`fastify.log.isLevelEnabled()` is missing from TypeScript types

[Matthew Pietz]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.26.2

Plugin version

No response

Node.js version

18.19.1

Operating system

Windows

Operating system version (i.e. 20.04, 11.3, 10)

10

Description

Pino exposes a function logger.isLevelEnabled() which is available withing Fastify, but the TypeScript typing doesn't implement it. The type FastifyBaseLogger should be updated to extend pino.Logger in order to have the exact interface which matches what pino is exposing.

Conveniently, pino.Logger also implements child() so that can be removed from Fastify's types.

Inside types/logger.d.ts:

export interface FastifyBaseLogger<CustomLevels extends string = never>
  extends pino.Logger<CustomLevels> {}

Steps to Reproduce

With the following TypeScript:

import Fastify from "fastify"

const server = fastify({ logger: true })

console.log(`Trace enabled: `, server.log.isLevelEnabled("trace"))

Expected Behavior

The value of server.log should expose the full Pino interface.

[KaKa]

I would say it is a wontfix because we need to support custom logger with minimal pino interface.
Chasing it back and forth to provide complete pino API and compatible minimal interface by default is not realistic currently.

As a workaround, you can supply the pino interface to generic argument of TypeScript.

cc @fastify/typescript

[Matthew Pietz]

That makes sense. Supporting custom loggers wasn't on my mind but perhaps it requires some more thought...

The generic could extend the BaseLogger, but default to Pino's full logger. That should support the current API contract. I feel like this should still merit consideration as the current TypeScript types are masking existing default functionality.

[KaKa]

The generic could extend the BaseLogger, but default to Pino's full logger.

That sound do-able. We may try to see how it works.

[Matthew Pietz]

I took a stab at it in the PR above ^