terraform: implement destroy planning basics from state

terraform/context.go

@@ -516,8 +516,19 @@ func (c *Context) Plan() (*Plan, error) {
 	c.diff.init()
 	c.diffLock.Unlock()
 
-	// Build the graph
-	graph, err := c.Graph(&ContextGraphOpts{Validate: true})
+	// Build the graph. We have a branch here since for the pure-destroy
+	// plan (c.destroy) we use a much simpler graph builder that simply
+	// walks the state and reverses edges.
+	var graph *Graph
+	var err error
+	if c.destroy && X_newDestroy {
+		graph, err = (&DestroyPlanGraphBuilder{
+			Module: c.module,
+			State:  c.state,
+		}).Build(RootModulePath)
+	} else {
+		graph, err = c.Graph(&ContextGraphOpts{Validate: true})
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -540,11 +551,16 @@ func (c *Context) Plan() (*Plan, error) {
 		p.Diff.DeepCopy()
 	}
 
-	// Now that we have a diff, we can build the exact graph that Apply will use
-	// and catch any possible cycles during the Plan phase.
-	if _, err := c.Graph(&ContextGraphOpts{Validate: true}); err != nil {
-		return nil, err
+	// We don't do the reverification during the new destroy plan because
+	// it will use a different apply process.
+	if !(c.destroy && X_newDestroy) {
+		// Now that we have a diff, we can build the exact graph that Apply will use
+		// and catch any possible cycles during the Plan phase.
+		if _, err := c.Graph(&ContextGraphOpts{Validate: true}); err != nil {
+			return nil, err
+		}
 	}
+
 	var errs error
 	if len(walker.ValidationErrors) > 0 {
 		errs = multierror.Append(errs, walker.ValidationErrors...)

terraform/graph_builder_destroy_plan.go

@@ -0,0 +1,49 @@
+package terraform
+
+import (
+	"github.com/hashicorp/terraform/config/module"
+	"github.com/hashicorp/terraform/dag"
+)
+
+// DestroyPlanGraphBuilder implements GraphBuilder and is responsible for
+// planning a pure-destroy.
+//
+// Planning a pure destroy operation is simple because we can ignore most
+// ordering configuration and simply reverse the state.
+type DestroyPlanGraphBuilder struct {
+	// Module is the root module for the graph to build.
+	Module *module.Tree
+
+	// State is the current state
+	State *State
+}
+
+// See GraphBuilder
+func (b *DestroyPlanGraphBuilder) Build(path []string) (*Graph, error) {
+	return (&BasicGraphBuilder{
+		Steps:    b.Steps(),
+		Validate: true,
+	}).Build(path)
+}
+
+// See GraphBuilder
+func (b *DestroyPlanGraphBuilder) Steps() []GraphTransformer {
+	concreteResource := func(a *NodeAbstractResource) dag.Vertex {
+		return &NodePlanDestroyableResource{
+			NodeAbstractResource: a,
+		}
+	}
+
+	steps := []GraphTransformer{
+		// Creates all the nodes represented in the state.
+		&StateTransformer{
+			Concrete: concreteResource,
+			State:    b.State,
+		},
+
+		// Single root
+		&RootTransformer{},
+	}
+
+	return steps
+}

terraform/node_resource_plan_destroy.go

@@ -0,0 +1,55 @@
+package terraform
+
+import (
+	"fmt"
+)
+
+// NodePlanDestroyableResource represents a resource that is "applyable":
+// it is ready to be applied and is represented by a diff.
+type NodePlanDestroyableResource struct {
+	*NodeAbstractResource
+}
+
+// GraphNodeEvalable
+func (n *NodePlanDestroyableResource) EvalTree() EvalNode {
+	addr := n.NodeAbstractResource.Addr
+
+	// stateId is the ID to put into the state
+	stateId := addr.stateId()
+	if addr.Index > -1 {
+		stateId = fmt.Sprintf("%s.%d", stateId, addr.Index)
+	}
+
+	// Build the instance info. More of this will be populated during eval
+	info := &InstanceInfo{
+		Id:   stateId,
+		Type: addr.Type,
+	}
+
+	// Declare a bunch of variables that are used for state during
+	// evaluation. Most of this are written to by-address below.
+	var diff *InstanceDiff
+	var state *InstanceState
+
+	return &EvalSequence{
+		Nodes: []EvalNode{
+			&EvalReadState{
+				Name:   stateId,
+				Output: &state,
+			},
+			&EvalDiffDestroy{
+				Info:   info,
+				State:  &state,
+				Output: &diff,
+			},
+			&EvalCheckPreventDestroy{
+				Resource: n.Config,
+				Diff:     &diff,
+			},
+			&EvalWriteDiff{
+				Name: stateId,
+				Diff: &diff,
+			},
+		},
+	}
+}

terraform/transform_state.go

@@ -0,0 +1,65 @@
+package terraform
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/hashicorp/terraform/dag"
+)
+
+// StateTransformer is a GraphTransformer that adds the elements of
+// the state to the graph.
+//
+// This transform is used for example by the DestroyPlanGraphBuilder to ensure
+// that only resources that are in the state are represented in the graph.
+type StateTransformer struct {
+	Concrete ConcreteResourceNodeFunc
+
+	State *State
+}
+
+func (t *StateTransformer) Transform(g *Graph) error {
+	// If the state is nil or empty (nil is empty) then do nothing
+	if t.State.Empty() {
+		return nil
+	}
+
+	// Go through all the modules in the diff.
+	log.Printf("[TRACE] StateTransformer: starting")
+	var nodes []dag.Vertex
+	for _, ms := range t.State.Modules {
+		log.Printf("[TRACE] StateTransformer: Module: %v", ms.Path)
+
+		// Go through all the resources in this module.
+		for name, rs := range ms.Resources {
+			log.Printf("[TRACE] StateTransformer: Resource %q: %#v", name, rs)
+
+			// Add the resource to the graph
+			addr, err := parseResourceAddressInternal(name)
+			if err != nil {
+				panic(fmt.Sprintf(
+					"Error parsing internal name, this is a bug: %q", name))
+			}
+
+			// Very important: add the module path for this resource to
+			// the address. Remove "root" from it.
+			addr.Path = ms.Path[1:]
+
+			// Add the resource to the graph
+			abstract := &NodeAbstractResource{Addr: addr}
+			var node dag.Vertex = abstract
+			if f := t.Concrete; f != nil {
+				node = f(abstract)
+			}
+
+			nodes = append(nodes, node)
+		}
+	}
+
+	// Add all the nodes to the graph
+	for _, n := range nodes {
+		g.Add(n)
+	}
+
+	return nil
+}