mlog: add Logger.WithKV, slightly change Message type to support it

mlog/mlog.go

@@ -186,7 +186,7 @@ func (str String) String() string {
 type Message struct {
 	Level
 	Description Stringer
-	KV          KV
+	KVer
 }
 
 func stringSlice(kv KV) [][2]string {
@@ -219,12 +219,14 @@ func DefaultFormat(w io.Writer, msg Message) error {
 		}
 	}
 	write("~ %s -- %s", msg.Level.String(), msg.Description.String())
-	if len(msg.KV) > 0 {
+	if msg.KVer != nil {
+		if kv := msg.KV(); len(kv) > 0 {
 			write(" --")
-		for _, kve := range stringSlice(msg.KV) {
+			for _, kve := range stringSlice(kv) {
 				write(" %s=%s", kve[0], kve[1])
 			}
 		}
+	}
 	write("\n")
 	return err
 }
@@ -253,6 +255,7 @@ type Logger struct {
 	w        io.Writer
 	h        Handler
 	maxLevel uint
+	kv       KVer
 
 	testMsgWrittenCh chan struct{} // only initialized/used in tests
 }
@@ -301,6 +304,16 @@ func (l *Logger) WithHandler(h Handler) *Logger {
 	return l
 }
 
+// WithKV returns a copy of the Logger which will use the merging of the given
+// KVers as a base KVer for all log messages. If the original Logger already had
+// a base KVer (via a previous WithKV call) then this set will be merged onto
+// that one.
+func (l *Logger) WithKV(kvs ...KVer) *Logger {
+	l = l.clone()
+	l.kv = MergeInto(l.kv, kvs...)
+	return l
+}
+
 // Log can be used to manually log a message of some custom defined Level. kvs
 // will be Merge'd automatically. If the Level is a fatal (Uint() == 0) then
 // calling this will never return, and the process will have os.Exit(1) called.
@@ -309,6 +322,10 @@ func (l *Logger) Log(msg Message) {
 		return
 	}
 
+	if l.kv != nil {
+		msg.KVer = MergeInto(l.kv, msg.KVer)
+	}
+
 	if err := l.h(msg); err != nil {
 		go l.Error("Logger.Handler returned error", ErrKV(err))
 		return
@@ -327,7 +344,7 @@ func mkMsg(lvl Level, descr string, kvs ...KVer) Message {
 	return Message{
 		Level:       lvl,
 		Description: String(descr),
-		KV:          Merge(kvs...).KV(),
+		KVer:        Merge(kvs...),
 	}
 }
 

mlog/mlog_test.go

@@ -101,6 +101,15 @@ func TestLogger(t *T) {
 		assertOut("~ WARN -- BAZ\n"),
 		assertOut("~ ERROR -- buz\n"),
 	))
+
+	l3 := l2.WithKV(KV{"a": 1})
+	l3.Info("foo", KV{"b": 2})
+	l3.Info("bar", KV{"a": 2, "b": 3})
+	massert.Fatal(t, massert.All(
+		assertOut("~ INFO -- FOO -- a=\"1\" b=\"2\"\n"),
+		assertOut("~ INFO -- BAR -- a=\"2\" b=\"3\"\n"),
+	))
+
 }
 
 func TestDefaultFormat(t *T) {
@@ -122,13 +131,13 @@ func TestDefaultFormat(t *T) {
 	msg := Message{Level: InfoLevel, Description: String("this is a test")}
 	massert.Fatal(t, assertFormat("INFO -- this is a test", msg))
 
-	msg.KV = KV{}.KV()
+	msg.KVer = KV{}
 	massert.Fatal(t, assertFormat("INFO -- this is a test", msg))
 
-	msg.KV = KV{"foo": "a"}.KV()
+	msg.KVer = KV{"foo": "a"}
 	massert.Fatal(t, assertFormat("INFO -- this is a test -- foo=\"a\"", msg))
 
-	msg.KV = KV{"foo": "a", "bar": "b"}.KV()
+	msg.KVer = KV{"foo": "a", "bar": "b"}
 	massert.Fatal(t,
 		assertFormat("INFO -- this is a test -- bar=\"b\" foo=\"a\"", msg))
 }