Verify that all validation flags are backward compatible

See #10699, i.e. adding a flag should always reduce the
number of acceptable scripts.

Co-authored-by: Johnson Lau <jl2012@xbt.hk>

src/test/transaction_tests.cpp

@@ -22,6 +22,7 @@
 #include <streams.h>
 #include <test/util/transaction_utils.h>
 #include <util/strencodings.h>
+#include <util/string.h>
 #include <validation.h>
 
 #include <functional>
@@ -230,6 +231,21 @@ BOOST_AUTO_TEST_CASE(tx_valid)
             if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, ~verify_flags, txdata, strTest, /* expect_valid */ true)) {
                 BOOST_ERROR("Tx unexpectedly failed: " << strTest);
             }
+
+            // Backwards compatibility of script verification flags: Removing any flag(s) should not invalidate a valid transaction
+            for (size_t i = 0; i < mapFlagNames.size(); ++i) {
+                // Removing individual flags
+                unsigned int flags = TrimFlags(~(verify_flags | (1U << i)));
+                if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, flags, txdata, strTest, /* expect_valid */ true)) {
+                    BOOST_ERROR("Tx unexpectedly failed with flag " << ToString(i) << " unset: " << strTest);
+                }
+                // Removing random combinations of flags
+                flags = TrimFlags(~(verify_flags | (unsigned int)InsecureRandBits(mapFlagNames.size())));
+                if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, flags, txdata, strTest, /* expect_valid */ true)) {
+                    BOOST_ERROR("Tx unexpectedly failed with random flags " << ToString(flags) << ": " << strTest);
+                }
+            }
+
             // Check that flags are maximal: transaction should fail if any unset flags are set.
             for (auto flags_excluding_one: ExcludeIndividualFlags(verify_flags)) {
                 if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, ~flags_excluding_one, txdata, strTest, /* expect_valid */ false)) {
@@ -302,6 +318,21 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
             if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, verify_flags, txdata, strTest, /* expect_valid */ false)) {
                 BOOST_ERROR("Tx unexpectedly passed: " << strTest);
             }
+
+            // Backwards compatibility of script verification flags: Adding any flag(s) should not validate an invalid transaction
+            for (size_t i = 0; i < mapFlagNames.size(); i++) {
+                unsigned int flags = FillFlags(verify_flags | (1U << i));
+                // Adding individual flags
+                if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, flags, txdata, strTest, /* expect_valid */ false)) {
+                    BOOST_ERROR("Tx unexpectedly passed with flag " << ToString(i) << " set: " << strTest);
+                }
+                // Adding random combinations of flags
+                flags = FillFlags(verify_flags | (unsigned int)InsecureRandBits(mapFlagNames.size()));
+                if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, flags, txdata, strTest, /* expect_valid */ false)) {
+                    BOOST_ERROR("Tx unexpectedly passed with random flags " << ToString(flags) << ": " << strTest);
+                }
+            }
+
             // Check that flags are minimal: transaction should succeed if any set flags are unset.
             for (auto flags_excluding_one: ExcludeIndividualFlags(verify_flags)) {
                 if (!CheckTxScripts(tx, mapprevOutScriptPubKeys, mapprevOutValues, flags_excluding_one, txdata, strTest, /* expect_valid */ true)) {