fieldmask_derive 0.2.0

derive macros for the fieldmask crate
Documentation 
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use proc_macro::TokenStream;
use quote::{ToTokens, quote};
use syn::parse_macro_input;

use super::ast::Input;

pub fn maskable_atomic_impl(input: TokenStream) -> TokenStream {
    let Input {
        generics,
        ty,
        update_as_field_fn,
        merge_fn,
        option_project_fn,
        ..
    } = parse_macro_input!(input);

    let (impl_generics, _ty_generics, where_clauses) = generics.split_for_impl();
    let update_as_field_fn = update_as_field_fn
        .map(|item| item.to_token_stream())
        .unwrap_or_else(|| {
            quote! {
                fn update_as_field(
                    &mut self,
                    source: Self,
                    _mask: &<Self as ::fieldmask::Maskable>::Mask,
                    _options: &::fieldmask::UpdateOptions,
                ) {
                    *self = source;
                }
            }
        });
    let merge_fn = merge_fn
        .map(|item| item.to_token_stream())
        .unwrap_or_else(|| {
            quote! {
                fn merge(
                    &mut self,
                    source: Self,
                    _options: &::fieldmask::UpdateOptions,
                ) {
                    if source != ::core::default::Default::default() {
                        *self = source;
                    }
                }
            }
        });
    let option_project_fn = option_project_fn
        .map(|item| item.to_token_stream())
        .unwrap_or_else(|| {
            quote! {
                fn option_project(
                    this: &mut ::core::option::Option<Self>,
                    _mask: &<Self as ::fieldmask::Maskable>::Mask,
                    options: &::fieldmask::ProjectOptions,
                ) {
                    if options.normalize && this == &::core::option::Option::Some(::core::default::Default::default()) {
                        *this = ::core::option::Option::None;
                    }
                }
            }
        });

    quote! {
        impl #impl_generics ::fieldmask::Maskable for #ty
        #where_clauses
        {
            type Mask = ();

            fn empty_mask() -> Self::Mask {}

            fn full_mask() -> Self::Mask {}

            fn make_mask_include_field<'a>(
                _mask: &mut Self::Mask,
                field_path: &[&'a ::core::primitive::str],
            ) -> ::core::result::Result<(), ::fieldmask::DeserializeMaskError<'a>> {
                if field_path.is_empty() {
                    return ::core::result::Result::Ok(());
                }
                ::core::result::Result::Err(::fieldmask::DeserializeMaskError::FieldNotFound {
                    type_name: ::core::stringify!(#ty),
                    field: field_path[0],
                })
            }
        }

        impl #impl_generics ::fieldmask::SelfMaskable for #ty
        #where_clauses
        {
            fn project(&mut self, _mask: &Self::Mask, _options: &::fieldmask::ProjectOptions) {}

            #update_as_field_fn
            #merge_fn
        }

        impl #impl_generics ::fieldmask::OptionMaskable for #ty
        #where_clauses
        {
            #option_project_fn

            fn option_update_as_field(
                this: &mut ::core::option::Option<Self>,
                source: ::core::option::Option<Self>,
                mask: &<Self as ::fieldmask::Maskable>::Mask,
                options: &::fieldmask::UpdateOptions,
            ) {
                match (this.as_mut(), source) {
                    (::core::option::Option::Some(this), ::core::option::Option::Some(source)) => {
                        ::fieldmask::SelfMaskable::update_as_field(this, source, mask, options);
                    }
                    (::core::option::Option::Some(this), ::core::option::Option::None) => {
                        ::fieldmask::SelfMaskable::update_as_field(
                            this,
                            ::core::default::Default::default(),
                            mask,
                            options,
                        );
                    }
                    (::core::option::Option::None, ::core::option::Option::Some(mut source)) => {
                        ::fieldmask::SelfMaskable::project(&mut source, mask, &::core::default::Default::default());
                        *this = ::core::option::Option::Some(source);
                    }
                    (::core::option::Option::None, ::core::option::Option::None) => {}
                }
            }

            fn option_merge(
                this: &mut ::core::option::Option<Self>,
                source: ::core::option::Option<Self>,
                options: &::fieldmask::UpdateOptions,
            ) {
                match (this.as_mut(), source) {
                    (::core::option::Option::Some(this), ::core::option::Option::Some(source)) => {
                        ::fieldmask::SelfMaskable::merge(this, source, options);
                    }
                    (_, ::core::option::Option::None) => {}
                    (::core::option::Option::None, source) => {
                        *this = source;
                    }
                }
            }
        }
    }
    .into()
}