docstr: Input tensor with length on dimension 1 
docstr_tok: ["Input","tensor","with","length","on","dimension","1"]
code: def forward(self, x: pt.Tensor) -> pt.Tensor:
      """Input tensor with length on dimension 1"""
      mask = pt.full(
          (x.shape[1], x.shape[1]),
          fill_value=1,
          device=x.device,
          dtype=pt.bool,
      )
      mask = pt.triu(mask, diagonal=1)
      return mask.detach()
  
imports: from dataclasses import dataclass
  from typing import Optional, Tuple
  import torch
  import sockeye.layers
  from sockeye import constants
  from .None import config
label_desc: Use image node_id 1 for calling the AutoRegressiveMask obj's underlying member method code with example usage: obj.forward(x) and returns: mask