debug_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 Debug but do not bound any generics.
pub fn derive_debug_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 input_ident = &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() => .field(stringify!(#i), &self.#i) ),
                    );

                quote::quote!(
                    fmt.debug_struct(stringify!(#input_ident))
                        #( #fields )*
                        .finish()
                )
            }
            syn::Fields::Unnamed(unnamed) => {
                let fields = unnamed
                    .unnamed
                    .iter()
                    .enumerate()
                    .map(|(i, _)| syn::Index::from(i))
                    .map(|i| quote::quote_spanned!(i.span() => .field(&self.#i) ));

                quote::quote!(
                    fmt.debug_tuple(stringify!(#input_ident))
                        #( #fields )*
                        .finish()
                )
            }
            syn::Fields::Unit => quote::quote!(fmt.write_str(stringify!(#input_ident))),
        },
        syn::Data::Enum(enum_) => {
            let variants = enum_.variants.iter().map(|variant| {
                let ident = &variant.ident;
                let full_variant_str = format!("{}::{}", input_ident, ident);
                match &variant.fields {
                    syn::Fields::Named(named) => {
                        let captured = named.named.iter().map(|i| &i.ident);
                        let debugged = captured.clone().map(|i| {
                            quote::quote_spanned!(i.span() =>
                                .field(stringify!(#i), &#i)
                            )
                        });
                        quote::quote!(
                            Self::#ident { #( ref #captured, )* } => {
                                fmt.debug_struct(#full_variant_str)
                                    #( #debugged )*
                                    .finish()
                            }
                        )
                    }
                    syn::Fields::Unnamed(unnamed) => {
                        let captured = unnamed
                            .unnamed
                            .iter()
                            .enumerate()
                            .map(|(i, f)| syn::Ident::new(&format!("_{}", i), f.span()));
                        let debugged = captured
                            .clone()
                            .map(|i| quote::quote_spanned!(i.span() => .field(&#i)));
                        quote::quote!(
                            Self::#ident ( #( ref #captured, )* ) => {
                                fmt.debug_tuple(#full_variant_str)
                                    #( #debugged )*
                                    .finish()
                            }
                        )
                    }
                    syn::Fields::Unit => quote::quote!(
                        Self::#ident => fmt.write_str(#full_variant_str)
                    ),
                }
            });

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

    quote::quote!(
        const _: () = {
            impl #impl_generics core::fmt::Debug for #input_ident #ty_generics #where_clause {
                fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
                    #impl_
                }
            }
        };
    )
    .into()
}