clone_no_bound.rs

// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use syn::spanned::Spanned;

/// Derive Clone but do not bound any generic.
pub fn derive_clone_no_bound(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input: syn::DeriveInput = match syn::parse(input) {
        Ok(input) => input,
        Err(e) => return e.to_compile_error().into(),
    };

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

    let impl_ = match input.data {
        syn::Data::Struct(struct_) => match struct_.fields {
            syn::Fields::Named(named) => {
                let fields = named.named.iter().map(|i| &i.ident).map(|i| {
                    quote::quote_spanned!(i.span() =>
                        #i: core::clone::Clone::clone(&self.#i)
                    )
                });

                quote::quote!( Self { #( #fields, )* } )
            }
            syn::Fields::Unnamed(unnamed) => {
                let fields = unnamed
                    .unnamed
                    .iter()
                    .enumerate()
                    .map(|(i, _)| syn::Index::from(i))
                    .map(|i| {
                        quote::quote_spanned!(i.span() =>
                            core::clone::Clone::clone(&self.#i)
                        )
                    });

                quote::quote!( Self ( #( #fields, )* ) )
            }
            syn::Fields::Unit => {
                quote::quote!(Self)
            }
        },
        syn::Data::Enum(enum_) => {
            let variants = enum_.variants.iter().map(|variant| {
                let ident = &variant.ident;
                match &variant.fields {
                    syn::Fields::Named(named) => {
                        let captured = named.named.iter().map(|i| &i.ident);
                        let cloned = captured.clone().map(|i| {
                            quote::quote_spanned!(i.span() =>
                                #i: core::clone::Clone::clone(#i)
                            )
                        });
                        quote::quote!(
                            Self::#ident { #( ref #captured, )* } => Self::#ident { #( #cloned, )*}
                        )
                    }
                    syn::Fields::Unnamed(unnamed) => {
                        let captured = unnamed
                            .unnamed
                            .iter()
                            .enumerate()
                            .map(|(i, f)| syn::Ident::new(&format!("_{}", i), f.span()));
                        let cloned = captured.clone().map(|i| {
                            quote::quote_spanned!(i.span() =>
                                core::clone::Clone::clone(#i)
                            )
                        });
                        quote::quote!(
                            Self::#ident ( #( ref #captured, )* ) => Self::#ident ( #( #cloned, )*)
                        )
                    }
                    syn::Fields::Unit => quote::quote!( Self::#ident => Self::#ident ),
                }
            });

            quote::quote!(match self {
                #( #variants, )*
            })
        }
        syn::Data::Union(_) => {
            let msg = "Union type not supported by `derive(CloneNoBound)`";
            return syn::Error::new(input.span(), msg).to_compile_error().into();
        }
    };

    quote::quote!(
        const _: () = {
            impl #impl_generics core::clone::Clone for #name #ty_generics #where_clause {
                fn clone(&self) -> Self {
                    #impl_
                }
            }
        };
    )
    .into()
}