText name="interaction" value="$json_thread" granularity="word"/>
+</View>

src/examples/nested_labels/index.js

@@ -0,0 +1,5 @@
+import config from './config.xml';
+import tasks from './tasks.json';
+import annotation from './annotations/nested-labels.json';
+
+export const NestedLabels = { config, tasks, annotation };

src/tags/control/Label.js

@@ -157,6 +157,30 @@ const Model = types.model({
       // if that's the only selected label, the only labelset assigned to region,
       // and we are trying to unselect it, then don't allow that
       // (except for rare labelsets that allow empty labels)
+
+      // Don't allow selecting a different top-level label when we've already labeled it: DI-1502
+      if (
+        labels.selectedLabels.length === 1 &&
+        !self.selected &&
+        labels.selectedLabels[0].value !== self.value &&
+        !labels.selectedLabels[0].alias // Hack: we only gave sub-labels aliases
+      ) {
+        return false;
+      }
+
+      // If this is only top level label and there are sub labels, don't allow deselect
+      if (
+        labels.selectedLabels.length === 1 &&
+        self.selected &&
+        labels.selectedLabels[0].value == self.value &&
+        !labels.selectedLabels[0].alias && // Hack: we only gave sub-labels aliases
+        region.labelings.length > 1
+      ) {
+        console.log('can\'t deselect top level label w sub label!')
+
+        return false;
+      }
+
       if (
         labels.selectedLabels.length === 1 &&
         self.selected &&