wally-tx: add type-to-string for a wally-tx

and then use it to print out things

bitcoin/tx.c

@@ -632,8 +632,17 @@ static char *fmt_bitcoin_txid(const tal_t *ctx, const struct bitcoin_txid *txid)
 	return hexstr;
 }
 
+static char *fmt_wally_tx(const tal_t *ctx, const struct wally_tx *tx)
+{
+	u8 *lin = linearize_wtx(ctx, tx);
+	char *s = tal_hex(ctx, lin);
+	tal_free(lin);
+	return s;
+}
+
 REGISTER_TYPE_TO_STRING(bitcoin_tx, fmt_bitcoin_tx);
 REGISTER_TYPE_TO_STRING(bitcoin_txid, fmt_bitcoin_txid);
+REGISTER_TYPE_TO_STRING(wally_tx, fmt_wally_tx);
 
 void fromwire_bitcoin_txid(const u8 **cursor, size_t *max,
 			   struct bitcoin_txid *txid)

common/type_to_string.h

@@ -37,6 +37,7 @@ union printable_types {
 	const struct fee_states *fee_states;
 	const char *charp_;
 	const struct wally_psbt *wally_psbt;
+	const struct wally_tx *wally_tx;
 };
 
 #define type_to_string(ctx, type, ptr)					\

wallet/walletrpc.c

@@ -99,8 +99,9 @@ static void wallet_withdrawal_broadcast(struct bitcoind *bitcoind UNUSED,
 		was_pending(command_success(cmd, response));
 	} else {
 		was_pending(command_fail(cmd, LIGHTNINGD,
-					 "Error broadcasting transaction: %s. Unsent tx discarded",
-					 output));
+					 "Error broadcasting transaction: %s. Unsent tx discarded %s",
+					 output,
+					 type_to_string(tmpctx, struct wally_tx, txb->wtx)));
 	}
 }