fix: port webpack fix for __webpack_module__ name collision by Copilot · Pull Request #12956 · web-infra-dev/rspack

Copilot · 2026-02-05T09:28:50Z

Ports webpack fix from PR #20265 to resolve name collision when user code declares module at top level while using __webpack_module__.id or __webpack_module__.

Problem:

console.log(__webpack_module__.id);
const module = 'layout';  // Collision: SyntaxError in generated code

Generated code creates illegal redeclaration:

((module) => {
  console.log(module.id);
  const module = 'layout';  // SyntaxError: Identifier 'module' has already been declared
})

Changes:

Detection: Added pre_declarator and pre_statement hooks in APIPlugin to detect top-level declarations of module (variable, function, or class)
Switching: Set module_argument to RspackModule when collision detected, changing parameter name from module to __webpack_module__
Template update: Modified ModuleArgumentDependency to emit init fragments with internal variables (__webpack_internal_module_id__, __webpack_internal_module__) when collision occurs
Core: Added PartialEq + Eq traits to ModuleArgument enum

Fixed output:

((__webpack_module__) => {
  var __webpack_internal_module_id__ = __webpack_module__.id;
  console.log(__webpack_internal_module_id__);
  const module = 'layout';  // No collision
})

Upstream reference: webpack/webpack#20265

Original prompt

This section details on the original issue you should resolve

<issue_title>[Bug]: fix: port webpack fix for issue #20264 (PR #20265)</issue_title>
<issue_description>### Description

We need to port a bug fix from Webpack to Rspack.

Upstream Context:

Webpack Issue: __webpack_module__ is rewritten to module, causing identifier collision with user-defined const module webpack/webpack#20264

Webpack PR (The Fix): refactor: avoid module variable conflict in __webpack_module__ API webpack/webpack#20265

Task:
Please analyze the logic changes in the Webpack JS implementation and apply the equivalent logic to Rspack's Rust implementation.

Goal:
Ensure the Rspack implementation handles the path resolution logic correctly as per the upstream fix.

Context for Copilot

Source language: JavaScript (Webpack)

Target language: Rust (Rspack)

Please be careful with Rust types and Path handling.
</issue_description>

<agent_instructions>I need to port logic from an external source. The reference logic is in this Webpack PR: webpack/webpack#20265. Please replicate this logic in the corresponding Rust files in this workspace.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes [Bug]: fix: port webpack fix for issue #20264 (PR #20265) #12955

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

- Add PartialEq, Eq to ModuleArgument enum - Implement pre_declarator hook to detect 'module' variable declarations - Implement pre_statement hook to detect 'module' function/class declarations - Update ModuleArgumentDependency template to use internal variables when collision detected - Add test cases for collision scenarios Co-authored-by: SyMind <19852293+SyMind@users.noreply.github.com>

Use fixed names for internal variables to match webpack's approach: - __webpack_internal_module_id__ for .id property - __webpack_internal_module_loaded__ for .loaded property - __webpack_internal_module__ for module itself Co-authored-by: SyMind <19852293+SyMind@users.noreply.github.com>

Copilot

Pull request overview

This PR ports a bug fix from webpack (PR #20265) to resolve name collision issues when user code declares a variable, function, or class named module at the top level while also using __webpack_module__.id or __webpack_module__. The fix prevents SyntaxError from illegal redeclarations in the generated code.

Changes:

Added collision detection for top-level module declarations using parser plugin hooks
Modified code generation to use internal variables when collisions are detected
Added PartialEq and Eq traits to ModuleArgument enum for comparison

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
`crates/rspack_core/src/module.rs`	Added `PartialEq` and `Eq` traits to `ModuleArgument` enum to enable comparison in collision detection logic
`crates/rspack_plugin_javascript/src/parser_plugin/api_plugin.rs`	Implemented `pre_declarator` and `pre_statement` hooks to detect top-level declarations of `module` and set `module_argument` to `RspackModule` when collision detected
`crates/rspack_plugin_javascript/src/dependency/module_argument_dependency.rs`	Modified template to emit init fragments with internal variables (`__webpack_internal_module_id__`, `__webpack_internal_module__`) when collision occurs, avoiding redeclaration errors
`tests/rspack-test/normalCases/parsing/webpack-module-collision/with-var-collision.js`	Test case for variable declaration collision with `__webpack_module__.id`
`tests/rspack-test/normalCases/parsing/webpack-module-collision/with-function-collision.js`	Test case for function declaration collision with `__webpack_module__.id`
`tests/rspack-test/normalCases/parsing/webpack-module-collision/with-class-collision.js`	Test case for class declaration collision with `__webpack_module__.id`
`tests/rspack-test/normalCases/parsing/webpack-module-collision/with-module-var-collision.js`	Test case for variable declaration collision with `__webpack_module__`
`tests/rspack-test/normalCases/parsing/webpack-module-collision/index.js`	Test suite with assertions verifying correct handling of all collision scenarios

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github-actions · 2026-02-06T04:10:44Z

📦 Binary Size-limit

Comparing 4585d68 to refactor: rename derefOption to stealCell and migrate atomicRefCell to Stealcell (#12974) by hardfist

❌ Size increased by 256bytes from 48.59MB to 48.59MB (⬆️0.00%)

github-actions · 2026-02-06T04:11:08Z

Rsdoctor Bundle Diff Analysis

Found 5 projects in monorepo, 5 projects with changes.

📊 Quick Summary

Project	Total Size	Change
react-10k	5.7 MB	-
react-1k	825.4 KB	-
react-5k	2.7 MB	-
ui-components	2.2 MB	-
rome	984.2 KB	-

📋 Detailed Reports (Click to expand)

📁 react-10k

Path: ../build-tools-performance/cases/react-10k/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	5.7 MB	-	-
📄 JavaScript	5.7 MB	-	-
🎨 CSS	21.0 B	-	-
🌐 HTML	0 B	-	-
📁 Other Assets	0 B	-	-

📁 react-1k

Path: ../build-tools-performance/cases/react-1k/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	825.4 KB	-	-
📄 JavaScript	825.4 KB	-	-
🎨 CSS	0 B	-	-
🌐 HTML	0 B	-	-
📁 Other Assets	0 B	-	-

📁 react-5k

Path: ../build-tools-performance/cases/react-5k/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	2.7 MB	-	-
📄 JavaScript	2.7 MB	-	-
🎨 CSS	21.0 B	-	-
🌐 HTML	0 B	-	-
📁 Other Assets	0 B	-	-

📁 ui-components

Path: ../build-tools-performance/cases/ui-components/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	2.2 MB	-	-
📄 JavaScript	2.0 MB	-	-
🎨 CSS	267.8 KB	-	-
🌐 HTML	0 B	-	-
📁 Other Assets	0 B	-	-

📁 rome

Path: ../build-tools-performance/cases/rome/dist/rsdoctor-data.json

⚠️ No baseline data found - Unable to perform comparison analysis

Metric	Current	Baseline	Change
📊 Total Size	984.2 KB	-	-
📄 JavaScript	984.2 KB	-	-
🎨 CSS	0 B	-	-
🌐 HTML	0 B	-	-
📁 Other Assets	0 B	-	-

Generated by Rsdoctor GitHub Action

codspeed-hq · 2026-02-06T04:24:28Z

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing copilot/port-webpack-fix-to-rspark (4585d68) with main (aed1ab4)¹}

Summary

✅ 16 untouched benchmarks
⏩ 1 skipped benchmark²

No successful run was found on main (3576494) during the generation of this report, so aed1ab4 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩
1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

cloudflare-workers-and-pages · 2026-02-06T07:44:11Z

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* Initial plan * feat: port webpack fix for __webpack_module__ name collision - Implement pre_declarator hook to detect 'module' variable declarations - Implement pre_statement hook to detect 'module' function/class declarations - Add test cases for collision scenarios Co-authored-by: SyMind <19852293+SyMind@users.noreply.github.com> * fix: use fixed internal variable names for consistency Co-authored-by: SyMind <19852293+SyMind@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: SyMind <19852293+SyMind@users.noreply.github.com> Co-authored-by: Cong-Cong <dacongsama@live.com>

…12988) fix: port webpack fix for __webpack_module__ name collision (#12956) * Initial plan * feat: port webpack fix for __webpack_module__ name collision - Implement pre_declarator hook to detect 'module' variable declarations - Implement pre_statement hook to detect 'module' function/class declarations - Add test cases for collision scenarios * fix: use fixed internal variable names for consistency --------- Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com> Co-authored-by: SyMind <19852293+SyMind@users.noreply.github.com>

Initial plan

aa52a04

Copilot AI assigned Copilot and SyMind Feb 5, 2026

Copilot started work on behalf of SyMind February 5, 2026 09:29 View session

Copilot AI and others added 2 commits February 5, 2026 09:39

Copilot AI changed the title ~~[WIP] Port Webpack bug fix for path resolution to Rspack~~ fix: port webpack fix for __webpack_module__ name collision Feb 5, 2026

Copilot AI requested a review from SyMind February 5, 2026 09:56

Copilot finished work on behalf of SyMind February 5, 2026 09:56

SyMind marked this pull request as ready for review February 6, 2026 03:52

Copilot AI review requested due to automatic review settings February 6, 2026 03:52

Copilot started reviewing on behalf of SyMind February 6, 2026 03:53 View session

github-actions bot added the release: bug fix release: bug related release(mr only) label Feb 6, 2026

Copilot AI reviewed Feb 6, 2026

View reviewed changes

SyMind added 2 commits February 6, 2026 12:49

fix cargo clippy

b906846

Merge branch 'main' into copilot/port-webpack-fix-to-rspark

eb16bf9

SyMind added 2 commits February 8, 2026 11:36

Merge branch 'main' into copilot/port-webpack-fix-to-rspark

5f60191

fix: e2e test failed

4585d68

SyMind force-pushed the copilot/port-webpack-fix-to-rspark branch from f20f6c1 to 4585d68 Compare February 9, 2026 04:01

JSerFeng approved these changes Feb 9, 2026

View reviewed changes

SyMind merged commit 5e3f3b2 into main Feb 9, 2026
49 checks passed

SyMind deleted the copilot/port-webpack-fix-to-rspark branch February 9, 2026 05:07

SyMind mentioned this pull request Feb 9, 2026

fix: port webpack fix for __webpack_module__ name collision for v1.x #12988

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fix: port webpack fix for __webpack_module__ name collision#12956

fix: port webpack fix for __webpack_module__ name collision#12956
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