elastic/kibana

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

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#214,725 opened on Mar 17, 2025

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Feature:LoggingTeam:Coregood first issue

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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

Research direction
Use the provided RegExp to locate all log.debug and log.trace calls that use JSON.stringify eagerly. Replace them with the lazy form using a callback. Ensure the logger is from @kbn/logger.
Tech stack
typescript
Domain
backend
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
TypeScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70