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Re: gcc visibility used by moz


Jason Merrill <jason@redhat.com> writes:

> Benjamin Smedberg wrote:
> > Jason Merrill wrote:
> >
> >> Do you agree with implicitly giving template instantiations the
> >> minimum visibility of the template and arguments unless explicitly
> >> overridden?
> > This is not what I would naturally expect, coming from a
> > dllimport/export mindset, but I don't think it's a problem from the
> > mozilla POV: all of our exports are explicitly declared if/when we
> > use hidden visibility pragmas.
> > Is a pragma considered an explicit override? e.g.
> > class nsIAbstract {
> >   virtual void Bar();
> > };
> > #pragma GCC visibility push(default)
> > nsIAbstract* Getter();
> > #pragma GCC visibility pop
> 
> For a namespace-scope entity like this, yes (class members and
> template instantiations use the visibility of their class and template
> in preference to the current #pragma).
> 
> >> Also, do you agree with warning about a class with greater
> >> visibility than its data members/bases?
> > Sure... I would really like to disable this warning if possible,
> > since it will be produced thousands of times in a mozilla build ;-)
> 
> I find that surprising, since it sounds like VC++ gives the same
> warning about a dllexport class with a non-dllexport base.

I think that if the aim is to have VC++ compatibility, that should be
separate from the 'right' solution.  Apple has a flag,
-fvisibility-ms-compat, which attempts to achieve this, and which
we'll probably contribute for 4.3.

There are some things that this flag does which you definitely
wouldn't want in well-structured code and other things which the flag
does which may limit the C++ features you'll be able to use in future
(like serialisation if that ever gets standardized).


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