Do not filter out the target nodes when obtaining the details panel

app/api_topology.go

@@ -38,11 +38,12 @@ func handleTopology(ctx context.Context, renderer render.Renderer, decorator ren
 // Individual nodes.
 func handleNode(ctx context.Context, renderer render.Renderer, decorator render.Decorator, report report.Report, w http.ResponseWriter, r *http.Request) {
 	var (
-		vars       = mux.Vars(r)
-		topologyID = vars["topology"]
-		nodeID     = vars["id"]
-		rendered   = renderer.Render(report, decorator)
-		node, ok   = rendered[nodeID]
+		vars             = mux.Vars(r)
+		topologyID       = vars["topology"]
+		nodeID           = vars["id"]
+		preciousRenderer = render.PreciousNodeRenderer{nodeID, renderer}
+		rendered         = preciousRenderer.Render(report, decorator)
+		node, ok         = rendered[nodeID]
 	)
 	if !ok {
 		http.NotFound(w, r)

render/filters.go

@@ -10,6 +10,28 @@ import (
 	"github.com/weaveworks/scope/report"
 )
 
+// PreciousNodeRenderer ensures a node is never filtered out by decorators
+type PreciousNodeRenderer struct {
+	PreciousNodeID string
+	Renderer
+}
+
+func (p PreciousNodeRenderer) Render(rpt report.Report, dct Decorator) report.Nodes {
+	undecoratedNodes := p.Renderer.Render(rpt, nil)
+	preciousNode, foundBeforeDecoration := undecoratedNodes[p.PreciousNodeID]
+	finalNodes := applyDecorator{ConstantRenderer(undecoratedNodes)}.Render(rpt, dct)
+	if _, ok := finalNodes[p.PreciousNodeID]; !ok && foundBeforeDecoration {
+		finalNodes[p.PreciousNodeID] = preciousNode
+	}
+	return finalNodes
+}
+
+func (p PreciousNodeRenderer) Stats(rpt report.Report, dct Decorator) Stats {
+	// default to the underlying renderer
+	// TODO: we don't take into account the precious node, so we may be off by one
+	return p.Renderer.Stats(rpt, dct)
+}
+
 // CustomRenderer allow for mapping functions that received the entire topology
 // in one call - useful for functions that need to consider the entire graph.
 // We should minimise the use of this renderer type, as it is very inflexible.

render/render.go

@@ -185,3 +185,14 @@ func (cr conditionalRenderer) Stats(rpt report.Report, dct Decorator) Stats {
 	}
 	return Stats{}
 }
+
+// ConstantRenderer renders a fixed set of nodes
+type ConstantRenderer report.Nodes
+
+func (c ConstantRenderer) Render(_ report.Report, _ Decorator) report.Nodes {
+	return report.Nodes(c)
+}
+
+func (c ConstantRenderer) Stats(_ report.Report, _ Decorator) Stats {
+	return Stats{}
+}