table panel: assume string dates to be on UTC (#47246)

* add tests for display processor relating to datetimes as strings

Co-authored-by: Oscar Kilhed <oscar.kilhed@grafana.com>

packages/grafana-data/src/field/displayProcessor.test.ts

@@ -414,6 +414,46 @@ describe('Date display options', () => {
     expect(processor('2020-08-01T08:48:43.783337Z').text).toEqual('2020-08-01 08:48:43');
   });
 
+  it('should handle ISO string dates when in other timezones than UTC', () => {
+    const processor = getDisplayProcessor({
+      timeZone: 'CET',
+      field: {
+        type: FieldType.time,
+        config: {},
+      },
+      theme: createTheme(),
+    });
+
+    expect(processor('2020-08-01T08:48:43.783337Z').text).toEqual('2020-08-01 10:48:43'); //DST
+    expect(processor('2020-12-01T08:48:43.783337Z').text).toEqual('2020-12-01 09:48:43'); //STD
+  });
+
+  it('should handle ISO string dates with timezone offset', () => {
+    const processor = getDisplayProcessor({
+      timeZone: 'utc',
+      field: {
+        type: FieldType.time,
+        config: {},
+      },
+      theme: createTheme(),
+    });
+
+    expect(processor('2020-12-01T08:48:43.783337+02:00').text).toEqual('2020-12-01 06:48:43');
+  });
+
+  it('should handle ISO string dates without timezone qualifier by assuming UTC', () => {
+    const processor = getDisplayProcessor({
+      timeZone: 'CET',
+      field: {
+        type: FieldType.time,
+        config: {},
+      },
+      theme: createTheme(),
+    });
+
+    expect(processor('2020-12-01T08:48:43.783337').text).toEqual('2020-12-01 09:48:43');
+  });
+
   describe('number formatting for string values', () => {
     it('should preserve string unchanged if unit is strings', () => {
       const processor = getDisplayProcessor({

packages/grafana-data/src/field/displayProcessor.ts

@@ -6,7 +6,7 @@ import { Field, FieldType } from '../types/dataFrame';
 import { DisplayProcessor, DisplayValue } from '../types/displayValue';
 import { getValueFormat, isBooleanUnit } from '../valueFormats/valueFormats';
 import { getValueMappingResult } from '../utils/valueMappings';
-import { dateTime, dateTimeParse } from '../datetime';
+import { toUtc, dateTimeParse } from '../datetime';
 import { KeyValue, TimeZone } from '../types';
 import { getScaleCalculator } from './scale';
 import { GrafanaTheme2 } from '../themes/types';
@@ -77,7 +77,7 @@ export function getDisplayProcessor(options?: DisplayProcessorOptions): DisplayP
     const isStringUnit = unit === 'string';
 
     if (hasDateUnit && typeof value === 'string') {
-      value = dateTime(value).valueOf();
+      value = toUtc(value).valueOf();
     }
 
     let numeric = isStringUnit ? NaN : anyToNumber(value);