[Lens] Fix crash in transition from unique count to last value

x-pack/plugins/lens/public/indexpattern_datasource/operations/layer_helpers.test.ts

@@ -2181,7 +2181,7 @@ describe('state_helpers', () => {
       expect(errors).toHaveLength(1);
     });
 
-    it('should consider incompleteColumns before layer columns', () => {
+    it('should ignore incompleteColumns when checking for errors', () => {
       const savedRef = jest.fn().mockReturnValue(['error 1']);
       const incompleteRef = jest.fn();
       operationDefinitionMap.testReference.getErrorMessage = savedRef;
@@ -2206,9 +2206,9 @@ describe('state_helpers', () => {
         },
         indexPattern
       );
-      expect(savedRef).not.toHaveBeenCalled();
-      expect(incompleteRef).toHaveBeenCalled();
-      expect(errors).toBeUndefined();
+      expect(savedRef).toHaveBeenCalled();
+      expect(incompleteRef).not.toHaveBeenCalled();
+      expect(errors).toHaveLength(1);
 
       delete operationDefinitionMap.testIncompleteReference;
     });

x-pack/plugins/lens/public/indexpattern_datasource/operations/layer_helpers.ts

@@ -870,12 +870,7 @@ export function getErrorMessages(
 ): string[] | undefined {
   const errors: string[] = Object.entries(layer.columns)
     .flatMap(([columnId, column]) => {
-      // If we're transitioning to another operation, check for "new" incompleteColumns rather
-      // than "old" saved operation on the layer
-      const columnFinalRef =
-        layer.incompleteColumns?.[columnId]?.operationType || column.operationType;
-      const def = operationDefinitionMap[columnFinalRef];
-
+      const def = operationDefinitionMap[column.operationType];
       if (def.getErrorMessage) {
         return def.getErrorMessage(layer, columnId, indexPattern);
       }

x-pack/test/functional/apps/lens/smokescreen.ts

@@ -514,6 +514,28 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       );
     });
 
+    it('should transition from unique count to last value', async () => {
+      await PageObjects.visualize.navigateToNewVisualization();
+      await PageObjects.visualize.clickVisType('lens');
+      await PageObjects.lens.goToTimeRange();
+
+      await PageObjects.lens.configureDimension({
+        dimension: 'lnsXY_yDimensionPanel > lns-empty-dimension',
+        operation: 'cardinality',
+        field: 'ip',
+      });
+      await PageObjects.lens.configureDimension({
+        dimension: 'lnsXY_yDimensionPanel > lns-dimensionTrigger',
+        operation: 'last_value',
+        field: 'bytes',
+        isPreviousIncompatible: true,
+      });
+
+      expect(await PageObjects.lens.getDimensionTriggerText('lnsXY_yDimensionPanel')).to.eql(
+        'Last value of bytes'
+      );
+    });
+
     it('should allow to change index pattern', async () => {
       await PageObjects.lens.switchFirstLayerIndexPattern('log*');
       expect(await PageObjects.lens.getFirstLayerIndexPattern()).to.equal('log*');