performance (rendering): Make Node merge a mutating operation.

We only ever call it in contexts where we don't need the original node
to be untouched.

probe/probe_internal_test.go

@@ -28,7 +28,7 @@ func TestApply(t *testing.T) {
 		from report.Topology
 		via  string
 	}{
-		{endpointNode.Merge(report.MakeNode("c").WithTopology(report.Endpoint)), r.Endpoint, endpointNodeID},
+		{endpointNode.WithTopology(report.Endpoint), r.Endpoint, endpointNodeID},
 	} {
 		if want, have := tuple.want, tuple.from.Nodes[tuple.via]; !reflect.DeepEqual(want, have) {
 			t.Errorf("want %+v, have %+v", want, have)

render/render.go

@@ -180,9 +180,11 @@ func (ret *joinResults) mapChild(from, to string) {
 // Note it is not safe to mix calls to add() with addChild(), addChildAndChildren() or addUnmappedChild()
 func (ret *joinResults) add(from string, m report.Node) {
 	if existing, ok := ret.nodes[m.ID]; ok {
-		m = m.Merge(existing)
+		existing.UnsafeMerge(m)
+		ret.nodes[m.ID] = existing
+	} else {
+		ret.nodes[m.ID] = m
 	}
-	ret.nodes[m.ID] = m
 	ret.mapChild(from, m.ID)
 }
 

report/node.go

@@ -173,29 +173,22 @@ func (n Node) WithChild(child Node) Node {
 	return n
 }
 
-// Merge mergses the individual components of a node and returns a
-// fresh node.
-func (n Node) Merge(other Node) Node {
-	id := n.ID
-	if id == "" {
-		id = other.ID
+// UnsafeMerge merges the individual components of a node, modifying the original
+func (n *Node) UnsafeMerge(other Node) {
+	if n.ID == "" {
+		n.ID = other.ID
 	}
-	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,
-		Sets:      n.Sets.Merge(other.Sets),
-		Adjacency: n.Adjacency.Merge(other.Adjacency),
-		Latest:    n.Latest.Merge(other.Latest),
-		Metrics:   n.Metrics.Merge(other.Metrics),
-		Parents:   n.Parents.Merge(other.Parents),
-		Children:  n.Children.Merge(other.Children),
+	if n.Topology == "" {
+		n.Topology = other.Topology
+	} else if other.Topology != "" && n.Topology != other.Topology {
+		panic("Cannot merge nodes with different topology types: " + n.Topology + " != " + other.Topology)
 	}
+	n.Sets = n.Sets.Merge(other.Sets)
+	n.Adjacency = n.Adjacency.Merge(other.Adjacency)
+	n.Latest = n.Latest.Merge(other.Latest)
+	n.Metrics = n.Metrics.Merge(other.Metrics)
+	n.Parents = n.Parents.Merge(other.Parents)
+	n.Children = n.Children.Merge(other.Children)
 }
 
 // UnsafeUnMerge removes data from n that would be added by merging other,

report/topology.go

@@ -127,9 +127,11 @@ func (t Topology) WithLabel(label, labelPlural string) Topology {
 // in that it mutates the Topology, to solve issues of GC pressure.
 func (t Topology) AddNode(node Node) {
 	if existing, ok := t.Nodes[node.ID]; ok {
-		node = node.Merge(existing)
+		existing.UnsafeMerge(node)
+		t.Nodes[node.ID] = existing
+	} else {
+		t.Nodes[node.ID] = node
 	}
-	t.Nodes[node.ID] = node
 }
 
 // ReplaceNode adds node to the topology under key nodeID; if a
@@ -262,8 +264,9 @@ func (n Nodes) Merge(other Nodes) Nodes {
 // UnsafeMerge merges the other object into this one, modifying the original.
 func (n *Nodes) UnsafeMerge(other Nodes) {
 	for k, v := range other {
-		if existing, ok := (*n)[k]; ok { // don't overwrite
-			(*n)[k] = v.Merge(existing)
+		if existing, ok := (*n)[k]; ok {
+			existing.UnsafeMerge(v)
+			(*n)[k] = existing
 		} else {
 			(*n)[k] = v
 		}