Merge #16956: validation: Make GetWitnessCommitmentIndex public

fa607c2 validation: Make GetWitnessCommitmentIndex public (MarcoFalke)

Pull request description:

  `GenerateCoinbaseCommitment` is public and can be used in unit tests to update the witness commitment after the list of txs in a block has been changed. However, for it to work, the existing commitment (added by default in `CreateNewBlock`) must be removed (and thus its index must be known).

  Make that possible by exposing the `GetWitnessCommitmentIndex` helper function in the header.

ACKs for top commit:
  jb55:
    ACK fa607c2
  jamesob:
    ACK bitcoin/bitcoin@fa607c2
  promag:
    ACK fa607c2.
  fanquake:
    ACK fa607c2 - This unblocks work in #15845.

Tree-SHA512: d563aa2c201d5fb4874e506a28f468c37e457cc8a20229c377178af08c22d3be44e19ee6e8e524b6de99236cd5f2c9e39b8009d88c26854aa774737912bd5889

Author: fanquake

src/validation.cpp

@@ -3280,9 +3280,7 @@ bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& pa
     return (height >= params.SegwitHeight);
 }
 
-// Compute at which vout of the block's coinbase transaction the witness
-// commitment occurs, or -1 if not found.
-static int GetWitnessCommitmentIndex(const CBlock& block)
+int GetWitnessCommitmentIndex(const CBlock& block)
 {
     int commitpos = -1;
     if (!block.vtx.empty()) {

src/validation.h

@@ -384,6 +384,9 @@ bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& pa
 /** When there are blocks in the active chain with missing data, rewind the chainstate and remove them from the block index */
 bool RewindBlockIndex(const CChainParams& params) LOCKS_EXCLUDED(cs_main);
 
+/** Compute at which vout of the block's coinbase transaction the witness commitment occurs, or -1 if not found */
+int GetWitnessCommitmentIndex(const CBlock& block);
+
 /** Update uncommitted block structures (currently: only the witness reserved value). This is safe for submitted blocks. */
 void UpdateUncommittedBlockStructures(CBlock& block, const CBlockIndex* pindexPrev, const Consensus::Params& consensusParams);