versionbits: simplify state transitions

This removes the DEFINED->FAILED transition and changes the
STARTED->FAILED transition to only occur if signalling didn't pass the
threshold. This ensures that it is always possible for activation to
occur, no matter what settings are chosen, or the speed at which blocks
are found.

Github-Pull: #21377
Rebased-From: f054f6bcd2c2ce5fea84cf8681013f85a444e7ea

1 files changed, 7 insertions, 10 deletions

diff --git a/src/test/fuzz/versionbits.cpp b/src/test/fuzz/versionbits.cpp
index 5d859c911c..645c0d23c0 100644
--- a/src/test/fuzz/versionbits.cpp
+++ b/src/test/fuzz/versionbits.cpp
@@ -144,19 +144,14 @@ void test_one_input(const std::vector<uint8_t>& buffer)
         // pick the timestamp to switch based on a block
         // note states will change *after* these blocks because mediantime lags
         int start_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * (max_periods - 3));
-        int end_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(start_block, period * (max_periods - 3));
+        int end_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * (max_periods - 3));
 
         start_time = block_start_time + start_block * interval;
         timeout = block_start_time + end_block * interval;
 
-        assert(start_time <= timeout);
-
         // allow for times to not exactly match a block
         if (fuzzed_data_provider.ConsumeBool()) start_time += interval / 2;
         if (fuzzed_data_provider.ConsumeBool()) timeout += interval / 2;
-
-        // this may make timeout too early; if so, don't run the test
-        if (start_time > timeout) return;
     } else {
         if (fuzzed_data_provider.ConsumeBool()) {
             start_time = Consensus::BIP9Deployment::ALWAYS_ACTIVE;
@@ -292,13 +287,12 @@ void test_one_input(const std::vector<uint8_t>& buffer)
         assert(since == 0);
         assert(exp_state == ThresholdState::DEFINED);
         assert(current_block->GetMedianTimePast() < checker.m_begin);
-        assert(current_block->GetMedianTimePast() < checker.m_end);
         break;
     case ThresholdState::STARTED:
         assert(current_block->GetMedianTimePast() >= checker.m_begin);
-        assert(current_block->GetMedianTimePast() < checker.m_end);
         if (exp_state == ThresholdState::STARTED) {
             assert(blocks_sig < threshold);
+            assert(current_block->GetMedianTimePast() < checker.m_end);
         } else {
             assert(exp_state == ThresholdState::DEFINED);
         }
@@ -308,7 +302,6 @@ void test_one_input(const std::vector<uint8_t>& buffer)
             assert(current_block->nHeight + 1 < min_activation);
         } else {
             assert(exp_state == ThresholdState::STARTED);
-            assert(current_block->GetMedianTimePast() < checker.m_end);
             assert(blocks_sig >= threshold);
         }
         break;
@@ -318,7 +311,11 @@ void test_one_input(const std::vector<uint8_t>& buffer)
         break;
     case ThresholdState::FAILED:
         assert(never_active_test || current_block->GetMedianTimePast() >= checker.m_end);
-        assert(exp_state != ThresholdState::LOCKED_IN && exp_state != ThresholdState::ACTIVE);
+        if (exp_state == ThresholdState::STARTED) {
+            assert(blocks_sig < threshold);
+        } else {
+            assert(exp_state == ThresholdState::FAILED);
+        }
         break;
     default:
         assert(false);