Use miniflare's handleStructuredLogs option instead of handleRuntimeStdio for processing workerd output

[dario-piotrowicz]

Fixes https://jira.cfdata.org/browse/DEVX-2250

Note

Disclaimer, this change doesn't make much of a difference, the only benefit here is consistency with Wrangler and the Vite plugin, as well as maybe potential benefits down the line (such as for example if we wanted to start using a logger in vitest-pool-workers)

I just had this old Jira ticket for it so to clean it up I just asked Claude to implement this and then simply reviewed and tested the changes (most of the changes here as made by Claude).

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• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: mostly internal change

A picture of a cute animal (not mandatory, but encouraged)

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[changeset-bot]

🦋 Changeset detected

Latest commit: 3a1d99d

The changes in this PR will be included in the next version bump.

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[github-actions]

✅ All changesets look good

[ask-bonk]

After thorough review, here's my assessment:

1. The core change is clean: switching from handleRuntimeStdio (raw stream processing) to handleStructuredLogs (structured JSON log processing). This is correct and aligns with how wrangler and vite-plugin-cloudflare already work.

2. The symbolizerWarning constant is now dead code in the sense that miniflare's wrapStructuredLogsHandler already filters it via isInternal(). However, having it in ignoreMessages is purely redundant (not buggy) — it's a defense-in-depth measure. Not worth flagging.

3. The unused import type { Readable } from "node:stream" was correctly removed.

4. The WorkerdStructuredLog type is correctly imported from miniflare.

5. The handleStructuredLogs function properly routes error/warn to stderr and everything else to stdout, with the ignoreMessages filter applied first.

6. The test correctly uses __console (the original workerd console saved before Vitest patches it) to verify that output routing works end-to-end.

7. The changeset is appropriate — patch for a bug fix/internal improvement.

8. The formatting changes are just oxfmt reformatting — not worth flagging per review rules.

No logic bugs, no security issues, no backward compatibility concerns, no incorrect API behavior.

LGTM

github run

[pkg-pr-new]

create-cloudflare

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@cloudflare/kv-asset-handler

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miniflare

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@cloudflare/pages-shared

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@cloudflare/unenv-preset

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@cloudflare/vite-plugin

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@cloudflare/vitest-pool-workers

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@cloudflare/workers-editor-shared

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wrangler

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commit: 3a1d99d

[workers-devprod]

Codeowners approval required for this PR:

• ✅ @cloudflare/wrangler

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.