refactor: disable default std::hash for CTransactionRef

The default std::hash for shared_ptr compares by pointer.

CTransactionRefHash or a custom hasher should be used instead.

Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

src/primitives/transaction.h

@@ -403,4 +403,16 @@ struct CMutableTransaction
 typedef std::shared_ptr<const CTransaction> CTransactionRef;
 template <typename Tx> static inline CTransactionRef MakeTransactionRef(Tx&& txIn) { return std::make_shared<const CTransaction>(std::forward<Tx>(txIn)); }
 
+namespace std {
+/** Disable default std::hash for CTransactionRef to prevent accidentally
+ *  comparing by pointer. Use CTransactionRefHash or provide a custom
+ *  hasher. */
+template <>
+struct hash<CTransactionRef> {
+    hash() = delete;
+    // Belt-and-suspenders, already implied by the above.
+    size_t operator()(const CTransactionRef&) const = delete;
+};
+} // namespace std
+
 #endif // BITCOIN_PRIMITIVES_TRANSACTION_H