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From: "andyg1001 at hotmail dot co.uk" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/53166] New: static_assert produces bogus warning
Date: Mon, 30 Apr 2012 10:20:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D53166

             Bug #: 53166
           Summary: static_assert produces bogus warning
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: andyg1001@hotmail.co.uk


The following code produces a bogus compilation warning:


template <typename X, X a>
struct A {
    static_assert(a !=3D nullptr, "oops");
};

int a1;
A<int*, &a1> a2;     // this produces a bogus warning
A<int*, nullptr> a3; // correctly generates static assertion


The bogus warning is for the declaration of "a2" saying "the address of =E2=
=80=98a1=E2=80=99
will never be NULL".  This is, of course, true but is exactly what the
static_assert is intended to ensure! (cf. the declaration of "a3").  Here is
the output from gcc:

$ gcc-4.7 -c --std=3Dc++11 bugreport.cpp -Wall -Werror
bugreport.cpp: In instantiation of =E2=80=98struct A<int*, (& a1)>=E2=80=99:
bugreport.cpp:7:14:   required from here
bugreport.cpp:2:10: error: the address of =E2=80=98a1=E2=80=99 will never b=
e NULL
[-Werror=3Daddress]
bugreport.cpp: In instantiation of =E2=80=98struct A<int*, 0u>=E2=80=99:
bugreport.cpp:8:18:   required from here
bugreport.cpp:3:5: error: static assertion failed: oops
cc1plus: all warnings being treated as errors

My expectation would be that the static_assert should silently pass, not ca=
use
a warning in this case.  Compare the output that clang gives:

bugreport.cpp:3:5: error: static_assert failed "oops"
    static_assert(a !=3D nullptr, "oops");
    ^             ~~~~~~~~~~~~
bugreport.cpp:8:18: note: in instantiation of template class 'A<int *,
nullptr>' requested here=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
A<int*, nullptr> a3; // correctly generates static assertion
                 ^
1 error generated.