Prometheus: don't override displayName property (#29441)

* Prometheus: don't override displayName property

* Rename displayName to displayNameFromDS for consistency

public/app/plugins/datasource/prometheus/result_transformer.test.ts

 import { DataFrame } from '@grafana/data';
 import { transform } from './result_transformer';
 
+const matrixResponse = {
+  status: 'success',
+  data: {
+    resultType: 'matrix',
+    result: [
+      {
+        metric: { __name__: 'test', job: 'testjob' },
+        values: [
+          [1, '10'],
+          [2, '0'],
+        ],
+      },
+    ],
+  },
+};
+
 describe('Prometheus Result Transformer', () => {
   const options: any = { target: {}, query: {} };
   describe('When nothing is returned', () => {
@@ -306,46 +322,14 @@ describe('Prometheus Result Transformer', () => {
     });
 
     it('should fill null values', () => {
-      const response = {
-        status: 'success',
-        data: {
-          resultType: 'matrix',
-          result: [
-            {
-              metric: { __name__: 'test', job: 'testjob' },
-              values: [
-                [1, '10'],
-                [2, '0'],
-              ],
-            },
-          ],
-        },
-      };
-
-      const result = transform({ data: response } as any, { ...options, query: { step: 1, start: 0, end: 2 } });
+      const result = transform({ data: matrixResponse } as any, { ...options, query: { step: 1, start: 0, end: 2 } });
 
       expect(result[0].fields[0].values.toArray()).toEqual([0, 1000, 2000]);
       expect(result[0].fields[1].values.toArray()).toEqual([null, 10, 0]);
     });
 
     it('should use __name__ label as series name', () => {
-      const response = {
-        status: 'success',
-        data: {
-          resultType: 'matrix',
-          result: [
-            {
-              metric: { __name__: 'test', job: 'testjob' },
-              values: [
-                [1, '10'],
-                [2, '0'],
-              ],
-            },
-          ],
-        },
-      };
-
-      const result = transform({ data: response } as any, {
+      const result = transform({ data: matrixResponse } as any, {
         ...options,
         query: {
           step: 1,
@@ -384,6 +368,12 @@ describe('Prometheus Result Transformer', () => {
       expect(result[0].name).toBe('{job="testjob"}');
     });
 
+    it('should not set displayName for ValueFields', () => {
+      const result = transform({ data: matrixResponse } as any, options);
+      expect(result[0].fields[1].config.displayName).toBeUndefined();
+      expect(result[0].fields[1].config.displayNameFromDS).toBe('test{job="testjob"}');
+    });
+
     it('should align null values with step', () => {
       const response = {
         status: 'success',

public/app/plugins/datasource/prometheus/result_transformer.ts

@@ -139,10 +139,10 @@ function transformToDataFrame(data: MatrixOrVectorResult, options: TransformOpti
       dps.push([t, null]);
     }
     fields.push(getTimeField(dps, true));
-    fields.push(getValueField({ data: dps, parseValue: false, labels, displayName: name }));
+    fields.push(getValueField({ data: dps, parseValue: false, labels, displayNameFromDS: name }));
   } else {
     fields.push(getTimeField([data.value]));
-    fields.push(getValueField({ data: [data.value], labels, displayName: name }));
+    fields.push(getValueField({ data: [data.value], labels, displayNameFromDS: name }));
   }
 
   return {
@@ -224,7 +224,7 @@ type ValueFieldOptions = {
   valueName?: string;
   parseValue?: boolean;
   labels?: Labels;
-  displayName?: string;
+  displayNameFromDS?: string;
 };
 
 function getValueField({
@@ -232,13 +232,13 @@ function getValueField({
   valueName = TIME_SERIES_VALUE_FIELD_NAME,
   parseValue = true,
   labels,
-  displayName,
+  displayNameFromDS,
 }: ValueFieldOptions): MutableField {
   return {
     name: valueName,
     type: FieldType.number,
     config: {
-      displayName,
+      displayNameFromDS,
     },
     labels,
     values: new ArrayVector<number | null>(data.map(val => (parseValue ? parseSampleValue(val[1]) : val[1]))),