fix(calendar): Clamp date arithmetic rollovers

`CalendarDay.set` now does an additional check when date
rollover occurs, clamping the value to the last date of the
passed month.

As a side note, when will `Temporal` be baseline available.

Closes #1710

Author: rkaraivanov

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased]
+### Fixed
+  - #### Calendar & Date picker
+    - Incorrect date rollover for in certain scenarios [#1710](https://github.com/IgniteUI/igniteui-webcomponents/issues/1710)
+
 ## [6.0.1] - 2025-05-28
 ### Added
 - #### Radio group

src/components/calendar/model.spec.ts

@@ -127,20 +127,15 @@ describe('Calendar day model', () => {
       const nonLeapFebruary = leapFebruary.set({ year: 2023 });
       let { year, month, date } = nonLeapFebruary;
 
-      // Shift to first day of next month -> 2024/03/01
-      expect([year, month, date]).to.eql([2023, 2, 1]);
-
-      const lastDayOfJuly = new CalendarDay({
-        year: 2024,
-        month: 6,
-        date: 31,
-      });
+      // Shift to last day of the current month -> 2023-02-28
+      expect([year, month, date]).to.eql([2023, 1, 28]);
 
+      const lastDayOfJuly = new CalendarDay({ year: 2024, month: 6, date: 31 });
       const lastDayOfApril = lastDayOfJuly.set({ month: 3 });
       ({ year, month, date } = lastDayOfApril);
 
-      // April does not have 31 days so shift to first day of May
-      expect([year, month, date]).to.eql([2024, 4, 1]);
+      // April does not have 31 days so clamp to the last day of April
+      expect([year, month, date]).to.eql([2024, 3, 30]);
     });
   });
 

src/components/calendar/model.ts

@@ -27,7 +27,7 @@ function checkRollover(original: CalendarDay, modified: CalendarDay) {
 
 /* blazorSuppress */
 export class CalendarDay {
-  private _date!: Date;
+  private readonly _date: Date;
 
   /** Constructs and returns the current day. */
   public static get today() {
@@ -56,11 +56,21 @@ export class CalendarDay {
    * Returns a new instance with values replaced.
    */
   public set(args: Partial<CalendarDayParams>) {
-    return new CalendarDay({
-      year: args.year ?? this.year,
-      month: args.month ?? this.month,
-      date: args.date ?? this.date,
-    });
+    const year = args.year ?? this.year;
+    const month = args.month ?? this.month;
+    const date = args.date ?? this.date;
+
+    const temp = new Date(year, month, date);
+
+    if (date > 0 && temp.getMonth() !== month) {
+      return new CalendarDay({
+        year,
+        month,
+        date: new Date(year, month + 1, 0).getDate(),
+      });
+    }
+
+    return new CalendarDay({ year, month, date });
   }
 
   public add(unit: DayInterval, value: number) {

src/components/date-picker/date-picker.spec.ts

@@ -1,7 +1,11 @@
 import { elementUpdated, expect, fixture, html } from '@open-wc/testing';
 import { spy } from 'sinon';
 import IgcCalendarComponent from '../calendar/calendar.js';
-import { getCalendarDOM, getDayViewDOM } from '../calendar/helpers.spec.js';
+import {
+  getCalendarDOM,
+  getDOMDate,
+  getDayViewDOM,
+} from '../calendar/helpers.spec.js';
 import { CalendarDay, toCalendarDay } from '../calendar/model.js';
 import { DateRangeType } from '../calendar/types.js';
 import {
@@ -897,6 +901,43 @@ describe('Date picker', () => {
       expect(picker.open).to.be.true;
     });
 
+    it('issue 1710', async () => {
+      const activeDate = new CalendarDay({ year: 2025, month: 4, date: 29 });
+      const targetDate = activeDate.add('day', 2);
+
+      // Select the last date of May
+      picker.activeDate = activeDate.native;
+      await picker.show();
+
+      const calendarDOM = getCalendarDOM(calendar);
+      const lastOfMay = getDOMDate(targetDate, calendarDOM.views.days);
+
+      simulateClick(lastOfMay);
+      await elementUpdated(picker);
+
+      expect(checkDatesEqual(picker.value!, targetDate));
+
+      // Open the picker and switch to months view
+      await picker.show();
+
+      simulateClick(calendarDOM.navigation.months);
+      await elementUpdated(picker);
+
+      const monthElements = Array.from(
+        calendarDOM.views.months.renderRoot.querySelectorAll<HTMLElement>(
+          '[role="gridcell"]'
+        )
+      );
+
+      const monthNames = new Set(monthElements.map((each) => each.innerText));
+      const selectedMonths = monthElements.filter((each) =>
+        each.matches('[aria-selected="true"]')
+      );
+
+      expect(monthNames).lengthOf(12);
+      expect(selectedMonths).lengthOf(1);
+    });
+
     describe('Readonly state', () => {
       describe('Dropdown mode', () => {
         beforeEach(async () => {