fix the Vitest integration to support Workers that want Node.js compatibility is only v1 in production (#9331)

It does this by adding the `nodejs_compat_v2` flag (if missing) and removing `no_nodejs_compat_v2` flag (if found).

This does mean that the Vitest tests are running with a slightly different environment to production, but this has always been the case in other ways.

Fixes #8988

Author: petebacondarwin

.changeset/shy-beans-warn.md

@@ -0,0 +1,9 @@
+---
+"@cloudflare/vitest-pool-workers": patch
+---
+
+fix the Vitest integration to support Workers that want Node.js compatibility is only v1 in production
+
+It does this by adding the `nodejs_compat_v2` flag (if missing) and removing `no_nodejs_compat_v2` flag (if found).
+
+This does mean that the Vitest tests are running with a slightly different environment to production, but this has always been the case in other ways.

fixtures/vitest-pool-workers-examples/basics-integration-auxiliary/vitest.config.ts

@@ -10,6 +10,9 @@ export default defineWorkersProject({
 					// Configuration for the test runner Worker
 					compatibilityDate: "2024-01-01",
 					compatibilityFlags: [
+						// This illustrates a Worker that in production only wants v1 of Node.js compatibility.
+						// The Vitest pool integration will need to remove this flag since the `MockAgent` requires v2.
+						"no_nodejs_compat_v2",
 						"nodejs_compat",
 						// Required to use `WORKER.scheduled()`. This is an experimental
 						// compatibility flag, and cannot be enabled in production.

packages/vitest-pool-workers/src/pool/index.ts

@@ -407,12 +407,18 @@ function buildProjectWorkerOptions(
 		}
 	}
 
-	const { mode } = getNodeCompat(
+	const { hasNoNodejsCompatV2Flag, mode } = getNodeCompat(
 		runnerWorker.compatibilityDate,
 		runnerWorker.compatibilityFlags
 	);
 
 	if (mode !== "v2") {
+		if (hasNoNodejsCompatV2Flag) {
+			runnerWorker.compatibilityFlags.splice(
+				runnerWorker.compatibilityFlags.indexOf("no_nodejs_compat_v2"),
+				1
+			);
+		}
 		runnerWorker.compatibilityFlags.push("nodejs_compat_v2");
 	}