[FIX] dates: use UTC to represent naive date times

(see also the previous commit)

The issue
---------

Steps to reproduce:

- change your machine timezone to Jakarta
- enter "3/8/2023" in a cell
=> it becomes "3/7/2023"

Other steps to reproduce:

- change your machine timezone to Jakarta
- npm run test
=> some tests are failing.

Spreadsheet date times are naive date times, they do not carry any timezone
information. A date(time) in spreadsheet is just a number with a format
after all.

We are currently using javascript native Date objects everywhere in the code to
represent spreadsheet dates.
And we are mixing UTC (new Date(timestamp)) and localized Dates
(new Date(year, month, day, ...)) at some places. This is a mistake.

Because of an (un)lucky combination of mistakes, it mostly works by chance for
most timezones.
But going back to the faulty Jakarta case: one can notice that
INITIAL_1900_DAY is UTC+0707 while INITIAL_JS_DAY is UTC+0700 (7 minutes
offset). The timezone offset changed over time.

Some of the mistakes where we mix up things:

- INITIAL_1900_DAY is localized, but INITIAL_JS_DAY is UTC.
- numberToJsDate: we create the date from the value as if it was UTC,
  but then set the time as if it was localized.

This commit
-----------

The idea to fix the issue is to avoid mixing localized and UTC Dates.
To represent naive date times, we will always use UTC Date objects.

closes #3397

Task: 3666703
X-original-commit: 651f9bb
Signed-off-by: Pierre Rousseau (pro) <pro@odoo.com>
Signed-off-by: Lucas Lefèvre (lul) <lul@odoo.com>

src/helpers/dates.ts

@@ -15,21 +15,27 @@ export interface InternalDate {
   readonly jsDate?: ReadonlyDateTime;
 }
 
+/**
+ * A DateTime object that can be used to manipulate spreadsheet dates.
+ * Conceptually, a spreadsheet date is simply a number with a date format,
+ * and it is timezone-agnostic.
+ * This DateTime object consistently uses UTC time to represent a naive date and time.
+ */
 export class DateTime {
   private jsDate: Date;
   constructor(year: number, month: number, day: number, hours = 0, minutes = 0, seconds = 0) {
-    this.jsDate = new Date(year, month, day, hours, minutes, seconds, 0);
+    this.jsDate = new Date(Date.UTC(year, month, day, hours, minutes, seconds, 0));
   }
 
   static fromTimestamp(timestamp: number) {
     const date = new Date(timestamp);
     return new DateTime(
-      date.getFullYear(),
-      date.getMonth(),
-      date.getDate(),
-      date.getHours(),
-      date.getMinutes(),
-      date.getSeconds()
+      date.getUTCFullYear(),
+      date.getUTCMonth(),
+      date.getUTCDate(),
+      date.getUTCHours(),
+      date.getUTCMinutes(),
+      date.getUTCSeconds()
     );
   }
 
@@ -54,51 +60,51 @@ export class DateTime {
   }
 
   getFullYear() {
-    return this.jsDate.getFullYear();
+    return this.jsDate.getUTCFullYear();
   }
 
   getMonth() {
-    return this.jsDate.getMonth();
+    return this.jsDate.getUTCMonth();
   }
 
   getDate() {
-    return this.jsDate.getDate();
+    return this.jsDate.getUTCDate();
   }
 
   getDay() {
-    return this.jsDate.getDay();
+    return this.jsDate.getUTCDay();
   }
 
   getHours() {
-    return this.jsDate.getHours();
+    return this.jsDate.getUTCHours();
   }
 
   getMinutes() {
-    return this.jsDate.getMinutes();
+    return this.jsDate.getUTCMinutes();
   }
 
   getSeconds() {
-    return this.jsDate.getSeconds();
+    return this.jsDate.getUTCSeconds();
   }
 
   setFullYear(year: number) {
     this.jsDate.setFullYear(year);
   }
 
   setDate(date: number) {
-    this.jsDate.setDate(date);
+    this.jsDate.setUTCDate(date);
   }
 
   setHours(hours: number) {
-    this.jsDate.setHours(hours);
+    this.jsDate.setUTCHours(hours);
   }
 
   setMinutes(minutes: number) {
-    this.jsDate.setMinutes(minutes);
+    this.jsDate.setUTCMinutes(minutes);
   }
 
   setSeconds(seconds: number) {
-    this.jsDate.setSeconds(seconds);
+    this.jsDate.setUTCSeconds(seconds);
   }
 }
 

tests/functions/module_date.test.ts

@@ -6,8 +6,10 @@ import {
   evaluateGridText,
 } from "../test_helpers/helpers";
 
+// All these tests should pass no matter the machine timezone.
+
 describe("DATE formula", () => {
-  test("functional tests on cell arguments CHECK TIMEZONE IF FAILS", () => {
+  test("functional tests on cell arguments", () => {
     // prettier-ignore
     const grid = {
       // YEAR / MONTH / DAY