displaythis-impl 1.0.23

use crate::ast::{Enum, Field, Input, Struct};
use proc_macro2::TokenStream;
use quote::{format_ident, quote, ToTokens};
use syn::{DeriveInput, Member, Result};

pub fn derive(node: &DeriveInput) -> Result<TokenStream> {
    let input = Input::from_syn(node)?;
    input.validate()?;
    Ok(match input {
        Input::Struct(input) => impl_struct(input),
        Input::Enum(input) => impl_enum(input),
    })
}

fn impl_struct(input: Struct) -> TokenStream {
    let ty = &input.ident;
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let display_body = if let Some(display) = &input.attrs.display {
        let use_as_display = if display.has_bonus_display {
            Some(quote! {
                #[allow(unused_imports)]
                use displaythis::private::{DisplayAsDisplay, PathAsDisplay};
            })
        } else {
            None
        };
        let pat = fields_pat(&input.fields);
        Some(quote! {
            #use_as_display
            #[allow(unused_variables, deprecated)]
            let Self #pat = self;
            #display
        })
    } else {
        None
    };
    let display_impl = display_body.map(|body| {
        quote! {
            #[allow(unused_qualifications)]
            impl #impl_generics std::fmt::Display for #ty #ty_generics #where_clause {
                #[allow(clippy::used_underscore_binding)]
                fn fmt(&self, __formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
                    #body
                }
            }
        }
    });

    quote! {
        #display_impl
    }
}

fn impl_enum(input: Enum) -> TokenStream {
    let ty = &input.ident;
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

    let display_impl = if input.has_display() {
        let use_as_display = if input.variants.iter().any(|v| {
            v.attrs
                .display
                .as_ref()
                .map_or(false, |display| display.has_bonus_display)
        }) {
            Some(quote! {
                #[allow(unused_imports)]
                use displaythis::private::{DisplayAsDisplay, PathAsDisplay};
            })
        } else {
            None
        };
        let void_deref = if input.variants.is_empty() {
            Some(quote!(*))
        } else {
            None
        };
        let arms = input.variants.iter().map(|variant| {
            let display = match &variant.attrs.display {
                Some(display) => display.to_token_stream(),
                None => {
                    let only_field = match &variant.fields[0].member {
                        Member::Named(ident) => ident.clone(),
                        Member::Unnamed(index) => format_ident!("_{}", index),
                    };
                    quote!(std::fmt::Display::fmt(#only_field, __formatter))
                }
            };
            let ident = &variant.ident;
            let pat = fields_pat(&variant.fields);
            quote! {
                #ty::#ident #pat => #display
            }
        });
        Some(quote! {
            #[allow(unused_qualifications)]
            impl #impl_generics std::fmt::Display for #ty #ty_generics #where_clause {
                fn fmt(&self, __formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
                    #use_as_display
                    #[allow(unused_variables, deprecated, clippy::used_underscore_binding)]
                    match #void_deref self {
                        #(#arms,)*
                    }
                }
            }
        })
    } else {
        None
    };

    quote! {
        #display_impl
    }
}

fn fields_pat(fields: &[Field]) -> TokenStream {
    let mut members = fields.iter().map(|field| &field.member).peekable();
    match members.peek() {
        Some(Member::Named(_)) => quote!({ #(#members),* }),
        Some(Member::Unnamed(_)) => {
            let vars = members.map(|member| match member {
                Member::Unnamed(member) => format_ident!("_{}", member),
                Member::Named(_) => unreachable!(),
            });
            quote!((#(#vars),*))
        }
        None => quote!({}),
    }
}