Permit full precomputation in PrecomputedTransactionData

At verification time, the to be precomputed data can be inferred from
the transaction itself. For signing, the necessary witnesses don't
exist yet, so just permit precomputing everything in that case.

Author: sipa

src/script/interpreter.cpp

@@ -1420,7 +1420,7 @@ uint256 GetSpentScriptsSHA256(const std::vector<CTxOut>& outputs_spent)
 } // namespace
 
 template <class T>
-void PrecomputedTransactionData::Init(const T& txTo, std::vector<CTxOut>&& spent_outputs)
+void PrecomputedTransactionData::Init(const T& txTo, std::vector<CTxOut>&& spent_outputs, bool force)
 {
     assert(!m_spent_outputs_ready);
 
@@ -1431,9 +1431,9 @@ void PrecomputedTransactionData::Init(const T& txTo, std::vector<CTxOut>&& spent
     }
 
     // Determine which precomputation-impacting features this transaction uses.
-    bool uses_bip143_segwit = false;
-    bool uses_bip341_taproot = false;
-    for (size_t inpos = 0; inpos < txTo.vin.size(); ++inpos) {
+    bool uses_bip143_segwit = force;
+    bool uses_bip341_taproot = force;
+    for (size_t inpos = 0; inpos < txTo.vin.size() && !(uses_bip143_segwit && uses_bip341_taproot); ++inpos) {
         if (!txTo.vin[inpos].scriptWitness.IsNull()) {
             if (m_spent_outputs_ready && m_spent_outputs[inpos].scriptPubKey.size() == 2 + WITNESS_V1_TAPROOT_SIZE &&
                 m_spent_outputs[inpos].scriptPubKey[0] == OP_1) {
@@ -1478,8 +1478,8 @@ PrecomputedTransactionData::PrecomputedTransactionData(const T& txTo)
 }
 
 // explicit instantiation
-template void PrecomputedTransactionData::Init(const CTransaction& txTo, std::vector<CTxOut>&& spent_outputs);
-template void PrecomputedTransactionData::Init(const CMutableTransaction& txTo, std::vector<CTxOut>&& spent_outputs);
+template void PrecomputedTransactionData::Init(const CTransaction& txTo, std::vector<CTxOut>&& spent_outputs, bool force);
+template void PrecomputedTransactionData::Init(const CMutableTransaction& txTo, std::vector<CTxOut>&& spent_outputs, bool force);
 template PrecomputedTransactionData::PrecomputedTransactionData(const CTransaction& txTo);
 template PrecomputedTransactionData::PrecomputedTransactionData(const CMutableTransaction& txTo);
 

src/script/interpreter.h

@@ -168,7 +168,7 @@ struct PrecomputedTransactionData
     PrecomputedTransactionData() = default;
 
     template <class T>
-    void Init(const T& tx, std::vector<CTxOut>&& spent_outputs);
+    void Init(const T& tx, std::vector<CTxOut>&& spent_outputs, bool force = false);
 
     template <class T>
     explicit PrecomputedTransactionData(const T& tx);