feat: disable cache-copy-layers in multistage builds; closes 2065

pkg/dockerfile/dockerfile.go

@@ -58,6 +58,10 @@ func ParseStages(opts *config.KanikoOptions) ([]instructions.Stage, []instructio
 		return nil, nil, errors.Wrap(err, "parsing dockerfile")
 	}
 
+	if opts.CacheCopyLayers && len(stages) >= 2 {
+		return nil, nil, errors.New("kaniko does not support caching copy layers in multistage builds")
+	}
+
 	metaArgs, err = expandNested(metaArgs, opts.BuildArgs)
 	if err != nil {
 		return nil, nil, errors.Wrap(err, "expanding meta ARGs")

pkg/dockerfile/dockerfile_test.go

@@ -29,6 +29,39 @@ import (
 	"github.com/moby/buildkit/frontend/dockerfile/instructions"
 )
 
+func Test_ParseStages_NoMultistageWithCacheCopy(t *testing.T) {
+	dockerfile := `
+	FROM scratch as first
+	COPY testfile /
+
+	FROM scratch as second
+	COPY --from=second testfile /
+	`
+	tmpfile, err := ioutil.TempFile("", "Dockerfile.test")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.Remove(tmpfile.Name())
+
+	if _, err := tmpfile.Write([]byte(dockerfile)); err != nil {
+		t.Fatal(err)
+	}
+	if err := tmpfile.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	opts := &config.KanikoOptions{
+		DockerfilePath:  tmpfile.Name(),
+		CacheCopyLayers: true,
+	}
+
+	_, _, err = ParseStages(opts)
+	if err == nil {
+		t.Fatal("expected ParseStages to fail on MultiStage build if CacheCopyLayers=true")
+	}
+}
+
 func Test_ParseStages_ArgValueWithQuotes(t *testing.T) {
 	dockerfile := `
 	ARG IMAGE="ubuntu:16.04"