xpay: in future, don't MPP to pay bolt12 invoices unless invoice explicitly says so.

We don't want to enable this yet, since we only just fixed CLN this release!

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

doc/developers-guide/deprecations.md

@@ -37,6 +37,7 @@ hidden: false
 | close.tx                             | Field              | v24.11           | v25.11         | Use txs array instead                                                                                                                  |
 | close.txid                           | Field              | v24.11           | v25.11         | Use txids array instead                                                                                                                |
 | experimental-offers                  | Config             | v24.11           | v25.05         | Now the default                                                                                                                        |
+| xpay.ignore_bolt12_mpp               | Field              | v25.05           | v25.11         | Try MPP even if the BOLT12 invoice doesn't explicitly allow it (CLN didn't until 25.02)                                                |
 
 Inevitably there are features which need to change: either to be generalized, or removed when they can no longer be supported.
 

plugins/xpay/xpay.c

@@ -1560,7 +1560,10 @@ static struct command_result *json_xpay_core(struct command *cmd,
 			if (payment->payinfos[i]->cltv_expiry_delta > payment->final_cltv)
 				payment->final_cltv = payment->payinfos[i]->cltv_expiry_delta;
 		}
-		payment->disable_mpp = false;
+		/* We will start honoring this flag in future */
+		payment->disable_mpp = !feature_offered(b12inv->invoice_features, OPT_BASIC_MPP);
+		if (payment->disable_mpp && command_deprecated_in_ok(cmd, "ignore_bolt12_mpp", "v25.05", "v25.11"))
+			payment->disable_mpp = false;
 	} else {
 		struct bolt11 *b11
 			= bolt11_decode(tmpctx, payment->invstring,