Merge bitcoin/bitcoin#25877: refactor: Do not use CScript for tapleaf scripts until the tapleaf version is known

dee89438b82e94474ebaa31367035f98b4636dac Abstract out ComputeTapbranchHash (Russell O'Connor)
8e3fc9942729716e95907008fcf36eee758c3a6a Do not use CScript for tapleaf scripts until the tapleaf version is known (Russell O'Connor)

Pull request description:

  While BIP-341 calls the contents of tapleaf a "script", only in the case that the tapleaf version is `0xc0` is this script known to be a tapscript.  Otherwise the tapleaf "script" is simply an uninterpreted string of bytes.

  This PR corrects the issue where the type `CScript` is used prior to the tapleaf version being known to be a tapscript.  This prevents `CScript` methods from erroneously being called on non-tapscript data.

  A second commit abstracts out the TapBranch hash computation in the same manner that the TapLeaf computation is already abstracted.  These two abstractions ensure that the TapLeaf and TapBranch tagged hashes are always constructed properly.

ACKs for top commit:
  ajtowns:
    ACK dee89438b82e94474ebaa31367035f98b4636dac
  instagibbs:
    ACK dee89438b82e94474ebaa31367035f98b4636dac
  achow101:
    ACK dee89438b82e94474ebaa31367035f98b4636dac
  sipa:
    ACK dee89438b82e94474ebaa31367035f98b4636dac
  aureleoules:
    reACK dee89438b82e94474ebaa31367035f98b4636dac - I verified that there is no behavior change.

Tree-SHA512: 4a1d37f3e9a1890e7f5eadcf65562688cc451389581fe6e2da0feb2368708edacdd95392578d8afff05270d88fc61dce732d83d1063d84d12cf47b5f4633ec7e

1 files changed, 5 insertions, 5 deletions

diff --git a/src/script/standard.h b/src/script/standard.h
index f08258af4f..18cf5c8c88 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -217,7 +217,7 @@ struct TaprootSpendData
      *  inference can reconstruct the full tree. Within each set, the control
      *  blocks are sorted by size, so that the signing logic can easily
      *  prefer the cheapest one. */
-    std::map<std::pair<CScript, int>, std::set<std::vector<unsigned char>, ShortestVectorFirstComparator>> scripts;
+    std::map<std::pair<std::vector<unsigned char>, int>, std::set<std::vector<unsigned char>, ShortestVectorFirstComparator>> scripts;
     /** Merge other TaprootSpendData (for the same scriptPubKey) into this. */
     void Merge(TaprootSpendData other);
 };
@@ -229,7 +229,7 @@ private:
     /** Information about a tracked leaf in the Merkle tree. */
     struct LeafInfo
     {
-        CScript script;                      //!< The script.
+        std::vector<unsigned char> script;   //!< The script.
         int leaf_version;                    //!< The leaf version for that script.
         std::vector<uint256> merkle_branch;  //!< The hashing partners above this leaf.
     };
@@ -296,7 +296,7 @@ public:
     /** Add a new script at a certain depth in the tree. Add() operations must be called
      *  in depth-first traversal order of binary tree. If track is true, it will be included in
      *  the GetSpendData() output. */
-    TaprootBuilder& Add(int depth, const CScript& script, int leaf_version, bool track = true);
+    TaprootBuilder& Add(int depth, Span<const unsigned char> script, int leaf_version, bool track = true);
     /** Like Add(), but for a Merkle node with a given hash to the tree. */
     TaprootBuilder& AddOmitted(int depth, const uint256& hash);
     /** Finalize the construction. Can only be called when IsComplete() is true.
@@ -314,7 +314,7 @@ public:
     /** Compute spending data (after Finalize()). */
     TaprootSpendData GetSpendData() const;
     /** Returns a vector of tuples representing the depth, leaf version, and script */
-    std::vector<std::tuple<uint8_t, uint8_t, CScript>> GetTreeTuples() const;
+    std::vector<std::tuple<uint8_t, uint8_t, std::vector<unsigned char>>> GetTreeTuples() const;
     /** Returns true if there are any tapscripts */
     bool HasScripts() const { return !m_branch.empty(); }
 };
@@ -325,6 +325,6 @@ public:
  * std::nullopt is returned. Otherwise, a vector of (depth, script, leaf_ver) tuples is
  * returned, corresponding to a depth-first traversal of the script tree.
  */
-std::optional<std::vector<std::tuple<int, CScript, int>>> InferTaprootTree(const TaprootSpendData& spenddata, const XOnlyPubKey& output);
+std::optional<std::vector<std::tuple<int, std::vector<unsigned char>, int>>> InferTaprootTree(const TaprootSpendData& spenddata, const XOnlyPubKey& output);
 
 #endif // BITCOIN_SCRIPT_STANDARD_H