invoice: ignore dead-end heuristic on explicitly specified channels.

This makes testing easier, and makes sense: lightningd might not
*know* about other connected channels, depending on gossip, but if the
user specifies it we should obey it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: JSON: `invoice` `exposeprivatechannels` now includes explicitly named channels even if they seem like dead-ends.

doc/lightning-invoice.7.md

@@ -56,7 +56,7 @@ logic, which will use unpublished channels only if there are no
 published channels. If *true* unpublished channels are always considered
 as a route hint candidate; if *false*, never.  If it is a short channel id
 (e.g. *1x1x3*) or array of short channel ids, only those specific channels
-will be considered candidates, even if they are public.
+will be considered candidates, even if they are public or dead-ends.
 
 The route hint is selected from the set of incoming channels of which:
 peer’s balance minus their reserves is at least *msatoshi*, state is

lightningd/invoice.c

@@ -640,7 +640,11 @@ static void gossipd_incoming_channels_reply(struct subd *gossipd,
 					 &inchans[i].short_channel_id)) {
 				tal_arr_remove(&inchans, i);
 				tal_arr_remove(&inchan_deadends, i);
-			}
+				i--;
+			} else
+				/* If they specify directly, we don't
+				 * care if it's a deadend */
+				inchan_deadends[i] = false;
 		}
 
 		/* If they told us to use scids and we couldn't, fail. */

tests/test_invoices.py

@@ -284,13 +284,13 @@ def test_invoice_routeboost_private(node_factory, bitcoind):
     assert r['cltv_expiry_delta'] == 6
 
     # Ask it explicitly to use a channel it can't (insufficient capacity)
-    inv = l2.rpc.invoice(msatoshi=10, label="inv5", description="?", exposeprivatechannels=scid2)
-    assert 'warning_deadends' in inv
-    assert 'warning_capacity' not in inv
+    inv = l2.rpc.invoice(msatoshi=(10**5) * 1000 + 1, label="inv5", description="?", exposeprivatechannels=scid2)
+    assert 'warning_deadends' not in inv
+    assert 'warning_capacity' in inv
     assert 'warning_offline' not in inv
 
     # Give it two options and it will pick one with suff capacity.
-    inv = l2.rpc.invoice(msatoshi=10, label="inv6", description="?", exposeprivatechannels=[scid2, scid])
+    inv = l2.rpc.invoice(msatoshi=(10**5) * 1000 + 1, label="inv6", description="?", exposeprivatechannels=[scid2, scid])
     assert 'warning_capacity' not in inv
     assert 'warning_offline' not in inv
     assert 'warning_deadends' not in inv
@@ -302,6 +302,24 @@ def test_invoice_routeboost_private(node_factory, bitcoind):
     assert r['fee_proportional_millionths'] == 10
     assert r['cltv_expiry_delta'] == 6
 
+    # It will use an explicit exposeprivatechannels even if it thinks its a dead-end
+    l0.rpc.close(l1.info['id'])
+    l0.wait_for_channel_onchain(l1.info['id'])
+    bitcoind.generate_block(1)
+    wait_for(lambda: l2.rpc.listchannels(scid_dummy)['channels'] == [])
+
+    inv = l2.rpc.invoice(msatoshi=123456, label="inv7", description="?", exposeprivatechannels=scid)
+    assert 'warning_capacity' not in inv
+    assert 'warning_offline' not in inv
+    assert 'warning_deadends' not in inv
+    # Route array has single route with single element.
+    r = only_one(only_one(l1.rpc.decodepay(inv['bolt11'])['routes']))
+    assert r['pubkey'] == l1.info['id']
+    assert r['short_channel_id'] == l1.rpc.listchannels()['channels'][0]['short_channel_id']
+    assert r['fee_base_msat'] == 1
+    assert r['fee_proportional_millionths'] == 10
+    assert r['cltv_expiry_delta'] == 6
+
 
 def test_invoice_expiry(node_factory, executor):
     l1, l2 = node_factory.line_graph(2, fundchannel=True)