fix(material-luxon-adapter): zone on DateTime ignored (angular#26887)

Fixes a bug where the timezone on the Luxon DateTime is thrown away during conversion to string,
resulting in using the Luxon defaultZone regardless of how the particular DateTime is configured.

Fixes angular#26869

src/material-luxon-adapter/adapter/luxon-date-adapter.spec.ts

@@ -9,7 +9,7 @@
 import {LOCALE_ID} from '@angular/core';
 import {TestBed, waitForAsync} from '@angular/core/testing';
 import {DateAdapter, MAT_DATE_LOCALE} from '@angular/material/core';
-import {DateTime} from 'luxon';
+import {DateTime, FixedOffsetZone, Settings} from 'luxon';
 import {LuxonDateModule} from './index';
 import {MAT_LUXON_DATE_ADAPTER_OPTIONS} from './luxon-date-adapter';
 
@@ -351,6 +351,16 @@ describe('LuxonDateAdapter', () => {
     expect(date).toEqual('2. jan. 2017');
   });
 
+  it('should format with a different timezone', () => {
+    Settings.defaultZone = FixedOffsetZone.parseSpecifier('UTC-12');
+
+    let date = adapter.format(DateTime.local(2017, JAN, 2, {zone: 'UTC-12'}), 'DD');
+    expect(date).toEqual('Jan 2, 2017');
+
+    date = adapter.format(DateTime.local(2017, JAN, 2, {zone: 'UTC+12'}), 'DD');
+    expect(date).toEqual('Jan 2, 2017');
+  });
+
   it('should throw when attempting to format invalid date', () => {
     expect(() => adapter.format(DateTime.fromMillis(NaN), 'LL/dd/yyyy')).toThrowError(
       /LuxonDateAdapter: Cannot format invalid date\./,

src/material-luxon-adapter/adapter/luxon-date-adapter.ts

@@ -193,10 +193,11 @@ export class LuxonDateAdapter extends DateAdapter<LuxonDateTime> {
     if (!this.isValid(date)) {
       throw Error('LuxonDateAdapter: Cannot format invalid date.');
     }
-    return date
-      .setLocale(this.locale)
-      .setZone(this._useUTC ? 'utc' : undefined)
-      .toFormat(displayFormat);
+    if (this._useUTC) {
+      return date.setLocale(this.locale).setZone('utc').toFormat(displayFormat);
+    } else {
+      return date.setLocale(this.locale).toFormat(displayFormat);
+    }
   }
 
   addCalendarYears(date: LuxonDateTime, years: number): LuxonDateTime {