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Use field span in rustc_macros when emitting decode call #92011

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Jan 3, 2022
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Use field span in rustc_macros when emitting decode call #92011

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26 changes: 15 additions & 11 deletions compiler/rustc_macros/src/serialize.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
use proc_macro2::TokenStream;
use quote::quote;
use quote::{quote, quote_spanned};
use syn::parse_quote;
use syn::spanned::Spanned;

pub fn type_decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
let decoder_ty = quote! { __D };
Expand Down Expand Up @@ -104,27 +105,30 @@ fn decodable_body(
}

fn decode_field(field: &syn::Field, index: usize, is_struct: bool) -> proc_macro2::TokenStream {
let field_span = field.ident.as_ref().map_or(field.ty.span(), |ident| ident.span());

let decode_inner_method = if let syn::Type::Reference(_) = field.ty {
quote! { ::rustc_middle::ty::codec::RefDecodable::decode }
} else {
quote! { ::rustc_serialize::Decodable::decode }
};
let (decode_method, opt_field_name) = if is_struct {
let field_name = field.ident.as_ref().map_or_else(|| index.to_string(), |i| i.to_string());
(
proc_macro2::Ident::new("read_struct_field", proc_macro2::Span::call_site()),
quote! { #field_name, },
)
(proc_macro2::Ident::new("read_struct_field", field_span), quote! { #field_name, })
} else {
(
proc_macro2::Ident::new("read_enum_variant_arg", proc_macro2::Span::call_site()),
quote! {},
)
(proc_macro2::Ident::new("read_enum_variant_arg", field_span), quote! {})
};

let __decoder = quote! { __decoder };
// Use the span of the field for the method call, so
// that backtraces will point to the field.
let decode_call = quote_spanned! {field_span=>
::rustc_serialize::Decoder::#decode_method(
#__decoder, #opt_field_name #decode_inner_method)
};

quote! {
match ::rustc_serialize::Decoder::#decode_method(
__decoder, #opt_field_name #decode_inner_method) {
match #decode_call {
::std::result::Result::Ok(__res) => __res,
::std::result::Result::Err(__err) => return ::std::result::Result::Err(__err),
}
Expand Down