entry: break out time, level and message from data

formatter.go

@@ -1,5 +1,9 @@
 package logrus
 
+import (
+	"time"
+)
+
 // The Formatter interface is used to implement a custom Formatter. It takes an
 // `Entry`. It exposes all the fields, including the default ones:
 //
@@ -13,3 +17,41 @@ package logrus
 type Formatter interface {
 	Format(*Entry) ([]byte, error)
 }
+
+type internalFormatter struct {
+}
+
+// This is to not silently overwrite `time`, `msg` and `level` fields when
+// dumping it. If this code wasn't there doing:
+//
+//  logrus.WithField("level", 1).Info("hello")
+//
+// Would just silently drop the user provided level. Instead with this code
+// it'll logged as:
+//
+//  {"level": "info", "fields.level": 1, "msg": "hello", "time": "..."}
+//
+// It's not exported because it's still using Data in an opionated way. It's to
+// avoid code duplication between the two default formatters.
+func (f *internalFormatter) prefixFieldClashes(entry *Entry) {
+	_, ok := entry.Data["time"]
+	if ok {
+		entry.Data["fields.time"] = entry.Data["time"]
+	}
+
+	entry.Data["time"] = entry.Time.Format(time.RFC3339)
+
+	_, ok = entry.Data["msg"]
+	if ok {
+		entry.Data["fields.msg"] = entry.Data["msg"]
+	}
+
+	entry.Data["msg"] = entry.Message
+
+	_, ok = entry.Data["level"]
+	if ok {
+		entry.Data["fields.level"] = entry.Data["level"]
+	}
+
+	entry.Data["level"] = entry.Level.String()
+}