fix single snapshot

pkg/executor/build.go

@@ -318,6 +318,12 @@ func (s *stageBuilder) build() error {
 	}
 
 	initSnapshotTaken := false
+	if s.opts.SingleSnapshot {
+		if err := s.initSnapshotWithTimings(); err != nil {
+			return err
+		}
+		initSnapshotTaken = true
+	}
 
 	cacheGroup := errgroup.Group{}
 	for index, command := range s.cmds {
@@ -348,14 +354,12 @@ func (s *stageBuilder) build() error {
 				return false
 			}
 		}()
-		if !initSnapshotTaken && !command.ProvidesFilesToSnapshot() {
+		if !initSnapshotTaken && !isCacheCommand && !command.ProvidesFilesToSnapshot() {
 			// Take initial snapshot if command does not expect to return
 			// a list of files.
-				t := timing.Start("Initial FS snapshot")
+			if err := s.initSnapshotWithTimings(); err != nil {
-				if err := s.snapshotter.Init(); err != nil {
 				return err
 			}
-				timing.DefaultRun.Stop(t)
 			initSnapshotTaken = true
 		}
 
@@ -423,20 +427,13 @@ func (s *stageBuilder) takeSnapshot(files []string) (string, error) {
 	return snapshot, err
 }
 
-func (s *stageBuilder) singleSnapshot(index int) bool {
+func (s *stageBuilder) shouldTakeSnapshot(index int, files []string, provideFiles bool) bool {
 	isLastCommand := index == len(s.stage.Commands)-1
 
 	// We only snapshot the very end with single snapshot mode on.
 	if s.opts.SingleSnapshot {
 		return isLastCommand
 	}
-  return false
-}
-
-func (s *stageBuilder) shouldTakeSnapshot(index int, files []string, provideFiles bool) bool {
-	if s.singleSnapshot(index){
-		return true
-	}
 
 	// Always take snapshots if we're using the cache.
 	if s.opts.Cache {
@@ -846,3 +843,12 @@ func ResolveCrossStageInstructions(stages []instructions.Stage) map[string]strin
 	logrus.Debugf("Built stage name to index map: %v", nameToIndex)
 	return nameToIndex
 }
+
+func (s stageBuilder) initSnapshotWithTimings() error {
+	t := timing.Start("Initial FS snapshot")
+	if err := s.snapshotter.Init(); err != nil {
+		return err
+	}
+	timing.DefaultRun.Stop(t)
+	return nil
+}