feat: add warning nudges for cross-region event triggers

[shettyvarun268]

This PR implements robust cross-region latency warnings within the Firebase Functions deployment pipeline to nudge developers away from unnecessary cross-region network hops. When an event-triggered function (such as Firestore or Cloud Storage) is explicitly assigned or defaults to us-central1 while its backing event resource operates in a distinct non-US location, the CLI now issues a user-friendly warning nudge encouraging explicit collocation with the event trigger's region. This validation integrates globally following Gen 2 EventArc trigger resolution, correctly handles US multi-region databases (such as nam5) to avoid false positives, and leaves deployment executions unblocked to prevent service disruptions.

[gemini-code-assist]

Code Review

This pull request introduces a warning to alert users when a function in us-central1 is triggered by a resource in a different region, helping to avoid unnecessary cross-region network hops. The review feedback suggests refining the logic to exclude the us multi-region to prevent false positives and improving test isolation by moving cache clearing to the beforeEach block in the test suite.

[gemini-code-assist]

The current logic triggers a warning for the us multi-region (commonly used for Cloud Storage), which includes us-central1. This results in a false positive warning for a valid configuration. Additionally, the suggestion to 'explicitly assign this function to ${ep.eventTrigger.region}' is not applicable for multi-regions like us or nam5 as they are not valid deployment regions for functions.

Consider adding us to the exclusion list and simplifying the loop logic.

  // Warn if an event function defaults to or is assigned to us-central1 but its trigger is elsewhere,
  // to avoid unnecessary cross-region network hops. We ignore nam5 and us since they cover us-central1.
  for (const ep of backend.allEndpoints(want)) {
    const triggerRegion = ep.eventTrigger?.region;
    if (
      ep.region === "us-central1" &&
      backend.isEventTriggered(ep) &&
      triggerRegion &&
      triggerRegion !== "us-central1" &&
      triggerRegion !== "nam5" &&
      triggerRegion !== "us"
    ) {
      utils.logLabeledWarning(
        "functions",
        `Function ${ep.id} located in us-central1 uses a trigger located in ${triggerRegion}. ` +
          `To avoid unnecessary cross-region network hops, you should explicitly assign this function to ${triggerRegion}.`,
      );
    }
  }

[gemini-code-assist]

To ensure test isolation and prevent side effects from the Firestore service cache between test cases, firestoreService.clearCache() should be called in the beforeEach block.

Suggested change

	beforeEach(() => {
	storageStub = sinon.stub(storage, "getBucket").throws("unexpected call to storage.getBucket");
	firestoreStub = sinon
	.stub(firestore, "getDatabase")
	.throws("unexpected call to firestore.getDatabase");
	});
	beforeEach(() => {
	storageStub = sinon.stub(storage, "getBucket").throws("unexpected call to storage.getBucket");
	firestoreStub = sinon
	.stub(firestore, "getDatabase")
	.throws("unexpected call to firestore.getDatabase");
	firestoreService.clearCache();
	});

[gemini-code-assist]

This manual cache clearing is redundant if moved to the beforeEach block.

Suggested change

	const logLabeledWarningStub = sinon.stub(utils, "logLabeledWarning");
	firestoreService.clearCache();
	const logLabeledWarningStub = sinon.stub(utils, "logLabeledWarning");