fix(theme/eject): allow treeshaking manually the theme/index file #2895

SoonIter · 2025-12-15T12:52:54Z

Summary

If we craft a manual export * treeshaking optimizer, it can tackle both the bundle size problem and the prior issue where CSS couldn't be treeshaken effectively.

// before

// theme/index.tsx
const Search = () => {
  return <MySearch />
}

export * from '@rspress/core/theme-original';  // @rspress/core/theme-original contains { Search, Button, Banner }
export { Search }

// after
Got export * to export { Search, Button, Banner }, optimized to the following file

// theme/index.tsx
const Search = () => {
  return <MySearch />
}

export { /* Search */ , Button, Banner } from '@rspress/core/theme-original'; // unfold
export { Search }

Related Issue

Checklist

Tests updated (or not required).
Documentation updated (or not required).

netlify · 2025-12-15T12:53:00Z

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github-actions · 2025-12-15T12:55:13Z

Rsdoctor Bundle Diff Analysis

📁 web

Path: website/doc_build/web/rsdoctor-data.json

📌 Baseline Commit: 6b800772c9 | PR: #2880

Metric	Current	Baseline	Change
📊 Total Size	14.6 MB	14.6 MB	5.4 KB (0.0%)
📄 JavaScript	14.0 MB	14.0 MB	5.6 KB (0.0%)
🎨 CSS	113.5 KB	113.7 KB	-206.0 B (-0.2%)
🌐 HTML	0 B	0 B	N/A
📁 Other Assets	480.4 KB	480.4 KB	0 B (0.0%)

📦 Download Diff Report: web Bundle Diff

Generated by Rsdoctor GitHub Action

Copilot

Pull request overview

This PR introduces an export star optimizer that transforms export * statements into explicit named exports to enable better tree-shaking. The optimizer uses regex-based parsing to identify all exports from referenced modules and replaces wildcard exports with explicit export lists, excluding locally-defined exports to avoid conflicts.

Implements an AST-like transformation using regex patterns to parse and transform export statements
Adds a webpack/rspack loader that applies the optimization to theme index files during build
Includes test coverage using memfs for file system mocking

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 21 comments.

Show a summary per file

File	Description
packages/core/src/node/theme/loader.ts	Implements the rspack loader that applies the export star optimization transform
packages/core/src/node/theme/exportStarOptimizerTransform.ts	Core transformation logic that parses exports and replaces `export *` with named exports
packages/core/src/node/theme/exportStarOptimizerTransform.test.ts	Test suite covering basic transformation scenarios using memfs
packages/core/src/node/initRsbuild.ts	Integrates the loader into the build pipeline for theme index files
packages/core/rslib.config.ts	Applies the optimizer during library build and adds loader entry point

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Copilot · 2025-12-15T13:00:24Z

packages/core/src/node/initRsbuild.ts

+          sideEffects: false,
+        });
+        themeIndexRule
+          .use('EXPORT_STAR_OPTIMIZE')


The loader use name 'EXPORT_STAR_OPTIMIZE' is in SCREAMING_SNAKE_CASE while other loaders in the codebase typically use descriptive strings in kebab-case or regular naming. Consider using a more conventional name like 'export-star-optimizer' for consistency.

Suggested change

.use('EXPORT_STAR_OPTIMIZE')

.use('export-star-optimizer')

Copilot · 2025-12-15T13:00:25Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+      const varExportRegex = /export\s+(?:const|let|var)\s+(\w+)/g;
+      let match: RegExpExecArray | null;
+      while ((match = varExportRegex.exec(cleanCode)) !== null) {
+        exports.add(match[1]);


The same regex bug exists in getModuleExports: /export\s+(?:const|let|var)\s+(\w+)/g only captures the first variable in multi-variable declarations like 'export const a = 1, b = 2;'. This inconsistency with parseLocalExports should be fixed to handle comma-separated declarations.

Suggested change

const varExportRegex = /export\s+(?:const|let|var)\s+(\w+)/g;

let match: RegExpExecArray | null;

while ((match = varExportRegex.exec(cleanCode)) !== null) {

exports.add(match[1]);

const varExportRegex = /export\s+(?:const|let|var)\s+([^;]+)/g;

let match: RegExpExecArray | null;

while ((match = varExportRegex.exec(cleanCode)) !== null) {

// match[1] contains the full variable declaration list, e.g. "a = 1, b = 2"

const varList = match[1];

// Split by commas not inside brackets (to avoid destructuring confusion)

varList.split(',').forEach(decl => {

// Remove any default value assignment and destructuring

// Only match simple variable names (skip destructuring for now)

const nameMatch = /^\s*([a-zA-Z_$][\w$]*)/.exec(decl.trim());

if (nameMatch) {

exports.add(nameMatch[1]);

}

});

Copilot · 2025-12-15T13:00:25Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+        // Handle `name as alias`.
+        const parts = n.trim().split(/\s+as\s+/);
+        return parts[parts.length - 1].trim();
+      });


The parsing logic for 'export { name as alias }' is incorrect. When splitting by 'as', parts[parts.length - 1] gets the alias (exported name), but for local exports in the parseLocalExports method, we should track the alias, not the original name. However, this logic seems backwards - it should store the exported name (after 'as'), which is correct. But the logic for adding names from lines 49 doesn't properly validate empty strings after trim(), which could add empty entries to localExports if there are trailing commas or extra spaces.

Suggested change

});

}).filter(name => name.length > 0);

Copilot · 2025-12-15T13:00:25Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+    while ((match = exportStarRegex.exec(code)) !== null) {
+      const fullMatch = match[0];
+      const source = match[1];
+      const startIndex = match.index;
+      const endIndex = startIndex + fullMatch.length;
+
+      // Get exports of the target module.
+      const moduleExports = await this.getModuleExports(source);


Each 'export *' statement triggers an async module resolution and file read operation in getModuleExports. If a file has multiple 'export *' statements referencing the same module, this module will be resolved and read multiple times. Consider caching the results of getModuleExports by module path to avoid redundant I/O operations.

Suggested change

while ((match = exportStarRegex.exec(code)) !== null) {

const fullMatch = match[0];

const source = match[1];

const startIndex = match.index;

const endIndex = startIndex + fullMatch.length;

// Get exports of the target module.

const moduleExports = await this.getModuleExports(source);

// Cache to avoid redundant module resolution and file reads.

const moduleExportsCache = new Map<string, Set<string>>();

while ((match = exportStarRegex.exec(code)) !== null) {

const fullMatch = match[0];

const source = match[1];

const startIndex = match.index;

const endIndex = startIndex + fullMatch.length;

// Get exports of the target module, using cache if available.

let moduleExports: Set<string>;

if (moduleExportsCache.has(source)) {

moduleExports = moduleExportsCache.get(source)!;

} else {

moduleExports = await this.getModuleExports(source);

moduleExportsCache.set(source, moduleExports);

}

Copilot · 2025-12-15T13:00:26Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+   * Parse source code to collect local exports.
+   */
+  parseLocalExports(code: string): void {
+    // 移除注释


Chinese comment in code. Consider translating to English for consistency with the rest of the codebase. The comment reads "移除注释" which means "Remove comments".

Suggested change

// 移除注释

// Remove comments

Copilot · 2025-12-15T13:00:29Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+    const resolver = new rspack.experiments.resolver.ResolverFactory({
+      extensions: ['.ts', '.tsx', '.mjs', '.js', '.jsx', '.json'],
+      mainFiles: ['index'],
+      mainFields: ['module', 'browser', 'main'],
+      alias: {},
+    });


A new ResolverFactory instance is created on every call to getModuleExports. This is inefficient, especially when processing multiple 'export *' statements. Consider creating the resolver once (e.g., in the constructor or as a class property) and reusing it across all resolutions, similar to the pattern used in flattenMdxContent.ts and reactAlias.ts in this codebase.

Copilot · 2025-12-15T13:00:29Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+   */
+  removeComments(code: string): string {
+    // 移除单行注释
+    code = code.replace(/\/\/.*$/gm, '');


The regex for removing single-line comments will incorrectly remove URLs and strings that contain '//', such as 'https://example.com' or strings like 'const url = "http://foo"'. This could corrupt valid code. Consider using a more robust comment removal approach that respects string literals and template literals, or use a proper AST-based parser.

Copilot · 2025-12-15T13:00:30Z

packages/core/rslib.config.ts

+          setup(api) {
+            api.transform(
+              { test: /src\/theme\/index\.ts/ },
+              ({ code, resourcePath }) => {


The transform function is defined inline as an async function but is not explicitly marked as async in the api.transform call. This could lead to issues if the transform is expected to return a Promise. Ensure the transform callback properly handles the async nature of exportStarOptimizerTransform by either using async/await or returning the Promise.

Suggested change

({ code, resourcePath }) => {

async ({ code, resourcePath }) => {

Copilot · 2025-12-15T13:00:30Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error);
+      console.warn(`无法解析模块 ${modulePath}: ${message}`);
+      return new Set();
+    }


When module resolution fails, the method returns an empty Set and only logs a warning. This silently causes the 'export *' statement to be replaced with nothing, which changes the semantic behavior of the code. If a module genuinely exists but fails to resolve, this could break the application. Consider either preserving the original 'export *' statement on resolution failure, or making the error more visible (e.g., throwing an error in non-production builds).

Copilot · 2025-12-15T13:00:30Z

packages/core/src/node/theme/exportStarOptimizerTransform.ts

+  removeComments(code: string): string {
+    // 移除单行注释
+    code = code.replace(/\/\/.*$/gm, '');
+    // 移除多行注释


Chinese comment in code. Consider translating to English for consistency. The comment reads "移除多行注释" which means "Remove multi-line comments".

Suggested change

// 移除多行注释

// Remove multi-line comments

Copilot AI review requested due to automatic review settings December 15, 2025 12:52

github-actions bot added the change: fix label Dec 15, 2025

Copilot started reviewing on behalf of SoonIter December 15, 2025 12:53 View session

Copilot AI reviewed Dec 15, 2025

View reviewed changes

chore: update

8b7a410

SoonIter force-pushed the syt/loader-polish branch from 2c4dbb6 to 8b7a410 Compare December 15, 2025 13:11

SoonIter added 4 commits December 15, 2025 21:22

chore: update

53aa4ec

chore: update

c416faf

chore: update

0e1ce27

chore: update

84f8aca

-      const varExportRegex = /export\s+(?:const|let|var)\s+(\w+)/g;
-      let match: RegExpExecArray | null;
-      while ((match = varExportRegex.exec(cleanCode)) !== null) {
-        exports.add(match[1]);
+      const varExportRegex = /export\s+(?:const|let|var)\s+([^;]+)/g;
+      let match: RegExpExecArray | null;
+      while ((match = varExportRegex.exec(cleanCode)) !== null) {
+        // match[1] contains the full variable declaration list, e.g. "a = 1, b = 2"
+        const varList = match[1];
+        // Split by commas not inside brackets (to avoid destructuring confusion)
+        varList.split(',').forEach(decl => {
+          // Remove any default value assignment and destructuring
+          // Only match simple variable names (skip destructuring for now)
+          const nameMatch = /^\s*([a-zA-Z_$][\w$]*)/.exec(decl.trim());
+          if (nameMatch) {
+            exports.add(nameMatch[1]);
+          }
+        });

	({ code, resourcePath }) => {
	async ({ code, resourcePath }) => {

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fix(theme/eject): allow treeshaking manually the theme/index file #2895

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SoonIter commented Dec 15, 2025 •

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