Visualizer: add node for vertices with incoming edges too

lib/mosaik/graph/visualizer.rb

@@ -17,6 +17,18 @@ def to_dot
         # Set of visited edges (to avoid duplicates in undirected graphs)
         visited = Set.new
 
+        # List of vertices with incoming or outgoing edges
+        coupled_vertices = graph
+          .vertices
+          .values
+          .select { |v| v.edges.any? } + graph
+            .vertices
+            .values
+            .map { |v| v.edges.keys }
+            .flatten(2)
+            .uniq
+            .map { |id| graph.find_vertex(id) }
+
         [
           graph.directed ? "digraph {" : "graph {",
           (if graph.clusters.any?
@@ -41,7 +53,7 @@ def to_dot
             .values
             .map do |vertex|
             [
-              ("\"#{vertex.id}\" [shape=circle, width=1, fixedsize=true, fontsize=12, style=filled, fillcolor=lightblue]" if vertex.edges.any? || !options[:hide_uncoupled]),
+              ("\"#{vertex.id}\" [shape=circle, width=1, fixedsize=true, fontsize=12, style=filled, fillcolor=lightblue]" if vertex.in?(coupled_vertices) || !options[:hide_uncoupled]),
               *vertex
                 .edges
                 .flat_map do |key, edges|

spec/mosaik/graph/visualizer_spec.rb

@@ -117,15 +117,13 @@
         graph.add_vertex("vertex1")
         graph.add_vertex("vertex2")
         graph.add_vertex("vertex3")
-        graph.add_edge("vertex1", "vertex2")
-        graph.add_edge("vertex2", "vertex3", foo: "bar", baz: "bat")
+        graph.add_edge("vertex1", "vertex2", foo: "bar", baz: "bat")
 
         expect(visualizer.to_dot).to eq <<~DOT
           digraph {
             "vertex1" [shape=circle, width=1, fixedsize=true, fontsize=12, style=filled, fillcolor=lightblue]
-            "vertex1" -> "vertex2"
+            "vertex1" -> "vertex2" [label="foo: bar, baz: bat"]
             "vertex2" [shape=circle, width=1, fixedsize=true, fontsize=12, style=filled, fillcolor=lightblue]
-            "vertex2" -> "vertex3" [label="foo: bar, baz: bat"]
           }
         DOT
       end