fix(core): avoid triggering on timer and on idle on the server (angular#59177)

This commit updates defer block logic to avoid triggering `on idle` and `on timer` on the server for regular SSR mode (when incremental hydration is not enabled). Triggering the mentioned condition resulted in invoking `setTimeout` calls, which delayed serialization on the server during SSR (the process was waiting for the timeouts to clear).

PR Close angular#59177

Author: AndrewKushnir

packages/core/src/defer/triggering.ts

@@ -73,11 +73,17 @@ export function scheduleDelayedTrigger(
 ) {
   const lView = getLView();
   const tNode = getCurrentTNode()!;
-  const injector = lView[INJECTOR];
-  const lDetails = getLDeferBlockDetails(lView, tNode);
 
   renderPlaceholder(lView, tNode);
 
+  // Exit early to avoid invoking `scheduleFn`, which would
+  // add `setTimeout` call and potentially delay serialization
+  // on the server unnecessarily.
+  if (!shouldTriggerDeferBlock(TriggerType.Regular, lView)) return;
+
+  const injector = lView[INJECTOR];
+  const lDetails = getLDeferBlockDetails(lView, tNode);
+
   const cleanupFn = scheduleFn(
     () => triggerDeferBlock(TriggerType.Regular, lView, tNode),
     injector,

packages/platform-server/test/full_app_hydration_spec.ts

@@ -3052,6 +3052,41 @@ describe('platform-server full application hydration integration', () => {
         expect(clientRootNode.outerHTML).toContain('<my-lazy-cmp>Hi!</my-lazy-cmp>');
       });
 
+      it('should not trigger `setTimeout` calls for `on timer` triggers on the server', async () => {
+        const setTimeoutSpy = spyOn(globalThis, 'setTimeout').and.callThrough();
+
+        @Component({
+          selector: 'my-lazy-cmp',
+          standalone: true,
+          template: 'Hi!',
+        })
+        class MyLazyCmp {}
+
+        @Component({
+          standalone: true,
+          selector: 'app',
+          imports: [MyLazyCmp],
+          template: `
+            @defer (on timer(123ms)) {
+              <my-lazy-cmp />
+            }
+          `,
+        })
+        class SimpleComponent {}
+
+        const html = await ssr(SimpleComponent);
+
+        const ssrContents = getAppContents(html);
+        expect(ssrContents).toContain('<app ngh');
+
+        // Make sure that there were no `setTimeout` calls with the # of ms
+        // defined in the `on timer` trigger.
+        for (let i = 0; i < setTimeoutSpy.calls.count(); i++) {
+          const args = setTimeoutSpy.calls.argsFor(i);
+          expect(args[1]).not.toBe(123, 'on timer was triggered during SSR unexpectedly');
+        }
+      });
+
       it('should hydrate a placeholder block', async () => {
         @Component({
           selector: 'my-lazy-cmp',