}

	var overlayJSON OverlayJSON
	if err := json.Unmarshal(b, &overlayJSON); err != nil {
		return fmt.Errorf("parsing overlay JSON: %v", err)
	}

	return initFromJSON(overlayJSON)
}

func initFromJSON(overlayJSON OverlayJSON) error {
	// Canonicalize the paths in the overlay map.
	// Use reverseCanonicalized to check for collisions:
	// no two 'from' paths should canonicalize to the same path.

			t.Fatal(err)
		}
	}

	var overlayJSON OverlayJSON
	if err := json.Unmarshal(a.Comment, &overlayJSON); err != nil {
		t.Fatal("parsing overlay JSON:", err)
	}

	if err := initFromJSON(overlayJSON); err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { overlay = nil })
}

func TestIsDir(t *testing.T) {
	initOverlay(t, `
{
	"Replace": {