[Development] Dropping the variadic version of QSKIP

[Olivier Goffart]

On Wednesday 10 July 2013 09:46:48 Thiago Macieira wrote:
> On quarta-feira, 10 de julho de 2013 15.09.41, Albert Astals Cid wrote:
> > Hi all, in 14cd2678396ed1450a72aeffa99c1504743ea415 a variadic version of
> > QSKIP was added so that the old Qt4 version of
> > 
> >    QSKIP(statement, mode)
> > 
> > would compile on C++11 enabled compilers silently ignoring the mode.
> > 
> > This has a down side, it is causing that code like
> > 
> >    QSKIP("HOLA");
> > 
> > gives
> > 
> >   warning: ISO C99 requires rest arguments to be used [enabled by default]
> > 
> > when compiled with -pedantic and C++11
> > 
> > Furthermore, things like
> > 
> >   QSKIP("HOLA", SkipSingle);
> > 
> > don't compile anymore because moc complains
> > 
> >   main.cpp:11: Error: Macro argument mismatch.
> > 
> > So it doesn't seem it makes much sense to keep the variadic version of
> > QSKIP to enable the compatibility with the old Qt4 syntax if moc is not
> > accepting it anymore.
> > 
> > Would you guys accept a patch that drops the variadic version of QSKIP?
> 
> Well, there is a moc bug in the parsing of variadic macros, evidently.

There is no bug.

The QSKIP is defined depending on Q_COMPILER_VARIADIC_MACROS which itslef is 
defined depending on a builtin gcc macro wich is not given to moc.
So moc beleive QSKIP only take one argument.
The solution would be to add a || defined (Q_MOC_RUN)

Arguably, moc could perhaps be more error tollerent in this case.

> Is there any way we can use the rest arguments without making them take
> effect? Such as by making a string out of them that doesn't get used
> anywhere:
> 
> #define QSKIP(x, ...)
>  { static const char _[] = #__VA_ARGS__; } \
>  [existing code]

That's not the problem.  GCC's warning message is not obtimal.  clang is (as 
usual :-p) better:

  warning: must specify at least one argument for '...' parameter of variadic     
  macro [-Wgnu]

In other words: the problem is that one call  QSKIP with only one argument 
instead of at least 2.

maybe something like:
#define QSKIP(...)  QSKIP2(__VA_ARGS__ , _)

-- 
Olivier 

Woboq - Qt services and support - http://woboq.com - http://code.woboq.org