fix(kit): avoid mutating cached ESM config in layer resolution #33779

Flo0806 · 2025-11-27T22:25:22Z

🔗 Linked issue

Resolves: #33733

📚 Description

Fixes .output being created in layer subdirectory instead of project root when layers use ESM configs (.mjs, .js with "type": "module", or from node_modules).

The bug occurred because layer.config.rootDir ??= layer.cwd! directly mutated the cached ESM module object. On subsequent builds, the cached object already had rootDir set to the layer's directory.

Fix: Create a shallow copy via spread operator instead of mutating the original.

bolt-new-by-stackblitz · 2025-11-27T22:25:25Z

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coderabbitai · 2025-11-27T22:27:58Z

Walkthrough

The change modifies the layer configuration handling in the loader config module to prevent mutation of cached layer configuration objects. It introduces a resolved root directory value that defaults to the layer config's existing rootDir or falls back to layer.cwd. The layer configuration is then rewritten as a shallow copy with the resolved rootDir applied. Additionally, the processed-layers tracking mechanism is updated to use this resolved rootDir value instead of the original layer.config.rootDir, which prevents duplicate processing when rootDir was previously undefined.

Possibly related PRs

fix(kit): do not skip layer with defined srcDir #32487: Modifies how a layer's root and src directories are resolved and checked to determine whether a layer should be processed or skipped.
fix(nuxt): make patterns relative to srcDir in buildCache #32260: Adjusts how a layer's directory is resolved using a config value with fallback to layer.cwd to guide subsequent logic flow.

Pre-merge checks and finishing touches

❌ 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%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: avoiding mutation of cached ESM config objects in layer resolution to fix the .output directory issue.
Description check	✅ Passed	The description clearly explains the bug, root cause, and fix related to ESM config mutation in layer resolution, matching the changeset objectives.
Linked Issues check	✅ Passed	The code changes directly address issue #33733 by preventing mutation of cached ESM config objects through creating a shallow copy, ensuring .output is generated in the correct directory.
Out of Scope Changes check	✅ Passed	All changes in packages/kit/src/loader/config.ts are focused on fixing the ESM config mutation bug; no unrelated modifications are present.

✨ Finishing touches

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📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 81356f8 and 60476d4.

📒 Files selected for processing (1)

packages/kit/src/loader/config.ts (1 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

**/*.{ts,tsx,vue}

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Follow standard TypeScript conventions and best practices

Files:

packages/kit/src/loader/config.ts

**/*.{ts,tsx,js,jsx,vue}

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**/*.{ts,tsx,js,jsx,vue}: Use clear, descriptive variable and function names
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Files:

packages/kit/src/loader/config.ts

🧠 Learnings (1)

📚 Learning: 2024-11-05T15:22:54.759Z

Learnt from: GalacticHypernova
Repo: nuxt/nuxt PR: 26468
File: packages/nuxt/src/components/plugins/loader.ts:24-24
Timestamp: 2024-11-05T15:22:54.759Z
Learning: In `packages/nuxt/src/components/plugins/loader.ts`, the references to `resolve` and `distDir` are legacy code from before Nuxt used the new unplugin VFS and will be removed.

Applied to files:

packages/kit/src/loader/config.ts

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GitHub Check: codeql (javascript-typescript)
GitHub Check: code
GitHub Check: semantic-pr

🔇 Additional comments (2)

packages/kit/src/loader/config.ts (2)

83-88: Excellent fix for the ESM cache mutation issue.

The solution correctly prevents mutation of cached ESM config objects by creating a shallow copy before assigning rootDir. The approach is sound:

resolvedRootDir explicitly captures the intended value before modification

The spread operator creates a new object, leaving the cached module untouched

Gracefully handles undefined layer.config with the fallback to an empty object

This directly addresses the root cause described in issue #33733 where subsequent builds incorrectly placed .output in layer subdirectories.

91-92: Consistent tracking logic with the resolved value.

Updating the duplicate layer detection to use resolvedRootDir maintains consistency with the new approach and avoids any dependency on the potentially mutated config object. The logic remains functionally equivalent whilst being more explicit about the value being tracked.

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pkg-pr-new · 2025-11-27T22:35:13Z

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@nuxt/kit

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nuxt

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@nuxt/schema

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@nuxt/webpack-builder

npm i https://pkg.pr.new/@nuxt/webpack-builder@33779

commit: 60476d4

codspeed-hq · 2025-11-27T22:42:53Z

CodSpeed Performance Report

Merging #33779 will not alter performance

_{Comparing Flo0806:fix/layer-esm-cache-mutation (60476d4) with main (81356f8)}

Summary

✅ 10 untouched

fix(kit): avoid mutating cached ESM config in layer resolution

60476d4

Flo0806 requested a review from danielroe as a code owner November 27, 2025 22:25

github-actions bot added 4.x bug labels Nov 27, 2025

danielroe approved these changes Dec 9, 2025

View reviewed changes

danielroe merged commit 42ff3df into nuxt:main Dec 9, 2025
54 of 56 checks passed

github-actions bot mentioned this pull request Dec 9, 2025

v4.2.2 #33687

Merged

danielroe pushed a commit that referenced this pull request Dec 9, 2025

fix(kit): do not add resolved rootDir to cached layer config (#33779)

989b12c

github-actions bot mentioned this pull request Dec 9, 2025

v3.20.2 #33696

Merged

coderabbitai bot mentioned this pull request Dec 11, 2025

🐞 Can't import variables from ordered layers in nuxt config #33855

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fix(kit): avoid mutating cached ESM config in layer resolution #33779

fix(kit): avoid mutating cached ESM config in layer resolution #33779

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fix(kit): avoid mutating cached ESM config in layer resolution #33779

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Flo0806 commented Nov 27, 2025

🔗 Linked issue

📚 Description

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bolt-new-by-stackblitz bot commented Nov 27, 2025

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coderabbitai bot commented Nov 27, 2025

Walkthrough

Possibly related PRs

Pre-merge checks and finishing touches

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pkg-pr-new bot commented Nov 27, 2025

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codspeed-hq bot commented Nov 27, 2025

CodSpeed Performance Report

Merging #33779 will not alter performance

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