terraform: put destroy nodes into the graph

terraform/graph_builder.go

@@ -95,6 +95,9 @@ func (b *BuiltinGraphBuilder) Steps() []GraphTransformer {
 			},
 		},
 
+		// Create the destruction nodes
+		&DestroyTransformer{},
+
 		// Make sure we create one root
 		&RootTransformer{},
 	}

terraform/graph_builder_test.go

@@ -106,8 +106,12 @@ const testBasicGraphBuilderStr = `
 
 const testBuiltinGraphBuilderBasicStr = `
 aws_instance.db
+  aws_instance.db (destroy)
+aws_instance.db (destroy)
   provider.aws
 aws_instance.web
+  aws_instance.web (destroy)
+aws_instance.web (destroy)
   aws_instance.db
   provider.aws
 provider.aws
@@ -115,10 +119,14 @@ provider.aws
 
 const testBuiltinGraphBuilderModuleStr = `
 aws_instance.web
+  aws_instance.web (destroy)
+aws_instance.web (destroy)
   aws_security_group.firewall
   module.consul (expanded)
   provider.aws
 aws_security_group.firewall
+  aws_security_group.firewall (destroy)
+aws_security_group.firewall (destroy)
   provider.aws
 module.consul (expanded)
   aws_security_group.firewall

terraform/graph_config_node.go

@@ -243,6 +243,21 @@ func (n *GraphNodeConfigResource) ProvisionedBy() []string {
 	return result
 }
 
+// GraphNodeDestroyable
+func (n *GraphNodeConfigResource) DestroyNode() dag.Vertex {
+	return &GraphNodeConfigResourceDestroy{Resource: n.Resource}
+}
+
+// GraphNodeConfigResourceDestroy represents the logical destroy step for
+// a resource.
+type GraphNodeConfigResourceDestroy struct {
+	Resource *config.Resource
+}
+
+func (n *GraphNodeConfigResourceDestroy) Name() string {
+	return fmt.Sprintf("%s (destroy)", n.Resource.Id())
+}
+
 // graphNodeModuleExpanded represents a module where the graph has
 // been expanded. It stores the graph of the module as well as a reference
 // to the map of variables.

terraform/test-fixtures/transform-destroy-basic/main.tf

@@ -0,0 +1,5 @@
+resource "aws_instance" "foo" {}
+
+resource "aws_instance" "bar" {
+    value = "${aws_instance.foo.value}"
+}

terraform/transform_destroy.go

@@ -0,0 +1,54 @@
+package terraform
+
+import (
+	"github.com/hashicorp/terraform/dag"
+)
+
+// GraphNodeDestroyable is the interface that nodes that can be destroyed
+// must implement. This is used to automatically handle the creation of
+// destroy nodes in the graph and the dependency ordering of those destroys.
+type GraphNodeDestroyable interface {
+	// DestroyNode returns the node used for the destroy. This vertex
+	// should not be in the graph yet.
+	DestroyNode() dag.Vertex
+}
+
+// DestroyTransformer is a GraphTransformer that creates the destruction
+// nodes for things that _might_ be destroyed.
+type DestroyTransformer struct{}
+
+func (t *DestroyTransformer) Transform(g *Graph) error {
+	for _, v := range g.Vertices() {
+		// If it is not a destroyable, we don't care
+		dn, ok := v.(GraphNodeDestroyable)
+		if !ok {
+			continue
+		}
+
+		// Grab the destroy side of the node and connect it through
+		n := dn.DestroyNode()
+		if n == nil {
+			continue
+		}
+
+		// Add it to the graph
+		g.Add(n)
+
+		// Inherit all the edges from the old node
+		downEdges := g.DownEdges(v).List()
+		for _, edgeRaw := range downEdges {
+			g.Connect(dag.BasicEdge(n, edgeRaw.(dag.Vertex)))
+		}
+
+		// Remove all the edges from the old now
+		for _, edgeRaw := range downEdges {
+			g.RemoveEdge(dag.BasicEdge(v, edgeRaw.(dag.Vertex)))
+		}
+
+		// Add a new edge to connect the node to be created to
+		// the destroy node.
+		g.Connect(dag.BasicEdge(v, n))
+	}
+
+	return nil
+}

terraform/transform_destroy_test.go

@@ -0,0 +1,41 @@
+package terraform
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestDestroyTransformer(t *testing.T) {
+	mod := testModule(t, "transform-destroy-basic")
+
+	g := Graph{Path: RootModulePath}
+	{
+		tf := &ConfigTransformer{Module: mod}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	{
+		tf := &DestroyTransformer{}
+		if err := tf.Transform(&g); err != nil {
+			t.Fatalf("err: %s", err)
+		}
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTransformDestroyBasicStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
+const testTransformDestroyBasicStr = `
+aws_instance.bar
+  aws_instance.bar (destroy)
+aws_instance.bar (destroy)
+  aws_instance.foo
+aws_instance.foo
+  aws_instance.foo (destroy)
+aws_instance.foo (destroy)
+`