Update Backend to incorporate environments

Add the missing methods/arguments to handle Terraform environments in
Backends. Extra functionality simply returns defaults for now.

backend/backend.go

@@ -12,6 +12,8 @@ import (
 	"github.com/hashicorp/terraform/terraform"
 )
 
+const DefaultStateName = "default"
+
 // Backend is the minimal interface that must be implemented to enable Terraform.
 type Backend interface {
 	// Ask for input and configure the backend. Similar to
@@ -25,6 +27,13 @@ type Backend interface {
 	// to load the state. If the state.State is a state.Locker, it's up to the
 	// caller to call Lock and Unlock as needed.
 	State() (state.State, error)
+
+	// States returns a list of configured named states and the current state.
+	States() ([]string, string, error)
+
+	// ChangeState changes to the named state. If this doesn't exist it'll be
+	// created.
+	ChangeState(name string) error
 }
 
 // Enhanced implements additional behavior on top of a normal backend.

backend/legacy/backend.go

@@ -3,6 +3,7 @@ package legacy
 import (
 	"fmt"
 
+	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/state"
 	"github.com/hashicorp/terraform/state/remote"
 	"github.com/hashicorp/terraform/terraform"
@@ -60,3 +61,11 @@ func (b *Backend) State() (state.State, error) {
 
 	return &remote.State{Client: b.client}, nil
 }
+
+func (b *Backend) States() ([]string, string, error) {
+	return []string{backend.DefaultStateName}, backend.DefaultStateName, nil
+}
+
+func (b *Backend) ChangeState(name string) error {
+	return nil
+}

backend/local/backend.go

@@ -96,6 +96,14 @@ func (b *Local) Configure(c *terraform.ResourceConfig) error {
 	return f(c)
 }
 
+func (b *Local) States() ([]string, string, error) {
+	return []string{backend.DefaultStateName}, backend.DefaultStateName, nil
+}
+
+func (b *Local) ChangeState(name string) error {
+	return nil
+}
+
 func (b *Local) State() (state.State, error) {
 	// If we have a backend handling state, defer to that.
 	if b.Backend != nil {

backend/nil.go

@@ -29,3 +29,12 @@ func (Nil) State() (state.State, error) {
 	// We have to return a non-nil state to adhere to the interface
 	return &state.InmemState{}, nil
 }
+
+func (Nil) States() ([]string, string, error) {
+	// The default state always exists
+	return []string{DefaultStateName}, DefaultStateName, nil
+}
+
+func (Nil) ChangeState(string) error {
+	return nil
+}

backend/remote-state/backend.go

@@ -6,6 +6,7 @@ package remotestate
 import (
 	"context"
 
+	"github.com/hashicorp/terraform/backend"
 	"github.com/hashicorp/terraform/helper/schema"
 	"github.com/hashicorp/terraform/state"
 	"github.com/hashicorp/terraform/state/remote"
@@ -46,6 +47,14 @@ func (b *Backend) Configure(rc *terraform.ResourceConfig) error {
 	return b.Backend.Configure(rc)
 }
 
+func (b *Backend) States() ([]string, string, error) {
+	return []string{backend.DefaultStateName}, backend.DefaultStateName, nil
+}
+
+func (b *Backend) ChangeState(name string) error {
+	return nil
+}
+
 func (b *Backend) State() (state.State, error) {
 	// This shouldn't happen
 	if b.client == nil {