From e32ba1599c599e75b1da3393f71f633de860505f Mon Sep 17 00:00:00 2001
From: glozow <gloriajzhao@gmail.com>
Date: Thu, 11 May 2023 17:50:05 +0100
Subject: [PATCH] [txpackages] IsChildWithParentsTree()

Many edge cases exist when parents in a child-with-parents package can
spend each other. However, this pattern should also be uncommon in
normal use cases.
---
 src/policy/packages.cpp      | 15 +++++++++++++++
 src/policy/packages.h        |  4 ++++
 src/test/txpackage_tests.cpp |  3 +++
 3 files changed, 22 insertions(+)

diff --git a/src/policy/packages.cpp b/src/policy/packages.cpp
index fd272a2642e..47a9274a311 100644
--- a/src/policy/packages.cpp
+++ b/src/policy/packages.cpp
@@ -88,3 +88,18 @@ bool IsChildWithParents(const Package& package)
     return std::all_of(package.cbegin(), package.cend() - 1,
                        [&input_txids](const auto& ptx) { return input_txids.count(ptx->GetHash()) > 0; });
 }
+
+bool IsChildWithParentsTree(const Package& package)
+{
+    if (!IsChildWithParents(package)) return false;
+    std::unordered_set<uint256, SaltedTxidHasher> parent_txids;
+    std::transform(package.cbegin(), package.cend() - 1, std::inserter(parent_txids, parent_txids.end()),
+                   [](const auto& ptx) { return ptx->GetHash(); });
+    // Each parent must not have an input who is one of the other parents.
+    return std::all_of(package.cbegin(), package.cend() - 1, [&](const auto& ptx) {
+        for (const auto& input : ptx->vin) {
+            if (parent_txids.count(input.prevout.hash) > 0) return false;
+        }
+        return true;
+    });
+}
diff --git a/src/policy/packages.h b/src/policy/packages.h
index 702667b8ade..cf37857e4bb 100644
--- a/src/policy/packages.h
+++ b/src/policy/packages.h
@@ -63,4 +63,8 @@ bool CheckPackage(const Package& txns, PackageValidationState& state);
  */
 bool IsChildWithParents(const Package& package);
 
+/** Context-free check that a package IsChildWithParents() and none of the parents depend on each
+ * other (the package is a "tree").
+ */
+bool IsChildWithParentsTree(const Package& package);
 #endif // BITCOIN_POLICY_PACKAGES_H
diff --git a/src/test/txpackage_tests.cpp b/src/test/txpackage_tests.cpp
index 571b58156f7..a8318e9fdbe 100644
--- a/src/test/txpackage_tests.cpp
+++ b/src/test/txpackage_tests.cpp
@@ -162,6 +162,7 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         BOOST_CHECK_EQUAL(state.GetResult(), PackageValidationResult::PCKG_POLICY);
         BOOST_CHECK_EQUAL(state.GetRejectReason(), "package-not-sorted");
         BOOST_CHECK(IsChildWithParents({tx_parent, tx_child}));
+        BOOST_CHECK(IsChildWithParentsTree({tx_parent, tx_child}));
     }
 
     // 24 Parents and 1 Child
@@ -187,6 +188,7 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         PackageValidationState state;
         BOOST_CHECK(CheckPackage(package, state));
         BOOST_CHECK(IsChildWithParents(package));
+        BOOST_CHECK(IsChildWithParentsTree(package));
 
         package.erase(package.begin());
         BOOST_CHECK(IsChildWithParents(package));
@@ -219,6 +221,7 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         BOOST_CHECK(IsChildWithParents({tx_parent, tx_parent_also_child}));
         BOOST_CHECK(IsChildWithParents({tx_parent, tx_child}));
         BOOST_CHECK(IsChildWithParents({tx_parent, tx_parent_also_child, tx_child}));
+        BOOST_CHECK(!IsChildWithParentsTree({tx_parent, tx_parent_also_child, tx_child}));
         // IsChildWithParents does not detect unsorted parents.
         BOOST_CHECK(IsChildWithParents({tx_parent_also_child, tx_parent, tx_child}));
         BOOST_CHECK(CheckPackage({tx_parent, tx_parent_also_child, tx_child}, state));