Return early from ReceiveBlock if already sycned (#13089)

* Return early from ReceiveBlock if already sycned

* Fix bad setup test

beacon-chain/blockchain/receive_block.go

@@ -3,6 +3,7 @@ package blockchain
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"time"
 
 	"github.com/pkg/errors"
@@ -58,6 +59,11 @@ type SlashingReceiver interface {
 func (s *Service) ReceiveBlock(ctx context.Context, block interfaces.ReadOnlySignedBeaconBlock, blockRoot [32]byte) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.ReceiveBlock")
 	defer span.End()
+	// Return early if the block has been synced
+	if s.InForkchoice(blockRoot) {
+		log.WithField("blockRoot", fmt.Sprintf("%#x", blockRoot)).Debug("Ignoring already synced block")
+		return nil
+	}
 	receivedTime := time.Now()
 	s.blockBeingSynced.set(blockRoot)
 	defer s.blockBeingSynced.unset(blockRoot)

testing/spectest/shared/common/forkchoice/builder_test.go

@@ -26,6 +26,9 @@ func TestBuilderInvalidBlock(t *testing.T) {
 	blk, err := blocks.NewSignedBeaconBlock(util.NewBeaconBlock())
 	require.NoError(t, err)
 	builder := NewBuilder(t, st, blk)
+	blk, err = blocks.NewSignedBeaconBlock(util.NewBeaconBlock())
+	blk.SetSlot(2)
+	require.NoError(t, err)
 	builder.InvalidBlock(t, blk)
 }