rig-derive 0.41.0

//! `#[derive(Embed)]`: implement `Embed` for structs with `#[embed]` fields.

use proc_macro2::TokenStream;
use quote::quote;
use syn::{DataStruct, Meta};

use crate::resolve::CrateRefs;

mod basic;
mod custom;

use basic::{add_struct_bounds, basic_embed_fields};
use custom::custom_embed_fields;

pub(crate) const EMBED: &str = "embed";

pub(crate) fn expand_derive_embedding(input: &mut syn::DeriveInput) -> syn::Result<TokenStream> {
    let refs = CrateRefs::resolve();
    let core = &refs.core;
    let embed_trait = quote!(#core::embeddings::embed::Embed);

    let name = &input.ident;
    let data = &input.data;
    let generics = &mut input.generics;

    let target_stream = match data {
        syn::Data::Struct(data_struct) => {
            reject_conflicting_embed_attributes(data_struct)?;

            let (basic_targets, basic_target_size) = data_struct.basic(generics, &embed_trait);
            let (custom_targets, custom_target_size) = data_struct.custom()?;

            // If there are no fields tagged with `#[embed]` or `#[embed(embed_with = "...")]`, return an empty TokenStream.
            // ie. do not implement `Embed` trait for the struct.
            if basic_target_size + custom_target_size == 0 {
                return Err(syn::Error::new_spanned(
                    name,
                    "Add at least one field tagged with #[embed] or #[embed(embed_with = \"...\")].",
                ));
            }

            quote! {
                #basic_targets;
                #custom_targets;
            }
        }
        _ => {
            return Err(syn::Error::new_spanned(
                input,
                "Embed derive macro should only be used on structs",
            ));
        }
    };

    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let r#gen = quote! {
        impl #impl_generics #embed_trait for #name #ty_generics #where_clause {
            fn embed(&self, embedder: &mut #core::embeddings::embed::TextEmbedder) -> Result<(), #core::embeddings::embed::EmbedError> {
                #target_stream;

                Ok(())
            }
        }
    };

    Ok(r#gen)
}

/// A field carrying both `#[embed]` and `#[embed(embed_with = "...")]` would be
/// embedded twice, and of two `#[embed(embed_with = "...")]` attributes only
/// the first would be honored; make both conflicts errors instead.
fn reject_conflicting_embed_attributes(data_struct: &DataStruct) -> syn::Result<()> {
    for field in &data_struct.fields {
        let basic = field
            .attrs
            .iter()
            .any(|attr| matches!(&attr.meta, Meta::Path(path) if path.is_ident(EMBED)));
        let mut custom_attrs = field
            .attrs
            .iter()
            .filter(|attr| matches!(&attr.meta, Meta::List(_)) && attr.path().is_ident(EMBED));
        let custom = custom_attrs.next().is_some();
        if basic && custom {
            return Err(syn::Error::new_spanned(
                field,
                "a field cannot combine `#[embed]` and `#[embed(embed_with = \"...\")]`",
            ));
        }
        if let Some(duplicate) = custom_attrs.next() {
            return Err(syn::Error::new_spanned(
                duplicate,
                "a field cannot have more than one `#[embed(embed_with = \"...\")]` attribute",
            ));
        }
    }
    Ok(())
}

trait StructParser {
    // Handles fields tagged with `#[embed]`
    fn basic(
        &self,
        generics: &mut syn::Generics,
        embed_trait: &TokenStream,
    ) -> (TokenStream, usize);

    // Handles fields tagged with `#[embed(embed_with = "...")]`
    fn custom(&self) -> syn::Result<(TokenStream, usize)>;
}

impl StructParser for DataStruct {
    fn basic(
        &self,
        generics: &mut syn::Generics,
        embed_trait: &TokenStream,
    ) -> (TokenStream, usize) {
        let embed_targets = basic_embed_fields(self)
            // Iterate over every field tagged with `#[embed]`
            .map(|field| {
                add_struct_bounds(generics, &field.ty, embed_trait);

                let field_name = &field.ident;

                quote! {
                    self.#field_name
                }
            })
            .collect::<Vec<_>>();

        (
            quote! {
                #(#embed_targets.embed(embedder)?;)*
            },
            embed_targets.len(),
        )
    }

    fn custom(&self) -> syn::Result<(TokenStream, usize)> {
        let embed_targets = custom_embed_fields(self)?
            // Iterate over every field tagged with `#[embed(embed_with = "...")]`
            .into_iter()
            .map(|(field, custom_func_path)| {
                let field_name = &field.ident;

                quote! {
                    #custom_func_path(embedder, self.#field_name.clone())?;
                }
            })
            .collect::<Vec<_>>();

        Ok((
            quote! {
                #(#embed_targets)*
            },
            embed_targets.len(),
        ))
    }
}