[Bug c++/57941] New: [c++11] confusing error message with invalid constexpr constructor in template struct

["f.heckenbach@fh-soft.de" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57941

            Bug ID: 57941
           Summary: [c++11] confusing error message with invalid constexpr
                    constructor in template struct
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.heckenbach@fh-soft.de

% cat test.cpp
template <typename T> struct a
{
  int i;
  constexpr a (): i (b ()) { }
  constexpr int b () { return c (); }
  int c () const { throw 42; }
  constexpr operator bool () { return true; }
};

static_assert (a <int> (), "foo");
%g++-4.7 -std=c++11 test.cpp 
test.cpp:10:1: error: non-constant condition for static assertion
test.cpp:10:1: error: 'constexpr a<T>::a() [with T = int]' called in a constant
expression
test.cpp:4:13: note: 'constexpr a<T>::a() [with T = int]' is not usable as a
constexpr function because:
%

Because what?

This message is particularly confusing if other unrelated messages appear
afterwards, as it wrongly claims those to be the reason for this one.

(I understand that the program is wrong, it's just about the message.)