fix: use module condition and main fields for bundling

[pi0]

Before runtimes adopting ESM, bundlers and package authors made up a convention to use top level module field to indicate bundler-friendly-ESM entry. This convention then confused and added to the exports object as an export condition.

Neither of the export condition or field is respected by any runtime but only by bundlers. Standard is the exports field and import condition.

This PR adds module to default conditions to be consistent with rolldown and esbuild (rolldown/rolldown#4703) and fixing bundling issues.

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Project	Deployment	Review	Updated (UTC)
nitro.build	Ready	Preview, Comment	Dec 18, 2025 2:03pm

[coderabbitai]

Caution

Review failed

The pull request is closed.

📝 Walkthrough

Walkthrough

Removed explicit mainFields configuration from Rolldown and Rollup, added "module" to default export conditions in the resolver, filtered out "module" in Vite externalConditions, and removed hardcoded exportConditions from the standard preset to rely on the centralized defaults.

Changes

Cohort / File(s)	Change Summary
Build Tool Configuration src/build/rolldown/config.ts, src/build/rollup/config.ts	Removed explicit mainFields: ["main"] from resolve/nodeResolve plugin configuration; removed an associated comment. Module resolution now relies on default resolution behavior.
Export Conditions Configuration src/config/resolvers/export-conditions.ts	Added "module" to the default export conditions set (now ["import","default","module"]) with an explanatory comment about compatibility use.
External Conditions Filtering src/build/vite/env.ts	Updated externalConditions filtering to exclude "module" in addition to "browser" and "wasm", changing which conditions are considered for externalization.
Preset Configuration src/presets/standard/preset.ts	Removed hardcoded exportConditions: ["import", "default"] from the standard preset so it uses the centralized resolver defaults.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Focus attention on:
  • Interaction between adding "module" to default export conditions and filtering "module" in Vite externals (possible resolution mismatches)
  • Ensuring presets now inherit the intended defaults after removal of hardcoded exportConditions
  • Verifying removal of mainFields does not regress resolution for existing dependencies

Possibly related PRs

• refactor!: overhaul externals support #3799 — Related changes to module-resolution/export-condition behavior affecting externals.
• refactor(vite): keep SSR bundle external dependencies #3854 — Modifies externalization behavior in src/build/vite/env.ts similar to these edits.
• refactor: env runners #3836 — Also adjusts createNitroEnvironment/createServiceEnvironment logic in src/build/vite/env.ts, overlapping affected code paths.

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 (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title follows conventional commits format with 'fix:' prefix and clearly describes the main change of adding the 'module' condition and main fields for bundling.
Description check	✅ Passed	The PR description is directly related to the changeset, providing detailed context about the 'module' condition, its historical usage, and the motivation for the changes across multiple files.

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📜 Recent review details

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 85a16ef and 96d4f19.

📒 Files selected for processing (2)

• src/build/vite/env.ts (2 hunks)
• src/config/resolvers/export-conditions.ts (1 hunks)

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[coderabbitai]

Actionable comments posted: 3

📜 Review details

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 7f42bc1 and 85a16ef.

📒 Files selected for processing (5)

• src/build/rolldown/config.ts (0 hunks)
• src/build/rollup/config.ts (0 hunks)
• src/build/vite/env.ts (1 hunks)
• src/config/resolvers/export-conditions.ts (1 hunks)
• src/presets/standard/preset.ts (0 hunks)

💤 Files with no reviewable changes (3)

• src/build/rolldown/config.ts
• src/build/rollup/config.ts
• src/presets/standard/preset.ts

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (3)

• GitHub Check: tests-rollup (windows-latest)
• GitHub Check: tests-rollup (ubuntu-latest)
• GitHub Check: tests-rolldown (windows-latest)

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commit: 85a16ef