nodejs_compat flag (#478)

Author: GregBrimble

packages/core/src/plugins/core.ts

@@ -25,6 +25,7 @@ import webStreams from "stream/web";
 import { URL, URLSearchParams } from "url";
 import { TextDecoder, TextEncoder } from "util";
 import {
+  AdditionalModules,
   CompatibilityFlag,
   Context,
   ModuleRule,
@@ -70,6 +71,7 @@ import {
 } from "../standards";
 import { assertsInRequest } from "../standards/helpers";
 import type { BindingsOptions } from "./bindings";
+import { additionalModules } from "./node";
 
 const DEFAULT_MODULE_RULES: ModuleRule[] = [
   { type: "ESModule", include: ["**/*.mjs"] },
@@ -411,6 +413,7 @@ export class CorePlugin extends Plugin<CoreOptions> implements CoreOptions {
 
   readonly upstreamURL?: URL;
   readonly #globals: Context;
+  readonly #additionalModules?: AdditionalModules;
 
   constructor(ctx: PluginContext, options?: CoreOptions) {
     super(ctx);
@@ -421,6 +424,11 @@ export class CorePlugin extends Plugin<CoreOptions> implements CoreOptions {
       );
     }
 
+    const nodejsCompat = ctx.compat.isEnabled("nodejs_compat");
+    if (nodejsCompat) {
+      this.#additionalModules = additionalModules;
+    }
+
     const extraGlobals: Context = {};
 
     // Make sure the kFormDataFiles flag is set correctly when constructing
@@ -652,11 +660,13 @@ export class CorePlugin extends Plugin<CoreOptions> implements CoreOptions {
 
   async setup(): Promise<SetupResult> {
     const globals = this.#globals;
+    const additionalModules = this.#additionalModules;
 
     // First, try to load script from string, no need to watch any files
     if (this.script !== undefined) {
       return {
         globals,
+        additionalModules,
         script: { filePath: STRING_SCRIPT_PATH, code: this.script },
       };
     }
@@ -689,11 +699,16 @@ export class CorePlugin extends Plugin<CoreOptions> implements CoreOptions {
       scriptPath = path.resolve(this.ctx.rootPath, scriptPath);
       const code = await fs.readFile(scriptPath, "utf8");
       watch.push(scriptPath);
-      return { globals, script: { filePath: scriptPath, code }, watch };
+      return {
+        globals,
+        additionalModules,
+        script: { filePath: scriptPath, code },
+        watch,
+      };
     }
 
     // If we couldn't load a script yet, keep watching package.json anyways, it
     // might get edited with a path
-    return { globals, watch };
+    return { globals, additionalModules, watch };
   }
 }

packages/core/src/plugins/node/async_hooks.ts

@@ -0,0 +1,6 @@
+import async_hooks from "node:async_hooks";
+
+export class AsyncHooksModule {
+  AsyncLocalStorage = async_hooks.AsyncLocalStorage;
+  AsyncResource = async_hooks.AsyncResource;
+}

packages/core/src/plugins/node/index.ts

@@ -0,0 +1,5 @@
+import { AsyncHooksModule } from "./async_hooks";
+
+export const additionalModules = {
+  "node:async_hooks": { default: new AsyncHooksModule() },
+};

packages/core/test/plugins/core.spec.ts

@@ -654,6 +654,20 @@ test("CorePlugin: setup: uses actual time if option enabled", async (t) => {
   });
 });
 
+test("CorePlugin: nodejs_compat compatibiltiy flag includes Node.js modules", async (t) => {
+  const compat = new Compatibility(undefined, ["nodejs_compat"]);
+
+  const plugin = new CorePlugin(
+    { ...ctx, compat },
+    { compatibilityFlags: ["nodejs_compat"] }
+  );
+  const additionalModules = (await plugin.setup()).additionalModules;
+  t.deepEqual(
+    Object.keys(additionalModules?.["node:async_hooks"].default ?? {}),
+    ["AsyncLocalStorage", "AsyncResource"]
+  );
+});
+
 // Test stream constructors
 test("CorePlugin: setup: ReadableStream/WriteableStream constructors only enabled if compatibility flag enabled", async (t) => {
   // Check without "streams_enable_constructors" compatibility flag (should throw)

packages/shared/src/compat.ts

@@ -11,6 +11,7 @@ export interface CompatibilityFeature {
 // will get a type error if they try to use an unsupported flag via the API,
 // and they won't be logged in the "Enabled Compatibility Flags" section.
 export type CompatibilityEnableFlag =
+  | "nodejs_compat"
   | "streams_enable_constructors"
   | "transformstream_enable_standard_constructor"
   | "r2_list_honor_include"
@@ -31,6 +32,9 @@ export type CompatibilityFlag =
   | CompatibilityDisableFlag;
 
 const FEATURES: CompatibilityFeature[] = [
+  {
+    enableFlag: "nodejs_compat",
+  },
   {
     defaultAsOf: "2022-11-30",
     enableFlag: "streams_enable_constructors",