candding 0.1.0

Pure candle embeddings for Rust with no ONNX: dense, sparse, multi-vector and rerank models today, image models on the roadmap
Documentation 
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use candle_core::DType;
use candle_core::Tensor;
use candle_nn::VarBuilder;

use super::bias::RelativeAttentionBias;
use super::config::MPNetConfig;
use super::embeddings::MPNetEmbeddings;
use super::layer::MPNetLayer;
use crate::error::Result;
use crate::layers::mask::AttentionMask;
use crate::models::Encoder;
use crate::models::EncoderInput;

pub struct MPNetModel {
  embeddings: MPNetEmbeddings,
  bias: RelativeAttentionBias,
  layers: Vec<MPNetLayer>,
  config: MPNetConfig,
}

/// Manual because the blocks don't derive `Debug`; the tests need it for `unwrap_err`.
impl std::fmt::Debug for MPNetModel {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    f.debug_struct("MPNetModel").finish_non_exhaustive()
  }
}

impl MPNetModel {
  /// The checkpoint uses bare names with no `mpnet.` prefix and has no LM head, so there is no prefix probe.
  pub fn load(config: MPNetConfig, vb: VarBuilder) -> Result<Self> {
    config.ensure_supported()?;
    let embeddings = MPNetEmbeddings::load(&config, vb.pp("embeddings"))?;
    let bias = RelativeAttentionBias::load(&config, vb.pp("encoder.relative_attention_bias"))?;
    let layers = (0..config.num_hidden_layers)
      .map(|i| MPNetLayer::load(&config, vb.pp(format!("encoder.layer.{i}"))))
      .collect::<Result<Vec<_>>>()?;
    Ok(Self {
      embeddings,
      bias,
      layers,
      config,
    })
  }
}

impl Encoder for MPNetModel {
  /// The bias is computed once per forward and reaches every layer inside the mask, where the reference adds it.
  fn forward(&self, input: &EncoderInput) -> Result<Tensor> {
    let mut hidden = self.embeddings.forward(input.input_ids)?;
    let seq = hidden.dim(1)?;
    let bias = self.bias.forward(seq, hidden.device())?;
    let mask = AttentionMask::padding_with_bias(
      input.attention_mask,
      input.lengths,
      &bias,
      self.config.num_attention_heads,
      self.config.head_dim(),
      hidden.dtype(),
    )?;
    for layer in &self.layers {
      hidden = layer.forward(&hidden, &mask)?;
    }
    Ok(hidden)
  }

  fn hidden_size(&self) -> usize {
    self.config.hidden_size
  }

  /// The sequence limit (512), not the table height (514).
  fn max_position_embeddings(&self) -> usize {
    self.config.sequence_limit()
  }

  fn weights_dtype(&self) -> DType {
    self.embeddings.weights_dtype()
  }
}

#[cfg(test)]
mod tests;