kvserver: return destination from AdminScatter

AdminScatter now returns the RangeInfos of each range that is scatter by
the request. The returned RangeInfos can be used to determine the
leaseholder of the range after the scattering of the range.

Release note: None

pkg/kv/kvserver/replica_command.go

@@ -2395,14 +2395,23 @@ func (r *Replica) adminScatter(
 		}
 	}
 
-	desc := r.Desc()
+	desc, lease := r.GetDescAndLease(ctx)
 	return roachpb.AdminScatterResponse{
-		Ranges: []roachpb.AdminScatterResponse_Range{{
-			Span: roachpb.Span{
-				Key:    desc.StartKey.AsRawKey(),
-				EndKey: desc.EndKey.AsRawKey(),
+		// TODO(pbardea): This is here for compatibility with 20.1, remove in 21.1.
+		DeprecatedRanges: []roachpb.AdminScatterResponse_Range{
+			{
+				Span: roachpb.Span{
+					Key:    desc.StartKey.AsRawKey(),
+					EndKey: desc.EndKey.AsRawKey(),
+				},
+			},
+		},
+		RangeInfos: []roachpb.RangeInfo{
+			{
+				Desc:  desc,
+				Lease: lease,
 			},
-		}},
+		},
 	}, nil
 }
 

pkg/roachpb/api.go

@@ -402,11 +402,40 @@ func (r *AdminScatterResponse) combine(c combinable) error {
 		if err := r.ResponseHeader.combine(otherR.Header()); err != nil {
 			return err
 		}
-		r.Ranges = append(r.Ranges, otherR.Ranges...)
+
+		// Combined responses will always have only RangeInfo set, rather than
+		// DeprecatedRanges.
+		// TODO(pbardea): Remove in 21.1.
+		r.maybeUpgrade()
+		otherR.maybeUpgrade()
+		r.RangeInfos = append(r.RangeInfos, otherR.RangeInfos...)
 	}
 	return nil
 }
 
+// maybeUpgrade will upgrade responses from 20.1 clients to look like 20.2
+// responses.
+// It converts the DeprecatedRanges field of the response to the equivalent
+// RangeInfos and nils out DeprecatedRanges. Note that the converted RangeInfos
+// will have an empty lease and only have the start and end key of the range
+// descriptor populated.
+func (r *AdminScatterResponse) maybeUpgrade() {
+	if len(r.RangeInfos) == 0 {
+		r.RangeInfos = make([]RangeInfo, len(r.DeprecatedRanges))
+		for i, respRange := range r.DeprecatedRanges {
+			r.RangeInfos[i] = RangeInfo{
+				// respRange.Span's keys are not local keys. The keys were created with
+				// AsRawKey(), so converting back is safe.
+				Desc: RangeDescriptor{
+					StartKey: RKey(respRange.Span.Key),
+					EndKey:   RKey(respRange.Span.EndKey),
+				},
+			}
+		}
+	}
+	r.DeprecatedRanges = nil
+}
+
 var _ combinable = &AdminScatterResponse{}
 
 // Header implements the Request interface.