thiserror_impl/
fallback.rs

1use crate::expand::call_site_ident;
2use crate::private;
3use proc_macro2::TokenStream;
4use quote::quote;
5use syn::DeriveInput;
6
7pub(crate) fn expand(input: &DeriveInput, error: syn::Error) -> TokenStream {
8    let ty = call_site_ident(&input.ident);
9    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
10
11    let error = error.to_compile_error();
12
13    quote! {
14        #error
15
16        #[allow(unused_qualifications)]
17        #[automatically_derived]
18        impl #impl_generics ::thiserror::#private::Error for #ty #ty_generics #where_clause
19        where
20            // Work around trivial bounds being unstable.
21            // https://github.com/rust-lang/rust/issues/48214
22            for<'workaround> #ty #ty_generics: ::core::fmt::Debug,
23        {}
24
25        #[allow(unused_qualifications)]
26        #[automatically_derived]
27        impl #impl_generics ::core::fmt::Display for #ty #ty_generics #where_clause {
28            fn fmt(&self, __formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
29                ::core::unreachable!()
30            }
31        }
32    }
33}