dag: Fix graph printing type mismatch

Dependencies were being sorted, but their types were not, causing
incorrect printing.

dag/graph.go

@@ -202,16 +202,17 @@ func (g *Graph) StringWithNodeTypes() string {
 
 		// Alphabetize dependencies
 		deps := make([]string, 0, targets.Len())
-		targetNodes := make([]Vertex, 0, targets.Len())
+		targetNodes := make(map[string]Vertex)
 		for _, target := range targets.List() {
-			deps = append(deps, VertexName(target))
-			targetNodes = append(targetNodes, target)
+			dep := VertexName(target)
+			deps = append(deps, dep)
+			targetNodes[dep] = target
 		}
 		sort.Strings(deps)
 
 		// Write dependencies
-		for i, d := range deps {
-			buf.WriteString(fmt.Sprintf("  %s - %T\n", d, targetNodes[i]))
+		for _, d := range deps {
+			buf.WriteString(fmt.Sprintf("  %s - %T\n", d, targetNodes[d]))
 		}
 	}