[Bug c++/52718] -Wzero-as-null-pointer-constant: misleading location for 0 as default argument

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52718

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 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 = 10000);
> };

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 10000 to 16 [-Wconstant-conversion]
  Bar(Foo = 10000);
            ^~~~~
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.