fix: route dev-server response logging through Vite's logger

[marwan562]

Fixes #16825

Summary

In the dev server, every SSR response is logged to the console (e.g. 200 GET /) via a raw console.log from log_response in the runtime server/internal.js. Because it bypasses Vite's logger, logLevel and customLogger have no effect on it.

This change routes dev-server response logging through Vite's resolved logger:

• format_response(status, request) in packages/kit/src/runtime/server/internal.js is now a pure function that returns the formatted line instead of printing it, so the caller decides how to emit it.
• The dev middleware (packages/kit/src/exports/vite/dev/index.js) emits the line via vite_dev_server.config.logger — logger.info for statuses < 400 and logger.error for >= 400. This means:
  • logLevel: "warn" (or "error"/"silent") now suppresses successful-request lines, while errors remain visible
  • a user-supplied customLogger receives the lines
• Prerender logging (packages/kit/src/core/postbuild/prerender.js) is unchanged in behaviour — it still prints only >= 400 responses via console.log.
• Renamed log_response -> format_response in the generated server module (core/sync/write_server.js) and the internal type declaration to match the new contract.

Testing

• Added unit tests for format_response covering plain pages, data requests, route-resolution requests, remote-function requests, and error responses (all pass).
• pnpm tsc-native and oxfmt --check pass on the changed files.

Changesets

patch for @sveltejs/kit.

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 4fcce71:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/4fcce71590aacac9d3b4dd7bd9f503c90d405a02

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16858

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4fcce71

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[Rich-Harris]

thank you!