slogerr

slogerr provides Error and NamedError helpers for Go's log/slog package, inspired by the equivalent functions in uber-go/zap.

Each helper returns a slog.Attr that encodes structured error information:

• msg — the error message from err.Error()
• verbose — the %+v representation, added only when it differs from msg (e.g. errors carrying a stack trace)
• causes — the individual errors when err wraps multiple errors via errors.Join or fmt.Errorf("%w %w", ...)

Installation

go get github.com/utgwkk/slogerr

Usage

import (
    "errors"
    "log/slog"

    "github.com/utgwkk/slogerr"
)

// Basic usage — key is "error"
slog.Info("request failed", slogerr.Error(err))

// Custom key
slog.Info("request failed", slogerr.NamedError("cause", err))

// nil is a no-op: returns a zero-value slog.Attr that handlers skip
slog.Info("maybe failed", slogerr.Error(nil))

// errors.Join: individual causes are recorded under "causes"
joined := errors.Join(errors.New("db error"), errors.New("timeout"))
slog.Info("multiple errors", slogerr.Error(joined))

Output format

The attribute value is a slog.GroupValue, so with slog.NewJSONHandler the output looks like:

Simple error

{"msg":"request failed","error":{"msg":"something went wrong"}}

Error with verbose representation (e.g. from github.com/pkg/errors)

{"msg":"request failed","error":{"msg":"something went wrong","verbose":"something went wrong\nmain.main()\n\t/app/main.go:42"}}

Joined errors

{"msg":"request failed","error":{"msg":"db error\ntimeout","causes":{"0":{"msg":"db error"},"1":{"msg":"timeout"}}}}

Note: slog's type system has no native array kind; causes are represented as a group with numeric string keys ("0", "1", ...) rather than a JSON array.

Acknowledgments

This library is inspired by the Error and NamedError functions in uber-go/zap (MIT License, Copyright (c) 2016–2024 Uber Technologies, Inc.).