[Bug c++/83950] [8 regression] error: no matching function for call to ‘folly::dynamic::at(size_t&) const’

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83950

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Sunil Pandey from comment #0)
> This bug appear during latest HHVM build with GCC 8. GCC 7 works fine.
> 
> $ cat AsyncLog.cpp
> template <typename a, a b> struct c { static constexpr a d = b; };
> template <typename> struct e : c<bool, false> {};
> template <int, typename a = void> struct f { typedef a h; };
> typedef int size_t;
> namespace folly {
> struct dynamic {
>   template <class, class = void> struct g;
>   dynamic(char *);
>   template <class k, class = typename g<k>::h> dynamic(k);
>   void at(dynamic) const;
>   const dynamic *j(dynamic);
> };
> template <class k> struct dynamic::g<k, typename f<e<k>::d>::h> {
>   using h = long;
> };
> }
> template <class> class l;
> struct m {
>   folly::dynamic json;
> };
> template <class n> class G : l<typename n::o> { const int &p(); };
> template <class n> const int &G<n>::p() {
>   m jpool;
>   auto json = jpool.json;
>   try {
>     auto jservers = json.j("");
>     for (size_t i;;)
>       jservers->at(i);
>   } catch (int) {
>   }
> }
> 
> 
> $ g++ --version
> g++ (GCC) 8.0.1 20180119 (experimental)
> Copyright (C) 2018 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> 
> $ g++ -O3 -c AsyncLog.cpp -w
> AsyncLog.cpp: In member function ‘const int& G<n>::p()’:
> AsyncLog.cpp:28:21: error: no matching function for call to
> ‘folly::dynamic::at(size_t&) const’
>        jservers->at(i);
>                      ^
> AsyncLog.cpp:10:8: note: candidate: ‘void folly::dynamic::at(folly::dynamic)
> const’
>    void at(dynamic) const;
>         ^~
> AsyncLog.cpp:10:8: note:   no known conversion for argument 1 from ‘size_t’
> {aka ‘int’} to ‘folly::dynamic’

What's the bug?  That error looks correct to me.