feat: Include background script in dev mode if user doesn't define one

src/core/build/__tests__/findEntrypoints.test.ts

@@ -210,10 +210,10 @@ describe('findEntrypoints', () => {
       },
     ],
   ])(
-    'should find and load content script entrypoint config from %s',
+    'should find and load background entrypoint config from %s',
     async (path, expected) => {
-      const options: ContentScriptEntrypoint['options'] = {
-        matches: ['<all_urls>'],
+      const options: BackgroundEntrypoint['options'] = {
+        type: 'module',
       };
       globMock.mockResolvedValueOnce([path]);
       importTsFileMock.mockResolvedValue(options);
@@ -226,6 +226,24 @@ describe('findEntrypoints', () => {
     },
   );
 
+  it("should include a virtual background script so dev reloading works when there isn't a background entrypoint defined by the user", async () => {
+    globMock.mockResolvedValueOnce([]);
+
+    const entrypoints = await findEntrypoints({
+      ...config,
+      command: 'serve',
+    });
+
+    expect(entrypoints).toHaveLength(1);
+    expect(entrypoints[0]).toEqual({
+      type: 'background',
+      inputPath: 'virtual:user-background',
+      name: 'background',
+      options: {},
+      outputDir: config.outDir,
+    });
+  });
+
   it.each<[string, GenericEntrypoint]>([
     // Sandbox
     [

src/core/build/findEntrypoints.ts

@@ -16,9 +16,10 @@ import JSON5 from 'json5';
 import { importTsFile } from '../utils/importTsFile';
 import glob from 'fast-glob';
 import { getEntrypointName } from '../utils/entrypoints';
+import { VIRTUAL_NOOP_BACKGROUND_MODULE_ID } from '../vite-plugins/noopBackground';
 
 /**
- * Return entrypoints and their configuration by looking through the
+ * Return entrypoints and their configuration by looking through the project's files.
  */
 export async function findEntrypoints(
   config: InternalConfig,
@@ -33,6 +34,7 @@ export async function findEntrypoints(
   const existingNames: Record<string, Entrypoint | undefined> = {};
 
   const entrypoints: Entrypoint[] = [];
+  let hasBackground = false;
   await Promise.all(
     relativePaths.map(async (relativePath) => {
       const path = resolve(config.entrypointsDir, relativePath);
@@ -63,6 +65,7 @@ export async function findEntrypoints(
           break;
         case 'background':
           entrypoint = await getBackgroundEntrypoint(config, path);
+          hasBackground = true;
           break;
         case 'content-script':
           entrypoint = await getContentScriptEntrypoint(
@@ -95,6 +98,11 @@ export async function findEntrypoints(
       existingNames[entrypoint.name] = entrypoint;
     }),
   );
+  if (config.command === 'serve' && !hasBackground) {
+    entrypoints.push(
+      await getBackgroundEntrypoint(config, VIRTUAL_NOOP_BACKGROUND_MODULE_ID),
+    );
+  }
   return entrypoints;
 }
 
@@ -195,10 +203,17 @@ async function getBackgroundEntrypoint(
   config: InternalConfig,
   path: string,
 ): Promise<BackgroundEntrypoint> {
-  const { main: _, ...options } =
-    await importTsFile<BackgroundScriptDefintition>(path, config);
-  if (options == null) {
-    throw Error('Background script does not have a default export');
+  let options: Omit<BackgroundScriptDefintition, 'main'> = {};
+  if (path !== VIRTUAL_NOOP_BACKGROUND_MODULE_ID) {
+    const defaultExport = await importTsFile<BackgroundScriptDefintition>(
+      path,
+      config,
+    );
+    if (defaultExport == null) {
+      throw Error('Background script does not have a default export');
+    }
+    const { main: _, ...moduleOptions } = defaultExport;
+    options = moduleOptions;
   }
   return {
     type: 'background',
@@ -257,6 +272,7 @@ const PATH_GLOB_TO_TYPE_MAP: Record<string, Entrypoint['type'] | 'ignored'> = {
   'devtools/index.html': 'devtools',
 
   'background.ts': 'background',
+  [VIRTUAL_NOOP_BACKGROUND_MODULE_ID]: 'background',
 
   'content.ts?(x)': 'content-script',
   'content/index.ts?(x)': 'content-script',

src/core/utils/getInternalConfig.ts

@@ -142,6 +142,7 @@ export async function getInternalConfig(
   );
   finalConfig.vite.plugins.push(plugins.devServerGlobals(finalConfig));
   finalConfig.vite.plugins.push(plugins.tsconfigPaths(finalConfig));
+  finalConfig.vite.plugins.push(plugins.noopBackground());
 
   finalConfig.vite.define ??= {};
   getGlobals(finalConfig).forEach((global) => {

src/core/vite-plugins/index.ts

@@ -5,3 +5,4 @@ export * from './multipageMove';
 export * from './unimport';
 export * from './virtualEntrypoint';
 export * from './tsconfigPaths';
+export * from './noopBackground';

src/core/vite-plugins/noopBackground.ts

@@ -0,0 +1,24 @@
+import { Plugin } from 'vite';
+
+/**
+ * In dev mode, if there's not a background script listed, we need to add one.
+ *
+ * This define's a virtual module that is basically just a noop.
+ */
+export function noopBackground(): Plugin {
+  const virtualModuleId = VIRTUAL_NOOP_BACKGROUND_MODULE_ID;
+  const resolvedVirtualModuleId = '\0' + virtualModuleId;
+  return {
+    name: 'wxt:noop-background',
+    resolveId(id) {
+      if (id === virtualModuleId) return resolvedVirtualModuleId;
+    },
+    load(id) {
+      if (id === resolvedVirtualModuleId) {
+        return `import { defineBackground } from 'wxt/client';\nexport default defineBackground(() => void 0)`;
+      }
+    },
+  };
+}
+
+export const VIRTUAL_NOOP_BACKGROUND_MODULE_ID = 'virtual:user-background';