Cannot transfer a reference to a slice across await bounds

Question

I'm struggling with the borrow checker when writing an interface for my services. The underlying meilisearch_sdk SDK requires that add_documents takes a reference to a slice, which cannot be transferred across await boundaries.

The line index.add_documents(&[document], Some(&id)).await produces the following error:

note: required for the cast to the object type `dyn futures::Future<Output = std::result::Result<meilisearch_sdk::tasks::Task, meilisearch_sdk::errors::Error>> + std::marker::Send`rustc
meili.rs(10, 143): future created by async block is not `Send`
meili.rs(13, 37): has type `&[D]` which is not `Send`
meili.rs(13, 60): await occurs here, with `&[document]` maybe used later

What is the correct way to approach / rectify this?

search.rs

#[async_trait]
pub trait SearchIndex {
    type IndexResult;
    type IndexError;
    async fn index_document<D>(&self, index: String, document: D) -> Result<Self::IndexResult, Self::IndexError> where D: SearchableDocument;
    async fn search_document(&self, index: String, query: String) -> Result<Self::IndexResult, Self::IndexError>;
}

index.rs

use meilisearch_sdk::{client::Client, errors::Error, tasks::Task};
use async_trait::async_trait;
use super::super::search::{SearchIndex, SearchableDocument};

#[async_trait]
impl SearchIndex for Client {
    type IndexResult = Task;
    type IndexError = Error;

    async fn index_document<D>(&self, index: &String, document:D ) -> Result<Self::IndexResult, Self::IndexError> where D: SearchableDocument {
        let index = self.index(index);
        let id = document.get_id();
        index.add_documents(&[document], Some(&id)).await
    }

}

add_documents

pub trait SearchableDocument: DeserializeOwned + Serialize + Debug + Send{}

pub async fn add_documents<T: DeserializeOwned + Serialize + std::fmt::Debug>(
        &self,
        documents: &[T],
        primary_key: Option<&str>,
    ) -> Result<Task, Error> {
        self.add_or_replace(documents, primary_key).await
    }

Cargo.toml

[dependencies]
serde = "1.0.136"
serde_json = "1.0.79"
rdkafka = "0.28.0"
tokio = { version = "1.17", features = ["rt-multi-thread", "macros"] }
meilisearch-sdk = "0.15.0"
futures = "0.3.21"
log = "0.4.16"
pretty_env_logger = "0.4.0"
async-trait = "0.1.53"