elastic/kibana

[logger] `log.debug` and `.trace` should prefer the lazy implementation

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#214725 opened on Mar 17, 2025

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Feature:LoggingTeam:Coregood first issue

Description

There are many places where we do patterns like log.debug(`${JSON.stringify({...})}`) in the Kibana code.

When the log level is set higher than debug, this implies unnecessary CPU blocks only to be discarded later.

We should audit all use cases like this and change them to the lazy form: ``````log.debug(() => ${JSON.stringify({...})})```.

@dgieselaar provided the following RegExp to find all use cases:

\.(?:debug|trace)\(\s*(?!((?:\([^)]*\)|\w+)\s*=>)).*?JSON\.stringify\s*\(

Please, bear in mind that some loggers don't support this. Make sure to only update the ones using the Logger from @kbn/logger.

Ideally, an autofixable ESlint rule would prevent this from happening again.

Contributor guide

Tech stack
typescriptnodejs
Domain
backendperformance
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScriptregular expressionsunderstanding of logging
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Use the provided regex to find all occurrences of log.debug/log.trace with JSON.stringify in non lazy form. Ensure the logger is from @kbn/logger. Replace with lazy callbacks. Consider creating an autofixable ESLint rule to prevent future regressions. Review existing comments for additional context.