lang: funcs: dage: Add a Graph method to improve the API

This also adds it to the GraphAPI so that users of it can pull out a
graph when needed. It's not likely to be used by the dage engine
consumers.

lang/funcs/dage/dage.go

@@ -504,6 +504,14 @@ func (obj *Engine) FindEdge(f1, f2 interfaces.Func) *interfaces.FuncEdge {
 	return fe
 }
 
+// Graph returns a copy of the contained graph.
+func (obj *Engine) Graph() *pgraph.Graph {
+	//obj.graphMutex.Lock()         // XXX: should this be a RLock?
+	//defer obj.graphMutex.Unlock() // XXX: should this be an RUnlock?
+
+	return obj.graph.Copy()
+}
+
 // Lock must be used before modifying the running graph. Make sure to Unlock
 // when done.
 // XXX: should Lock take a context if we want to bail mid-way?

lang/funcs/dage/txn.go

@@ -510,7 +510,7 @@ func (obj *graphTxn) commit() error {
 		//gv := &pgraph.Graphviz{
 		//	Filename: fmt.Sprintf("/tmp/txn-graphviz-%d.dot", d),
 		//	Graphs: map[*pgraph.Graph]*pgraph.GraphvizOpts{
-		//		engine.graph: nil,
+		//		obj.Graph(): nil,
 		//	},
 		//}
 		//if err := gv.Exec(); err != nil {

lang/funcs/dage/txn_test.go

@@ -115,6 +115,10 @@ func (obj *testGraphAPI) FindEdge(f1, f2 interfaces.Func) *interfaces.FuncEdge {
 	return fe
 }
 
+func (obj *testGraphAPI) Graph() *pgraph.Graph {
+	return obj.graph.Copy()
+}
+
 type testNullFunc struct {
 	name string
 }

lang/interfaces/func.go

@@ -262,6 +262,9 @@ type GraphAPI interface {
 	HasVertex(Func) bool
 	FindEdge(Func, Func) *FuncEdge
 	LookupEdge(*FuncEdge) (Func, Func, bool)
+
+	// Graph returns a copy of the current graph.
+	Graph() *pgraph.Graph
 }
 
 // Txn is the interface that the engine graph API makes available so that