From 9e72ef1a1f29af6aaf9d0f8512adcba9b1a61dd5 Mon Sep 17 00:00:00 2001
From: Tom Wilkie <tom@weave.works>
Date: Wed, 23 Sep 2015 06:20:27 +0000
Subject: [PATCH] Remove pseudo nodes that are made unconnected by filtering.

---
 render/render.go      | 15 +++++++++++
 render/render_test.go | 61 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/render/render.go b/render/render.go
index 52b693e62e..0222c4fcea 100644
--- a/render/render.go
+++ b/render/render.go
@@ -178,10 +178,12 @@ type Filter struct {
 // Render implements Renderer
 func (f Filter) Render(rpt report.Report) RenderableNodes {
 	output := RenderableNodes{}
+	inDegrees := map[string]int{}
 	for id, node := range f.Renderer.Render(rpt) {
 		if f.FilterFunc(node) {
 			output[id] = node
 		}
+		inDegrees[id] = 0
 	}
 
 	// Deleted nodes also need to be cut as destinations in adjacency lists.
@@ -190,11 +192,24 @@ func (f Filter) Render(rpt report.Report) RenderableNodes {
 		for _, dstID := range node.Adjacency {
 			if _, ok := output[dstID]; ok {
 				newAdjacency = newAdjacency.Add(dstID)
+				inDegrees[dstID]++
 			}
 		}
 		node.Adjacency = newAdjacency
 		output[id] = node
 	}
+
+	// Remove unconnected pseudo nodes, see #483.
+	for id, inDegree := range inDegrees {
+		if inDegree > 0 {
+			continue
+		}
+		node := output[id]
+		if !node.Pseudo || len(node.Adjacency) > 0 {
+			continue
+		}
+		delete(output, id)
+	}
 	return output
 }
 
diff --git a/render/render_test.go b/render/render_test.go
index ab30ba032c..3275e1293c 100644
--- a/render/render_test.go
+++ b/render/render_test.go
@@ -212,4 +212,65 @@ func TestFilterRender2(t *testing.T) {
 	}
 }
 
+func TestFilterUnconnectedPesudoNodes(t *testing.T) {
+	// Test pseudo nodes that are made unconnected by filtering
+	// are also removed.
+	{
+		nodes := render.RenderableNodes{
+			"foo": {ID: "foo", Node: report.MakeNode().WithAdjacent("bar")},
+			"bar": {ID: "bar", Node: report.MakeNode().WithAdjacent("baz")},
+			"baz": {ID: "baz", Node: report.MakeNode(), Pseudo: true},
+		}
+		renderer := render.Filter{
+			FilterFunc: func(node render.RenderableNode) bool {
+				return true
+			},
+			Renderer: mockRenderer{RenderableNodes: nodes},
+		}
+		want := nodes.Prune()
+		have := renderer.Render(report.MakeReport()).Prune()
+		if !reflect.DeepEqual(want, have) {
+			t.Error(test.Diff(want, have))
+		}
+	}
+	{
+		renderer := render.Filter{
+			FilterFunc: func(node render.RenderableNode) bool {
+				return node.ID != "bar"
+			},
+			Renderer: mockRenderer{RenderableNodes: render.RenderableNodes{
+				"foo": {ID: "foo", Node: report.MakeNode().WithAdjacent("bar")},
+				"bar": {ID: "bar", Node: report.MakeNode().WithAdjacent("baz")},
+				"baz": {ID: "baz", Node: report.MakeNode(), Pseudo: true},
+			}},
+		}
+		want := render.RenderableNodes{
+			"foo": {ID: "foo", Origins: report.IDList{}, Node: report.MakeNode()},
+		}
+		have := renderer.Render(report.MakeReport()).Prune()
+		if !reflect.DeepEqual(want, have) {
+			t.Error(test.Diff(want, have))
+		}
+	}
+	{
+		renderer := render.Filter{
+			FilterFunc: func(node render.RenderableNode) bool {
+				return node.ID != "bar"
+			},
+			Renderer: mockRenderer{RenderableNodes: render.RenderableNodes{
+				"foo": {ID: "foo", Node: report.MakeNode()},
+				"bar": {ID: "bar", Node: report.MakeNode().WithAdjacent("foo")},
+				"baz": {ID: "baz", Node: report.MakeNode().WithAdjacent("bar"), Pseudo: true},
+			}},
+		}
+		want := render.RenderableNodes{
+			"foo": {ID: "foo", Origins: report.IDList{}, Node: report.MakeNode()},
+		}
+		have := renderer.Render(report.MakeReport()).Prune()
+		if !reflect.DeepEqual(want, have) {
+			t.Error(test.Diff(want, have))
+		}
+	}
+}
+
 func newu64(value uint64) *uint64 { return &value }