r175326 - Rework the visibility computation algorithm in preparation

[Nico Weber]

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.)

Thanks,
Nico

ps: chromium side patch if anyone is curious:
https://codereview.chromium.org/12328142/