make -1 denote the "not used" value

core/blockchain.go

@@ -454,7 +454,7 @@ func NewBlockChain(db ethdb.Database, cacheConfig *CacheConfig, genesis *Genesis
 		if compat.RewindToTime > 0 {
 			bc.SetHeadWithTimestamp(compat.RewindToTime)
 		} else {
-			bc.SetHead(compat.RewindToBlock)
+			bc.SetHead(uint64(compat.RewindToBlock))
 		}
 		rawdb.WriteChainConfig(db, genesisHash, chainConfig)
 	}

core/genesis.go

@@ -354,7 +354,7 @@ func SetupGenesisBlockWithOverride(db ethdb.Database, triedb *triedb.Database, g
 		return newcfg, stored, errors.New("missing head header")
 	}
 	compatErr := storedcfg.CheckCompatible(newcfg, head.Number.Uint64(), head.Time)
-	if compatErr != nil && ((head.Number.Uint64() != 0 && compatErr.RewindByBlock) || (head.Time != 0 && compatErr.RewindToTime != 0)) {
+	if compatErr != nil && ((head.Number.Uint64() != 0 && compatErr.IsRewindByBlock()) || (head.Time != 0 && compatErr.RewindToTime != 0)) {
 		return newcfg, stored, compatErr
 	}
 	// Don't overwrite if the old is identical to the new

core/genesis_test.go

@@ -148,7 +148,6 @@ func testSetupGenesis(t *testing.T, scheme string) {
 				What:          "Homestead fork block",
 				StoredBlock:   big.NewInt(2),
 				NewBlock:      big.NewInt(3),
-				RewindByBlock: true,
 				RewindToBlock: 1,
 			},
 		},

params/config.go

@@ -605,7 +605,7 @@ func (c *ChainConfig) CheckCompatible(newcfg *ChainConfig, height uint64, time u
 		if err.RewindToTime > 0 {
 			btime = err.RewindToTime
 		} else {
-			bhead.SetUint64(err.RewindToBlock)
+			bhead.SetUint64(uint64(err.RewindToBlock))
 		}
 	}
 	return lasterr
@@ -841,10 +841,8 @@ type ConfigCompatError struct {
 	StoredTime, NewTime *uint64
 
 	// the block number to which the local chain must be rewound to correct the error
-	RewindToBlock uint64
+	// "-1" is used as a "not used" flag to denote it's rewinding by time instead
-
+	RewindToBlock int64
-	// the flag to tell whether it's rewinding by block or time
-	RewindByBlock bool
 
 	// the timestamp to which the local chain must be rewound to correct the error
 	RewindToTime uint64
@@ -865,10 +863,9 @@ func newBlockCompatError(what string, storedblock, newblock *big.Int) *ConfigCom
 		StoredBlock:   storedblock,
 		NewBlock:      newblock,
 		RewindToBlock: 0,
-		RewindByBlock: true,
 	}
 	if rew != nil && rew.Sign() > 0 {
-		err.RewindToBlock = rew.Uint64() - 1
+		err.RewindToBlock = int64(rew.Uint64() - 1)
 	}
 	return err
 }
@@ -887,6 +884,7 @@ func newTimestampCompatError(what string, storedtime, newtime *uint64) *ConfigCo
 		What:          what,
 		StoredTime:    storedtime,
 		NewTime:       newtime,
+		RewindToBlock: -1,
 		RewindToTime:  0,
 	}
 	if rew != nil && *rew != 0 {
@@ -895,6 +893,10 @@ func newTimestampCompatError(what string, storedtime, newtime *uint64) *ConfigCo
 	return err
 }
 
+func (err *ConfigCompatError) IsRewindByBlock() bool {
+	return err.RewindToBlock != -1
+}
+
 func (err *ConfigCompatError) Error() string {
 	if err.StoredBlock != nil {
 		return fmt.Sprintf("mismatching %s in database (have block %d, want block %d, rewindto block %d)", err.What, err.StoredBlock, err.NewBlock, err.RewindToBlock)

params/config_test.go

@@ -52,7 +52,6 @@ func TestCheckCompatible(t *testing.T) {
 				StoredBlock:   big.NewInt(0),
 				NewBlock:      nil,
 				RewindToBlock: 0,
-				RewindByBlock: true,
 			},
 		},
 		{
@@ -64,7 +63,6 @@ func TestCheckCompatible(t *testing.T) {
 				StoredBlock:   big.NewInt(0),
 				NewBlock:      big.NewInt(1),
 				RewindToBlock: 0,
-				RewindByBlock: true,
 			},
 		},
 		{
@@ -76,7 +74,6 @@ func TestCheckCompatible(t *testing.T) {
 				StoredBlock:   big.NewInt(10),
 				NewBlock:      big.NewInt(20),
 				RewindToBlock: 9,
-				RewindByBlock: true,
 			},
 		},
 		{
@@ -94,7 +91,6 @@ func TestCheckCompatible(t *testing.T) {
 				StoredBlock:   nil,
 				NewBlock:      big.NewInt(31),
 				RewindToBlock: 30,
-				RewindByBlock: true,
 			},
 		},
 		{
@@ -112,14 +108,15 @@ func TestCheckCompatible(t *testing.T) {
 				StoredTime:    newUint64(10),
 				NewTime:       newUint64(20),
 				RewindToTime:  9,
+				RewindToBlock: -1,
 			},
 		},
 	}
 
-	for _, test := range tests {
+	for i, test := range tests {
 		err := test.stored.CheckCompatible(test.new, test.headBlock, test.headTimestamp)
 		if !reflect.DeepEqual(err, test.wantErr) {
-			t.Errorf("error mismatch:\nstored: %v\nnew: %v\nheadBlock: %v\nheadTimestamp: %v\nerr: %v\nwant: %v", test.stored, test.new, test.headBlock, test.headTimestamp, err, test.wantErr)
+			t.Errorf("error mismatch:\nstored: %v\nnew: %v\nheadBlock: %v\nheadTimestamp: %v\nerr: %v\nwant: %v\nindex:%d", test.stored, test.new, test.headBlock, test.headTimestamp, err, test.wantErr, i)
 		}
 	}
 }