hooks.go

@@ -66,7 +66,9 @@ func OnMissingKey(h MissingKeyHandler) {
 	missingKeyHandler.Store(missingKeyHandlersState{handlers: []MissingKeyHandler{h}})
 }
 
-func appendMissingKeyHandler(h MissingKeyHandler) {
+// AddMissingKeyHandler appends a missing-key handler without replacing any
+// existing handlers.
+func AddMissingKeyHandler(h MissingKeyHandler) {
 	if h == nil {
 		return
 	}
@@ -75,6 +77,10 @@ func appendMissingKeyHandler(h MissingKeyHandler) {
 	missingKeyHandler.Store(current)
 }
 
+func appendMissingKeyHandler(h MissingKeyHandler) {
+	AddMissingKeyHandler(h)
+}
+
 func missingKeyHandlers() missingKeyHandlersState {
 	v := missingKeyHandler.Load()
 	if v == nil {

hooks_test.go

@@ -274,6 +274,35 @@ func TestOnMissingKey_Good(t *testing.T) {
 	assert.Equal(t, "hooks_test.go", filepath.Base(captured.CallerFile))
 }
 
+func TestAddMissingKeyHandler_Good(t *testing.T) {
+	svc, err := New()
+	require.NoError(t, err)
+	prev := Default()
+	SetDefault(svc)
+	t.Cleanup(func() {
+		SetDefault(prev)
+	})
+	svc.SetMode(ModeCollect)
+
+	OnMissingKey(nil)
+	t.Cleanup(func() {
+		OnMissingKey(nil)
+	})
+
+	var first, second int
+	AddMissingKeyHandler(func(MissingKey) {
+		first++
+	})
+	AddMissingKeyHandler(func(MissingKey) {
+		second++
+	})
+
+	_ = T("missing.multiple.handlers")
+
+	assert.Equal(t, 1, first)
+	assert.Equal(t, 1, second)
+}
+
 func TestOnMissingKey_Good_SubjectArgs(t *testing.T) {
 	svc, err := New()
 	require.NoError(t, err)