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// https://github.com/rust-lang/rust/issues/13101

use proc_macro2;

use ast;
use attr;
use matcher;
use syn;
use utils;

/// Derive `Eq` for `input`.
pub fn derive_eq(input: &ast::Input) -> proc_macro2::TokenStream {
    let name = &input.ident;

    let eq_trait_path = eq_trait_path();
    let generics = utils::build_impl_generics(
        input,
        &eq_trait_path,
        needs_eq_bound,
        |field| field.eq_bound(),
        |input| input.eq_bound(),
    );
    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

    quote! {
        #[allow(unused_qualifications)]
        impl #impl_generics #eq_trait_path for #name #ty_generics #where_clause {}
    }
}

/// Derive `PartialEq` for `input`.
pub fn derive_partial_eq(input: &ast::Input) -> Result<proc_macro2::TokenStream, String> {
    if let ast::Body::Enum(_) = input.body {
        if !input.attrs.partial_eq_on_enum() {
            return Err(
                "can't use `#[derivative(PartialEq)]` on an enumeration without \
                 `feature_allow_slow_enum`; see the documentation for more details"
                    .into(),
            );
        }
    }

    let body = matcher::Matcher::new(matcher::BindingStyle::Ref)
        .with_name("__self".into())
        .build_arms(input, |_, outer_arm_name, _, _, outer_bis| {
            let body = matcher::Matcher::new(matcher::BindingStyle::Ref)
                .with_name("__other".into())
                .build_arms(input, |_, inner_arm_name, _, _, inner_bis| {
                    if outer_arm_name == inner_arm_name {
                        let cmp = outer_bis.iter().zip(inner_bis).map(|(o, i)| {
                            let outer_name = &o.ident;
                            let inner_name = &i.ident;

                            if o.field.attrs.ignore_partial_eq() {
                                None
                            } else if let Some(compare_fn) = o.field.attrs.partial_eq_compare_with()
                            {
                                Some(quote!(&& #compare_fn(#outer_name, #inner_name)))
                            } else {
                                Some(quote!(&& #outer_name == #inner_name))
                            }
                        });

                        quote!(true #(#cmp)*)
                    } else {
                        quote!(false)
                    }
                });

            quote! {
                match *other {
                    #body
                }
            }
        });

    let name = &input.ident;

    let partial_eq_trait_path = partial_eq_trait_path();
    let generics = utils::build_impl_generics(
        input,
        &partial_eq_trait_path,
        needs_partial_eq_bound,
        |field| field.partial_eq_bound(),
        |input| input.partial_eq_bound(),
    );
    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

    Ok(quote! {
        #[allow(unused_qualifications)]
        impl #impl_generics #partial_eq_trait_path for #name #ty_generics #where_clause {
            fn eq(&self, other: &Self) -> bool {
                match *self {
                    #body
                }
            }
        }
    })
}

fn needs_partial_eq_bound(attrs: &attr::Field) -> bool {
    !attrs.ignore_partial_eq() && attrs.partial_eq_bound().is_none()
}

fn needs_eq_bound(attrs: &attr::Field) -> bool {
    !attrs.ignore_partial_eq() && attrs.eq_bound().is_none()
}

/// Return the path of the `Eq` trait, that is `::std::cmp::Eq`.
fn eq_trait_path() -> syn::Path {
    if cfg!(feature = "use_core") {
        parse_quote!(::core::cmp::Eq)
    } else {
        parse_quote!(::std::cmp::Eq)
    }
}

/// Return the path of the `PartialEq` trait, that is `::std::cmp::PartialEq`.
fn partial_eq_trait_path() -> syn::Path {
    if cfg!(feature = "use_core") {
        parse_quote!(::core::cmp::PartialEq)
    } else {
        parse_quote!(::std::cmp::PartialEq)
    }
}