MB-52355: Add more logging when maxCompositeFilters > Num SecKeys

* Adding the print in fillScans and not setExplodePositions to capture
  protoscans received from the query
* Index out of range panic was seen in setExplodedPositions function
  when accessing explodePositions array of size len(IndexInst.Defn.SecExprs)
* -- panic: runtime error: index out of range [4] with length 4
* Print the scans details and return error than panic
* Example print
  2022-06-17T02:37:02.185+05:30 [Error] SCAN##2 ReqID: ee9939aa-d17c-4705-9d60-91d773053bbd Defn: 9151033855720878966
	SecExprs: [`age`]
	Scans: <ud>([{ [150] 3 filterRange [{[{ 100 2}]  [100] 3 } {[{50 150 3}] [50] [150] 3 }] <nil>} {[200] [200] 3 range [{[{200 200 3}] [200] [200] 3 }] <nil>}])</ud>
	MaxCompositeFilters: 1
	ProtoScans:
		 protobuf scan 0 filters:<low:"null" high:"100" inclusion:2 >
		 protobuf scan 1 filters:<low:"50" high:"150" inclusion:3 >
		 protobuf scan 2 filters:<low:"200" high:"200" inclusion:3 >

Change-Id: Ibb017edb6e84af3d963e80f2549e28b69dc82d57

secondary/indexer/scan_request.go

@@ -85,6 +85,8 @@ type ScanRequest struct {
 	decodePositions  []bool
 	explodeUpto      int
 
+	maxCompositeFilters int
+
 	// New parameters for partitioned index
 	Sorted bool
 
@@ -1090,37 +1092,50 @@ func (r *ScanRequest) fillScans(protoScans []*protobuf.Scan) (localErr error) {
 	// Sort Index Points
 	sort.Sort(IndexPoints(points))
 	r.Scans = r.composeScans(points, filters)
-	return
-}
-
-// Populate list of positions of keys which need to be
-// exploded for composite filtering and index projection
-func (r *ScanRequest) setExplodePositions() {
 
-	if r.isPrimary {
-		return
-	}
-
-	maxCompositeFilters := 0
+	r.maxCompositeFilters = 0
 	for _, sc := range r.Scans {
 		if sc.ScanType != FilterRangeReq {
 			continue
 		}
 
 		for _, fl := range sc.Filters {
 			num := len(fl.CompositeFilters)
-			if num > maxCompositeFilters {
-				maxCompositeFilters = num
+			if num > r.maxCompositeFilters {
+				r.maxCompositeFilters = num
 			}
 		}
 	}
 
+	// Adding extra logs for MB-52355
+	if r.maxCompositeFilters > len(r.IndexInst.Defn.SecExprs) {
+		fmsg := "%v ReqID: %v Defn: %v \n\tSecExprs: %v \n\tScans: %v \n\tMaxCompositeFilters: %v \n\tProtoScans: %v"
+		var sb strings.Builder
+		for i, s := range protoScans {
+			sb.WriteString(fmt.Sprintf("\n\t\t protobuf scan %v %v", i, s.String()))
+		}
+		logging.Errorf(fmsg, r.LogPrefix, r.RequestId, r.DefnID, r.IndexInst.Defn.SecExprs,
+			logging.TagUD(r.Scans), r.maxCompositeFilters, sb.String())
+		return fmt.Errorf("invalid length of composite element filters in scan request")
+	}
+
+	return
+}
+
+// Populate list of positions of keys which need to be
+// exploded for composite filtering and index projection
+func (r *ScanRequest) setExplodePositions() {
+
+	if r.isPrimary {
+		return
+	}
+
 	if r.explodePositions == nil {
 		r.explodePositions = make([]bool, len(r.IndexInst.Defn.SecExprs))
 		r.decodePositions = make([]bool, len(r.IndexInst.Defn.SecExprs))
 	}
 
-	for i := 0; i < maxCompositeFilters; i++ {
+	for i := 0; i < r.maxCompositeFilters; i++ {
 		r.explodePositions[i] = true
 	}