fix confirmed spender height lookup

return a terminal height when a prevout has no confirmed spender, instead of zero.

previously, unspent outputs could get a height of zero which implies they were
spent by the genesis block. more specifically, outputs that are unspent because
the spending transaction was not confirmed would get marked as already spent by the
genesis block when attempting to broadcast the transaction.

also check the computed block link when short-circuiting find_strong(tx_link), so
unconfirmed duplicate tx links fall back to hash-based strong lookup instead of
returning a terminal block link.

Author: josibake

include/bitcoin/database/impl/query/consensus/consensus_strong.ipp

@@ -72,9 +72,9 @@ height_link CLASS::find_strong_spender_height(
     size_t out{};
     for (const auto& in: to_spenders(point))
         if (const auto tx = to_input_tx(in); get_tx_height(out, tx))
-            break;
+            return { system::possible_narrow_cast<height_link::integer>(out) };
 
-    return { system::possible_narrow_cast<height_link::integer>(out) };
+    return {};
 }
 
 // find_strong (block)
@@ -84,7 +84,7 @@ TEMPLATE
 header_link CLASS::find_strong(const tx_link& link) const NOEXCEPT
 {
     // Shortcuircuit hash-based search by testing self.
-    if (const auto fk = to_block(link); !link.is_terminal())
+    if (const auto fk = to_block(link); !fk.is_terminal())
         return fk;
 
     return find_strong(get_tx_key(link));

test/query/confirmed.cpp

@@ -144,6 +144,89 @@ BOOST_AUTO_TEST_CASE(query_confirmed__is_confirmed_tx__confirm__expected)
     BOOST_REQUIRE(query.is_confirmed_tx(2));
 }
 
+BOOST_AUTO_TEST_CASE(query_confirmed__find_strong__unconfirmed_duplicate__expected)
+{
+    settings settings{};
+    settings.path = TEST_DIRECTORY;
+    test::chunk_store store{ settings };
+    test::query_accessor query{ store };
+    BOOST_REQUIRE(!store.create(test::events_handler));
+    BOOST_REQUIRE(query.initialize(test::genesis));
+    BOOST_REQUIRE(query.set(test::block1a, context{ 0, 1, 0 }, false, false));
+    BOOST_REQUIRE(query.set_strong(1));
+
+    BOOST_REQUIRE(query.set(test::tx4));
+    const auto unconfirmed = query.to_tx(test::tx4.hash(false));
+
+    BOOST_REQUIRE(query.set(test::block_spend_1a, context{ 0, 2, 0 }, false, false));
+    BOOST_REQUIRE(query.set_strong(2));
+
+    BOOST_REQUIRE_EQUAL(query.find_strong(unconfirmed),
+        query.to_header(test::block_spend_1a.hash()));
+}
+
+BOOST_AUTO_TEST_CASE(query_confirmed__find_strong_spender_height__unspent__terminal)
+{
+    settings settings{};
+    settings.path = TEST_DIRECTORY;
+    test::chunk_store store{ settings };
+    test::query_accessor query{ store };
+    BOOST_REQUIRE(!store.create(test::events_handler));
+    BOOST_REQUIRE(query.initialize(test::genesis));
+    BOOST_REQUIRE(query.set(test::block1a, context{ 0, 1, 0 }, false, false));
+    BOOST_REQUIRE(query.set_strong(1));
+
+    const system::chain::point point
+    {
+        test::block1a.transactions_ptr()->front()->hash(false), 0
+    };
+
+    BOOST_REQUIRE(query.find_strong_spender_height(point).is_terminal());
+}
+
+BOOST_AUTO_TEST_CASE(query_confirmed__find_strong_spender_height__unconfirmed__terminal)
+{
+    settings settings{};
+    settings.path = TEST_DIRECTORY;
+    test::chunk_store store{ settings };
+    test::query_accessor query{ store };
+    BOOST_REQUIRE(!store.create(test::events_handler));
+    BOOST_REQUIRE(query.initialize(test::genesis));
+    BOOST_REQUIRE(query.set(test::block1a, context{ 0, 1, 0 }, false, false));
+    BOOST_REQUIRE(query.set_strong(1));
+    BOOST_REQUIRE(query.set(test::tx5));
+
+    const system::chain::point point
+    {
+        test::block1a.transactions_ptr()->front()->hash(false), 0
+    };
+
+    BOOST_REQUIRE(query.find_strong_spender_height(point).is_terminal());
+}
+
+BOOST_AUTO_TEST_CASE(query_confirmed__find_strong_spender_height__confirmed__expected)
+{
+    settings settings{};
+    settings.path = TEST_DIRECTORY;
+    test::chunk_store store{ settings };
+    test::query_accessor query{ store };
+    BOOST_REQUIRE(!store.create(test::events_handler));
+    BOOST_REQUIRE(query.initialize(test::genesis));
+    BOOST_REQUIRE(query.set(test::block1a, context{ 0, 1, 0 }, false, false));
+    BOOST_REQUIRE(query.set_strong(1));
+    BOOST_REQUIRE(query.set(test::block_spend_1a, context{ 0, 2, 0 }, false, false));
+    BOOST_REQUIRE(query.set_strong(2));
+
+    const system::chain::point point
+    {
+        test::block1a.transactions_ptr()->front()->hash(false), 0
+    };
+
+    const auto height = query.find_strong_spender_height(point);
+    BOOST_REQUIRE(!height.is_terminal());
+    BOOST_REQUIRE_EQUAL(height.value, 2u);
+}
+
 BOOST_AUTO_TEST_CASE(query_confirmed__is_confirmed_input__genesis__true)
 {
     settings settings{};