Allow message formatting using event data

README.md

@@ -352,6 +352,21 @@ output.FormatLevel = func(i interface{}) string {
 output.FormatMessage = func(i interface{}) string {
     return fmt.Sprintf("***%s****", i)
 }
+output.FormatMessageFromEvent = func(evt map[string]interface{}) zerolog.Formatter {
+    return func(i interface{}) string {
+        level := evt[zerolog.LevelFieldName]
+        switch level {
+        case zerolog.LevelInfoValue:
+            return fmt.Sprintf("=> %s %s", level, i)
+        case zerolog.LevelWarnValue:
+            return fmt.Sprintf("!! %s %s", level, i)
+        case zerolog.LevelErrorValue, zerolog.LevelFatalValue, zerolog.LevelPanicValue:
+            return fmt.Sprintf("XX %s %s", level, i)
+        default:
+            return fmt.Sprintf("%s", i)
+        }
+    }
+}
 output.FormatFieldName = func(i interface{}) string {
     return fmt.Sprintf("%s:", i)
 }

console.go

@@ -51,6 +51,9 @@ type Formatter func(interface{}) string
 // being able to differentiate formatting based on field name.
 type FormatterByFieldName func(interface{}, string) string
 
+// FormatterFromEvent generates a Formatter from an event.
+type FormatterFromEvent func(map[string]interface{}) Formatter
+
 // ConsoleWriter parses the JSON input and writes it in an
 // (optionally) colorized, human-friendly format to Out.
 type ConsoleWriter struct {
@@ -81,14 +84,15 @@ type ConsoleWriter struct {
 	// FieldsExclude defines contextual fields to not display in output.
 	FieldsExclude []string
 
-	FormatTimestamp     Formatter
-	FormatLevel         Formatter
-	FormatCaller        Formatter
-	FormatMessage       Formatter
-	FormatFieldName     Formatter
-	FormatFieldValue    Formatter
-	FormatErrFieldName  Formatter
-	FormatErrFieldValue Formatter
+	FormatTimestamp        Formatter
+	FormatLevel            Formatter
+	FormatCaller           Formatter
+	FormatMessage          Formatter
+	FormatMessageFromEvent FormatterFromEvent
+	FormatFieldName        Formatter
+	FormatFieldValue       Formatter
+	FormatErrFieldName     Formatter
+	FormatErrFieldValue    Formatter
 	// If this is configured it is used for "part" values and
 	// has precedence on FormatFieldValue
 	FormatPartValueByName FormatterByFieldName
@@ -101,9 +105,9 @@ type ConsoleWriter struct {
 // NewConsoleWriter creates and initializes a new ConsoleWriter.
 func NewConsoleWriter(options ...func(w *ConsoleWriter)) ConsoleWriter {
 	w := ConsoleWriter{
-		Out:          os.Stdout,
-		TimeFormat:   consoleDefaultTimeFormat,
-		PartsOrder:   consoleDefaultPartsOrder(),
+		Out:        os.Stdout,
+		TimeFormat: consoleDefaultTimeFormat,
+		PartsOrder: consoleDefaultPartsOrder(),
 	}
 
 	for _, opt := range options {
@@ -313,10 +317,12 @@ func (w ConsoleWriter) writePart(buf *bytes.Buffer, evt map[string]interface{},
 			f = w.FormatTimestamp
 		}
 	case MessageFieldName:
-		if w.FormatMessage == nil {
-			f = consoleDefaultFormatMessage(w.NoColor, evt[LevelFieldName])
-		} else {
+		if w.FormatMessageFromEvent != nil {
+			f = w.FormatMessageFromEvent(evt)
+		} else if w.FormatMessage != nil {
 			f = w.FormatMessage
+		} else {
+			f = consoleDefaultFormatMessage(w.NoColor, evt[LevelFieldName])
 		}
 	case CallerFieldName:
 		if w.FormatCaller == nil {

console_test.go

@@ -26,10 +26,22 @@ func ExampleConsoleWriter_customFormatters() {
 	out.FormatLevel = func(i interface{}) string { return strings.ToUpper(fmt.Sprintf("%-6s|", i)) }
 	out.FormatFieldName = func(i interface{}) string { return fmt.Sprintf("%s:", i) }
 	out.FormatFieldValue = func(i interface{}) string { return strings.ToUpper(fmt.Sprintf("%s", i)) }
+	out.FormatMessageFromEvent = func(evt map[string]interface{}) zerolog.Formatter {
+		return func(i interface{}) string {
+			level := evt[zerolog.LevelFieldName]
+			switch level {
+			case zerolog.LevelInfoValue, zerolog.LevelWarnValue, zerolog.LevelErrorValue, zerolog.LevelFatalValue, zerolog.LevelPanicValue:
+				return fmt.Sprintf("%s (%q formatted message)", i, level)
+			default:
+				return fmt.Sprintf("%s", i)
+			}
+		}
+	}
+
 	log := zerolog.New(out)
 
 	log.Info().Str("foo", "bar").Msg("Hello World")
-	// Output: <nil> INFO  | Hello World foo:BAR
+	// Output: <nil> INFO  | Hello World ("info" formatted message) foo:BAR
 }
 
 func ExampleConsoleWriter_partValueFormatter() {