[Bug c++/60420] New: [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[Bug c++/60420] New: [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

            Bug ID: 60420
           Summary: [C++11] Bogus "error: ‘const’ qualifiers cannot be
                    applied to ‘int&’" with lambda
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com

Google ref: b/13305941

Using current (r208339) trunk:

g++ -c -std=c++11 t.cc
t.cc: In instantiation of ‘struct fn(Iterator, Iterator) [with Iterator =
__gnu_cxx::__normal_iterator<int*, std::vector<int> >]::<lambda>’:
t.cc:6:45:   required from ‘void fn(Iterator, Iterator) [with Iterator =
__gnu_cxx::__normal_iterator<int*, std::vector<int> >]’
t.cc:11:26:   required from here
t.cc:6:38: error: ‘const’ qualifiers cannot be applied to ‘int&’
   auto x = [](const decltype(*begin) b) { };
                                      ^
t.cc: In instantiation of ‘struct fn(Iterator, Iterator) [with Iterator =
__gnu_cxx::__normal_iterator<const int*, std::vector<int> >]::<lambda>’:
t.cc:6:45:   required from ‘void fn(Iterator, Iterator) [with Iterator =
__gnu_cxx::__normal_iterator<const int*, std::vector<int> >]’
t.cc:16:26:   required from here
t.cc:6:38: error: ‘const’ qualifiers cannot be applied to ‘const int&’

Clang accepts this test case. GCC-4.8 gives up with "confused by earlier
errors, bailing out" after the first error.



#include <vector>

template <typename Iterator>
void fn(Iterator begin, Iterator end)
{
  auto x = [](const decltype(*begin) b) { };
}

void foo(std::vector<int> &vi)
{
  fn(vi.begin(), vi.end());
}

void bar(const std::vector<int>& vi)
{
  fn(vi.begin(), vi.end());
}
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Subject: [Bug tree-optimization/60419] [4.8 / 4.9 Regression] ICE Segmentation fault
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60419

Yury Gribov <y.gribov at samsung dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |y.gribov at samsung dot com

--- Comment #1 from Yury Gribov <y.gribov at samsung dot com> ---
Attached code seems to be Power-specific:
 ...
 /usr/include/eigen3/Eigen/src/Core/arch/AltiVec/PacketMath.h:483:56: error:
‘__builtin_vec_sld’ was not declared in this scope
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Subject: [Bug middle-end/60419] [4.8/4.9 Regression] ICE Segmentation fault
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`419

--- Comment #2 from Matthias Klose <doko at gcc dot gnu.org> ---
yes, the first attachment is for powepc64le-linux-gnu

[Bug c++/60420] [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-09-19
     Ever confirmed|0                           |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
In mainline we don't ICE anymore. This is enough to reproduce the issue:

struct Iterator
{
  int& operator*();
};

void foo(Iterator begin)
{
  auto x = [](const decltype(*begin)) { };
}

Note, anyway, that the EDG front-end warns.

[Bug c++/60420] [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot com

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I'm looking into this, and I don't see how we can accept this kind of code
given 8.3.2: "Cv-qualified references are ill-formed except when the
cv-qualifiers are introduced through the use of a typedef (7.1.3) or of a
template type argument (14.3), in which case the cv-qualifiers are ignored.".

Daniel, are you willing to comment?

[Bug c++/60420] [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
... unless the "or of a template type argument" part applies (but clang accepts
both the original testcase and my Comment #1?!?)

[Bug c++/60420] [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
In case a correct reduced reproducer would be:

struct MyIter
{
  int& operator*();
};

template<typename Iterator>
void foo(Iterator begin)
{
  auto x = [](const decltype(*begin)) { };
}

template void foo<MyIter>(MyIter);

[Bug c++/60420] [C++11] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[daniel.kruegler at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

--- Comment #5 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Paolo Carlini from comment #2)
> I'm looking into this, and I don't see how we can accept this kind of code
> given 8.3.2: "Cv-qualified references are ill-formed except when the
> cv-qualifiers are introduced through the use of a typedef (7.1.3) or of a
> template type argument (14.3), in which case the cv-qualifiers are ignored.".
> 
> Daniel, are you willing to comment?

The current wording is:

"Cv-qualified references are ill-formed except when the cv-qualifiers are
introduced through the use of a typedef-name (7.1.3, 14.1) or
decltype-specifier (7.1.6.2), in which case the cv-qualifiers are ignored."

Note that this change came in via CWG 1510 addressing CD3:

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1510
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Subject: [Bug c++/60420] [C++11] Bogus "error:=?UTF-8?Q? ‘const’ qualifiers cannot be applied to ‘int&’?=" with lambda
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id`420

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Ah, thanks, that explains everything!

[Bug c++/60420] [DR 1510] Bogus "error: ‘const’ qualifiers cannot be applied to ‘int&’" with lambda

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60420

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
                 CC|paolo.carlini at oracle dot com    |
         Resolution|---                         |FIXED
           Assignee|paolo.carlini at oracle dot com    |unassigned at gcc dot gnu.org
   Target Milestone|---                         |5.0

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Done for 5.0.