Re: Mac OS Sierra tab feature breaks C-x 5 2

[Anders Lindgren <andlind@gmail.com>]

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> Yeah, I’m not sure about this either. It strikes me as a bit suspect,
> but I don’t know that the alternatives are going to be any better.
>
> We could disable the warning:
>
>     #pragma clang diagnostic push
>     #pragma clang diagnostic ignored "-Wobjc-method-access"
>       if ([win respondsToSelector: @selector(setTabbingMode:)])
>         [win setTabbingMode: NSWindowTabbingModeDisallowed];
>     #pragma clang diagnostic pop
>
> which is, I think, the right thing to do, but that’s quite messy
> looking, and I suspect we’ll have to do the same for the gcc warning.
> I don’t know if we’d then have to do some #ifdef stuff to separate the
> clang and gcc stuff. This has the potential to get REALLY messy.
>

It's possible to encapsulate pragmas into preprocessor macros using the
_Pragma construct. In fact, config.h contains similar stuff, c.f.
_GL_INLINE_HEADER_BEGIN and _GL_INLINE_HEADER_END.


Another possibility is to cast `win` to `id`, which I’d guess would
> look like:
>
>     [(id)win setTabbingMode: NSWindowTabbingModeDisallowed];
>

I still get the same warning, so this is not a solution.


By the way, while digging around I came across a lot of stuff saying
> `@selector(setTabbingMode)` should give a warning if `setTabbingMode`
> doesn’t exist. Are you seeing one?
>

No, no warning is issued about that.

I believe that there are a number of #ifdef:s that could be rewritten in
this way, so we need something ergonomically. (If we could get rid of all
such ifdef:s there would not be a need for OS-version specific binaries.)


Given the options, I would say that a solution along the lines of
_GL_INLINE_HEADER_BEGIN would be best. The pros are:

* All the messy bits can be located in one place, and it can easily be
updated to match future compiler versions. (Should some compiler start to
warn about, say, `@selector(setTabbingMode)`, that too could be
incorporated in the macros.)
* There is a natural location to place documentation and to describe the
situation
* In the code that use the macros, there is a signal to the reader that
something special is going on
* It's possible to write formal tests, ensuring the macros work as intended.

Unlike _GL_INLINE_HEADER_BEGIN, we should not use a leading underscore, as
such identifiers are reserved for the compiler itself. Maybe
NS_SILENCE_MISSING_METHOD_WARNING_BEGIN and -_END? The end result would
look like:

      NS_SILENCE_MISSING_METHOD_WARNING_BEGIN
      if ([win respondsToSelector: @selector(setTabbingMode:)])
        [win setTabbingMode: NSWindowTabbingModeDisallowed];
      NS_SILENCE_MISSING_METHOD_WARNING_END

    -- Anders

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