[PATCH] PR14253: 'warn_unused' attribute for unused warning for non-POD types

[Lubos Lunak]

On Tuesday 16 of July 2013, Lubos Lunak wrote:
> On Tuesday 16 of July 2013, Richard Smith wrote:
> > On Tue, Jul 16, 2013 at 12:50 PM, Lubos Lunak <l.lunak at suse.cz> wrote:
> > > On Tuesday 16 of July 2013, Richard Smith wrote:
> > > > Consider:
> > > >
> > > > {
> > > >   my_lock(my_mutex); // A
> > > >   my_lock ml(my_mutex); // B
> > > >   my_string("foo"); // C
> > > >   my_string ms("foo"); // D
> > > > }
> > > >
> > > > We never warn for a class that is in category (1). my_lock would be
> > > > in category (2), so we warn on A but not B. my_string would be in
> > > > category (3), so we warn on both C and D.
> > > >
> > > > Which of these does the warn_unused attribute model?
> > >
> > >  It doesn't model anything. It prevents disabling of the
> > > unused-variable warning for whatever type that has the attribute.
> >
> > So which of the above behaviors do you get? (Or do you get something
> > else?)
>
>  I think you are talking about something slightly different. This is about
> the (-W)unused-variable warning. So A and C obviously don't apply.

 But since you ask, without looking at the code, presumably (-W)unused-result 
has code similar to unused-variable that also disables the warning if the 
type in question has non-trivial ctor/dtor, so you could do a similar 
modification there to enable the warning for types with warn_unused 
attribute.

> B and D 
> will cause the warning if the relevant variable has at most trivial
> ctor/dtor called (before my patch), or has at most even non-trivial
> ctor/dtor called but also has the attribute set (added by the patch).
> That's all.

-- 
 Lubos Lunak
 l.lunak at suse.cz