states/statemgr: don't panic if no state file is present on first write

states/statemgr/filesystem.go

@@ -123,6 +123,13 @@ func (s *Filesystem) WriteState(state *states.State) error {
 	// writing to a temp file on the same filesystem, and renaming the file over
 	// the original.
 
+	if s.readFile == nil {
+		err := s.RefreshState()
+		if err != nil {
+			return err
+		}
+	}
+
 	defer s.mutex()()
 
 	// We'll try to write our backup first, so we can be sure we've created
@@ -150,6 +157,9 @@ func (s *Filesystem) WriteState(state *states.State) error {
 	defer s.stateFileOut.Sync()
 
 	s.file = s.file.DeepCopy()
+	if s.file == nil {
+		s.file = NewStateFile()
+	}
 	s.file.State = state.DeepCopy()
 
 	if _, err := s.stateFileOut.Seek(0, os.SEEK_SET); err != nil {
@@ -164,7 +174,7 @@ func (s *Filesystem) WriteState(state *states.State) error {
 		return nil
 	}
 
-	if !statefile.StatesMarshalEqual(s.file.State, s.readFile.State) {
+	if s.readFile == nil || !statefile.StatesMarshalEqual(s.file.State, s.readFile.State) {
 		s.file.Serial++
 	}
 

states/statemgr/lineage.go

@@ -0,0 +1,32 @@
+package statemgr
+
+import (
+	"fmt"
+
+	uuid "github.com/hashicorp/go-uuid"
+
+	"github.com/hashicorp/terraform/states/statefile"
+	"github.com/hashicorp/terraform/version"
+)
+
+// NewLineage generates a new lineage identifier string. A lineage identifier
+// is an opaque string that is intended to be unique in space and time, chosen
+// when state is recorded at a location for the first time and then preserved
+// afterwards to allow Terraform to recognize when one state snapshot is a
+// predecessor or successor of another.
+func NewLineage() string {
+	lineage, err := uuid.GenerateUUID()
+	if err != nil {
+		panic(fmt.Errorf("Failed to generate lineage: %v", err))
+	}
+	return lineage
+}
+
+// NewStateFile creates a new statefile.File object, with a newly-minted
+// lineage identifier and serial 0, and returns a pointer to it.
+func NewStateFile() *statefile.File {
+	return &statefile.File{
+		Lineage:          NewLineage(),
+		TerraformVersion: version.SemVer,
+	}
+}