slogutil: replace level name

logutil/slogutil/slogutil.go

@@ -57,10 +57,7 @@ func New(c *Config) (l *slog.Logger) {
 		return newDefault(output, lvl, c.AddTimestamp)
 	}
 
-	var replaceAttr func(groups []string, a slog.Attr) (res slog.Attr)
-	if !c.AddTimestamp {
-		replaceAttr = RemoveTime
-	}
+	replaceAttr := replaceAttributes(!c.AddTimestamp)
 
 	var h slog.Handler
 	switch format {
@@ -103,6 +100,35 @@ func newDefault(output io.Writer, lvl slog.Level, addTimestamp bool) (l *slog.Lo
 	return slog.New(h)
 }
 
+// replaceAttributes is a function that returns
+// [slog.HandlerOptions.ReplaceAttr] for provided parameters.
+func replaceAttributes(removeTime bool) func(groups []string, a slog.Attr) (res slog.Attr) {
+	if !removeTime {
+		return ReplaceLevel
+	}
+
+	return func(groups []string, a slog.Attr) (res slog.Attr) {
+		return ReplaceLevel(groups, RemoveTime(groups, a))
+	}
+}
+
+// ReplaceLevel is a function for [slog.HandlerOptions.ReplaceAttr] that adds
+// [LevelTrace] custom name for level attribute.
+func ReplaceLevel(groups []string, a slog.Attr) (res slog.Attr) {
+	if len(groups) > 0 {
+		return a
+	}
+
+	if a.Key == slog.LevelKey {
+		lvl := a.Value.Any().(slog.Level)
+		if lvl == LevelTrace {
+			a.Value = slog.StringValue("TRACE")
+		}
+	}
+
+	return a
+}
+
 // RemoveTime is a function for [slog.HandlerOptions.ReplaceAttr] that removes
 // the "time" attribute.
 func RemoveTime(groups []string, a slog.Attr) (res slog.Attr) {

logutil/slogutil/slogutil_example_test.go

@@ -75,15 +75,16 @@ This is a very long text with many lines.`
 
 func ExampleNew_trace() {
 	l := slogutil.New(&slogutil.Config{
-		Level: slogutil.LevelTrace,
+		Format: slogutil.FormatText,
+		Level:  slogutil.LevelTrace,
 	})
 
 	l.Log(context.Background(), slogutil.LevelTrace, "test trace")
 	l.Info("test info")
 	l.Debug("test debug")
 
 	// Output:
-	// DEBUG-4 test trace
-	// INFO test info
-	// DEBUG test debug
+	// level=TRACE msg="test trace"
+	// level=INFO msg="test info"
+	// level=DEBUG msg="test debug"
 }