psbt: Change m_tap_tree to store just the tuples

Instead of having an entire TaprootBuilder which may or may not be
complete, and could potentially have future changes that interact oddly
with taproot tree tuples, have m_tap_tree be just the tuples.

When needed in other a TaprootBuilder for actual use, the tuples will be
added to a a TaprootBuilder that, in the future, can take in whatever
other data is needed as well.

Github-Pull: #25858
Rebased-From: 0577d423adda8e719d7611d03355680c8fbacab8

3 files changed, 19 insertions, 25 deletions

diff --git a/src/psbt.cpp b/src/psbt.cpp
index 6b75de91f8..6c6ea6a555 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -218,8 +218,14 @@ void PSBTOutput::FillSignatureData(SignatureData& sigdata) const
     for (const auto& key_pair : hd_keypaths) {
         sigdata.misc_pubkeys.emplace(key_pair.first.GetID(), key_pair);
     }
-    if (m_tap_tree.has_value() && m_tap_internal_key.IsFullyValid()) {
-        TaprootSpendData spenddata = m_tap_tree->GetSpendData();
+    if (!m_tap_tree.empty() && m_tap_internal_key.IsFullyValid()) {
+        TaprootBuilder builder;
+        for (const auto& [depth, leaf_ver, script] : m_tap_tree) {
+            builder.Add((int)depth, script, (int)leaf_ver, /*track=*/true);
+        }
+        assert(builder.IsComplete());
+        builder.Finalize(m_tap_internal_key);
+        TaprootSpendData spenddata = builder.GetSpendData();
 
         sigdata.tr_spenddata.internal_key = m_tap_internal_key;
         sigdata.tr_spenddata.Merge(spenddata);
@@ -244,7 +250,7 @@ void PSBTOutput::FromSignatureData(const SignatureData& sigdata)
         m_tap_internal_key = sigdata.tr_spenddata.internal_key;
     }
     if (sigdata.tr_builder.has_value()) {
-        m_tap_tree = sigdata.tr_builder;
+        m_tap_tree = sigdata.tr_builder->GetTreeTuples();
     }
     for (const auto& [pubkey, leaf_origin] : sigdata.taproot_misc_pubkeys) {
         m_tap_bip32_paths.emplace(pubkey, leaf_origin);
@@ -265,7 +271,7 @@ void PSBTOutput::Merge(const PSBTOutput& output)
     if (redeem_script.empty() && !output.redeem_script.empty()) redeem_script = output.redeem_script;
     if (witness_script.empty() && !output.witness_script.empty()) witness_script = output.witness_script;
     if (m_tap_internal_key.IsNull() && !output.m_tap_internal_key.IsNull()) m_tap_internal_key = output.m_tap_internal_key;
-    if (!m_tap_tree.has_value() && output.m_tap_tree.has_value()) m_tap_tree = output.m_tap_tree;
+    if (m_tap_tree.empty() && !output.m_tap_tree.empty()) m_tap_tree = output.m_tap_tree;
 }
 bool PSBTInputSigned(const PSBTInput& input)
 {
diff --git a/src/psbt.h b/src/psbt.h
index b8c35c9970..ddcdb8c68d 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -713,7 +713,7 @@ struct PSBTOutput
     CScript witness_script;
     std::map<CPubKey, KeyOriginInfo> hd_keypaths;
     XOnlyPubKey m_tap_internal_key;
-    std::optional<TaprootBuilder> m_tap_tree;
+    std::vector<std::tuple<uint8_t, uint8_t, CScript>> m_tap_tree;
     std::map<XOnlyPubKey, std::pair<std::set<uint256>, KeyOriginInfo>> m_tap_bip32_paths;
     std::map<std::vector<unsigned char>, std::vector<unsigned char>> unknown;
     std::set<PSBTProprietary> m_proprietary;
@@ -754,15 +754,11 @@ struct PSBTOutput
         }
 
         // Write taproot tree
-        if (m_tap_tree.has_value()) {
+        if (!m_tap_tree.empty()) {
             SerializeToVector(s, PSBT_OUT_TAP_TREE);
             std::vector<unsigned char> value;
             CVectorWriter s_value(s.GetType(), s.GetVersion(), value, 0);
-            const auto& tuples = m_tap_tree->GetTreeTuples();
-            for (const auto& tuple : tuples) {
-                uint8_t depth = std::get<0>(tuple);
-                uint8_t leaf_ver = std::get<1>(tuple);
-                CScript script = std::get<2>(tuple);
+            for (const auto& [depth, leaf_ver, script] : m_tap_tree) {
                 s_value << depth;
                 s_value << leaf_ver;
                 s_value << script;
@@ -858,13 +854,13 @@ struct PSBTOutput
                     } else if (key.size() != 1) {
                         throw std::ios_base::failure("Output Taproot tree key is more than one byte type");
                     }
-                    m_tap_tree.emplace();
                     std::vector<unsigned char> tree_v;
                     s >> tree_v;
                     SpanReader s_tree(s.GetType(), s.GetVersion(), tree_v);
                     if (s_tree.empty()) {
                         throw std::ios_base::failure("Output Taproot tree must not be empty");
                     }
+                    TaprootBuilder builder;
                     while (!s_tree.empty()) {
                         uint8_t depth;
                         uint8_t leaf_ver;
@@ -878,9 +874,10 @@ struct PSBTOutput
                         if ((leaf_ver & ~TAPROOT_LEAF_MASK) != 0) {
                             throw std::ios_base::failure("Output Taproot tree has a leaf with an invalid leaf version");
                         }
-                        m_tap_tree->Add((int)depth, script, (int)leaf_ver, true /* track */);
+                        m_tap_tree.push_back(std::make_tuple(depth, leaf_ver, script));
+                        builder.Add((int)depth, script, (int)leaf_ver, true /* track */);
                     }
-                    if (!m_tap_tree->IsComplete()) {
+                    if (!builder.IsComplete()) {
                         throw std::ios_base::failure("Output Taproot tree is malformed");
                     }
                     break;
@@ -934,11 +931,6 @@ struct PSBTOutput
             }
         }
 
-        // Finalize m_tap_tree so that all of the computed things are computed
-        if (m_tap_tree.has_value() && m_tap_tree->IsComplete() && m_tap_internal_key.IsFullyValid()) {
-            m_tap_tree->Finalize(m_tap_internal_key);
-        }
-
         if (!found_sep) {
             throw std::ios_base::failure("Separator is missing at the end of an output map");
         }
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index f365de7d0c..d654de1862 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1241,13 +1241,9 @@ static RPCHelpMan decodepsbt()
         }
 
         // Taproot tree
-        if (output.m_tap_tree.has_value()) {
+        if (!output.m_tap_tree.empty()) {
             UniValue tree(UniValue::VARR);
-            const auto& tuples = output.m_tap_tree->GetTreeTuples();
-            for (const auto& tuple : tuples) {
-                uint8_t depth = std::get<0>(tuple);
-                uint8_t leaf_ver = std::get<1>(tuple);
-                CScript script = std::get<2>(tuple);
+            for (const auto& [depth, leaf_ver, script] : output.m_tap_tree) {
                 UniValue elem(UniValue::VOBJ);
                 elem.pushKV("depth", (int)depth);
                 elem.pushKV("leaf_ver", (int)leaf_ver);