[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #21 from Paolo Carlini paolo.carlini at oracle dot com --- *** Bug 65324 has been marked as a duplicate of this bug. ***
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
--- Comment #12 from Matthew Woehlke mw_triad at users dot sourceforge.net
2012-11-01 17:47:04 UTC ---
Requires qt-devel installed, but has the benefit of being the exact issue I'm
having in production (on the chance it's something screwy about Qt...):
$ cat zero-as-pointer.cpp
#include QtGui/QLabel
int main()
{
QLabel label;
return 0;
}
$ g++ -std=c++11 -Werror=zero-as-null-pointer-constant zero-as-pointer.cpp
zero-as-pointer.cpp: In function ‘int main()’:
zero-as-pointer.cpp:5:10: error: zero as null pointer constant
[-Werror=zero-as-null-pointer-constant]
cc1plus: some warnings being treated as errors
Exit 1
$ g++ --version
g++ (GCC) 4.7.2 20120921 (Red Hat 4.7.2-2)
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
...maybe it got fixed in 4.7.3?
Note: the problem is this ctor:
explicit QLabel(QWidget *parent=0, Qt::WindowFlags f=0);
If I replace my declaration with:
QLabel label(nullptr, Qt::WindowFlags(nullptr));
...then I get no warning.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
--- Comment #13 from Matthew Woehlke mw_triad at users dot sourceforge.net
2012-11-01 17:56:49 UTC ---
...and with your example I do indeed get no warning.
Simplified test case:
$ cat zero-as-pointer.h
#pragma GCC system_header
class Foo
{
public:
Foo(void** = 0);
};
class Bar
{
public:
Bar(Foo = 0);
};
$ cat zero-as-pointer.cpp
#include zero-as-pointer.h
int main()
{
Bar bar;
return 0;
}
$ g++ -std=c++11 -Werror=zero-as-null-pointer-constant zero-as-pointer.cpp
zero-as-pointer.cpp: In function ‘int main()’:
zero-as-pointer.cpp:5:7: error: zero as null pointer constant
[-Werror=zero-as-null-pointer-constant]
cc1plus: some warnings being treated as errors
Apparently it is something about the 'Foo = 0' part (replace Foo with
Qt::WindowFlags in my 'real' example).
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #14 from Paolo Carlini paolo.carlini at oracle dot com 2012-11-01 19:07:10 UTC --- Ok, I can reproduce this. Note, I don't think it's the same issue reported here earlier. Apparently something is going wrong with the pragma. A WA is writing: Bar(Foo = Foo(0)); in this case the warning is correctly suppressed. The 0 in the Foo constructor doesn't matter, the warning is correctly suppressed and you can as well remove it from the testcase. I'm looking into this, hopefully can be fixed without reworking too many diagnostic things outside this specific warning proper.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
--- Comment #15 from Paolo Carlini paolo.carlini at oracle dot com 2012-11-01
20:52:15 UTC ---
This is what I meant when I said that the issue is different, and is much more
general than -Wzero-as-null-pointer-constant. Consider, eg, with -Woverflow:
#pragma GCC system_header
class Foo
{
public:
Foo(signed char);
};
class Bar
{
public:
Bar(Foo = 1);
};
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
--- Comment #16 from mwoehlke.floss at gmail dot com 2012-11-01 22:03:46 UTC ---
On 2012-11-01 16:52, paolo.carlini at oracle dot com wrote:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
--- Comment #15 from Paolo Carlini paolo.carlini at oracle dot com
2012-11-01 20:52:15 UTC ---
This is what I meant when I said that the issue is different, and is much more
general than -Wzero-as-null-pointer-constant. Consider, eg, with -Woverflow:
#pragma GCC system_header
class Foo
{
public:
Foo(signed char);
};
class Bar
{
public:
Bar(Foo = 1);
};
Would you prefer I open a new bug report?
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #17 from Paolo Carlini paolo.carlini at oracle dot com 2012-11-01 22:42:05 UTC --- If you like, sure. I want to emphasize again that the issue really is about the behavior of the pragma vs warnings for default arguments, *any* warning, and if you check is *very* old. Before filing a new PR please double check that the issue has not been discussed already and maybe resolved as wontfix for some reason. Thanks.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
Manuel López-Ibáñez manu at gcc dot gnu.org changed:
What|Removed |Added
CC||manu at gcc dot gnu.org
--- Comment #18 from Manuel López-Ibáñez manu at gcc dot gnu.org 2012-11-01
23:00:51 UTC ---
(In reply to comment #15)
This is what I meant when I said that the issue is different, and is much more
general than -Wzero-as-null-pointer-constant. Consider, eg, with -Woverflow:
#pragma GCC system_header
class Foo
{
public:
Foo(signed char);
};
class Bar
{
public:
Bar(Foo = 1);
};
The issue is that literals don't have locations, so input_location is used. And
input_location here is in the main file, so system_header doesn't apply. This
is why input_location must die.
Clang uses the correct location for warning, so it honors system_header
(requires -Wsystem-headers):
In file included from pr52718.c:1:
./pr52718.h:11:13: warning: implicit conversion from 'int' to 'signed char'
changes value from 1 to 16 [-Wconstant-conversion]
Bar(Foo = 1);
^
1 warning generated.
Ultimately, GCC needs to track the locations of literals like clang does.
Everything else is a hack around the main issue. This is PR43486. There have
been some recent attempts
http://gcc.gnu.org/ml/gcc-patches/2012-09/msg01222.html, but I am afraid that
work seems stalled for lack of time/help.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #19 from Matthew Woehlke mw_triad at users dot sourceforge.net 2012-11-01 23:04:42 UTC --- Reported as bug 55173. I'm not going to claim to understand bug 43486 sufficiently to know it is the same issue, but if you are sure, please feel free to close as duplicate.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #20 from Manuel López-Ibáñez manu at gcc dot gnu.org 2012-11-01 23:23:41 UTC --- (In reply to comment #19) Reported as bug 55173. I'm not going to claim to understand bug 43486 sufficiently to know it is the same issue, but if you are sure, please feel free to close as duplicate. Well, it is the same underlying issue. It could be worked-around case by case by passing some location (like the = location) down to the warning point. But this is likely quite a large refactoring. The alternative is some general infrastructure like the one proposed in: http://gcc.gnu.org/ml/gcc-patches/2012-09/msg01222.html, which would require an even more massive refactoring to be useful. In fact, that particular proposal would still require to pass down an explicit location, because it does not actually add locations to constants, but stores their location together with the assignment expression (and the assignment expression is not passed down to the point of warning, only the without-location constant).
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 Matthew Woehlke mw_triad at users dot sourceforge.net changed: What|Removed |Added CC||mw_triad at users dot ||sourceforge.net --- Comment #10 from Matthew Woehlke mw_triad at users dot sourceforge.net 2012-11-01 00:38:20 UTC --- This is not fixed (gcc 4.7.2) if the default parameter occurs in a system header. In such case, I would expect no warning at all. Instead, I get the old and confusing behavior of gcc warning at the point where the default parameter is used.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718
--- Comment #11 from Paolo Carlini paolo.carlini at oracle dot com 2012-11-01
01:28:26 UTC ---
I can't reproduce in mainline and 4_7-branch. This is what I tried:
a.h:
#pragma GCC system_header
void* fun(void* a = 0);
a.C:
#include a.h
int main()
{
fun();
}
if I compile a.C I get no warnings at all (I get warnings with the pragma
commented out, as expected, and in the right place, line #3 of a.h). Likewise,
everything is fine if inside a.h, a boo calls fun(). Do you have a better
testcase?
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 Paolo Carlini paolo.carlini at oracle dot com changed: What|Removed |Added Status|UNCONFIRMED |NEW Last reconfirmed||2012-03-29 Ever Confirmed|0 |1 --- Comment #1 from Paolo Carlini paolo.carlini at oracle dot com 2012-03-29 10:09:51 UTC --- Confirmed.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #2 from Paolo Carlini paolo.carlini at oracle dot com 2012-03-29 10:17:49 UTC --- I guess that first of all we want to fix this to warn at line #1 instead of #2: void* fun(void* a = 0); void* f2 = fun();
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 Paolo Carlini paolo.carlini at oracle dot com changed: What|Removed |Added CC||jason at gcc dot gnu.org --- Comment #3 from Paolo Carlini paolo.carlini at oracle dot com 2012-03-29 10:40:41 UTC --- Considering for simplicity the snippet in Comment #2, I'm not sure whether we should aim for an unconditional warning for line #1 or a conditional one for line #2 but referring to line #1. Eg, whether we want to avoid warning for: void* fun(void* a = 0); void* f2 = fun(nullptr); (currently we avoid warning for the latter, which may not be bad, but we fail completely to refer to line #1)
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #4 from Jason Merrill jason at gcc dot gnu.org 2012-03-29 16:18:34 UTC --- Since The names in the default argument are bound, and the semantic constraints are checked, at the point where the default argument appears I think it makes sense to give this warning at that point as well.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #5 from Paolo Carlini paolo.carlini at oracle dot com 2012-03-29 17:06:15 UTC --- I see, thanks. Like we just error out at line #1 for: void* fun(void* a = 1); void* f2 = fun(nullptr);
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 Paolo Carlini paolo.carlini at oracle dot com changed: What|Removed |Added Status|NEW |ASSIGNED AssignedTo|unassigned at gcc dot |paolo.carlini at oracle dot |gnu.org |com --- Comment #6 from Paolo Carlini paolo.carlini at oracle dot com 2012-03-29 17:07:49 UTC --- On it.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #7 from paolo at gcc dot gnu.org paolo at gcc dot gnu.org 2012-03-29 22:45:56 UTC --- Author: paolo Date: Thu Mar 29 22:45:46 2012 New Revision: 185983 URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=185983 Log: /cp 2012-03-29 Paolo Carlini paolo.carl...@oracle.com PR c++/52718 * decl.c (check_default_argument): With -Wzero-as-null-pointer-constant warn for a zero as null pointer constant default argument. /testsuite 2012-03-29 Paolo Carlini paolo.carl...@oracle.com PR c++/52718 * g++.dg/warn/Wzero-as-null-pointer-constant-5.C: New. Added: trunk/gcc/testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-5.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/decl.c trunk/gcc/testsuite/ChangeLog
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 Paolo Carlini paolo.carlini at oracle dot com changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution||FIXED Target Milestone|--- |4.7.1 --- Comment #9 from Paolo Carlini paolo.carlini at oracle dot com 2012-03-29 23:21:44 UTC --- Fixed for 4.7.1 and mainline.
[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718 --- Comment #8 from paolo at gcc dot gnu.org paolo at gcc dot gnu.org 2012-03-29 23:21:09 UTC --- Author: paolo Date: Thu Mar 29 23:21:02 2012 New Revision: 185984 URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=185984 Log: /cp 2012-03-29 Paolo Carlini paolo.carl...@oracle.com PR c++/52718 * decl.c (check_default_argument): With -Wzero-as-null-pointer-constant warn for a zero as null pointer constant default argument. /testsuite 2012-03-29 Paolo Carlini paolo.carl...@oracle.com PR c++/52718 * g++.dg/warn/Wzero-as-null-pointer-constant-5.C: New. Added: branches/gcc-4_7-branch/gcc/testsuite/g++.dg/warn/Wzero-as-null-pointer-constant-5.C Modified: branches/gcc-4_7-branch/gcc/cp/ChangeLog branches/gcc-4_7-branch/gcc/cp/decl.c branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
