Merge pull request #35157 from hashicorp/jbardin/depends-on-references

Reduce redundant walks when resolving module `depends_on`

internal/dag/dag.go

@@ -30,14 +30,21 @@ func (g *AcyclicGraph) DirectedGraph() Grapher {
 
 // Returns a Set that includes every Vertex yielded by walking down from the
 // provided starting Vertex v.
-func (g *AcyclicGraph) Ancestors(v Vertex) (Set, error) {
+func (g *AcyclicGraph) Ancestors(vs ...Vertex) (Set, error) {
 	s := make(Set)
 	memoFunc := func(v Vertex, d int) error {
 		s.Add(v)
 		return nil
 	}
 
-	if err := g.DepthFirstWalk(g.downEdgesNoCopy(v), memoFunc); err != nil {
+	start := make(Set)
+	for _, v := range vs {
+		for _, dep := range g.downEdgesNoCopy(v) {
+			start.Add(dep)
+		}
+	}
+
+	if err := g.DepthFirstWalk(start, memoFunc); err != nil {
 		return nil, err
 	}
 
@@ -46,14 +53,21 @@ func (g *AcyclicGraph) Ancestors(v Vertex) (Set, error) {
 
 // Returns a Set that includes every Vertex yielded by walking up from the
 // provided starting Vertex v.
-func (g *AcyclicGraph) Descendents(v Vertex) (Set, error) {
+func (g *AcyclicGraph) Descendents(vs ...Vertex) (Set, error) {
 	s := make(Set)
 	memoFunc := func(v Vertex, d int) error {
 		s.Add(v)
 		return nil
 	}
 
-	if err := g.ReverseDepthFirstWalk(g.upEdgesNoCopy(v), memoFunc); err != nil {
+	start := make(Set)
+	for _, v := range vs {
+		for _, dep := range g.upEdgesNoCopy(v) {
+			start.Add(dep)
+		}
+	}
+
+	if err := g.ReverseDepthFirstWalk(start, memoFunc); err != nil {
 		return nil, err
 	}
 

internal/terraform/transform_reference.go

@@ -437,17 +437,18 @@ func (m ReferenceMap) parentModuleDependsOn(g *Graph, depender graphNodeDependsO
 
 		deps, fromParentModule := m.dependsOn(g, mod)
 		for _, dep := range deps {
-			// add the dependency
-			res = append(res, dep)
-
-			// and check any transitive resource dependencies for more resources
-			ans, _ := g.Ancestors(dep)
-			for _, v := range ans {
-				if isDependableResource(v) {
-					res = append(res, v)
-				}
+			if isDependableResource(dep) {
+				res = append(res, dep)
 			}
 		}
+
+		ans, _ := g.Ancestors(deps...)
+		for _, v := range ans {
+			if isDependableResource(v) {
+				res = append(res, v)
+			}
+		}
+
 		fromModule = fromModule || fromParentModule
 	}