Ensure Temporal prototypes aren't writable

Port of tc39/proposal-temporal#1974

Author: justingrant

lib/index.ts

@@ -8,4 +8,29 @@
 import * as Temporal from './temporal';
 import * as Intl from './intl';
 import { toTemporalInstant } from './legacydate';
+
+// Work around https://github.com/babel/babel/issues/2025.
+const types = [
+  Temporal.Instant,
+  Temporal.Calendar,
+  Temporal.PlainDate,
+  Temporal.PlainDateTime,
+  Temporal.Duration,
+  Temporal.PlainMonthDay,
+  // Temporal.Now, // plain object (not a constructor), so no `prototype`
+  Temporal.PlainTime,
+  Temporal.TimeZone,
+  Temporal.PlainYearMonth,
+  Temporal.ZonedDateTime
+];
+for (const type of types) {
+  const descriptor = Object.getOwnPropertyDescriptor(type, 'prototype') as PropertyDescriptor;
+  if (descriptor.configurable || descriptor.enumerable || descriptor.writable) {
+    descriptor.configurable = false;
+    descriptor.enumerable = false;
+    descriptor.writable = false;
+    Object.defineProperty(type, 'prototype', descriptor);
+  }
+}
+
 export { Temporal, Intl, toTemporalInstant };

lib/init.ts

@@ -12,7 +12,7 @@ Object.defineProperty(globalThis, 'Temporal', {
   enumerable: false,
   configurable: true
 });
-const globalTemporal = (globalThis as any).Temporal;
+const globalTemporal = (globalThis as unknown as { Temporal: typeof Temporal }).Temporal;
 copy(globalTemporal, Temporal);
 Object.defineProperty(globalTemporal, Symbol.toStringTag, {
   value: 'Temporal',

lib/intl.ts

@@ -174,8 +174,6 @@ Object.defineProperty(DateTimeFormatImpl, 'name', {
   value: 'DateTimeFormat'
 });
 
-export const DateTimeFormat = DateTimeFormatImpl as unknown as typeof Intl.DateTimeFormat;
-
 DateTimeFormatImpl.supportedLocalesOf = function (
   locales: Params['supportedLocalesOf'][0],
   options: Params['supportedLocalesOf'][1]
@@ -199,6 +197,15 @@ if ('formatRangeToParts' in IntlDateTimeFormat.prototype) {
 
 DateTimeFormatImpl.prototype = Object.create(IntlDateTimeFormat.prototype, properties);
 
+// Ensure that the prototype isn't writeable.
+Object.defineProperty(DateTimeFormatImpl, 'prototype', {
+  writable: false,
+  enumerable: false,
+  configurable: false
+});
+
+export const DateTimeFormat = DateTimeFormatImpl as unknown as typeof Intl.DateTimeFormat;
+
 function resolvedOptions(this: DateTimeFormatImpl): Return['resolvedOptions'] {
   return this[ORIGINAL].resolvedOptions();
 }