code: func (f *Field) RotatePieceRight(piece *Piece, x, y int, angle Angle) Angle {
  	if piece.collides(f, x, y, angle.RotateRight()) {
  		return angle
  	}
  	return angle.RotateRight()
  }
docs: // RotatePieceRight tries to rotate the piece to the right
  // and returns the piece's next angle.