fix: handle undefined values in mergeRsbuildConfig

Author: chenjiahan

packages/core/src/mergeConfig.ts

@@ -119,19 +119,22 @@ const normalizeConfigStructure = <T = RsbuildConfig>(config: T): T => {
 };
 
 export const mergeRsbuildConfig = <T = RsbuildConfig>(
-  ...originalConfigs: T[]
+  ...originalConfigs: (T | undefined)[]
 ): T => {
-  const configs = originalConfigs.map(normalizeConfigStructure);
+  const configs = originalConfigs
+    .filter((config) => config !== undefined)
+    .map(normalizeConfigStructure);
 
   // In most cases there will be two configs so we perform this check first
   if (configs.length === 2) {
     return merge(configs[0], configs[1]) as T;
   }
-
-  if (configs.length < 2) {
+  if (configs.length === 1) {
     return configs[0];
   }
-
+  if (configs.length === 0) {
+    return {} as T;
+  }
   return configs.reduce(
     (result, config) => merge(result, config) as T,
     {} as T,

packages/core/tests/mergeConfig.test.ts

@@ -489,4 +489,36 @@ describe('mergeRsbuildConfig', () => {
       },
     });
   });
+
+  it('should accept `undefined` value', () => {
+    const config: RsbuildConfig = {
+      source: {
+        entry: {
+          index: 'src/index.ts',
+        },
+      },
+    };
+
+    expect(mergeRsbuildConfig(config, undefined)).toEqual(config);
+    expect(mergeRsbuildConfig(undefined, config)).toEqual(config);
+    expect(
+      mergeRsbuildConfig(undefined, config, {
+        source: {
+          entry: {
+            index2: 'src/index2.ts',
+          },
+        },
+      }),
+    ).toEqual({
+      source: {
+        entry: {
+          index: 'src/index.ts',
+          index2: 'src/index2.ts',
+        },
+      },
+    });
+    expect(mergeRsbuildConfig(undefined, undefined, undefined)).toEqual(
+      undefined,
+    );
+  });
 });

website/docs/en/api/javascript-api/core.mdx

@@ -316,7 +316,9 @@ The `mergeRsbuildConfig` function takes multiple configuration objects as parame
 - **Type:**
 
 ```ts
-function mergeRsbuildConfig(...configs: RsbuildConfig[]): RsbuildConfig;
+function mergeRsbuildConfig(
+  ...configs: (RsbuildConfig | undefined)[]
+): RsbuildConfig;
 ```
 
 ### Basic example

website/docs/zh/api/javascript-api/core.mdx

@@ -316,7 +316,9 @@ loadEnv({ processEnv: { ...process.env } });
 - **类型：**
 
 ```ts
-function mergeRsbuildConfig(...configs: RsbuildConfig[]): RsbuildConfig;
+function mergeRsbuildConfig(
+  ...configs: (RsbuildConfig | undefined)[]
+): RsbuildConfig;
 ```
 
 ### 基础示例