r175326 - Rework the visibility computation algorithm in preparation

[John McCall]

On Feb 27, 2013, at 7:19 AM, Nico Weber <thakis at chromium.org> wrote:
> On Wed, Feb 27, 2013 at 3:32 PM, Nico Weber <thakis at chromium.org> wrote:
>> On Tue, Feb 26, 2013 at 11:37 PM, John McCall <rjmccall at apple.com> wrote:
>>> On Feb 26, 2013, at 2:36 PM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
>>>>> We should just not cache visibility for types.
>>>> 
>>>> Can do. I will send a patch.
>>> 
>>> Thanks!  As you're doing so, please change it to use the same LinkageInfo structure that NamedDecl uses.  You'll need to make it a non-member type and possibly pull it into its own header.
>> 
>> As of clang r176164 chromium's components build works again, with just
>> 6 additional explicit EXPORTs on predeclared types used in template
>> instantiations. Thanks for the help!
> 
> …while the clang build is happy with these changes, the gcc build
> breaks with them because gcc warns
> 
> test.cc:6: warning: type attributes ignored after type is already defined
> 
> on code like
> 
> $ cat test.cc
> #define EXPORT __attribute__((visibility("default")))
> 
> class Layer;
> class EXPORT Layer {
> };
> class EXPORT Layer;
> 
> Due to the template instantiation requiring the EXPORT on the
> declaration of Layer happening in one header and the definition of
> Layer happening in another, it depends on header include order if gcc
> is happy or not.
> 
> Do you have a better suggestion than putting the EXPORTed declaration
> of Layer into an #ifdef __clang__ block? Requiring this would be
> pretty ugly. (It's only 3 files for us so we'll live, but the user
> experience is a lot worse than in gcc / msvc.)

Maybe use an EXPORT_FORWARD_DECL macro?

That seems like a good bug to file against GCC, by the way.  There's
no reason for them to warn about a *redundant* attribute on a
redeclaration.

John.