fix(cli): json reporter file

[ematipico]

Summary

Biome wasn't writing anything on file when the JSON reporter was specified.

Used AI for this. It was a simple change.

Test Plan

Added a test

Docs

[changeset-bot]

🦋 Changeset detected

Latest commit: 7d6aab8

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

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

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📥 Commits

Reviewing files that changed from the base of the PR and between 4612133 and 7d6aab8.

⛔ Files ignored due to path filters (1)

• crates/biome_cli/tests/snapshots/main_cases_reporter_json/reports_diagnostics_json_check_command_file.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (2)

• .changeset/fix-json-reporter-file-output.md
• crates/biome_cli/src/runner/impls/finalizers/default.rs

---

Walkthrough

This pull request introduces a fix for the JSON reporter to respect the --reporter-file flag. Previously, JSON output was always written to stdout regardless of the reporter destination setting. A changeset file documents the patch, and the implementation in default.rs has been updated to dynamically select the output writer based on whether the reporter targets a file or the console.

Suggested labels

A-CLI, A-Diagnostic

Suggested reviewers

• Netail
• siketyan

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix(cli): json reporter file' directly addresses the main change: fixing JSON reporter output to files instead of stdout.
Description check	✅ Passed	The description clearly relates to the changeset, explaining the problem (JSON reporter not writing to file) and confirming a test was added.

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• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/json-reporter-stdout

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[ematipico]

Tests are passing. Going to merge this. I need it for the ecosystem CI ASAP