rpc: update AbandonChannel to remove state from cnct, nursery and graph

In this commit, we update the `AbandonChannel` method to also remove the
state from the countract court as well as the channel graph. Abandoning
a channel is now a three step process: remove from the open channel
state, remove from the graph, remove from the contract court. Between
any step it's possible that the users restarts the process all over
again. As a result, each of the steps below are intended to be
idempotent.

We also update the integration test to assert that no channel is found
in the graph any longer. Before this commit, this test would fail as the
channel was still found in the graph, which can cause other issues for
an operational daemon.

Fixes #3716.

lntest/itest/lnd_test.go

@@ -13155,11 +13155,17 @@ func testAbandonChannel(net *lntest.NetworkHarness, t *harnessTest) {
 
 	ctxt, _ := context.WithTimeout(ctxb, channelOpenTimeout)
 	chanPoint := openChannelAndAssert(
-		ctxt, t, net, net.Alice, net.Bob, channelParam)
+		ctxt, t, net, net.Alice, net.Bob, channelParam,
+	)
+	txid, err := lnd.GetChanPointFundingTxid(chanPoint)
+	if err != nil {
+		t.Fatalf("unable to get txid: %v", err)
+	}
+	chanPointStr := fmt.Sprintf("%v:%v", txid, chanPoint.OutputIndex)
 
 	// Wait for channel to be confirmed open.
 	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
-	err := net.Alice.WaitForNetworkChannelOpen(ctxt, chanPoint)
+	err = net.Alice.WaitForNetworkChannelOpen(ctxt, chanPoint)
 	if err != nil {
 		t.Fatalf("alice didn't report channel: %v", err)
 	}
@@ -13168,6 +13174,25 @@ func testAbandonChannel(net *lntest.NetworkHarness, t *harnessTest) {
 		t.Fatalf("bob didn't report channel: %v", err)
 	}
 
+	// Now that the channel is open, we'll obtain its channel ID real quick
+	// so we can use it to query the graph below.
+	listReq := &lnrpc.ListChannelsRequest{}
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	aliceChannelList, err := net.Alice.ListChannels(ctxt, listReq)
+	if err != nil {
+		t.Fatalf("unable to fetch alice's channels: %v", err)
+	}
+	var chanID uint64
+	for _, channel := range aliceChannelList.Channels {
+		if channel.ChannelPoint == chanPointStr {
+			chanID = channel.ChanId
+		}
+	}
+
+	if chanID == 0 {
+		t.Fatalf("unable to find channel")
+	}
+
 	// Send request to abandon channel.
 	abandonChannelRequest := &lnrpc.AbandonChannelRequest{
 		ChannelPoint: chanPoint,
@@ -13180,9 +13205,8 @@ func testAbandonChannel(net *lntest.NetworkHarness, t *harnessTest) {
 	}
 
 	// Assert that channel in no longer open.
-	listReq := &lnrpc.ListChannelsRequest{}
 	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
-	aliceChannelList, err := net.Alice.ListChannels(ctxt, listReq)
+	aliceChannelList, err = net.Alice.ListChannels(ctxt, listReq)
 	if err != nil {
 		t.Fatalf("unable to list channels: %v", err)
 	}
@@ -13230,9 +13254,26 @@ func testAbandonChannel(net *lntest.NetworkHarness, t *harnessTest) {
 			len(aliceClosedList.Channels))
 	}
 
-	// Now that we're done with the test, the channel can be closed. This is
-	// necessary to avoid unexpected outcomes of other tests that use Bob's
-	// lnd instance.
+	// Ensure that the channel can no longer be found in the channel graph.
+	_, err = net.Alice.GetChanInfo(ctxb, &lnrpc.ChanInfoRequest{
+		ChanId: chanID,
+	})
+	if !strings.Contains(err.Error(), "marked as zombie") {
+		t.Fatalf("channel shouldn't be found in the channel " +
+			"graph!")
+	}
+
+	// Calling AbandonChannel again, should result in no new errors, as the
+	// channel has already been removed.
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	_, err = net.Alice.AbandonChannel(ctxt, abandonChannelRequest)
+	if err != nil {
+		t.Fatalf("unable to abandon channel a second time: %v", err)
+	}
+
+	// Now that we're done with the test, the channel can be closed. This
+	// is necessary to avoid unexpected outcomes of other tests that use
+	// Bob's lnd instance.
 	ctxt, _ = context.WithTimeout(ctxb, channelCloseTimeout)
 	closeChannelAndAssert(ctxt, t, net, net.Bob, chanPoint, true)