[llvm] r216170 - Make format_object_base's destructor protected and non-virtual.

[Owen Anderson]

> On Aug 22, 2014, at 11:02 AM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> On Fri, Aug 22, 2014 at 10:38 AM, Owen Anderson <resistor at mac.com> wrote:
>> 
>> On Aug 21, 2014, at 2:14 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> 
>> On Thu, Aug 21, 2014 at 1:34 PM, Justin Bogner <mail at justinbogner.com>
>> wrote:
>> 
>> Benjamin Kramer <benny.kra at googlemail.com> writes:
>> 
>> Author: d0k
>> Date: Thu Aug 21 06:22:05 2014
>> New Revision: 216170
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=216170&view=rev
>> Log:
>> Make format_object_base's destructor protected and non-virtual.
>> 
>> It's not meant to be used with operator delete and this avoids
>> emitting virtual dtors for every derived format object.
>> 
>> 
>> This change is obviously for the better, but it triggers a warning when
>> building with clang 3.4 (and probably every clang back to 2.9 or so),
>> which is pretty unfortunate.
>> 
>> The problem is, until r208449, we didn't know not to warn about this on
>> final classes or when the destructor was protected. I'm not entirely
>> sure what we should do here, but this is likely to break anyone who
>> builds with -Werror for a while.
>> 
>> 
>> Only if they don't update their compiler - I usually just roll my
>> clang release compiler (disabling -Werror) when this sort of thing
>> comes up.
>> 
>> For those who want to use old/pre-installed/official release clangs
>> rather than more recent iterations, they can just disable -Werror
>> (it's not the default anyway).
>> 
>> 
>> This isn’t a workable solution for some of us who are tied to specific
>> toolchain releases and can’t upgrade on a moment’s notice.  And even if I’m
>> not building with -Werror, this change generates hundreds or thousands of
>> warnings across an LLVM build, which makes it practically impossible to do
>> any development work because of my own work getting lost in the sea of
>> noise.
> 
> You can disable the warning - as with bad MSVC/GCC warnings, we
> usually rely on buildbots/other developers to catch the bugs that slip
> through from users on compilers with buggy diagnostics.

Actually, you can’t.  The CMake build system forcibly enables -Wnon-virtual-dtor.

—Owen