fix(vite): respect bun/deno export conditions in dev server by pi0x · Pull Request #4397 · nitrojs/nitro

pi0x · 2026-06-30T10:44:34Z

When the Nitro dev server runs under Bun (bun --bun) or Deno, the Vite module runner resolves the node export condition, so packages are loaded through their node entry instead of their runtime-native one.

This PR adds _devRuntimeConditions(ctx), used by both the Nitro and service environments, to prepend the host runtime's export condition:

under Bun → prepend "bun"
under Deno → prepend "deno"

Scope

This only applies in dev and only with the default node-worker runner, where the module runner executes in a worker thread of the same host runtime (Bun ⇒ Bun, Deno ⇒ Deno).

Process-based runners (bun-process, deno-process, node-process, …) and miniflare execute in a different runtime than the host, so the host-detected condition is intentionally not applied to them — otherwise it would leak the wrong condition into their resolution.

This is a generic fix to honor bun/deno export conditions; it is not tied to any single dependency.

When the Nitro dev server runs under Bun or Deno, the Vite module runner resolved the `node` export condition, so `srvx`'s `FastResponse` became the node adapter's `NodeResponse` wrapper. `Bun.serve`/`Deno.serve` strictly require a native `Response` and reject it, crashing the dev server. Prepend the matching `bun`/`deno` export condition in dev so packages like `srvx` resolve to their runtime-native adapter (native `Response`). `node` stays as a fallback; production builds are unaffected. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

vercel · 2026-06-30T10:44:40Z

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Project	Deployment	Actions	Updated (UTC)
nitro.build	Ready	Preview, Comment	Jun 30, 2026 12:41pm

coderabbitai · 2026-06-30T10:45:03Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 6810721b-9dfe-4525-bc8f-1284243e0f66

📥 Commits

Reviewing files that changed from the base of the PR and between dbc1e86 and 4f26c1c.

📒 Files selected for processing (1)

src/build/vite/env.ts

🚧 Files skipped from review as they are similar to previous changes (1)

src/build/vite/env.ts

📝 Walkthrough

Walkthrough

Adds dev-only export condition selection for Bun and Deno in src/build/vite/env.ts, and centralizes dev runner resolution for _loadRunner and _isWorkerdRunner.

Changes

Dev runtime export conditions

Layer / File(s)	Summary
_resolveConditions helper and environment call sites `src/build/vite/env.ts`	Adds `_resolveConditions(ctx)` to prepend Bun or Deno to `exportConditions` during non-workerd dev, and updates both environment constructors to use it.
_devRunner shared lookup `src/build/vite/env.ts`	Factors dev runner selection into `_devRunner(ctx)`, then reuses it in `_loadRunner` and `_isWorkerdRunner(ctx)`.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

vite: dev server breaks under bun --bun runtime due to "node" export condition #4228: Adjusts dev-time export conditions for Bun/Deno runtime selection, matching the new runtime-condition handling here.

Possibly related PRs

nitrojs/nitro#3836: Both change src/build/vite/env.ts and refactor dev runner/environment setup logic.
nitrojs/nitro#3886: Both adjust how exportConditions are assembled in Nitro’s Vite environment setup.
nitrojs/nitro#4338: Both modify runner selection and workerd/miniflare detection in src/build/vite/env.ts.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% 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
Title check	✅ Passed	It follows conventional commits and accurately describes the Bun/Deno export-condition fix in dev.
Description check	✅ Passed	The description is directly related to the changeset and explains the dev-server export-condition behavior.
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 fix/vite-runtime-conditions

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pkg-pr-new · 2026-06-30T10:47:43Z

Open in StackBlitz

npm i https://pkg.pr.new/nitro@4397

commit: 4f26c1c

…nner Only prepend the host bun/deno condition when the module runner shares the host runtime (default node-worker). Process-based and miniflare runners execute in a different runtime and must not inherit it. Also dedupe runner name resolution into a shared _devRunner() helper. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Externalized deps in dev now resolve their bun/deno-native entry too, matching the bundled `conditions` behavior. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

The helper runs on all paths (it early-returns outside dev/node-worker), so the `dev` prefix was misleading. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pi0x requested a review from pi0 as a code owner June 30, 2026 10:44

vercel Bot deployed to Preview June 30, 2026 10:46 View deployment

pi0x changed the title ~~fix(vite): use runtime-native export conditions for bun/deno dev server~~ fix(vite): respect bun/deno export conditions in dev server Jun 30, 2026

vercel Bot deployed to Preview June 30, 2026 12:17 View deployment

fix(vite): apply runtime export conditions to dev externalConditions

dbc1e86

Externalized deps in dev now resolve their bun/deno-native entry too, matching the bundled `conditions` behavior. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

vercel Bot deployed to Preview June 30, 2026 12:37 View deployment

refactor(vite): rename _devRuntimeConditions to _resolveConditions

4f26c1c

The helper runs on all paths (it early-returns outside dev/node-worker), so the `dev` prefix was misleading. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

vercel Bot deployed to Preview June 30, 2026 12:41 View deployment

pi0 merged commit 1310a58 into main Jun 30, 2026
13 checks passed

pi0 deleted the fix/vite-runtime-conditions branch June 30, 2026 12:45

This was referenced Jun 30, 2026

Bun throws error when not having Node installed #4182

Closed

fix(config): prepend bun export condition under bun runtime #4229

Closed

pi0x added a commit that referenced this pull request Jul 2, 2026

fix(vite): respect bun/deno export conditions in dev server (#4397)

7427e3b

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fix(vite): respect bun/deno export conditions in dev server#4397

fix(vite): respect bun/deno export conditions in dev server#4397
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