Fix WithLatests() fixup on duplicate keys

The fixup() method was modifying a copy of its input, so you could get
duplicate keys in the output.

Thankfully this is rare: in most cases WithLatests() is called with
fields that are not duplicates of existing ones.

report/map_helpers.go

@@ -148,19 +148,21 @@ func (m StringLatestMap) Swap(i, j int)      { m[i], m[j] = m[j], m[i] }
 func (m StringLatestMap) Less(i, j int) bool { return m[i].key < m[j].key }
 
 // sort entries and shuffle down any duplicates
-func (m StringLatestMap) fixup() {
-	sort.Sort(m)
-	for i := 1; i < len(m); {
-		if m[i-1].key == m[i].key {
-			if m[i-1].Timestamp.Before(m[i].Timestamp) {
-				m = append(m[:i-1], m[i:]...)
+func (m *StringLatestMap) fixup() {
+	n := *m
+	sort.Sort(n)
+	for i := 1; i < len(n); {
+		if n[i-1].key == n[i].key {
+			if n[i-1].Timestamp.Before(n[i].Timestamp) {
+				n = append(n[:i-1], n[i:]...)
 			} else {
-				m = append(m[:i], m[i+1:]...)
+				n = append(n[:i], n[i+1:]...)
 			}
 		} else {
 			i++
 		}
 	}
+	*m = n
 }
 
 // add several entries at the same timestamp

report/node_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/weaveworks/common/mtime"
 	"github.com/weaveworks/common/test"
 	"github.com/weaveworks/scope/report"
@@ -16,6 +17,22 @@ const (
 	Domain = "domain"
 )
 
+func TestWithLatest(t *testing.T) {
+	mtime.NowForce(time.Now())
+	defer mtime.NowReset()
+
+	latests1 := map[string]string{Name: "x"}
+	latests2 := map[string]string{PID: "123"}
+	node1 := report.MakeNode("node1").WithLatests(latests1)
+	assert.Equal(t, 1, node1.Latest.Len())
+	node2 := node1.WithLatests(latests1)
+	assert.Equal(t, node1, node2)
+	node3 := node1.WithLatests(latests2)
+	assert.Equal(t, 2, node3.Latest.Len())
+	node4 := node1.WithLatests(latests2)
+	assert.Equal(t, node3, node4)
+}
+
 func TestMergeNodes(t *testing.T) {
 	mtime.NowForce(time.Now())
 	defer mtime.NowReset()