always wrap remote state in a BackupState

Use a local backup for remote state operations. This allows for manual
recovery in the case of a put failure.

backend/local/backend.go

@@ -170,9 +170,30 @@ func (b *Local) DeleteState(name string) error {
 }
 
 func (b *Local) State(name string) (state.State, error) {
+	statePath, stateOutPath, backupPath := b.StatePaths(name)
+
 	// If we have a backend handling state, defer to that.
 	if b.Backend != nil {
-		return b.Backend.State(name)
+		s, err := b.Backend.State(name)
+		if err != nil {
+			return nil, err
+		}
+
+		// make sure we always have a backup state, unless it disabled
+		if backupPath == "" {
+			return s, nil
+		}
+
+		// see if the delegated backend returned a BackupState of its own
+		if s, ok := s.(*state.BackupState); ok {
+			return s, nil
+		}
+
+		s = &state.BackupState{
+			Real: s,
+			Path: backupPath,
+		}
+		return s, nil
 	}
 
 	if s, ok := b.states[name]; ok {
@@ -183,8 +204,6 @@ func (b *Local) State(name string) (state.State, error) {
 		return nil, err
 	}
 
-	statePath, stateOutPath, backupPath := b.StatePaths(name)
-
 	// Otherwise, we need to load the state.
 	var s state.State = &state.LocalState{
 		Path:    statePath,

backend/local/backend_test.go

@@ -169,6 +169,11 @@ func TestLocal_addAndRemoveStates(t *testing.T) {
 // verify it's being called.
 type testDelegateBackend struct {
 	*Local
+
+	// return a sentinel error on these calls
+	stateErr  bool
+	statesErr bool
+	deleteErr bool
 }
 
 var errTestDelegateState = errors.New("State called")
@@ -176,22 +181,39 @@ var errTestDelegateStates = errors.New("States called")
 var errTestDelegateDeleteState = errors.New("Delete called")
 
 func (b *testDelegateBackend) State(name string) (state.State, error) {
+	if b.stateErr {
 		return nil, errTestDelegateState
 	}
+	s := &state.LocalState{
+		Path:    "terraform.tfstate",
+		PathOut: "terraform.tfstate",
+	}
+	return s, nil
+}
 
 func (b *testDelegateBackend) States() ([]string, error) {
+	if b.statesErr {
 		return nil, errTestDelegateStates
 	}
+	return []string{"default"}, nil
+}
 
 func (b *testDelegateBackend) DeleteState(name string) error {
+	if b.deleteErr {
 		return errTestDelegateDeleteState
 	}
+	return nil
+}
 
 // verify that the MultiState methods are dispatched to the correct Backend.
 func TestLocal_multiStateBackend(t *testing.T) {
 	// assign a separate backend where we can read the state
 	b := &Local{
-		Backend: &testDelegateBackend{},
+		Backend: &testDelegateBackend{
+			stateErr:  true,
+			statesErr: true,
+			deleteErr: true,
+		},
 	}
 
 	if _, err := b.State("test"); err != errTestDelegateState {
@@ -205,7 +227,43 @@ func TestLocal_multiStateBackend(t *testing.T) {
 	if err := b.DeleteState("test"); err != errTestDelegateDeleteState {
 		t.Fatal("expected errTestDelegateDeleteState, got:", err)
 	}
+}
 
+// verify that a remote state backend is always wrapped in a BackupState
+func TestLocal_remoteStateBackup(t *testing.T) {
+	// assign a separate backend to mock a remote state backend
+	b := &Local{
+		Backend: &testDelegateBackend{},
+	}
+
+	s, err := b.State("default")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bs, ok := s.(*state.BackupState)
+	if !ok {
+		t.Fatal("remote state is not backed up")
+	}
+
+	if bs.Path != DefaultStateFilename+DefaultBackupExtension {
+		t.Fatal("bad backup location:", bs.Path)
+	}
+
+	// do the same with a named state, which should use the local env directories
+	s, err = b.State("test")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bs, ok = s.(*state.BackupState)
+	if !ok {
+		t.Fatal("remote state is not backed up")
+	}
+
+	if bs.Path != filepath.Join(DefaultEnvDir, "test", DefaultStateFilename+DefaultBackupExtension) {
+		t.Fatal("bad backup location:", bs.Path)
+	}
 }
 
 // change into a tmp dir and return a deferable func to change back and cleanup