consensus/cometbft: Fail ImmutableState creation if version is missing

.changelog/6040.bugfix.md

@@ -0,0 +1,8 @@
+go/consensus/cometbft: Fail ImmutableState creation if version is missing
+
+Previously, when an `ImmutableState` was requested for a block version that
+didn't exist, the function would silently default to the latest available
+block. This could lead to inconsistencies since clients might receive state
+for a different block than expected. With this change, calls to create
+an `ImmutableState` for a missing version now explicitly fail with a
+"version not found" error, ensuring that such cases are handled properly.

go/consensus/cometbft/abci/state.go

@@ -283,17 +283,25 @@ func (s *applicationState) GetCurrentEpoch(ctx context.Context) (beacon.EpochTim
 	if blockHeight == 0 {
 		return beacon.EpochInvalid, nil
 	}
+
+	latestHeight := blockHeight
+	if abciCtx := api.FromCtx(ctx); abciCtx != nil {
+		// If request was made from an ABCI application context, then use blockHeight + 1,
+		// to fetch the epoch at current (future) height.
+		latestHeight++
+	}
+
 	// Check if there is an epoch transition scheduled for the current height. This should be taken
 	// into account when GetCurrentEpoch is called before the time keeping app does the transition.
-	future, err := s.timeSource.GetFutureEpoch(ctx, blockHeight+1)
+	future, err := s.timeSource.GetFutureEpoch(ctx, latestHeight)
 	if err != nil {
-		return beacon.EpochInvalid, fmt.Errorf("failed to get future epoch for height %d: %w", blockHeight+1, err)
+		return beacon.EpochInvalid, fmt.Errorf("failed to get future epoch for height %d: %w", latestHeight, err)
 	}
 	if future != nil && future.Height == blockHeight+1 {
 		return future.Epoch, nil
 	}
 
-	currentEpoch, err := s.timeSource.GetEpoch(ctx, blockHeight+1)
+	currentEpoch, err := s.timeSource.GetEpoch(ctx, latestHeight)
 	if err != nil {
 		return beacon.EpochInvalid, fmt.Errorf("failed to get epoch for height %d: %w", blockHeight+1, err)
 	}

go/consensus/cometbft/api/state.go

@@ -294,7 +294,10 @@ func NewImmutableState(ctx context.Context, state ApplicationQueryState, version
 	if state.BlockHeight() == 0 {
 		return nil, consensus.ErrNoCommittedBlocks
 	}
-	if version <= 0 || version > state.BlockHeight() {
+	if version > state.BlockHeight() {
+		return nil, consensus.ErrVersionNotFound
+	}
+	if version <= 0 {
 		version = state.BlockHeight()
 	}
 

go/consensus/cometbft/apps/staking/slashing.go

@@ -69,7 +69,7 @@ func onEvidenceByzantineConsensus(
 	// validator from being scheduled in the next epoch.
 	if penalty.FreezeInterval > 0 {
 		var epoch beacon.EpochTime
-		epoch, err = ctx.AppState().GetEpoch(context.Background(), ctx.BlockHeight()+1)
+		epoch, err = ctx.AppState().GetEpoch(context.Background(), ctx.BlockHeight())
 		if err != nil {
 			return err
 		}