Temporal use same time as Date.now() + compat flag & tests

src/workerd/api/tests/BUILD.bazel

@@ -296,6 +296,11 @@ wd_test(
     data = ["actor-alarms-name-test.js"],
 )
 
+wd_test(
+    src = "temporal-test.wd-test",
+    data = ["temporal-test.js"],
+)
+
 wd_test(
     src = "tail-worker-test.wd-test",
     args = [

src/workerd/api/tests/temporal-hidden-test.js

@@ -2,15 +2,42 @@
 // Licensed under the Apache 2.0 license found in the LICENSE file or at:
 //     https://opensource.org/licenses/Apache-2.0
 
+// Verifies that the `no_temporal` compatibility flag removes the Temporal API.
+//
+// V8 installs Temporal on every context, because --harmony-temporal is
+// process-wide and cannot vary per isolate. Gating it per Worker therefore
+// means deleting what V8 already installed, so the absence asserted here is
+// the result of jsg::deleteTemporalGlobals() running at context creation
+// rather than of V8 declining to install anything.
+
 import { strictEqual } from 'node:assert';
 
-// V8 is built with Temporal, which it enables by default; workerd turns it off with
-// --noharmony-temporal so the API surface stays unchanged.
-export const temporalIsHidden = {
+export const temporalGlobalIsAbsent = {
   test() {
+    // `typeof` on an undeclared identifier evaluates to "undefined" rather
+    // than throwing, which is exactly the check applications use to decide
+    // whether to install a polyfill. It is the property that matters to them,
+    // so it is the property asserted here.
     strictEqual(typeof Temporal, 'undefined');
+
+    // V8 installs the global as a lazy accessor with replace-on-access, so it
+    // would still be present as a property even if nothing had read it. Check
+    // for the property too, not just for a successful read.
     strictEqual('Temporal' in globalThis, false);
-    strictEqual(Date.prototype.toTemporalInstant, undefined);
+    strictEqual(Object.hasOwn(globalThis, 'Temporal'), false);
+  },
+};
+
+export const dateBridgeIsAbsent = {
+  test() {
+    // Genesis::InitializeGlobal_harmony_temporal() installs
+    // Date.prototype.toTemporalInstant alongside the global, so it is a second
+    // route into the API and has to be absent as well.
+    strictEqual(typeof Date.prototype.toTemporalInstant, 'undefined');
     strictEqual('toTemporalInstant' in Date.prototype, false);
+
+    // Date itself must be otherwise untouched by the deletion.
+    strictEqual(new Date(0).getTime(), 0);
+    strictEqual(typeof Date.now(), 'number');
   },
 };

src/workerd/api/tests/temporal-hidden-test.wd-test

@@ -7,7 +7,7 @@ const unitTests :Workerd.Config = (
         modules = [
           (name = "worker", esModule = embed "temporal-hidden-test.js")
         ],
-        compatibilityFlags = ["nodejs_compat"],
+        compatibilityFlags = ["nodejs_compat", "no_temporal"],
       )
     ),
   ],