Function show_fieldless_enum_concat_str 

fn show_fieldless_enum_concat_str(
    cx: &ExtCtxt<'_>,
    span: Span,
    def: &EnumDef,
    fmt: Box<Expr>,
) -> Option<(ThinVec<Stmt>, Box<Expr>)>

Special case for fieldless enums with no discriminants. Builds

impl ::core::fmt::Debug for A {
    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
        static __NAMES: &str = "ABBBCC";
        static __OFFSET: [usize; 4] =[0, 1, 4, 6];
        let __d = ::core::intrinsics::discriminant_value(self) as usize;
        ::core::fmt::Formatter::debug_c_like_enums_write_str(f, __NAMES, &__OFFSET, __d)
    }
}