lightningd: make sure we register all addresses at opening if peer doesn't support OPT_SHUTDOWN_ANYSEGWIT.

We select the close key index at opening time, but the non-DF code didn't correctly register the
address as possibly used for P2WPKH for older nodes.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: wallet: we could miss our own returned outputs on mutual closes if peer doesn't support option_shutdown_anysegwit (you will still need to rescan after update, if this happened to you!)
Reported-by: Grubles

Author: rustyrussell

lightningd/opening_control.c

@@ -122,8 +122,14 @@ wallet_commit_channel(struct lightningd *ld,
 	/* FIXME: P2TR for elements! */
 	if (chainparams->is_elements)
 		addrtype = ADDR_BECH32;
-	else
+	else if (feature_negotiated(ld->our_features,
+				    uc->peer->their_features,
+				    OPT_SHUTDOWN_ANYSEGWIT))
 		addrtype = ADDR_P2TR;
+	else
+		/* They *may* update to OPT_SHUTDOWN_ANYSEGWIT by the
+		 * time we close, so be prepared for both. */
+		addrtype = ADDR_ALL;
 
 	/* Get a key to use for closing outputs from this tx */
 	final_key_idx = wallet_get_newindex(ld, addrtype);

tests/test_closing.py

@@ -4277,7 +4277,6 @@ def censoring_sendrawtx(r):
     l1.daemon.wait_for_log(r"Low-priority anchorspend aiming for block {} \(feerate 7500\)".format(height + 12))
 
 
-@pytest.mark.xfail(strict=True)
 @unittest.skipIf(TEST_NETWORK != 'regtest', "elementsd doesn't use p2tr anyway")
 def test_onchain_close_no_p2tr(node_factory, bitcoind):
     """Closing with a peer which doesn't support OPT_SHUTDOWN_ANYSEGWIT"""