Normative: Add Temporal[@@toStringTag].

Fixes #1539.

Co-authored-by: Jordan Harband <ljharb@gmail.com>

polyfill/lib/shim.mjs

@@ -13,6 +13,12 @@ Object.defineProperty(globalThis, 'Temporal', {
   configurable: true
 });
 copy(globalThis.Temporal, Temporal);
+Object.defineProperty(globalThis.Temporal, Symbol.toStringTag, {
+  value: 'Temporal',
+  writable: false,
+  enumerable: false,
+  configurable: true
+});
 copy(globalThis.Temporal.Now, Temporal.Now);
 copy(globalThis.Intl, Intl);
 Object.defineProperty(globalThis.Date.prototype, 'toTemporalInstant', {

polyfill/test/Temporal/toStringTag/prop-desc.js

@@ -0,0 +1,15 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal-@@tostringtag
+includes: [propertyHelper.js]
+features: [Symbol.toStringTag, Temporal]
+---*/
+
+verifyProperty(Temporal, Symbol.toStringTag, {
+  value: "Temporal",
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

polyfill/test/Temporal/toStringTag/string.js

@@ -0,0 +1,9 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal-@@tostringtag
+features: [Symbol.toStringTag, Temporal]
+---*/
+
+assert.sameValue(String(Temporal), "[object Temporal]");

spec/temporal.html

@@ -14,6 +14,15 @@ <h1>The Temporal Object</h1>
     <li>does not have a [[Call]] internal method; it cannot be invoked as a function.</li>
   </ul>
 
+  <emu-clause id="sec-value-properties-of-the-temporal-object">
+    <h1>Value Properties of the Temporal Object</h1>
+    <emu-clause id="sec-temporal-@@tostringtag">
+      <h1>Temporal [ @@toStringTag ]</h1>
+      <p>The initial value of the @@toStringTag property is the String value *"Temporal"*.</p>
+      <p>This property has the attributes { [[Writable]]: *false*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.</p>
+    </emu-clause>
+  </emu-clause>
+
   <emu-clause id="sec-constructor-properties-of-the-temporal-object">
     <h1>Constructor Properties of the Temporal Object</h1>
     <emu-clause id="sec-temporal-instant">