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.

1 files changed, 7 insertions, 10 deletions

diff --git a/src/test/fuzz/versionbits.cpp b/src/test/fuzz/versionbits.cpp
index 4177323233..9186821836 100644
--- a/src/test/fuzz/versionbits.cpp
+++ b/src/test/fuzz/versionbits.cpp
@@ -147,19 +147,14 @@ FUZZ_TARGET_INIT(versionbits, initialize)
         // 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;
@@ -297,13 +292,12 @@ FUZZ_TARGET_INIT(versionbits, initialize)
         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);
         }
@@ -313,7 +307,6 @@ FUZZ_TARGET_INIT(versionbits, initialize)
             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;
@@ -323,7 +316,11 @@ FUZZ_TARGET_INIT(versionbits, initialize)
         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);