> On Dec 18, 2014, at 6:18 PM, Richard Smith <[email protected]> wrote:
> On Wed, Dec 17, 2014 at 6:58 PM, Nico Weber <[email protected]
> <mailto:[email protected]>> wrote:
> Don't drop attributes when checking explicit specializations.
>
> Consider a template class with attributes on a method, and an explicit
> specialization of that method:
>
> template <int>
> struct A {
> void foo() final;
> };
>
> template <>
> void A<0>::foo() {}
>
> In this example, the attribute is `final`, but it might also be an
> __attribute__((visibility("foo"))), noreturn, inline, etc. clang's current
> behavior is to strip all attributes, which for some attributes is wrong
> (the snippet above allows a subclass of A<0> to override the final method, for
> example) and for others disagrees with gcc (__attribute__((visibility()))).
>
> So stop dropping attributes. r95845 added this code without a test case, and
> r176728 added the code for dropping attributes on parameters (with tests, but
> they still pass).
>
> As an additional wrinkle, do drop dllimport and dllexport, since that's how
> these two
> attributes work. (This is covered by existing tests.)
>
> Fixes PR21942.
>
> The approach is by Richard Smith, initial analysis and typing was done by me.
>
> Naturally, this makes sense to me =) It also matches GCC and EDG on all
> attributes I tested.
>
> John, do you remember why you added this code (a long long time ago)?
The behavior on attribute((visibility)) is intentional, I think. At the very
least, you have to allow for explicit specializations to override the
visibility of the template, using a general most-specific-rule-wins logic.
There may be other attributes like this.
We definitely shouldn’t be dropping *all* attributes, though.
John.
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