fix ModulePath for nodeExpandModule

ModulePath was incorrectly returning the parent module, because it did
not implement ReferenceOutside. With ReferenceOutside working correctly,
we can have ModulePath return the real path and remove the special case
for this during pruning.

terraform/node_module_expand.go

@@ -21,9 +21,10 @@ type nodeExpandModule struct {
 }
 
 var (
-	_ RemovableIfNotTargeted = (*nodeExpandModule)(nil)
-	_ GraphNodeEvalable      = (*nodeExpandModule)(nil)
-	_ GraphNodeReferencer    = (*nodeExpandModule)(nil)
+	_ RemovableIfNotTargeted    = (*nodeExpandModule)(nil)
+	_ GraphNodeEvalable         = (*nodeExpandModule)(nil)
+	_ GraphNodeReferencer       = (*nodeExpandModule)(nil)
+	_ GraphNodeReferenceOutside = (*nodeExpandModule)(nil)
 
 	// modules both record their expansion, and require expansion from their
 	// parent modules.
@@ -48,7 +49,7 @@ func (n *nodeExpandModule) ModulePath() addrs.Module {
 	// This node represents the module call within a module,
 	// so return the CallerAddr as the path as the module
 	// call may expand into multiple child instances
-	return n.Addr.Parent()
+	return n.Addr
 }
 
 // GraphNodeReferencer implementation
@@ -94,6 +95,11 @@ func (n *nodeExpandModule) References() []*addrs.Reference {
 	return appendResourceDestroyReferences(refs)
 }
 
+// GraphNodeReferenceOutside
+func (n *nodeExpandModule) ReferenceOutside() (selfPath, referencePath addrs.Module) {
+	return n.Addr, n.Addr.Parent()
+}
+
 // RemovableIfNotTargeted implementation
 func (n *nodeExpandModule) RemoveIfNotTargeted() bool {
 	// We need to add this so that this node will be removed if

terraform/transform_destroy_edge.go

@@ -187,9 +187,6 @@ func (t *pruneUnusedNodesTransformer) Transform(g *Graph) error {
 	for _, v := range g.Vertices() {
 		var path addrs.Module
 		switch v := v.(type) {
-		case instanceExpander:
-			path = v.expandsInstances()
-
 		case GraphNodeModulePath:
 			path = v.ModulePath()
 		default:

terraform/transform_module_expansion.go

@@ -3,6 +3,7 @@ package terraform
 import (
 	"log"
 
+	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs"
 	"github.com/hashicorp/terraform/dag"
 )
@@ -105,11 +106,22 @@ func (t *ModuleExpansionTransformer) transform(g *Graph, c *configs.Config, pare
 	t.closers[c.Path.String()] = closer
 
 	for _, childV := range g.Vertices() {
-		pather, ok := childV.(GraphNodeModulePath)
-		if !ok {
+		// don't connect a node to itself
+		if childV == v {
 			continue
 		}
-		if pather.ModulePath().Equal(c.Path) {
+
+		var path addrs.Module
+		switch t := childV.(type) {
+		case GraphNodeModulePath:
+			path = t.ModulePath()
+		case GraphNodeReferenceOutside:
+			path, _ = t.ReferenceOutside()
+		default:
+			continue
+		}
+
+		if path.Equal(c.Path) {
 			log.Printf("[TRACE] ModuleExpansionTransformer: %s must wait for expansion of %s", dag.VertexName(childV), c.Path)
 			g.Connect(dag.BasicEdge(childV, v))
 		}