def prune_linear_layer(layer: nn.Linear, index: torch.LongTensor, dim: int = 0) -> nn.Linear:
    """
    Prune a linear layer to keep only entries in index.

    Used to remove heads.

    Args:
        layer (`torch.nn.Linear`): The layer to prune.
        index (`torch.LongTensor`): The indices to keep in the layer.
        dim (`int`, *optional*, defaults to 0): The dimension on which to keep the indices.

    Returns:
        `torch.nn.Linear`: The pruned layer as a new layer with `requires_grad=True`.
    """
    index = index.to(layer.weight.device)
    W = layer.weight.index_select(dim, index).clone().detach()
    if layer.bias is not None:
        if dim == 1:
            b = layer.bias.clone().detach()
        else:
            b = layer.bias[index].clone().detach()
    new_size = list(layer.weight.size())
    new_size[dim] = len(index)
    new_layer = nn.Linear(new_size[1], new_size[0], bias=layer.bias is not None).to(layer.weight.device)
    new_layer.weight.requires_grad = False
    new_layer.weight.copy_(W.contiguous())
    new_layer.weight.requires_grad = True
    if layer.bias is not None:
        new_layer.bias.requires_grad = False
        new_layer.bias.copy_(b.contiguous())
        new_layer.bias.requires_grad = True
    return new_layer

    Prune a linear layer to keep only entries in index.

    Used to remove heads.

    Args:
        layer (`torch.nn.Linear`): The layer to prune.
        index (`torch.LongTensor`): The indices to keep in the layer.
        dim (`int`, *optional*, defaults to 0): The dimension on which to keep the indices.

    Returns:
        `torch.nn.Linear`: The pruned layer as a new layer with `requires_grad=True`.
    
dpkd/transformers/src/transformers/pytorch_utils.py