parse arg commands at the top of dockerfiles (#404)

* parse arg commands at the top of dockerfiles

* fix pointer reference bug and remove debugging

* fixing tests

* account for meta args with no value

* don't take fs snapshot if / is the only changed path

* move metaArgs inside KanikoStage

* removing unused property

* check for any directory instead of just /

* remove unnecessary check

pkg/executor/build.go

@@ -54,7 +54,7 @@ type stageBuilder struct {
 
 // newStageBuilder returns a new type stageBuilder which contains all the information required to build the stage
 func newStageBuilder(opts *config.KanikoOptions, stage config.KanikoStage) (*stageBuilder, error) {
-	sourceImage, err := util.RetrieveSourceImage(stage, opts.BuildArgs, opts)
+	sourceImage, err := util.RetrieveSourceImage(stage, opts)
 	if err != nil {
 		return nil, err
 	}
@@ -136,6 +136,7 @@ func (s *stageBuilder) build() error {
 	}
 
 	args := dockerfile.NewBuildArgs(s.opts.BuildArgs)
+	args.AddMetaArgs(s.stage.MetaArgs)
 	for index, command := range cmds {
 		if command == nil {
 			continue

pkg/executor/build_test.go

@@ -66,7 +66,7 @@ func Test_reviewConfig(t *testing.T) {
 }
 
 func stage(t *testing.T, d string) config.KanikoStage {
-	stages, err := dockerfile.Parse([]byte(d))
+	stages, _, err := dockerfile.Parse([]byte(d))
 	if err != nil {
 		t.Fatalf("error parsing dockerfile: %v", err)
 	}