regression: momentFormatToDateFns not handling literal date formats

apps/meteor/client/lib/utils/dateFormat.spec.ts

@@ -0,0 +1,43 @@
+import { formatDate, momentFormatToDateFns } from './dateFormat';
+
+describe('momentFormatToDateFns', () => {
+	it('maps locale tokens', () => {
+		expect(momentFormatToDateFns('L')).toBe('P');
+		expect(momentFormatToDateFns('LT')).toBe('p');
+		expect(momentFormatToDateFns('LTS')).toBe('pp');
+		expect(momentFormatToDateFns('LL')).toBe('PPP');
+		expect(momentFormatToDateFns('LLL')).toBe('PPP p');
+		expect(momentFormatToDateFns('LLLL')).toBe('EEEE, PPP p');
+	});
+
+	it('maps common tokens', () => {
+		expect(momentFormatToDateFns('YYYY-MM-DD HH:mm:ss')).toBe('yyyy-MM-dd HH:mm:ss');
+		expect(momentFormatToDateFns('MMMM Do YYYY, h:mm:ss a')).toBe('MMMM do yyyy, h:mm:ss a');
+	});
+
+	it('translates moment [literal] escape to date-fns single-quoted literal', () => {
+		expect(momentFormatToDateFns('[Today at] LT')).toBe("'Today at' p");
+		expect(momentFormatToDateFns('[Session started at] HH:mm [on] LL')).toBe("'Session started at' HH:mm 'on' PPP");
+	});
+
+	it("escapes embedded single quotes inside literals as ''", () => {
+		expect(momentFormatToDateFns("[it's] LT")).toBe("'it''s' p");
+	});
+
+	it('preserves empty literal blocks', () => {
+		expect(momentFormatToDateFns('[] LT')).toBe("'' p");
+	});
+});
+
+describe('formatDate', () => {
+	const sample = new Date('2026-04-24T20:30:45');
+
+	it('formats literal blocks with locale tokens without throwing', () => {
+		expect(() => formatDate(sample, '[Today at] LT')).not.toThrow();
+		expect(formatDate(sample, '[Today at] LT')).toMatch(/^Today at /);
+	});
+
+	it('formats date with year-month-day token string', () => {
+		expect(formatDate(sample, 'YYYY-MM-DD')).toBe('2026-04-24');
+	});
+});

apps/meteor/client/lib/utils/dateFormat.ts

@@ -6,6 +6,7 @@ export type DateInput = string | Date | number;
 /**
  * Map moment-style locale format tokens to date-fns format string.
  * Used for Message_DateFormat and Message_TimeFormat settings (defaults: LL, LT).
+ * Moment's `[literal]` escape syntax is translated to date-fns' `'literal'` syntax.
  */
 export const momentFormatToDateFns = (momentFormat: string): string => {
 	const tokenMap: Record<string, string> = {
@@ -39,12 +40,25 @@ export const momentFormatToDateFns = (momentFormat: string): string => {
 		A: 'a',
 		a: 'a',
 	};
-	let out = momentFormat;
 	const entries = Object.entries(tokenMap).sort(([a], [b]) => b.length - a.length);
-	for (const [mom, df] of entries) {
-		out = out.replace(new RegExp(mom.replace(/([.*+?^${}()|[\]\\])/g, '\\$1'), 'g'), df);
-	}
-	return out;
+
+	const replaceTokens = (input: string): string => {
+		let out = input;
+		for (const [mom, df] of entries) {
+			out = out.replace(new RegExp(mom.replace(/([.*+?^${}()|[\]\\])/g, '\\$1'), 'g'), df);
+		}
+		return out;
+	};
+
+	return momentFormat
+		.split(/(\[[^\]]*\])/g)
+		.map((part) => {
+			if (part.startsWith('[') && part.endsWith(']')) {
+				return `'${part.slice(1, -1).replace(/'/g, "''")}'`;
+			}
+			return replaceTokens(part);
+		})
+		.join('');
 };
 
 export const formatDate = (date: DateInput, formatStr: string, locale?: Locale): string => {