[Bug c++/50431] New: lambda bug for array size def

[Bug c++/50431] New: lambda bug for array size def

[zhudiqi at 163 dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

             Bug #: 50431
           Summary: lambda bug for array size def
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zhudiqi@163.com


This code is OK,
OK:
  constexpr auto sz = []()->long { return 100L; };
  int arr1[sz()];

  int arr2[[]()->long { return 100L; }()];

But these code will failed for g++ compiler 4.6.1.

BUG1:
  auto sz = []()->constexpr long { return 100L; };
  int arr[[]()->long { return 100L; }];

BUG2:
  //feature.cpp:51:38: internal compiler error: Segmentation fault
  int arr[[]()->long { return 100L; }];

[Bug c++/50431] lambda bug for array size def

[zhudiqi at 163 dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

--- Comment #1 from zhudiqi at 163 dot com 2011-09-16 11:36:15 UTC ---
Created attachment 25304
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25304
lambda for array size def

[Bug c++/50431] lambda bug for array size def

[zhudiqi at 163 dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

--- Comment #2 from zhudiqi at 163 dot com 2011-09-16 11:40:42 UTC ---
BUG1:
  auto sz = []()->constexpr long { return 100L; };
  int arr[sz()];

Why constexpr for lambda won't be compiled? Can i not use auto type for a
lambda variant?

[Bug c++/50431] [C++0x] bug in def array size with a lambda

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |4.7.0
           Keywords|                            |error-recovery,
                   |                            |ice-on-invalid-code
   Last reconfirmed|                            |2011-09-16
                 CC|                            |jason at gcc dot gnu.org
     Ever Confirmed|0                           |1
            Summary|bug in def array size with  |[C++0x] bug in def array
                   |a lambda                    |size with a lambda
      Known to fail|                            |4.6.1
           Severity|major                       |normal

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-16 11:50:50 UTC ---
This is not "major" severity because the code is invalid, so it's just error
handling.

(In reply to comment #0)
> BUG1:
>   auto sz = []()->constexpr long { return 100L; };

This is invalid, constexpr is not part of the return type, it's a function
specifier.  G++ correctly rejects it.  The "bailing out" is due to the next
line:

>   int arr[[]()->long { return 100L; }];

This is also invalid, but shouldn't cause an ICE, and 4.7 doesn't get an ICE
here:

l.cc:2:38: error: size of array 'arr' has non-integral type '<lambda()>'

4.6.1 segfaults here:
Program received signal SIGSEGV, Segmentation fault.
compute_array_index_type (name=0x2aaaaac1e738, size=0x0, complain=3)
    at ../../gcc-4.6.1/gcc/cp/decl.c:7561
7561                  type = TREE_TYPE (size);
(gdb) bt
#0  compute_array_index_type (name=0x2aaaaac1e738, size=0x0, complain=3)
    at ../../gcc-4.6.1/gcc/cp/decl.c:7561
#1  0x00000000004ab611 in create_array_type_for_decl (declarator=0x1327be0,
    declspecs=0x7fffffffe1c0, decl_context=NORMAL, initialized=0,
    attrlist=0x7fffffffe0c8) at ../../gcc-4.6.1/gcc/cp/decl.c:7825

[Bug c++/50431] [C++0x] bug in def array size with a lambda

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-16 13:47:49 UTC ---
(In reply to comment #2)
> BUG1:
>   auto sz = []()->constexpr long { return 100L; };
>   int arr[sz()];
> 
> Why constexpr for lambda won't be compiled? Can i not use auto type for a
> lambda variant?

The closure type's function call operator can be const but not constexpr.
You can use auto for a lambda, you just can't have a constexpr lambda.

Why do you want it to work?  

What advantage is there to using a lambda instead of named function? e.g.

  constexpr long sz() { return 100L; };
  int arr[sz()];

[Bug c++/50431] [C++0x] bug in def array size with a lambda

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

Paolo Carlini <paolo.carlini at oracle dot com> changed:

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

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-11-05 21:33:07 UTC ---
I guess we can close this as fixed in 4.7.0.

[Bug c++/50431] [C++0x] bug in def array size with a lambda

[zhudiqi at 163 dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50431

--- Comment #6 from zhudiqi at 163 dot com 2011-11-13 12:59:47 UTC ---
(In reply to comment #5)
> I guess we can close this as fixed in 4.7.0.

Yes, I think so.