feat: add override support

Author: edmundhung

packages/wrangler/e2e/create-server.test.ts

@@ -329,6 +329,103 @@ describe("createServer", { sequential: true }, () => {
 		});
 	});
 
+	it("overrides vars and secrets for config path workers", async ({
+		expect,
+	}) => {
+		await helper.seed({
+			"wrangler.jsonc": dedent`
+				{
+					"name": "var-overrides-worker",
+					"main": "src/index.ts",
+					"compatibility_date": "2026-05-20",
+					"vars": { "CONFIG_VAR": "from-config" },
+					"secrets": { "required": ["API_TOKEN", "SECRET_FROM_FILE"] }
+				}
+			`,
+			".dev.vars": dedent`
+				API_TOKEN=from-dev-vars
+				SECRET_FROM_FILE=from-dev-vars
+			`,
+			"src/index.ts": dedent`
+				export default {
+					fetch(request, env) {
+						return Response.json({
+							CONFIG_VAR: env.CONFIG_VAR,
+							API_TOKEN: env.API_TOKEN,
+							SECRET_FROM_FILE: env.SECRET_FROM_FILE,
+							ADDED_VAR: env.ADDED_VAR,
+							NULL_VAR: env.NULL_VAR,
+						});
+					}
+				};
+			`,
+		});
+
+		const server = createServer({
+			root: helper.tmpPath,
+			workers: [
+				{
+					configPath: "./wrangler.jsonc",
+					overrides: {
+						vars: {
+							CONFIG_VAR: "from-override",
+							ADDED_VAR: "from-override",
+							NULL_VAR: null,
+						},
+						secrets: {
+							API_TOKEN: "from-override",
+						},
+					},
+				},
+			],
+		});
+		onTestFinished(server.close);
+
+		await server.listen();
+
+		const response = await server.fetch("/");
+		await expect(response.json()).resolves.toEqual({
+			CONFIG_VAR: "from-override",
+			API_TOKEN: "from-override",
+			SECRET_FROM_FILE: "from-dev-vars",
+			ADDED_VAR: "from-override",
+			NULL_VAR: null,
+		});
+	});
+
+	it(`supports "nodejs_compat" flag`, async ({ expect }) => {
+		await helper.seed({
+			"wrangler.jsonc": dedent`
+				{
+					"name": "nodejs-compat-worker",
+					"main": "src/index.ts",
+					"compatibility_date": "2026-05-20",
+					"compatibility_flags": ["nodejs_compat"]
+				}
+			`,
+			"src/index.ts": dedent`
+				import { Stream } from "node:stream";
+
+				export default {
+					fetch() {
+						return new Response(String(typeof Stream));
+					}
+				};
+			`,
+		});
+
+		const server = createServer({
+			root: helper.tmpPath,
+			workers: [{ configPath: "./wrangler.jsonc" }],
+		});
+		onTestFinished(server.close);
+
+		await server.listen();
+
+		const response = await server.fetch("/");
+		await expect(response.text()).resolves.toBe("function");
+	});
+
 	it("supports Workers Sites", async ({ expect }) => {
 		await helper.seed({
 			"public/hello.txt": "Hello from Workers Sites",

packages/wrangler/src/api/server.ts

@@ -25,15 +25,21 @@ import type {
 	FetcherScheduledResult,
 } from "@cloudflare/workers-types/experimental";
 import type { Config, RawConfig } from "@cloudflare/workers-utils";
-import type { DispatchFetch, RequestInfo } from "miniflare";
+import type { DispatchFetch, Json, RequestInfo } from "miniflare";
 
 export type InlineConfig = Omit<RawConfig, "env">;
 
+export type ConfigOverrides = {
+	vars?: Record<string, Json>;
+	secrets?: Record<string, string>;
+};
+
 export type WorkerInput =
 	| {
 			root?: string;
 			configPath: string | URL;
 			env?: string;
+			overrides?: ConfigOverrides;
 	  }
 	| {
 			root?: string;
@@ -166,6 +172,15 @@ function resolveWorkerInputs(
 			"config" in input
 				? normalizeInlineWorkerConfig(input.config, root)
 				: undefined;
+		const overrides = "configPath" in input ? input.overrides : undefined;
+		const bindings = convertConfigToBindings(
+			inlineConfig ?? { vars: overrides?.vars },
+			{ usePreviewIds: true }
+		);
+
+		for (const [key, value] of Object.entries(overrides?.secrets ?? {})) {
+			bindings[key] = { type: "secret_text", value };
+		}
 
 		return {
 			// Uses an empty string to avoid dev env from auto discovering a config file and merging it with the inline config
@@ -177,9 +192,7 @@ function resolveWorkerInputs(
 			compatibilityFlags: inlineConfig?.compatibility_flags,
 			complianceRegion: inlineConfig?.compliance_region,
 			pythonModules: inlineConfig?.python_modules,
-			bindings: inlineConfig
-				? convertConfigToBindings(inlineConfig, { usePreviewIds: true })
-				: undefined,
+			bindings,
 			migrations: inlineConfig?.migrations,
 			containers: inlineConfig?.containers,
 			triggers: inlineConfig?.triggers?.crons?.map((cron) => ({

packages/wrangler/src/dev.ts

@@ -525,13 +525,21 @@ export function getBindings(
 	// getVarsForDev returns typed bindings: config vars are plain_text/json,
 	// while .dev.vars/.env vars are secret_text.
 	// When secrets is defined, only declared secret keys are loaded from files.
+	const secrets = configParam.secrets
+		? {
+				...configParam.secrets,
+				required: configParam.secrets?.required?.filter(
+					(secret) => inputBindings?.[secret]?.type !== "secret_text"
+				),
+			}
+		: undefined;
 	const vars = getVarsForDev(
 		configParam.userConfigPath,
 		envFiles,
 		configParam.vars,
 		env,
 		false,
-		configParam.secrets
+		secrets
 	);
 	for (const [name, binding] of Object.entries(vars)) {
 		// Only override plain_text/json/secret_text vars, not other binding types like kv_namespace