thiserror_impl/
fallback.rs

1use crate::expand::call_site_ident;
2use proc_macro2::TokenStream;
3use quote::quote;
4use syn::DeriveInput;
5
6pub(crate) fn expand(input: &DeriveInput, error: syn::Error) -> TokenStream {
7    let ty = call_site_ident(&input.ident);
8    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
9
10    let error = error.to_compile_error();
11
12    quote! {
13        #error
14
15        #[allow(unused_qualifications)]
16        #[automatically_derived]
17        impl #impl_generics ::thiserror::__private::Error for #ty #ty_generics #where_clause
18        where
19            // Work around trivial bounds being unstable.
20            // https://github.com/rust-lang/rust/issues/48214
21            for<'workaround> #ty #ty_generics: ::core::fmt::Debug,
22        {}
23
24        #[allow(unused_qualifications)]
25        #[automatically_derived]
26        impl #impl_generics ::core::fmt::Display for #ty #ty_generics #where_clause {
27            fn fmt(&self, __formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
28                ::core::unreachable!()
29            }
30        }
31    }
32}