fix(abstract-utxo): fix findDescriptorForOutput for taproot outputs

Issue: BTC-1786

Author: OttoAllmendinger

modules/abstract-utxo/src/core/descriptor/psbt/findDescriptors.ts

@@ -71,6 +71,19 @@ function findDescriptorForAnyDerivationPath(
   return undefined;
 }
 
+type WithBip32Derivation = { bip32Derivation?: { path: string }[] };
+type WithTapBip32Derivation = { tapBip32Derivation?: { path: string }[] };
+
+function getDerivationPaths(v: WithBip32Derivation | WithTapBip32Derivation): string[] | undefined {
+  if ('bip32Derivation' in v && v.bip32Derivation) {
+    return v.bip32Derivation.map((v) => v.path);
+  }
+  if ('tapBip32Derivation' in v && v.tapBip32Derivation) {
+    return v.tapBip32Derivation.map((v) => v.path).filter((v) => v !== '' && v !== 'm');
+  }
+  return undefined;
+}
+
 /**
  * @param input
  * @param descriptorMap
@@ -84,21 +97,11 @@ export function findDescriptorForInput(
   if (!script) {
     throw new Error('Missing script');
   }
-  if (input.bip32Derivation !== undefined) {
-    return findDescriptorForAnyDerivationPath(
-      script,
-      input.bip32Derivation.map((v) => v.path),
-      descriptorMap
-    );
-  }
-  if (input.tapBip32Derivation !== undefined) {
-    return findDescriptorForAnyDerivationPath(
-      script,
-      input.tapBip32Derivation.filter((v) => v.path !== '' && v.path !== 'm').map((v) => v.path),
-      descriptorMap
-    );
+  const derivationPaths = getDerivationPaths(input);
+  if (!derivationPaths) {
+    throw new Error('Missing derivation paths');
   }
-  throw new Error('Missing derivation path');
+  return findDescriptorForAnyDerivationPath(script, derivationPaths, descriptorMap);
 }
 
 /**
@@ -112,12 +115,9 @@ export function findDescriptorForOutput(
   output: PsbtOutput,
   descriptorMap: DescriptorMap
 ): DescriptorWithIndex | undefined {
-  if (!output.bip32Derivation) {
+  const derivationPaths = getDerivationPaths(output);
+  if (!derivationPaths) {
     return undefined;
   }
-  return findDescriptorForAnyDerivationPath(
-    script,
-    output.bip32Derivation.map((d) => d.path),
-    descriptorMap
-  );
+  return findDescriptorForAnyDerivationPath(script, derivationPaths, descriptorMap);
 }