perf: skip assets traversal if source map is disabled (#6457)

Author: chenjiahan

e2e/cases/source-map/multi-environments/index.test.ts

@@ -1,3 +1,5 @@
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
 import { expect, findFile, rspackTest } from '@e2e/helper';
 
 rspackTest(
@@ -12,12 +14,16 @@ rspackTest(
         path.includes('static/js/index.js.map') && !path.includes('web2'),
     );
     const web2JsMapPath = findFile(files, 'web2/static/js/index.js.map');
+    const sourceContent = readFileSync(
+      join(__dirname, './src/index.js'),
+      'utf-8',
+    );
 
     expect(JSON.parse(files[web1JsMapPath])).toEqual({
       version: 3,
       file: 'static/js/index.js',
       sources: ['../../../src/index.js'],
-      sourcesContent: ["console.log('hello');\n"],
+      sourcesContent: [sourceContent],
       names: ['console'],
       // cspell:disable-next-line
       mappings: 'AAAAA,QAAQ,GAAG,CAAC',
@@ -26,7 +32,7 @@ rspackTest(
       version: 3,
       file: 'static/js/index.js',
       sources: ['../../../../../src/index.js'],
-      sourcesContent: ["console.log('hello');\n"],
+      sourcesContent: [sourceContent],
       names: ['console'],
       // cspell:disable-next-line
       mappings: 'AAAAA,QAAQ,GAAG,CAAC',

packages/core/src/plugins/sourceMap.ts

@@ -32,6 +32,11 @@ export const pluginSourceMap = (): RsbuildPlugin => ({
       absoluteResourcePath: string;
     }) => absoluteResourcePath;
 
+    const enableCssSourceMap = (config: NormalizedEnvironmentConfig) => {
+      const { sourceMap } = config.output;
+      return typeof sourceMap === 'object' && sourceMap.css;
+    };
+
     api.modifyBundlerChain((chain, { bundler, environment }) => {
       const { config } = environment;
       const devtool = getDevtool(config);
@@ -42,8 +47,7 @@ export const pluginSourceMap = (): RsbuildPlugin => ({
 
       // When JS source map is disabled, but CSS source map is enabled,
       // add `SourceMapDevToolPlugin` to let Rspack generate CSS source map.
-      const { sourceMap } = config.output;
-      if (!devtool && typeof sourceMap === 'object' && sourceMap.css) {
+      if (!devtool && enableCssSourceMap(config)) {
         chain.plugin('source-map-css').use(bundler.SourceMapDevToolPlugin, [
           {
             test: /\.css$/,
@@ -61,6 +65,14 @@ export const pluginSourceMap = (): RsbuildPlugin => ({
       // Source maps has been extracted to separate files on this stage
       { stage: 'optimize-transfer' },
       ({ assets, compilation, sources, environment }) => {
+        // If source map is disabled, skip the processing.
+        if (
+          !compilation.options.devtool &&
+          !enableCssSourceMap(environment.config)
+        ) {
+          return;
+        }
+
         // If devtoolModuleFilenameTemplate is not the default template,
         // which means users want to customize it, skip the default processing.
         if (