Make backcend/legacy match new Backend iface

move the unsupported error value to backend.ErrNamedStatesNotSupported
to be used by any backend implementation.

backend/backend.go

@@ -6,6 +6,7 @@ package backend
 
 import (
 	"context"
+	"errors"
 
 	"github.com/hashicorp/terraform/config/module"
 	"github.com/hashicorp/terraform/state"
@@ -14,6 +15,9 @@ import (
 
 const DefaultStateName = "default"
 
+// Error value to return when a named state operation isn't supported
+var ErrNamedStatesNotSupported = errors.New("named states not supported")
+
 // Backend is the minimal interface that must be implemented to enable Terraform.
 type Backend interface {
 	// Ask for input and configure the backend. Similar to

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"
@@ -53,10 +54,22 @@ func (b *Backend) Configure(c *terraform.ResourceConfig) error {
 	return nil
 }
 
-func (b *Backend) State() (state.State, error) {
+func (b *Backend) State(name string) (state.State, error) {
+	if name != backend.DefaultStateName {
+		return nil, backend.ErrNamedStatesNotSupported
+	}
+
 	if b.client == nil {
 		panic("State called with nil remote state client")
 	}
 
 	return &remote.State{Client: b.client}, nil
 }
+
+func (b *Backend) States() ([]string, error) {
+	return nil, backend.ErrNamedStatesNotSupported
+}
+
+func (b *Backend) DeleteState(string) error {
+	return backend.ErrNamedStatesNotSupported
+}

backend/legacy/backend_test.go

@@ -34,7 +34,7 @@ func TestBackend(t *testing.T) {
 	}
 
 	// Grab state
-	s, err := b.State()
+	s, err := b.State(backend.DefaultStateName)
 	if err != nil {
 		t.Fatalf("err: %s", err)
 	}

backend/local/backend.go

@@ -27,8 +27,6 @@ const (
 	DefaultBackupExtension = ".backup"
 )
 
-var ErrEnvNotSupported = errors.New("environments not supported")
-
 // Local is an implementation of EnhancedBackend that performs all operations
 // locally. This is the "default" backend and implements normal Terraform
 // behavior as it is well known.