don't Copy() self on Merge()

Merge() is always returning a copy, so there is no need to Copy()
struct fields first before calling Merge() on them.

This reduces GC pressure (#1010) and helps overall app performance
(#1457).

report/node.go

@@ -194,23 +194,27 @@ func (n Node) Copy() Node {
 // Merge mergses the individual components of a node and returns a
 // fresh node.
 func (n Node) Merge(other Node) Node {
-	cp := n.Copy()
-	if cp.ID == "" {
-		cp.ID = other.ID
+	id := n.ID
+	if id == "" {
+		id = other.ID
 	}
-	if cp.Topology == "" {
-		cp.Topology = other.Topology
-	} else if other.Topology != "" && cp.Topology != other.Topology {
-		panic("Cannot merge nodes with different topology types: " + cp.Topology + " != " + other.Topology)
+	topology := n.Topology
+	if topology == "" {
+		topology = other.Topology
+	} else if other.Topology != "" && topology != other.Topology {
+		panic("Cannot merge nodes with different topology types: " + topology + " != " + other.Topology)
+	}
+	return Node{
+		ID:        id,
+		Topology:  topology,
+		Counters:  n.Counters.Merge(other.Counters),
+		Sets:      n.Sets.Merge(other.Sets),
+		Adjacency: n.Adjacency.Merge(other.Adjacency),
+		Edges:     n.Edges.Merge(other.Edges),
+		Controls:  n.Controls.Merge(other.Controls),
+		Latest:    n.Latest.Merge(other.Latest),
+		Metrics:   n.Metrics.Merge(other.Metrics),
+		Parents:   n.Parents.Merge(other.Parents),
+		Children:  n.Children.Merge(other.Children),
 	}
-	cp.Counters = cp.Counters.Merge(other.Counters)
-	cp.Sets = cp.Sets.Merge(other.Sets)
-	cp.Adjacency = cp.Adjacency.Merge(other.Adjacency)
-	cp.Edges = cp.Edges.Merge(other.Edges)
-	cp.Controls = cp.Controls.Merge(other.Controls)
-	cp.Latest = cp.Latest.Merge(other.Latest)
-	cp.Metrics = cp.Metrics.Merge(other.Metrics)
-	cp.Parents = cp.Parents.Merge(other.Parents)
-	cp.Children = cp.Children.Merge(other.Children)
-	return cp
 }

report/report.go

@@ -178,21 +178,22 @@ func (r Report) Copy() Report {
 // Merge merges another Report into the receiver and returns the result. The
 // original is not modified.
 func (r Report) Merge(other Report) Report {
-	cp := r.Copy()
-	cp.Endpoint = r.Endpoint.Merge(other.Endpoint)
-	cp.Process = r.Process.Merge(other.Process)
-	cp.Container = r.Container.Merge(other.Container)
-	cp.ContainerImage = r.ContainerImage.Merge(other.ContainerImage)
-	cp.Host = r.Host.Merge(other.Host)
-	cp.Pod = r.Pod.Merge(other.Pod)
-	cp.Service = r.Service.Merge(other.Service)
-	cp.Deployment = r.Deployment.Merge(other.Deployment)
-	cp.ReplicaSet = r.ReplicaSet.Merge(other.ReplicaSet)
-	cp.Overlay = r.Overlay.Merge(other.Overlay)
-	cp.Sampling = r.Sampling.Merge(other.Sampling)
-	cp.Window += other.Window
-	cp.Plugins = r.Plugins.Merge(other.Plugins)
-	return cp
+	return Report{
+		Endpoint:       r.Endpoint.Merge(other.Endpoint),
+		Process:        r.Process.Merge(other.Process),
+		Container:      r.Container.Merge(other.Container),
+		ContainerImage: r.ContainerImage.Merge(other.ContainerImage),
+		Host:           r.Host.Merge(other.Host),
+		Pod:            r.Pod.Merge(other.Pod),
+		Service:        r.Service.Merge(other.Service),
+		Deployment:     r.Deployment.Merge(other.Deployment),
+		ReplicaSet:     r.ReplicaSet.Merge(other.ReplicaSet),
+		Overlay:        r.Overlay.Merge(other.Overlay),
+		Sampling:       r.Sampling.Merge(other.Sampling),
+		Window:         r.Window + other.Window,
+		Plugins:        r.Plugins.Merge(other.Plugins),
+		ID:             fmt.Sprintf("%d", rand.Int63()),
+	}
 }
 
 // Topologies returns a slice of Topologies in this report