vendor/derivative/src/debug.rs

use proc_macro2;

use ast;
use attr;
use matcher;
use syn;
use syn::spanned::Spanned;
use utils;

pub fn derive(input: &ast::Input) -> proc_macro2::TokenStream {
    let debug_trait_path = debug_trait_path();
    let fmt_path = fmt_path();

    let formatter = quote_spanned! {input.span=> __f};

    let body = matcher::Matcher::new(matcher::BindingStyle::Ref, input.attrs.is_packed)
        .with_field_filter(|f: &ast::Field| !f.attrs.ignore_debug())
        .build_arms(input, "__arg", |_, _, arm_name, style, attrs, bis| {
            let field_prints = bis.iter().filter_map(|bi| {
                if bi.field.attrs.ignore_debug() {
                    return None;
                }

                if attrs.debug_transparent() {
                    return Some(quote_spanned! {arm_name.span()=>
                        #debug_trait_path::fmt(__arg_0, #formatter)
                    });
                }

                let arg_expr = &bi.expr;
                let arg_ident = &bi.ident;

                let dummy_debug = bi.field.attrs.debug_format_with().map(|format_fn| {
                    format_with(
                        bi.field,
                        &input.attrs.debug_bound(),
                        &arg_expr,
                        &arg_ident,
                        format_fn,
                        input.generics.clone(),
                    )
                });
                let expr = if bi.field.attrs.debug_format_with().is_some() {
                    quote_spanned! {arm_name.span()=>
                        &#arg_ident
                    }
                } else {
                    quote_spanned! {arm_name.span()=>
                        &&#arg_expr
                    }
                };

                let builder = if let Some(ref name) = bi.field.ident {
                    let name = name.to_string();
                    quote_spanned! {arm_name.span()=>
                        #dummy_debug
                        let _ = __debug_trait_builder.field(#name, #expr);
                    }
                } else {
                    quote_spanned! {arm_name.span()=>
                        #dummy_debug
                        let _ = __debug_trait_builder.field(#expr);
                    }
                };

                Some(builder)
            });

            let method = match style {
                ast::Style::Struct => "debug_struct",
                ast::Style::Tuple | ast::Style::Unit => "debug_tuple",
            };
            let method = syn::Ident::new(method, proc_macro2::Span::call_site());

            if attrs.debug_transparent() {
                quote_spanned! {arm_name.span()=>
                    #(#field_prints)*
                }
            } else {
                let name = arm_name.to_string();
                quote_spanned! {arm_name.span()=>
                    let mut __debug_trait_builder = #formatter.#method(#name);
                    #(#field_prints)*
                    __debug_trait_builder.finish()
                }
            }
        });

    let name = &input.ident;

    let generics = utils::build_impl_generics(
        input,
        &debug_trait_path,
        needs_debug_bound,
        |field| field.debug_bound(),
        |input| input.debug_bound(),
    );
    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

    // don't attach a span to prevent issue #58
    let match_self = quote!(match *self);
    quote_spanned! {input.span=>
        #[allow(unused_qualifications)]
        #[allow(clippy::unneeded_field_pattern)]
        impl #impl_generics #debug_trait_path for #name #ty_generics #where_clause {
            fn fmt(&self, #formatter: &mut #fmt_path::Formatter) -> #fmt_path::Result {
                #match_self {
                    #body
                }
            }
        }
    }
}

fn needs_debug_bound(attrs: &attr::Field) -> bool {
    !attrs.ignore_debug() && attrs.debug_bound().is_none()
}

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

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

/// Return the path of the `PhantomData` type, that is `::std::marker::PhantomData`.
fn phantom_path() -> syn::Path {
    if cfg!(feature = "use_core") {
        parse_quote!(::core::marker::PhantomData)
    } else {
        parse_quote!(::std::marker::PhantomData)
    }
}

fn format_with(
    f: &ast::Field,
    bounds: &Option<&[syn::WherePredicate]>,
    arg_expr: &proc_macro2::TokenStream,
    arg_ident: &syn::Ident,
    format_fn: &syn::Path,
    mut generics: syn::Generics,
) -> proc_macro2::TokenStream {
    let debug_trait_path = debug_trait_path();
    let fmt_path = fmt_path();
    let phantom_path = phantom_path();

    generics
        .make_where_clause()
        .predicates
        .extend(f.attrs.debug_bound().unwrap_or(&[]).iter().cloned());

    generics
        .params
        .push(syn::GenericParam::Lifetime(syn::LifetimeDef::new(
            parse_quote!('_derivative),
        )));
    let where_predicates = generics
        .type_params()
        .map(|ty| {
            let mut bounds = syn::punctuated::Punctuated::new();
            bounds.push(syn::TypeParamBound::Lifetime(syn::Lifetime::new(
                "'_derivative",
                proc_macro2::Span::call_site(),
            )));

            let path = syn::Path::from(syn::PathSegment::from(ty.ident.clone()));

            syn::WherePredicate::Type(syn::PredicateType {
                lifetimes: None,
                bounded_ty: syn::Type::Path(syn::TypePath { qself: None, path }),
                colon_token: Default::default(),
                bounds,
            })
        })
        .chain(bounds.iter().flat_map(|b| b.iter().cloned()))
        .collect::<Vec<_>>();
    generics
        .make_where_clause()
        .predicates
        .extend(where_predicates);

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

    let ty = f.ty;

    // Leave off the type parameter bounds, defaults, and attributes
    let phantom = generics.type_params().map(|tp| &tp.ident);

    let mut ctor_generics = generics.clone();
    *ctor_generics
        .lifetimes_mut()
        .last()
        .expect("There must be a '_derivative lifetime") = syn::LifetimeDef::new(parse_quote!('_));
    let (_, ctor_ty_generics, _) = ctor_generics.split_for_impl();
    let ctor_ty_generics = ctor_ty_generics.as_turbofish();

    // don't attach a span to prevent issue #58
    let match_self = quote!(match self.0);
    quote_spanned!(format_fn.span()=>
        let #arg_ident = {
            struct Dummy #impl_generics (&'_derivative #ty, #phantom_path <(#(#phantom,)*)>) #where_clause;

            impl #impl_generics #debug_trait_path for Dummy #ty_generics #where_clause {
                fn fmt(&self, __f: &mut #fmt_path::Formatter) -> #fmt_path::Result {
                    #match_self {
                        this => #format_fn(this, __f)
                    }
                }
            }

            Dummy #ctor_ty_generics (&&#arg_expr, #phantom_path)
        };
    )
}