core: NodeApplyableResource only depends on count and for_each

Only the count and for_each expressions are evaluated by this node type,
so it doesn't need to declare dependencies for any other refs in the
configuration body. Using this more refined set of dependencies means
we can avoid graph cycles in the case where one instance of a resource
refers to another instance of the same resource.

We'll still get cycles if count or for_each self-reference, but that's
forbidden anyway (caught during validate) and makes sense because those
two are whole-resource-level config rather than per-instance config.

terraform/node_resource_apply.go

@@ -2,6 +2,10 @@ package terraform
 
 import (
 	"log"
+
+	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/dag"
+	"github.com/hashicorp/terraform/lang"
 )
 
 // NodeApplyableResource represents a resource that is "applyable":
@@ -21,12 +25,32 @@ var (
 	_ GraphNodeEvalable             = (*NodeApplyableResource)(nil)
 	_ GraphNodeProviderConsumer     = (*NodeApplyableResource)(nil)
 	_ GraphNodeAttachResourceConfig = (*NodeApplyableResource)(nil)
+	_ GraphNodeReferencer           = (*NodeApplyableResource)(nil)
 )
 
 func (n *NodeApplyableResource) Name() string {
 	return n.NodeAbstractResource.Name() + " (prepare state)"
 }
 
+func (n *NodeApplyableResource) References() []*addrs.Reference {
+	if n.Config == nil {
+		log.Printf("[WARN] NodeApplyableResource %q: no configuration, so can't determine References", dag.VertexName(n))
+		return nil
+	}
+
+	var result []*addrs.Reference
+
+	// Since this node type only updates resource-level metadata, we only
+	// need to worry about the parts of the configuration that affect
+	// our "each mode": the count and for_each meta-arguments.
+	refs, _ := lang.ReferencesInExpr(n.Config.Count)
+	result = append(result, refs...)
+	refs, _ = lang.ReferencesInExpr(n.Config.ForEach)
+	result = append(result, refs...)
+
+	return result
+}
+
 // GraphNodeEvalable
 func (n *NodeApplyableResource) EvalTree() EvalNode {
 	addr := n.ResourceAddr()