[Bug c++/50075] New: ICE related to parameter deduction and initializer_list

[Bug c++/50075] New: ICE related to parameter deduction and initializer_list

[z0sh at sogetthis dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

             Bug #: 50075
           Summary: ICE related to parameter deduction and
                    initializer_list
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: z0sh@sogetthis.com
              Host: x86
            Target: x86


[Please rephrase the title with something more appropriate, I don't know how to
pin this down.]

I was trying to deduce the size parameter of an std::array<T,N> from the size
of an initializer list. The following code is probably not correct, but in any
event, it causes GCC 4.6.1 with -std=c++0x to crash:



#include <functional>
#include <array>

template <typename T, unsigned int N>
std::array<T, N> make_array_helper(const std::initializer_list<T> & il)
{
  return std::array<T, N>(il);
}

template <typename T>
auto make_array(const std::initializer_list<T> & il) ->
decltype(make_array(il))
{
  return make_array_helper<T, il.size()>(il);
}

int main()
{
  auto z = make_array({{1,2}});
}

[Bug c++/50075] ICE related to parameter deduction and initializer_list

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-08-13 14:00:45 UTC ---
obviously it shouldn't crash, but what you're trying  won't work, because
initializer_list::size is not constexpr, so il.size() is not a constant
expression

[Bug c++/50075] ICE related to parameter deduction and initializer_list

[z0sh at sogetthis dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

--- Comment #2 from Kerrek SB <z0sh at sogetthis dot com> 2011-08-13 14:09:20 UTC ---
Indeed, according to the FDIS size() is *not* constexpr, but I had initially
just checked the GCC implementation, in which it *is* declared as constexpr!
(This is in "c++/4.6.1/initializer_list".)

[Bug c++/50075] ICE related to parameter deduction and initializer_list

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-08-13 15:42:06 UTC ---
ah, sorry, I didn't check our impl - so then it should work, just isn't
portable

[Bug c++/50075] [C++0x] ICE related to parameter deduction and initializer_list

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-invalid-code
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011-08-13
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
   Target Milestone|---                         |4.7.0
     Ever Confirmed|0                           |1

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> 2011-08-13 22:00:34 UTC ---
The problem is the recursion:

template <typename T>
auto make_array(const std::initializer_list<T> & il) ->
decltype(make_array(il))

You're declaring make_array to have the same return type as itself.  4.6
happily goes down the rabbit hole until it runs out of stack.  4.7 complains
and then crashes for another reason, which I will fix.

[Bug c++/50075] [C++0x] ICE related to parameter deduction and initializer_list

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> 2011-08-14 04:41:49 UTC ---
Author: jason
Date: Sun Aug 14 04:41:43 2011
New Revision: 177743

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=177743
Log:
    PR c++/50075
    * name-lookup.c (local_bindings_p): New.
    * name-lookup.h: Declare it.
    * lex.c (unqualified_name_lookup_error): Use it.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/decltype32.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/lex.c
    trunk/gcc/cp/name-lookup.c
    trunk/gcc/cp/name-lookup.h
    trunk/gcc/testsuite/ChangeLog

[Bug c++/50075] [C++0x] ICE related to parameter deduction and initializer_list

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2011-08-14 04:43:39 UTC ---
Fixed for 4.7.

[Bug c++/50075] [C++0x] ICE related to parameter deduction and initializer_list

[z0sh at sogetthis dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50075

--- Comment #7 from Kerrek SB <z0sh at sogetthis dot com> 2011-08-15 13:57:51 UTC ---
This is great, thank you!