Merge commit '6eba9cd92c295c5389944f6adda1f1e83b2cb008' as 'subprojects/thiserror'

subprojects/thiserror/impl/src/fallback.rs

@@ -0,0 +1,33 @@
+use crate::expand::call_site_ident;
+use crate::private;
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::DeriveInput;
+
+pub(crate) fn expand(input: &DeriveInput, error: syn::Error) -> TokenStream {
+    let ty = call_site_ident(&input.ident);
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
+    let error = error.to_compile_error();
+
+    quote! {
+        #error
+
+        #[allow(unused_qualifications)]
+        #[automatically_derived]
+        impl #impl_generics ::thiserror::#private::Error for #ty #ty_generics #where_clause
+        where
+            // Work around trivial bounds being unstable.
+            // https://github.com/rust-lang/rust/issues/48214
+            for<'workaround> #ty #ty_generics: ::core::fmt::Debug,
+        {}
+
+        #[allow(unused_qualifications)]
+        #[automatically_derived]
+        impl #impl_generics ::core::fmt::Display for #ty #ty_generics #where_clause {
+            fn fmt(&self, __formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                ::core::unreachable!()
+            }
+        }
+    }
+}