[Bug c++/55173] New: GCC gives wrong location, and ignores -isystem, when warning about default arguments

[mw_triad at users dot sourceforge.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55173

             Bug #: 55173
           Summary: GCC gives wrong location, and ignores -isystem, when
                    warning about default arguments
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mw_triad@users.sourceforge.net


This came up originally related to bug 52718, but according to Paolo there, is
not actually related at all...

Consider the following header:

#pragma GCC system_header // or include via -isystem
class Foo
{
  Foo(void* = 0);
};
class Bar
{
  Bar(Foo = 0, void* = 0)
};

The following instantiation:

Bar bar;

...trips -Wzero-as-null-pointer-constant (also, the warning is reported in the
source file, not the header).

This appears to only happen when a default parameter implicitly invokes a
constructor, where the warning occurs in the constructor invocation. IOW, this:

Bar bar(nullptr);

...does not trigger a warning, as 'Foo(nullptr)' is okay.

Besides the less-helpful-than-desired diagnostic, this behavior is unfortunate,
as it prevents promoting warnings to errors in the face of such constructs, or
else forcing programmers to avoid use of default parameters.