Merge bitcoin/bitcoin#23325: mempool: delete exists(uint256) function

4307849256761fe2440d82bbec892d0e8e6b4dd4 [mempool] delete exists(uint256) function (glozow)
d50fbd4c5b4bc72415854d582cedf94541a46983 create explicit GenTxid::{Txid, Wtxid} ctors (glozow)

Pull request description:

  We use the same type for txids and wtxids, `uint256`. In places where we want the ability to pass either one, we distinguish them using `GenTxid`.

  The (overloaded) `CTxMemPool::exists()` function is defined as follows:
  ```c
  bool exists(const uint256& txid) const { return exists(GenTxid{false, txid}); }
  ```
  It always assumes that a uint256 is a txid, which is a footgunny interface.
  Querying by wtxid returns a false negative if the transaction has a witness. :bug:

  Another approach would be to try both:
  ```c
  bool exists(const uint256& txid) const { return exists(GenTxid{false, txid}) || exists(GenTxid{false, txid}); }
  ```
  But that's slower and wrongfully placing the burden on the callee; the caller always knows whether the hash is a txid or a wtxid.

ACKs for top commit:
  laanwj:
    Code review ACK 4307849256761fe2440d82bbec892d0e8e6b4dd4
  jnewbery:
    Tested and code review ACK 4307849256761fe2440d82bbec892d0e8e6b4dd4
  MarcoFalke:
    review ACK 4307849256761fe2440d82bbec892d0e8e6b4dd4 👘

Tree-SHA512: 8ed167a96f3124b6c14e41073c8358658114ce121a15a4cca2db7a5ac565903a6236e34e88ac03382b8bb8b68e3999abbfc5718bc8c22476554d6b49a5298eec

1 files changed, 2 insertions, 0 deletions

diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index 46db39f8db..d7a85015ef 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -393,6 +393,8 @@ class GenTxid
     uint256 m_hash;
 public:
     GenTxid(bool is_wtxid, const uint256& hash) : m_is_wtxid(is_wtxid), m_hash(hash) {}
+    static GenTxid Txid(const uint256& hash) { return GenTxid{false, hash}; }
+    static GenTxid Wtxid(const uint256& hash) { return GenTxid{true, hash}; }
     bool IsWtxid() const { return m_is_wtxid; }
     const uint256& GetHash() const { return m_hash; }
     friend bool operator==(const GenTxid& a, const GenTxid& b) { return a.m_is_wtxid == b.m_is_wtxid && a.m_hash == b.m_hash; }