*: Introduce version checking mechanism

server/api/config.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/gorilla/mux"
 	"github.com/juju/errors"
+	"github.com/pingcap/pd/pkg/error_code"
 	"github.com/pingcap/pd/server"
 	"github.com/unrolled/render"
 )
@@ -180,12 +181,12 @@ func (h *confHandler) SetClusterVersion(w http.ResponseWriter, r *http.Request)
 	}
 	version, ok := input["cluster-version"]
 	if !ok {
-		h.rd.JSON(w, http.StatusInternalServerError, "not set cluster version")
+		errorResp(h.rd, w, errcode.NewInvalidInputErr(errors.New("not set cluster-version")))
 		return
 	}
 	err := h.svr.SetClusterVersion(version)
 	if err != nil {
-		h.rd.JSON(w, http.StatusInternalServerError, err.Error())
+		errorResp(h.rd, w, errcode.NewInternalErr(err))
 		return
 	}
 	h.rd.JSON(w, http.StatusOK, nil)

server/server.go

@@ -548,8 +548,11 @@ func (s *Server) SetClusterVersion(v string) error {
 	if err != nil {
 		return errors.Trace(err)
 	}
+	err = s.scheduleOpt.persist(s.kv)
+	if err != nil {
+		return errors.Trace(err)
+	}
 	s.scheduleOpt.SetClusterVersion(*version)
-	s.scheduleOpt.persist(s.kv)
 	log.Infof("cluster version is updated to %s", v)
 	return nil
 }

server/version.go

@@ -25,17 +25,20 @@ type Feature int
 const (
 	Base Feature = iota
 	Version2_0
+	// RegionMerge supports the adjacent regions to be merge.
 	RegionMerge
+	// RaftLearner supports add a non-voting member in raft members.
 	RaftLearner
+	// BatchSplit can speed up the region split.
 	BatchSplit
 )
 
-var featuresDict = map[Feature]semver.Version{
-	Base:        {Major: 1},
-	Version2_0:  {Major: 2},
-	RegionMerge: {Major: 2, Minor: 0},
-	RaftLearner: {Major: 2, Minor: 0},
-	BatchSplit:  {Major: 2, Minor: 1},
+var featuresDict = map[Feature]string{
+	Base:        "1.0.0",
+	Version2_0:  "2.0.0",
+	RegionMerge: "2.0.0",
+	RaftLearner: "2.0.0",
+	BatchSplit:  "2.1.0",
 }
 
 // MinSupportedVersion returns the minimum support version for the specified feature.
@@ -44,7 +47,8 @@ func MinSupportedVersion(v Feature) semver.Version {
 	if !ok {
 		log.Fatalf("the corresponding version of the feature %d doesn't exist", v)
 	}
-	return target
+	version := MustParseVersion(target)
+	return *version
 }
 
 // ParseVersion wraps semver.NewVersion and handles compatibility issues.