cgp-macro-lib 0.7.0

Context-generic programming core component macros implemented as a library.
Documentation 
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use proc_macro2::Span;
use quote::quote;
use syn::spanned::Spanned;
use syn::token::{Brace, Eq, For, Impl};
use syn::{
    Error, Ident, ImplItem, ImplItemConst, ItemImpl, ItemTrait, Path, TraitItem, Visibility, parse2,
};

use crate::derive_component::delegate_fn::derive_delegated_fn_impl;
use crate::derive_component::delegate_type::derive_delegate_type_impl;
use crate::parse::TypeGenerics;

pub fn derive_use_context_impl(
    context_type: &Ident,
    consumer_trait: &ItemTrait,
    provider_trait: &ItemTrait,
) -> syn::Result<ItemImpl> {
    let consumer_trait_ident = &consumer_trait.ident;
    let provider_trait_ident = &provider_trait.ident;

    let provider_generics = TypeGenerics::try_from(&provider_trait.generics)?.generics;

    let consumer_generics = TypeGenerics::try_from(&consumer_trait.generics)?.generics;

    let mut impl_generics = provider_trait.generics.clone();

    let where_clause = impl_generics.make_where_clause();

    where_clause.predicates.push(parse2(quote! {
        #context_type : #consumer_trait_ident #consumer_generics
    })?);

    let mut impl_items: Vec<ImplItem> = Vec::new();

    for trait_item in provider_trait.items.iter() {
        match trait_item {
            TraitItem::Fn(trait_fn) => {
                let impl_fn = derive_delegated_fn_impl(&trait_fn.sig, &quote!( #context_type ))?;

                impl_items.push(ImplItem::Fn(impl_fn))
            }
            TraitItem::Type(trait_type) => {
                let type_name = &trait_type.ident;

                let type_generics = trait_type.generics.split_for_impl().1;

                let impl_type = derive_delegate_type_impl(
                    trait_type,
                    parse2(quote!(
                        #context_type :: #type_name #type_generics
                    ))?,
                );

                impl_items.push(ImplItem::Type(impl_type));
            }
            TraitItem::Const(trait_item_const) => {
                let const_ident = &trait_item_const.ident;
                let (_, type_generics, _) = trait_item_const.generics.split_for_impl();

                let impl_expr = parse2(quote! {
                    #context_type :: #const_ident #type_generics
                })?;

                let impl_item_const = ImplItemConst {
                    attrs: trait_item_const.attrs.clone(),
                    vis: Visibility::Inherited,
                    defaultness: None,
                    const_token: trait_item_const.const_token,
                    ident: trait_item_const.ident.clone(),
                    generics: trait_item_const.generics.clone(),
                    colon_token: trait_item_const.colon_token,
                    ty: trait_item_const.ty.clone(),
                    eq_token: Eq(Span::call_site()),
                    expr: impl_expr,
                    semi_token: trait_item_const.semi_token,
                };

                impl_items.push(ImplItem::Const(impl_item_const));
            }
            _ => {
                return Err(Error::new(
                    trait_item.span(),
                    format!("unsupported trait item: {trait_item:?}"),
                ));
            }
        }
    }

    let trait_path: Path = parse2(quote!( #provider_trait_ident #provider_generics ))?;

    let item = ItemImpl {
        attrs: provider_trait.attrs.clone(),
        defaultness: None,
        unsafety: provider_trait.unsafety,
        impl_token: Impl::default(),
        generics: impl_generics,
        trait_: Some((None, trait_path, For::default())),
        self_ty: Box::new(parse2(quote!(UseContext))?),
        brace_token: Brace::default(),
        items: impl_items,
    };

    Ok(item)
}