Helper function to load sharded safetensors files (#1481)

* Fix the quantized mistral example.

* Add a helper function to load sharded safetensors weights.

* Use the sharded loader.

candle-examples/src/lib.rs

@@ -117,3 +117,30 @@ pub fn save_image_resize<P: AsRef<std::path::Path>>(
     image.save(p).map_err(candle::Error::wrap)?;
     Ok(())
 }
+
+/// Loads the safetensors files for a model from the hub based on a json index file.
+pub fn hub_load_safetensors(
+    repo: &hf_hub::api::sync::ApiRepo,
+    json_file: &str,
+) -> Result<Vec<std::path::PathBuf>> {
+    let json_file = repo.get(json_file).map_err(candle::Error::wrap)?;
+    let json_file = std::fs::File::open(json_file)?;
+    let json: serde_json::Value =
+        serde_json::from_reader(&json_file).map_err(candle::Error::wrap)?;
+    let weight_map = match json.get("weight_map") {
+        None => candle::bail!("no weight map in {json_file:?}"),
+        Some(serde_json::Value::Object(map)) => map,
+        Some(_) => candle::bail!("weight map in {json_file:?} is not a map"),
+    };
+    let mut safetensors_files = std::collections::HashSet::new();
+    for value in weight_map.values() {
+        if let Some(file) = value.as_str() {
+            safetensors_files.insert(file.to_string());
+        }
+    }
+    let safetensors_files = safetensors_files
+        .iter()
+        .map(|v| repo.get(v).map_err(candle::Error::wrap))
+        .collect::<Result<Vec<_>>>()?;
+    Ok(safetensors_files)
+}