Make Taproot spends standard + policy limits

This adds a `TxoutType::WITNESS_V1_TAPROOT` for P2TR outputs, and permits spending
them in standardness rules. No corresponding `CTxDestination` is added for it,
as that isn't needed until we want wallet integration. The taproot validation flags
are also enabled for mempool transactions, and standardness rules are added
(stack item size limit, no annexes).

1 files changed, 3 insertions, 1 deletions

diff --git a/src/script/standard.h b/src/script/standard.h
index 6dbcd04968..721203385e 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -129,6 +129,7 @@ enum class TxoutType {
     NULL_DATA, //!< unspendable OP_RETURN script that carries data
     WITNESS_V0_SCRIPTHASH,
     WITNESS_V0_KEYHASH,
+    WITNESS_V1_TAPROOT,
     WITNESS_UNKNOWN, //!< Only for Witness versions not already defined above
 };
 
@@ -206,7 +207,8 @@ struct WitnessUnknown
  *  * ScriptHash: TxoutType::SCRIPTHASH destination (P2SH)
  *  * WitnessV0ScriptHash: TxoutType::WITNESS_V0_SCRIPTHASH destination (P2WSH)
  *  * WitnessV0KeyHash: TxoutType::WITNESS_V0_KEYHASH destination (P2WPKH)
- *  * WitnessUnknown: TxoutType::WITNESS_UNKNOWN destination (P2W???)
+ *  * WitnessUnknown: TxoutType::WITNESS_UNKNOWN/WITNESS_V1_TAPROOT destination (P2W???)
+ *    (taproot outputs do not require their own type as long as no wallet support exists)
  *  A CTxDestination is the internal data type encoded in a bitcoin address
  */
 typedef boost::variant<CNoDestination, PKHash, ScriptHash, WitnessV0ScriptHash, WitnessV0KeyHash, WitnessUnknown> CTxDestination;