common: don't abort() if wally_psbt_output_taproot_keypath_add() fails.

It fails on duplicates.  It would ideally succeed, but bug reported:

	https://github.com/ElementsProject/libwally-core/issues/509

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: JSON-RPC: `signpsbt` no longer crashes if asked to sign an already-signed PSBT with taproot paths.

common/close_tx.c

@@ -54,9 +54,11 @@ struct bitcoin_tx *create_close_tx(const tal_t *ctx,
 		assert((local_wallet_index == NULL) == (local_wallet_ext_key == NULL));
 		if (local_wallet_index) {
 			size_t script_len = tal_bytelen(script);
-			psbt_add_keypath_to_last_output(
-				tx, *local_wallet_index, local_wallet_ext_key,
-				is_p2tr(script, script_len, NULL));
+			/* Should not happen! */
+			if (!psbt_add_keypath_to_last_output(
+				    tx, *local_wallet_index, local_wallet_ext_key,
+				    is_p2tr(script, script_len, NULL)))
+				return tal_free(tx);
                 }
 		num_outputs++;
 	}

common/psbt_keypath.c

@@ -3,7 +3,11 @@
 #include <common/psbt_keypath.h>
 #include <common/utils.h>
 
-void psbt_output_set_keypath(u32 index, const struct ext_key *ext, bool is_taproot, struct wally_psbt_output *output) {
+bool psbt_output_set_keypath(u32 index,
+			     const struct ext_key *ext,
+			     bool is_taproot,
+			     struct wally_psbt_output *output)
+{
 	u8 fingerprint[BIP32_KEY_FINGERPRINT_LEN];
 	if (bip32_key_get_fingerprint(
 		    (struct ext_key *) ext, fingerprint, sizeof(fingerprint)) != WALLY_OK)
@@ -18,24 +22,29 @@ void psbt_output_set_keypath(u32 index, const struct ext_key *ext, bool is_tapro
 							  NULL, 0,
 							  fingerprint, sizeof(fingerprint),
 							  path, 1) != WALLY_OK)
-			abort();
+			return false;
 	} else {
 		if (wally_psbt_output_keypath_add(output,
 						  ext->pub_key, sizeof(ext->pub_key),
 						  fingerprint, sizeof(fingerprint),
 						  path, 1) != WALLY_OK)
-			abort();
+			return false;
 	}
 
+	return true;
 }
 
-void psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
+bool psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
 				     u32 key_index,
-					 const struct ext_key *ext,
-					 bool is_taproot) {
+				     const struct ext_key *ext,
+				     bool is_taproot)
+{
 	size_t outndx = tx->psbt->num_outputs - 1;
+	bool ok;
 
 	tal_wally_start();
-	psbt_output_set_keypath(key_index, ext, is_taproot, &tx->psbt->outputs[outndx]);
+	ok = psbt_output_set_keypath(key_index, ext, is_taproot, &tx->psbt->outputs[outndx]);
 	tal_wally_end(tx->psbt);
+
+	return ok;
 }

common/psbt_keypath.h

@@ -2,6 +2,7 @@
 #define LIGHTNING_COMMON_PSBT_KEYPATH_H
 
 #include "config.h"
+#include <ccan/compiler/compiler.h>
 #include <ccan/short_types/short_types.h>
 #include <wally_psbt.h>
 
@@ -15,11 +16,14 @@ struct wally_map;
  * @ext - extended public key of the immediate parent of the wallet key
  * @is_taproot - PSBT output has taproot script
  * @output - PSBT output to set
+ *
+ * This can fail, if it's adding the same thing twice (taproot only)
  */
-void psbt_output_set_keypath(u32 index,
-		      const struct ext_key *ext,
-			  bool is_taproot,
-		      struct wally_psbt_output *output);
+WARN_UNUSED_RESULT
+bool psbt_output_set_keypath(u32 index,
+			     const struct ext_key *ext,
+			     bool is_taproot,
+			     struct wally_psbt_output *output);
 
 /* psbt_add_keypath_to_last_output - augment the last output with the
  * given wallet keypath
@@ -29,9 +33,10 @@ void psbt_output_set_keypath(u32 index,
  * @ext - extended public key of the immediate parent of the wallet key
  * @is_taproot - if the output is taproot
  */
-void psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
+WARN_UNUSED_RESULT
+bool psbt_add_keypath_to_last_output(struct bitcoin_tx *tx,
 				     u32 index,
 				     const struct ext_key *ext,
-					 bool is_taproot);
+				     bool is_taproot);
 
 #endif /* LIGHTNING_COMMON_PSBT_KEYPATH_H */