tfmt-macros 0.4.0

`tfmt` macros
Documentation 
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extern crate proc_macro;

use proc_macro::TokenStream;
use proc_macro2::{Literal, Span};
use quote::quote;
use syn::{parse, parse_macro_input, parse_quote, Data, DeriveInput, Fields, GenericParam, Ident};

pub fn debug_gen(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);

    let mut generics = input.generics;

    for param in &mut generics.params {
        if let GenericParam::Type(type_param) = param {
            type_param.bounds.push(parse_quote!(tfmt::uDebug));
        }
    }

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

    let ident = &input.ident;
    let ts = match input.data {
        Data::Struct(data) => {
            let ident_s = ident.to_string();

            let body = match data.fields {
                Fields::Named(fields) => {
                    let fields = fields
                        .named
                        .iter()
                        .map(|field| {
                            let ident = field.ident.as_ref().expect("UNREACHABLE");
                            let name = ident.to_string();

                            quote!(field(#name, &self.#ident)?)
                        })
                        .collect::<Vec<_>>();

                    quote!(f.debug_struct(#ident_s)?#(.#fields)*.finish())
                }

                Fields::Unnamed(fields) => {
                    let fields = (0..fields.unnamed.len())
                        .map(|i| {
                            let i = Literal::u64_unsuffixed(i as u64);

                            quote!(field(&self.#i)?)
                        })
                        .collect::<Vec<_>>();

                    quote!(f.debug_tuple(#ident_s)?#(.#fields)*.finish())
                }

                Fields::Unit => quote!(f.write_str(#ident_s)),
            };

            quote!(
                impl #impl_generics tfmt::uDebug for #ident #ty_generics #where_clause {
                    fn fmt<W>(&self, f: &mut tfmt::Formatter<'_, W>) -> core::result::Result<(), W::Error>
                    where
                        W: tfmt::uWrite + ?Sized,
                    {
                        #body
                    }
                }

            )
        }

        Data::Enum(data) => {
            let arms = data
                .variants
                .iter()
                .map(|var| {
                    let variant = &var.ident;
                    let variant_s = variant.to_string();

                    match &var.fields {
                        Fields::Named(fields) => {
                            let mut pats = Vec::with_capacity(fields.named.len());
                            let mut methods = Vec::with_capacity(fields.named.len());
                            for field in &fields.named {
                                let ident = field.ident.as_ref().unwrap();
                                let ident_s = ident.to_string();

                                pats.push(quote!(#ident));
                                methods.push(quote!(field(#ident_s, #ident)?));
                            }

                            quote!(
                                #ident::#variant { #(#pats),* } => {
                                    f.debug_struct(#variant_s)?#(.#methods)*.finish()
                                }
                            )
                        }

                        Fields::Unnamed(fields) => {
                            let pats = &(0..fields.unnamed.len())
                                .map(|i| Ident::new(&format!("_{}", i), Span::call_site()))
                                .collect::<Vec<_>>();

                            quote!(
                                #ident::#variant(#(#pats),*) => {
                                    f.debug_tuple(#variant_s)?#(.field(#pats)?)*.finish()
                                }
                            )
                        }

                        Fields::Unit => quote!(
                            #ident::#variant => {
                                f.write_str(#variant_s)
                            }
                        ),
                    }
                })
                .collect::<Vec<_>>();

            let body = if arms.is_empty() {
                // Debug's implementation uses `::core::intrinsics::unreachable()`
                quote!(unsafe { core::unreachable!() })
            } else {
                quote!(
                    match self {
                        #(#arms),*
                    }
                )
            };

            quote!(
                impl #impl_generics tfmt::uDebug for #ident #ty_generics #where_clause {
                    fn fmt<W>(&self, f: &mut tfmt::Formatter<'_, W>) -> core::result::Result<(), W::Error>
                        where
                        W: tfmt::uWrite + ?Sized,
                    {
                        #body
                    }
                }
            )
        }

        Data::Union(..) => {
            return parse::Error::new(Span::call_site(), "this trait cannot be derived for unions")
                .to_compile_error()
                .into();
        }
    };

    ts.into()
}