feat: support build without config file

packages/core/src/cli/initConfig.ts

@@ -2,7 +2,11 @@ import path from 'node:path';
 import util from 'node:util';
 import { loadEnv, type RsbuildEntry } from '@rsbuild/core';
 import { loadConfig } from '../config';
-import type { RsbuildConfigOutputTarget, RslibConfig } from '../types';
+import type {
+  LibConfig,
+  RsbuildConfigOutputTarget,
+  RslibConfig,
+} from '../types';
 import { getAbsolutePath } from '../utils/helper';
 import { logger } from '../utils/logger';
 import type { BuildOptions, CommonOptions } from './commands';
@@ -85,16 +89,16 @@ export const applyCliOptions = (
       lib.autoExtension = options.autoExtension;
     if (options.autoExternal !== undefined)
       lib.autoExternal = options.autoExternal;
-    const output = lib.output ?? {};
+    lib.output ??= {};
     if (options.target !== undefined)
-      output.target = options.target as RsbuildConfigOutputTarget;
-    if (options.minify !== undefined) output.minify = options.minify;
-    if (options.clean !== undefined) output.cleanDistPath = options.clean;
+      lib.output.target = options.target as RsbuildConfigOutputTarget;
+    if (options.minify !== undefined) lib.output.minify = options.minify;
+    if (options.clean !== undefined) lib.output.cleanDistPath = options.clean;
     const externals = options.externals?.filter(Boolean) ?? [];
-    if (externals.length > 0) output.externals = externals;
+    if (externals.length > 0) lib.output.externals = externals;
     if (options.distPath) {
-      output.distPath = {
-        ...(typeof output.distPath === 'object' ? output.distPath : {}),
+      lib.output.distPath = {
+        ...(typeof lib.output.distPath === 'object' ? lib.output.distPath : {}),
         root: options.distPath,
       };
     }
@@ -103,7 +107,7 @@ export const applyCliOptions = (
 
 export async function initConfig(options: CommonOptions): Promise<{
   config: RslibConfig;
-  configFilePath: string;
+  configFilePath?: string;
   watchFiles: string[];
 }> {
   const cwd = process.cwd();
@@ -122,6 +126,13 @@ export async function initConfig(options: CommonOptions): Promise<{
     loader: options.configLoader,
   });
 
+  if (configFilePath === undefined) {
+    config.lib = [{} satisfies LibConfig];
+    logger.debug(
+      'No config file found. Falling back to CLI options for the default library.',
+    );
+  }
+
   config.source ||= {};
   config.source.define = {
     ...envs.publicVars,
@@ -136,6 +147,6 @@ export async function initConfig(options: CommonOptions): Promise<{
   return {
     config,
     configFilePath,
-    watchFiles: [configFilePath, ...envs.filePaths],
+    watchFiles: [configFilePath, ...envs.filePaths].filter(Boolean) as string[],
   };
 }

packages/core/src/config.ts

@@ -99,7 +99,10 @@ const findConfig = (basePath: string): string | undefined => {
   );
 };
 
-const resolveConfigPath = (root: string, customConfig?: string): string => {
+const resolveConfigPath = (
+  root: string,
+  customConfig?: string,
+): string | undefined => {
   if (customConfig) {
     const customConfigPath = isAbsolute(customConfig)
       ? customConfig
@@ -115,8 +118,7 @@ const resolveConfigPath = (root: string, customConfig?: string): string => {
   if (configFilePath) {
     return configFilePath;
   }
-
-  throw new Error(`${DEFAULT_CONFIG_NAME} not found in ${root}`);
+  return undefined;
 };
 
 export type ConfigLoader = 'auto' | 'jiti' | 'native';
@@ -133,9 +135,17 @@ export async function loadConfig({
   loader?: ConfigLoader;
 }): Promise<{
   content: RslibConfig;
-  filePath: string;
+  filePath?: string;
 }> {
   const configFilePath = resolveConfigPath(cwd, path);
+  if (!configFilePath) {
+    return {
+      content: {
+        lib: [],
+      },
+      filePath: undefined,
+    };
+  }
   const { content } = await loadRsbuildConfig({
     cwd: dirname(configFilePath),
     path: configFilePath,

tests/integration/cli/build/build.test.ts

@@ -142,15 +142,22 @@ describe('build command', async () => {
     `);
   });
 
-  test('should throw error if config file is absent, but it should work if the future', async () => {
+  test('should build when config file is absent', async () => {
     const fixturePath = path.join(__dirname, 'no-config');
     await fse.remove(path.join(fixturePath, 'dist'));
 
-    expect(() =>
-      runCliSync('build --format cjs', {
-        cwd: fixturePath,
-      }),
-    ).toThrowError(/rslib\.config not found in.*cli[\\/]build[\\/]no-config/);
+    runCliSync('build --dist-path=dist/a --syntax=es2015', {
+      cwd: fixturePath,
+    });
+
+    const files = await globContentJSON(path.join(fixturePath, 'dist'));
+    expect(files).toMatchInlineSnapshot(`
+      {
+        "<ROOT>/tests/integration/cli/build/no-config/dist/a/index.js": "const withoutConfig = 1000;
+      export { withoutConfig };
+      ",
+      }
+    `);
   });
 
   test('build options', async () => {

tests/integration/cli/build/no-config/src/index.ts

@@ -1 +1 @@
-export const withoutConfig = 'works';
+export const withoutConfig = 1_000;

website/docs/en/guide/basic/cli.mdx

@@ -62,6 +62,10 @@ Options:
   --tsconfig <path>      use specific tsconfig (relative to project root)
 ```
 
+:::note
+If the project does not provide an `rslib.config.*` file, the CLI falls back to a default single [lib](/config/lib/) configuration and applies all build options from the command line. You can still specify `--config` later once you need more complex setups.
+:::
+
 ### Environment variables
 
 Rslib supports injecting environment variables or expressions into the code during the build, which is helpful for distinguishing running environments or replacing constants. You can see more details in [Rsbuild - Environment variables](https://rsbuild.rs/guide/advanced/env-vars).

website/docs/zh/guide/basic/cli.mdx

@@ -62,6 +62,10 @@ Options:
   --tsconfig <path>      使用指定的 tsconfig（相对于项目根目录）
 ```
 
+:::note
+如果项目中不存在 `rslib.config.*` 文件，CLI 会退回到仅包含单个 [lib](/config/lib/) 的默认配置，并按照命令行参数执行构建。一旦需要更复杂的配置或多库产物，再补充配置文件即可。
+:::
+
 ### 环境变量
 
 Rslib 支持在构建过程中向代码中注入环境变量或表达式，这对于区分运行环境、替换常量值等场景很有帮助。你可以查看 [Rsbuild - 环境变量](https://rsbuild.rs/zh/guide/advanced/env-vars) 了解更多详细信息。