fix(plugin-less): lessLoaderOptions.lessOptions.plugins has lose it's prototype.

packages/core/src/internal.ts

@@ -16,7 +16,12 @@ export {
 } from './config';
 export type { InternalContext } from './types';
 export { setHTMLPlugin, getHTMLPlugin } from './pluginHelper';
-export { formatStats, getStatsOptions, prettyTime } from './helpers';
+export {
+  formatStats,
+  getStatsOptions,
+  prettyTime,
+  isPlainObject,
+} from './helpers';
 export { registerBuildHook, registerDevHook, onCompileDone } from './hooks';
 export { getChainUtils, getConfigUtils } from './provider/rspackConfig';
 export { chainToConfig, modifyBundlerChain } from './configChain';

packages/plugin-less/src/index.ts

@@ -5,6 +5,7 @@ import type {
   RsbuildPlugin,
   Rspack,
 } from '@rsbuild/core';
+import { __internalHelper } from '@rsbuild/core';
 import deepmerge from 'deepmerge';
 import { reduceConfigsWithContext } from 'reduce-configs';
 
@@ -75,7 +76,9 @@ const getLessLoaderOptions = (
   ): LessLoaderOptions => {
     const getLessOptions = () => {
       if (defaults.lessOptions && userOptions.lessOptions) {
-        return deepmerge(defaults.lessOptions, userOptions.lessOptions);
+        return deepmerge(defaults.lessOptions, userOptions.lessOptions, {
+          isMergeableObject: __internalHelper.isPlainObject,
+        });
       }
       return userOptions.lessOptions || defaults.lessOptions;
     };

packages/plugin-less/tests/__snapshots__/index.test.ts.snap

@@ -168,6 +168,66 @@ exports[`plugin-less > should add less-loader with excludes 1`] = `
 ]
 `;
 
+exports[`plugin-less > should add less-loader with plugins 1`] = `
+[
+  {
+    "resolve": {
+      "preferRelative": true,
+    },
+    "sideEffects": true,
+    "test": /\\\\\\.less\\$/,
+    "use": [
+      {
+        "loader": "<ROOT>/node_modules/<PNPM_INNER>/@rspack/core/dist/cssExtractLoader.js",
+      },
+      {
+        "loader": "<ROOT>/packages/core/compiled/css-loader/index.js",
+        "options": {
+          "importLoaders": 2,
+          "modules": {
+            "auto": true,
+            "exportGlobals": false,
+            "exportLocalsConvention": "camelCase",
+            "localIdentName": "[path][name]__[local]-[hash:base64:6]",
+            "namedExport": false,
+          },
+          "sourceMap": false,
+        },
+      },
+      {
+        "loader": "builtin:lightningcss-loader",
+        "options": {
+          "targets": [
+            "chrome >= 87",
+            "edge >= 88",
+            "firefox >= 78",
+            "safari >= 14",
+          ],
+        },
+      },
+      {
+        "loader": "<ROOT>/packages/plugin-less/compiled/less-loader/index.js",
+        "options": {
+          "implementation": "<ROOT>/packages/plugin-less/compiled/less/index.js",
+          "lessOptions": {
+            "javascriptEnabled": true,
+            "paths": [
+              "<ROOT>/node_modules",
+            ],
+            "plugins": [
+              {
+                "options": undefined,
+              },
+            ],
+          },
+          "sourceMap": false,
+        },
+      },
+    ],
+  },
+]
+`;
+
 exports[`plugin-less > should add less-loader with tools.less 1`] = `
 [
   {

packages/plugin-less/tests/index.test.ts

@@ -63,4 +63,30 @@ describe('plugin-less', () => {
     const bundlerConfigs = await rsbuild.initConfigs();
     expect(matchRules(bundlerConfigs[0], 'a.less')).toMatchSnapshot();
   });
+
+  it('should add less-loader with plugins', async () => {
+    class MockPlugin {
+      options?: any;
+      constructor(options?: any) {
+        this.options = options;
+      }
+      install(less: any, pluginManager: any) {}
+    }
+    const mockPlugin = new MockPlugin();
+    const rsbuild = await createRsbuild({
+      rsbuildConfig: {
+        plugins: [
+          pluginLess({
+            lessLoaderOptions: {
+              lessOptions: {
+                plugins: [mockPlugin],
+              },
+            },
+          }),
+        ],
+      },
+    });
+    const bundlerConfigs = await rsbuild.initConfigs();
+    expect(matchRules(bundlerConfigs[0], 'a.less')).toMatchSnapshot();
+  });
 });