terraform: unify destroy/apply graph builders

They're so similar we unify them, they only change in a select few
places. This is very similar to the old graph but is still much simpler.

terraform/context.go

@@ -392,23 +392,14 @@ func (c *Context) Apply() (*State, error) {
 	}
 
 	// Build the new graph. We do this no matter what so we can shadow it.
-	var newGraph *Graph
+	newGraph, err := (&ApplyGraphBuilder{
-	if c.destroy {
-		newGraph, err = (&DestroyApplyGraphBuilder{
-			Module:    c.module,
-			Diff:      c.diff,
-			State:     c.state,
-			Providers: c.components.ResourceProviders(),
-		}).Build(RootModulePath)
-	} else {
-		newGraph, err = (&ApplyGraphBuilder{
 		Module:       c.module,
 		Diff:         c.diff,
 		State:        c.state,
 		Providers:    c.components.ResourceProviders(),
 		Provisioners: c.components.ResourceProvisioners(),
+		Destroy:      c.destroy,
 	}).Build(RootModulePath)
-	}
 	if err != nil && !newGraphEnabled {
 		// If we had an error graphing but we're not using this graph, just
 		// set it to nil and record it as a shadow error.

terraform/graph_builder.go

@@ -26,6 +26,10 @@ type BasicGraphBuilder struct {
 func (b *BasicGraphBuilder) Build(path []string) (*Graph, error) {
 	g := &Graph{Path: path}
 	for _, step := range b.Steps {
+		if step == nil {
+			continue
+		}
+
 		if err := step.Transform(g); err != nil {
 			return g, err
 		}

terraform/graph_builder_apply.go

@@ -30,6 +30,9 @@ type ApplyGraphBuilder struct {
 
 	// DisableReduce, if true, will not reduce the graph. Great for testing.
 	DisableReduce bool
+
+	// Destroy, if true, represents a pure destroy operation
+	Destroy bool
 }
 
 // See GraphBuilder
@@ -77,7 +80,10 @@ func (b *ApplyGraphBuilder) Steps() []GraphTransformer {
 
 		// Destruction ordering
 		&DestroyEdgeTransformer{Module: b.Module, State: b.State},
+		GraphTransformIf(
+			func() bool { return !b.Destroy },
 			&CBDEdgeTransformer{Module: b.Module, State: b.State},
+		),
 
 		// Create all the providers
 		&MissingProviderTransformer{Providers: b.Providers, Factory: providerFactory},
@@ -87,8 +93,13 @@ func (b *ApplyGraphBuilder) Steps() []GraphTransformer {
 		&AttachProviderConfigTransformer{Module: b.Module},
 
 		// Provisioner-related transformations
+		GraphTransformIf(
+			func() bool { return !b.Destroy },
+			GraphTransformMulti(
 				&MissingProvisionerTransformer{Provisioners: b.Provisioners},
 				&ProvisionerTransformer{},
+			),
+		),
 
 		// Add root variables
 		&RootVariableTransformer{Module: b.Module},

terraform/graph_builder_destroy_apply.go

@@ -1,110 +0,0 @@
-package terraform
-
-import (
-	"github.com/hashicorp/terraform/config/module"
-	"github.com/hashicorp/terraform/dag"
-)
-
-// DestroyApplyGraphBuilder implements GraphBuilder and is responsible for
-// applying a pure-destroy plan.
-//
-// This graph builder is very similar to the ApplyGraphBuilder but
-// is slightly simpler.
-type DestroyApplyGraphBuilder struct {
-	// Module is the root module for the graph to build.
-	Module *module.Tree
-
-	// Diff is the diff to apply.
-	Diff *Diff
-
-	// State is the current state
-	State *State
-
-	// Providers is the list of providers supported.
-	Providers []string
-
-	// DisableReduce, if true, will not reduce the graph. Great for testing.
-	DisableReduce bool
-}
-
-// See GraphBuilder
-func (b *DestroyApplyGraphBuilder) Build(path []string) (*Graph, error) {
-	return (&BasicGraphBuilder{
-		Steps:    b.Steps(),
-		Validate: true,
-	}).Build(path)
-}
-
-// See GraphBuilder
-func (b *DestroyApplyGraphBuilder) Steps() []GraphTransformer {
-	// Custom factory for creating providers.
-	providerFactory := func(name string, path []string) GraphNodeProvider {
-		return &NodeApplyableProvider{
-			NameValue: name,
-			PathValue: path,
-		}
-	}
-
-	concreteResource := func(a *NodeAbstractResource) dag.Vertex {
-		return &NodeApplyableResource{
-			NodeAbstractResource: a,
-		}
-	}
-
-	steps := []GraphTransformer{
-		// Creates all the nodes represented in the diff.
-		&DiffTransformer{
-			Concrete: concreteResource,
-
-			Diff:   b.Diff,
-			Module: b.Module,
-			State:  b.State,
-		},
-
-		// Create orphan output nodes
-		&OrphanOutputTransformer{Module: b.Module, State: b.State},
-
-		// Attach the configuration to any resources
-		&AttachResourceConfigTransformer{Module: b.Module},
-
-		// Attach the state
-		&AttachStateTransformer{State: b.State},
-
-		// Destruction ordering. NOTE: For destroys, we don't need to
-		// do any CBD stuff, so that is explicitly not here.
-		&DestroyEdgeTransformer{Module: b.Module, State: b.State},
-
-		// Create all the providers
-		&MissingProviderTransformer{Providers: b.Providers, Factory: providerFactory},
-		&ProviderTransformer{},
-		&DisableProviderTransformer{},
-		&ParentProviderTransformer{},
-		&AttachProviderConfigTransformer{Module: b.Module},
-
-		// Add root variables
-		&RootVariableTransformer{Module: b.Module},
-
-		// Add module variables
-		&ModuleVariableTransformer{Module: b.Module},
-
-		// Add the outputs
-		&OutputTransformer{Module: b.Module},
-
-		// Connect references so ordering is correct
-		&ReferenceTransformer{},
-
-		// Add the node to fix the state count boundaries
-		&CountBoundaryTransformer{},
-
-		// Single root
-		&RootTransformer{},
-	}
-
-	if !b.DisableReduce {
-		// Perform the transitive reduction to make our graph a bit
-		// more sane if possible (it usually is possible).
-		steps = append(steps, &TransitiveReductionTransformer{})
-	}
-
-	return steps
-}

terraform/transform.go

@@ -19,3 +19,34 @@ type GraphTransformer interface {
 type GraphVertexTransformer interface {
 	Transform(dag.Vertex) (dag.Vertex, error)
 }
+
+// GraphTransformIf is a helper function that conditionally returns a
+// GraphTransformer given. This is useful for calling inline a sequence
+// of transforms without having to split it up into multiple append() calls.
+func GraphTransformIf(f func() bool, then GraphTransformer) GraphTransformer {
+	if f() {
+		return then
+	}
+
+	return nil
+}
+
+type graphTransformerMulti struct {
+	Transforms []GraphTransformer
+}
+
+func (t *graphTransformerMulti) Transform(g *Graph) error {
+	for _, t := range t.Transforms {
+		if err := t.Transform(g); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// GraphTransformMulti combines multiple graph transformers into a single
+// GraphTransformer that runs all the individual graph transformers.
+func GraphTransformMulti(ts ...GraphTransformer) GraphTransformer {
+	return &graphTransformerMulti{Transforms: ts}
+}