Recursive Arguments formatting

Author: nbdd0121

compiler/rustc_const_eval/src/const_eval/panic.rs

@@ -1,5 +1,6 @@
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, layout::LayoutOf, subst::Subst};
+use rustc_span::sym;
 use std::cell::Cell;
 use std::fmt::{self, Debug, Formatter};
 
@@ -154,6 +155,10 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
                 return self.fmt_arg(place.into(), fmt_trait, f);
             }
 
+            ty::Adt(adt, _) if self.tcx.is_diagnostic_item(sym::Arguments, adt.did) => {
+                return self.fmt_arguments(arg, f);
+            }
+
             // FIXME(nbdd0121): ty::Adt(..) => (),
             _ => {
                 let _ = write!(f, "<failed to format {}>", arg.layout.ty);

library/core/src/fmt/mod.rs

@@ -458,6 +458,7 @@ impl<'a> Arguments<'a> {
 ///
 /// [`format()`]: ../../std/fmt/fn.format.html
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "Arguments"]
 #[derive(Copy, Clone)]
 pub struct Arguments<'a> {
     // Format string pieces to print.