user codes: allow empty

return nil if error is nil
allow an empty user message

error_code_test.go

@@ -376,16 +376,20 @@ func TestOpErrorCode(t *testing.T) {
 	OpEquals(t, errcode.OpErrCode{Operation: "opcode", Err: has}, "opcode")
 }
 
+/*
 func assertPanics[T any](t *testing.T, f func() T) {
+	t.Helper()
 	var res T
 	defer func() {
 		if r := recover(); r == nil {
+			t.Helper()
 			t.Errorf("testPanic: did not panic, got: %v", res)
 		}
 	}()
 
 	res = f()
 }
+*/
 
 func TestUserMsg(t *testing.T) {
 	AssertUserMsg(t, "foo", "")
@@ -403,8 +407,12 @@ func TestUserMsg(t *testing.T) {
 	UserMsgEquals(t, um.AddTo(MinimalError{}), "modify")
 
 	umEmpty := errcode.UserMsg("")
-	assertPanics(t, func() errcode.ErrorCode { return umEmpty.AddTo(MinimalError{}) })
-	assertPanics(t, func() errcode.ErrorCode { return umEmpty.AddTo(nil) })
+	if errcode.GetUserMsg(umEmpty.AddTo(MinimalError{})) != "" {
+		t.Errorf("expected empty string")
+	}
+	if umEmpty.AddTo(nil) != nil {
+		t.Errorf("expected nil")
+	}
 
 	UserMsgEquals(t, ErrorWrapper{Err: ue}, "user")
 	UserMsgEquals(t, ErrorWrapper{Err: UserMsgErrorEmbed{EmbedUserMsg: errcode.EmbedUserMsg{Msg: "field"}}}, "field")

user.go

@@ -94,10 +94,10 @@ var _ HasUserMsg = (*UserMsgErrCode)(nil)    // assert implements interface
 var _ unwrapError = (*UserMsgErrCode)(nil)   // assert implements interface
 
 // AddUserMsg is constructed by UserMsg. It allows method chaining with AddTo.
-type AddUserMsg func(ErrorCode) UserMsgErrCode
+type AddUserMsg func(ErrorCode) UserCode
 
 // AddTo adds the user message from UserMsg to the given ErrorCode
-func (add AddUserMsg) AddTo(err ErrorCode) UserMsgErrCode {
+func (add AddUserMsg) AddTo(err ErrorCode) UserCode {
 	return add(err)
 }
 
@@ -109,19 +109,16 @@ func (add AddUserMsg) AddTo(err ErrorCode) UserMsgErrCode {
 //		return userMsg.AddTo(PathBlocked{start, end, obstacle})
 //	}
 func UserMsg(msg string) AddUserMsg {
-	return func(err ErrorCode) UserMsgErrCode {
+	return func(err ErrorCode) UserCode {
 		return WithUserMsg(msg, err)
 	}
 }
 
 // WithUserMsg creates a UserMsgErrCode
 // Panics if msg is empty or err is nil.
-func WithUserMsg(msg string, err ErrorCode) UserMsgErrCode {
+func WithUserMsg(msg string, err ErrorCode) UserCode {
 	if err == nil {
-		panic("WithUserMsg ErrorCode is nil")
-	}
-	if msg == "" {
-		panic("WithUserMsg msg is empty")
+		return nil
 	}
 	return UserMsgErrCode{Msg: msg, Err: err}
 }