multi: change RegisterAttempt error checking order

Move our more generic terminal check forward so that we only
need to handle a single class of expected errors. This change
is mirrored in our mock, and our reproducing tests are updated
to assert that this move catches both classes of errors we get.

channeldb/payment_control.go

@@ -290,18 +290,19 @@ func (p *PaymentControl) RegisterAttempt(paymentHash lntypes.Hash,
 			return err
 		}
 
-		// Ensure the payment is in-flight.
-		if err := ensureInFlight(p); err != nil {
-			return err
-		}
-
 		// We cannot register a new attempt if the payment already has
-		// reached a terminal condition:
+		// reached a terminal condition. We check this before
+		// ensureInFlight because it is a more general check.
 		settle, fail := p.TerminalInfo()
 		if settle != nil || fail != nil {
 			return ErrPaymentTerminal
 		}
 
+		// Ensure the payment is in-flight.
+		if err := ensureInFlight(p); err != nil {
+			return err
+		}
+
 		// Make sure any existing shards match the new one with regards
 		// to MPP options.
 		mpp := attempt.Route.FinalHop().MPP

channeldb/payment_control_test.go

@@ -1013,19 +1013,15 @@ func TestPaymentControlMultiShard(t *testing.T) {
 		// up in the Succeeded state. If both failed the payment should
 		// also be Failed at this poinnt.
 		finalStatus := StatusFailed
-		expRegErr := ErrPaymentAlreadyFailed
 		if test.settleFirst || test.settleLast {
 			finalStatus = StatusSucceeded
-			expRegErr = ErrPaymentAlreadySucceeded
 		}
 
 		assertPaymentStatus(t, pControl, info.PaymentHash, finalStatus)
 
 		// Finally assert we cannot register more attempts.
 		_, err = pControl.RegisterAttempt(info.PaymentHash, &b)
-		if err != expRegErr {
+		require.Equal(t, ErrPaymentTerminal, err)
-			t.Fatalf("expected error %v, got: %v", expRegErr, err)
-		}
 	}
 
 	for _, test := range tests {

routing/mock_test.go

@@ -325,6 +325,10 @@ func (m *mockControlTower) RegisterAttempt(phash lntypes.Hash,
 	_, settled := m.successful[phash]
 	_, failed := m.failed[phash]
 
+	if settled || failed {
+		return channeldb.ErrPaymentTerminal
+	}
+
 	if settled && !inFlight {
 		return channeldb.ErrPaymentAlreadySucceeded
 	}
@@ -333,10 +337,6 @@ func (m *mockControlTower) RegisterAttempt(phash lntypes.Hash,
 		return channeldb.ErrPaymentAlreadyFailed
 	}
 
-	if settled || failed {
-		return channeldb.ErrPaymentTerminal
-	}
-
 	// Add attempt to payment.
 	p.attempts = append(p.attempts, channeldb.HTLCAttempt{
 		HTLCAttemptInfo: *a,

routing/payment_lifecycle_test.go

@@ -619,7 +619,7 @@ func TestRouterPaymentStateMachine(t *testing.T) {
 			// A MP payment scenario when our path finding returns
 			// after we've just received a terminal failure, and
 			// demonstrates a bug where the payment will return with
-			// and "unexpected" ErrPaymentAlreadyFailed rather than
+			// and "unexpected" ErrPaymentTerminal rather than
 			// failing with a permanent error. This results in the
 			// payment getting stuck.
 			name: "MP path found after failure",
@@ -648,7 +648,7 @@ func TestRouterPaymentStateMachine(t *testing.T) {
 			routes: []*route.Route{
 				shard, shard,
 			},
-			paymentErr: channeldb.ErrPaymentAlreadyFailed,
+			paymentErr: channeldb.ErrPaymentTerminal,
 		},
 		{
 			// A MP payment scenario when our path finding returns