add a flag option (#10)

I don't like any of the names here, and we might want it to be in a
separate subpackage. This lets you say `--log-level=DEBUG` to set the
level. The default is still INFO.

---------

Signed-off-by: Jason Hall <jason@chainguard.dev>

examples/logger/main.go

@@ -2,18 +2,29 @@ package main
 
 import (
 	"context"
+	"flag"
 	"log/slog"
+	"os"
 
 	"github.com/chainguard-dev/clog"
+	"github.com/chainguard-dev/clog/slag"
 )
 
 func main() {
+	var level slag.Level
+	flag.Var(&level, "log-level", "log level")
+	flag.Parse()
+
+	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: &level})))
+
 	log := clog.NewLogger(slog.Default()).With("a", "b")
 	ctx := clog.WithLogger(context.Background(), log)
 
 	// Grab logger from context and use
-	clog.FromContext(ctx).With("foo", "bar").Infof("hello world")
+	clog.FromContext(ctx).With("foo", "bar").Debugf("hello debug world")
+	clog.FromContext(ctx).With("info", true).Infof("hello info world")
+	clog.FromContext(ctx).With("warn", 42).Warnf("hello warn world")
 
 	// Package level context loggers are also aware
-	clog.ErrorContext(ctx, "asdf")
+	clog.ErrorContext(ctx, "hello error world")
 }

logger.go

@@ -97,6 +97,10 @@ func (l *Logger) Handler() slog.Handler {
 }
 
 func wrap(ctx context.Context, logger *Logger, level slog.Level, msg string, args ...any) {
+	if !logger.Handler().Enabled(ctx, level) {
+		return
+	}
+
 	var pcs [1]uintptr
 	runtime.Callers(3, pcs[:]) // skip [Callers, Infof, wrapf]
 	r := slog.NewRecord(time.Now(), level, msg, pcs[0])
@@ -107,6 +111,10 @@ func wrap(ctx context.Context, logger *Logger, level slog.Level, msg string, arg
 // wrapf is like wrap, but uses fmt.Sprintf to format the message.
 // NOTE: args are passed to fmt.Sprintf, not as [slog.Attr].
 func wrapf(ctx context.Context, logger *Logger, level slog.Level, format string, args ...any) {
+	if !logger.Handler().Enabled(ctx, level) {
+		return
+	}
+
 	var pcs [1]uintptr
 	runtime.Callers(3, pcs[:]) // skip [Callers, Infof, wrapf]
 	r := slog.NewRecord(time.Now(), level, fmt.Sprintf(format, args...), pcs[0])

slag/flag.go

@@ -0,0 +1,16 @@
+package slag
+
+import "log/slog"
+
+type Level slog.Level
+
+func (l *Level) Set(s string) error {
+	var ll slog.Level
+	if err := ll.UnmarshalText([]byte(s)); err != nil {
+		return err
+	}
+	*l = Level(ll)
+	return nil
+}
+func (l *Level) String() string    { return slog.Level(*l).String() }
+func (l *Level) Level() slog.Level { return slog.Level(*l) }