[Bug c++/67910] New: Two autos in a single function confuses the type system

["guille at cal dot berkeley.edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67910

            Bug ID: 67910
           Summary: Two autos in a single function confuses the type
                    system
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guille at cal dot berkeley.edu
  Target Milestone: ---

The following code does not compile on 5.2.0:



struct A {};
struct B {};

static auto f(auto b) -> A { return A(); }

int main()
{
    A a = f(B());
    return 0;
}

whereas the following *does* compile:


struct A {};
struct B {};

static auto f(B b) -> A { return A(); }


int main()
{
    __attribute__((unused)) A a = f(B());
    return 0;
}


In the first (failing) case, the type system thinks that 'f' returns the same
type as the first auto *argument*, even though the return type is specified to
be 'A'.