[Bug c++/54336] New: [c++0x] diagnostics for functions with arg-dependent return types have bad signatures

[Bug c++/54336] New: [c++0x] diagnostics for functions with arg-dependent return types have bad signatures

[luto at mit dot edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54336

             Bug #: 54336
           Summary: [c++0x] diagnostics for functions with arg-dependent
                    return types have bad signatures
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: luto@mit.edu


This code:

template<typename T> auto func(T x) -> decltype(x.method())
{
  static_assert(false, "test");
}

fails to compile with:

decltype_return.cc: In function 'decltype (x.method()) func(T)':
decltype_return.cc:3:3: error: static assertion failed: test
   static_assert(false, "test");
   ^

What's 'decltype (x.method()) func(T)'?  x isn't defined.  'auto func(T x) ->
decltype(x.method())' or even 'decltype (x.method()) func (T x)' would be
better.

[Bug c++/54336] [c++0x] diagnostics for functions with arg-dependent return types have bad signatures

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54336

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-08-20 22:39:47 UTC ---
The issue is we decided that static_asserts which are dependent should be
resolved at definition time rather than instantiation time.

[Bug c++/54336] [c++0x] diagnostics for functions with arg-dependent return types have bad signatures

[luto at mit dot edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54336

--- Comment #2 from Andy Lutomirski <luto at mit dot edu> 2012-08-20 23:21:32 UTC ---
Fair enough.  Here's a better example:

struct A { int method(); };

template<typename T> auto func(T x) -> decltype(x.method())
{
  bogus(x);
}

int main() { func(A()); }

The error is:

decltype_return.cc: In instantiation of 'decltype (x.method()) func(T) [with T
= A; decltype (x.method()) = int]':
decltype_return.cc:8:22:   required from here
decltype_return.cc:5:3: error: 'bogus' was not declared in this scope
   bogus(x);
   ^

'decltype (x.method())' is still meaningless in that context.  Even just 'auto
func(T) [with ...; auto = int]' might be less puzzling.

(This is a very minor issue -- I just found it puzzling when I hit it earlier
today in an STL error message.)

[Bug c++/54336] [c++0x] diagnostics for functions with arg-dependent return types have bad signatures

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54336

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-06-01
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com
     Ever confirmed|0                           |1

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Mine.

[Bug c++/54336] [c++0x] diagnostics for functions with arg-dependent return types have bad signatures

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54336

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC and clang agree here and rejects the code.
ICC and MSVC accept the code.