Proposal: Enable Timestamps by Default in log.New()

[jamesainslie]

Problem

log.New() omits timestamps while log.Default() includes them. This inconsistency surprises users.

// log.Default() includes timestamps
log.Info("Hello world!")
// Output: 2023/01/23 14:23:45 INFO Hello world!

// log.New() does not
logger := log.New(os.Stderr)
logger.Info("Hello world!")
// Output: INFO Hello world!

Solution

Enable timestamps by default in log.New():

func New(w io.Writer) *Logger {
    return NewWithOptions(w, Options{
        ReportTimestamp: true,
    })
}

This uses DefaultTimeFormat ("2006/01/02 15:04:05"), matching log.Default() behavior.

Users can disable via NewWithOptions():

logger := log.NewWithOptions(os.Stderr, log.Options{
    ReportTimestamp: false,
})

Impact

Breaking change: Existing code using log.New() will now include timestamps.

Benefits:

• Consistent with log.Default()
• Matches user expectations
• Aligns with standard library behavior

API Compatibility with log/slog

The *Logger type already implements slog.Handler:

handler := log.NewWithOptions(os.Stderr, log.Options{
    ReportTimestamp: true,
    Level:           log.DebugLevel,
})
logger := slog.New(handler)

For a familiar slog-style API, add:

// HandlerOptions provides slog-style configuration.
type HandlerOptions struct {
    AddSource bool
    Level     Level
}

// NewTextHandler returns a Handler with text formatting.
// Timestamps are enabled by default.
func NewTextHandler(w io.Writer, opts *HandlerOptions) *Logger {
    if opts == nil {
        opts = &HandlerOptions{}
    }
    return NewWithOptions(w, Options{
        ReportTimestamp: true,
        Formatter:       TextFormatter,
        Level:           opts.Level,
        ReportCaller:    opts.AddSource,
    })
}

// NewJSONHandler returns a Handler with JSON formatting.
// Timestamps are enabled by default.
func NewJSONHandler(w io.Writer, opts *HandlerOptions) *Logger {
    if opts == nil {
        opts = &HandlerOptions{}
    }
    return NewWithOptions(w, Options{
        ReportTimestamp: true,
        Formatter:       JSONFormatter,
        Level:           opts.Level,
        ReportCaller:    opts.AddSource,
    })
}

Usage:

handler := log.NewTextHandler(os.Stderr, &log.HandlerOptions{
    Level: log.DebugLevel,
})
logger := slog.New(handler)

Implementation

• Update New() to set ReportTimestamp: true
• Add HandlerOptions, NewTextHandler(), NewJSONHandler()
• Update tests
• Document breaking change in release notes