Cleanup state file during Unlock

Close and remove the file descriptor from LocalState if we Unlock the
state. Also remove an empty state file if we created it and it was never
written to. This is mostly to clean up after tests, but doesn't hurt to
not leave empty files around.

state/local.go

@@ -39,6 +39,10 @@ type LocalState struct {
 
 	// the file handle corresponding to PathOut
 	stateFileOut *os.File
+	// created is set to tru if stateFileOut didn't exist before we created it.
+	// This is mostly so we can clean up emtpy files during tests, but doesn't
+	// hurt to remove file we never wrote to.
+	created bool
 
 	state     *terraform.State
 	readState *terraform.State
@@ -75,8 +79,26 @@ func (s *LocalState) Lock(reason string) error {
 }
 
 func (s *LocalState) Unlock() error {
+	// we can't be locked if we don't have a file
+	if s.stateFileOut == nil {
+		return nil
+	}
+
 	os.Remove(s.lockInfoPath())
-	return s.unlock()
+
+	fileName := s.stateFileOut.Name()
+
+	unlockErr := s.unlock()
+	s.stateFileOut.Close()
+	s.stateFileOut = nil
+
+	// clean up the state file if we created it an never wrote to it
+	stat, err := os.Stat(fileName)
+	if err == nil && stat.Size() == 0 && s.created {
+		os.Remove(fileName)
+	}
+
+	return unlockErr
 }
 
 // Open the state file, creating the directories and file as needed.
@@ -85,28 +107,25 @@ func (s *LocalState) createStateFiles() error {
 		s.PathOut = s.Path
 	}
 
-	f, err := createFileAndDirs(s.PathOut)
+	// yes this could race, but we only use it to clean up empty files
+	if _, err := os.Stat(s.PathOut); os.IsNotExist(err) {
+		s.created = true
+	}
+
+	// Create all the directories
+	if err := os.MkdirAll(filepath.Dir(s.PathOut), 0755); err != nil {
+		return err
+	}
+
+	f, err := os.OpenFile(s.PathOut, os.O_RDWR|os.O_CREATE, 0666)
 	if err != nil {
 		return err
 	}
+
 	s.stateFileOut = f
 	return nil
 }
 
-func createFileAndDirs(path string) (*os.File, error) {
-	// Create all the directories
-	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
-		return nil, err
-	}
-
-	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0666)
-	if err != nil {
-		return nil, err
-	}
-
-	return f, nil
-}
-
 // WriteState for LocalState always persists the state as well.
 // TODO: this should use a more robust method of writing state, by first
 // writing to a temp file on the same filesystem, and renaming the file over