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Use field span in rustc_macros when emitting decode call

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This will cause backtraces to point to the location of
the field in the struct/enum, rather than the derive macro.

This makes it clear which field was being decoded when the
backtrace was captured (which is especially useful if
there are multiple fields with the same type).
This commit is contained in:
Aaron Hill 2021-12-16 18:35:15 -05:00
parent 5531927e8a
commit 44fdb98764
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GPG Key ID: B4087E510E98B164
1 changed files with 15 additions and 11 deletions
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26
compiler/rustc_macros/src/serialize.rs
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@ -1,6 +1,7 @@
use proc_macro2::TokenStream; use proc_macro2::TokenStream;
use quote::quote; use quote::{quote, quote_spanned};
use syn::parse_quote; use syn::parse_quote;
use syn::spanned::Spanned;
pub fn type_decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream { pub fn type_decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
let decoder_ty = quote! { __D }; let decoder_ty = quote! { __D };
@ -104,6 +105,8 @@ fn decodable_body(
} }
fn decode_field(field: &syn::Field, index: usize, is_struct: bool) -> proc_macro2::TokenStream { 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 { let decode_inner_method = if let syn::Type::Reference(_) = field.ty {
quote! { ::rustc_middle::ty::codec::RefDecodable::decode } quote! { ::rustc_middle::ty::codec::RefDecodable::decode }
} else { } else {
@ -111,20 +114,21 @@ fn decode_field(field: &syn::Field, index: usize, is_struct: bool) -> proc_macro
}; };
let (decode_method, opt_field_name) = if is_struct { 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()); let field_name = field.ident.as_ref().map_or_else(|| index.to_string(), |i| i.to_string());
( (proc_macro2::Ident::new("read_struct_field", field_span), quote! { #field_name, })
proc_macro2::Ident::new("read_struct_field", proc_macro2::Span::call_site()),
quote! { #field_name, },
)
} else { } else {
( (proc_macro2::Ident::new("read_enum_variant_arg", field_span), quote! {})
proc_macro2::Ident::new("read_enum_variant_arg", proc_macro2::Span::call_site()), };
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! { quote! {
match ::rustc_serialize::Decoder::#decode_method( match #decode_call {
__decoder, #opt_field_name #decode_inner_method) {
::std::result::Result::Ok(__res) => __res, ::std::result::Result::Ok(__res) => __res,
::std::result::Result::Err(__err) => return ::std::result::Result::Err(__err), ::std::result::Result::Err(__err) => return ::std::result::Result::Err(__err),
} }