blockchain: error on v2 selection (#6730)

## Description

Remove v2 flag from toml

CHANGELOG_PENDING.md

@@ -24,6 +24,7 @@ Friendly reminder: We have a [bug bounty program](https://hackerone.com/tendermi
   - [libs/CList] \#6626 Automatically detach the prev/next elements in Remove function (@JayT106)
   - [fastsync/rpc] \#6620 Add TotalSyncedTime & RemainingTime to SyncInfo in /status RPC  (@JayT106)
   - [rpc/grpc] \#6725 Mark gRPC in the RPC layer as deprecated.
+  - [blockchain/v2] \#6730 Fast Sync v2 is deprecated, please use v0
 
 - Apps
   - [ABCI] \#6408 Change the `key` and `value` fields from `[]byte` to `string` in the `EventAttribute` type. (@alexanderbez)

UPGRADING.md

@@ -32,6 +32,8 @@ This guide provides instructions for upgrading to specific versions of Tendermin
 - configuration values starting with `priv-validator-` have moved to the new
   `priv-validator` section, without the `priv-validator-` prefix.
 
+* Fast Sync v2 has been deprecated, please use v0 to sync a node.
+
 ### CLI Changes
 
 * You must now specify the node mode (validator|full|seed) in `tendermint init [mode]`

config/config.go

@@ -961,7 +961,7 @@ func (cfg *FastSyncConfig) ValidateBasic() error {
 	case BlockchainV0:
 		return nil
 	case BlockchainV2:
-		return nil
+		return errors.New("fastsync version v2 is no longer supported. Please use v0")
 	default:
 		return fmt.Errorf("unknown fastsync version %s", cfg.Version)
 	}

config/config_test.go

@@ -131,7 +131,7 @@ func TestFastSyncConfigValidateBasic(t *testing.T) {
 
 	// tamper with version
 	cfg.Version = "v2"
-	assert.NoError(t, cfg.ValidateBasic())
+	assert.Error(t, cfg.ValidateBasic())
 
 	cfg.Version = "invalid"
 	assert.Error(t, cfg.ValidateBasic())

config/toml.go

@@ -442,7 +442,7 @@ fetchers = "{{ .StateSync.Fetchers }}"
 
 # Fast Sync version to use:
 #   1) "v0" (default) - the legacy fast sync implementation
-#   2) "v2" - complete redesign of v0, optimized for testability & readability
+#   2) "v2" - DEPRECATED, please use v0
 version = "{{ .FastSync.Version }}"
 
 #######################################################

node/setup.go

@@ -372,10 +372,7 @@ func createBlockchainReactor(
 		return reactorShim, reactor, nil
 
 	case cfg.BlockchainV2:
-		reactor := bcv2.NewBlockchainReactor(state.Copy(), blockExec, blockStore, fastSync, metrics)
-		reactor.SetLogger(logger)
-
-		return nil, reactor, nil
+		return nil, nil, errors.New("fastsync version v2 is no longer supported. Please use v0")
 
 	default:
 		return nil, nil, fmt.Errorf("unknown fastsync version %s", config.FastSync.Version)