fix(bundler): avoid shadowed __dirname in import.meta patch

[killagu]

Summary

• Avoid reading __dirname inside the generated Turbopack import.meta replacement.
• Derive patched import.meta.dirname from the resolved filename instead, so later generated lexical const __dirname declarations cannot trigger TDZ.
• Add an integration regression covering a patched chunk that declares const __dirname after the import.meta object.

Root Cause

The post-pack import.meta patch emitted typeof __dirname === "string" ? __dirname : ....
In cnpmcore's generated root chunk, Turbopack also emits a later const __dirname = ... in the same module scope. That lexical declaration shadows CommonJS __dirname for the whole scope, so even typeof __dirname throws ReferenceError: Cannot access __dirname before initialization before the later declaration runs.

This is a general shadowed-lexical-binding issue in Egg's import.meta output patch, not cnpmcore-specific application code.

Verification

• pnpm vitest run test/integration.test.ts from tools/egg-bundler
• pnpm --filter @eggjs/egg-bundler typecheck
• pnpm --filter @eggjs/egg-bundler lint
• pnpm --filter @eggjs/egg-bundler test
• cnpmcore 971784993927 local reproduction with egg@4.1.2-beta.9 dependencies:
  • bundle via local built egg-bundler plus app-level supports-color alias completed and produced dist-bundle-tdz-fix/worker.js
  • timeout 20s node dist-bundle-tdz-fix/worker.js no longer hit the __dirname TDZ blocker
  • new first runtime blocker is Cannot find native binding for @cnpmjs/packument-linux-x64-gnu / packument.linux-x64-gnu.node

Summary by CodeRabbit

• Bug Fixes

  • Fixed bundled outputs so import metadata derives the directory from the computed filename, ensuring correct behavior when a module-local dirname is present.

• Tests

  • Updated and added integration tests to verify bundler behavior when dirname is shadowed and when patching import metadata.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 2a1c7ec0-4b1a-4ef5-b610-48deb170e824

📥 Commits

Reviewing files that changed from the base of the PR and between ba21354 and ca921a6.

📒 Files selected for processing (2)

• tools/egg-bundler/src/lib/Bundler.ts
• tools/egg-bundler/test/integration.test.ts

🚧 Files skipped from review as they are similar to previous changes (2)

• tools/egg-bundler/src/lib/Bundler.ts
• tools/egg-bundler/test/integration.test.ts

---

📝 Walkthrough

Walkthrough

The bundler now generates import.meta.dirname purely from the computed filename (by locating the last '/' or '' and applying slicing rules including drive-letter/root edge cases), removing any conditional runtime fallback to __dirname; import.meta.filename and url remain filename-based.

Changes

Import.meta dirname calculation

Layer / File(s)	Summary
Core Implementation tools/egg-bundler/src/lib/Bundler.ts	#renderImportMetaObject() stops emitting a typeof __dirname === "string" ? __dirname : ... fallback and instead inlines a function that derives dirname from filename using lastIndexOf for '/' and '\' with conditional slicing (handles drive letters and root-like cases), defaulting to "." when no separator is present.
URL / Filename generation (unchanged) tools/egg-bundler/src/lib/Bundler.ts	url and filename continue to be emitted based on filename (path separator normalization into a file:/// URL).
Integration Tests tools/egg-bundler/test/integration.test.ts	Removed an assertion that bundle-manifest.chunks excludes *.js.map entries; added a test that runs a bundled chunk in a vm sandbox with a provided __dirname binding and asserts the patched import.meta.dirname equals the sandbox __dirname across filename inputs (verifies shadowed/local __dirname is not used).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• feat(bundler): patch turbopack import.meta output #5905: Related adjustments to bundler import.meta post-processing that rewrite import.meta to runtime expressions.

Poem

🐰
I nibble paths beneath the moonlit line,
No runtime shadow steals what’s mine.
From filename I carve the place,
A tidy dirname, snug in space.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title directly addresses the main change: fixing the bundler to avoid issues with shadowed __dirname in the import.meta patch, which is the core motivation for computing dirname from filename instead of reading __dirname.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests
• Commit unit tests in branch agent/egg-dev/0a638d6f

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.04%. Comparing base (5baa1ed) to head (ca921a6).
⚠️ Report is 1 commits behind head on next.

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #5916   +/-   ##
=======================================
  Coverage   85.03%   85.04%           
=======================================
  Files         667      667           
  Lines       19123    19123           
  Branches     3723     3723           
=======================================
+ Hits        16262    16263    +1     
+ Misses       2468     2467    -1     
  Partials      393      393           

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[Copilot]

Pull request overview

This PR fixes a runtime TDZ failure in egg-bundler’s post-pack Turbopack import.meta patching by removing references to __dirname, which can be shadowed by later lexical const __dirname declarations in the same module scope.

Changes:

• Update the generated Turbopack import.meta replacement to derive import.meta.dirname purely from the resolved filename (avoiding __dirname access).
• Add an integration regression test covering a chunk that declares const __dirname after the patched import.meta object.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tools/egg-bundler/src/lib/Bundler.ts	Adjusts generated import.meta object patch to avoid __dirname TDZ by deriving dirname from filename.
tools/egg-bundler/test/integration.test.ts	Adds a regression test ensuring patched chunks don’t touch a shadowed __dirname binding.

[gemini-code-assist]

Code Review

This pull request simplifies the dirname calculation in Bundler.ts by removing the check for a global __dirname and adds an integration test to ensure import.meta patching works correctly when __dirname is shadowed. A review comment points out that the current regex-based calculation returns an empty string for files at the root directory and suggests a fallback to match Node.js behavior.

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