Re: src/nsterm.m: fix window tabbing on macOS

["Paul W. Rankin" via "Emacs development discussions." <emacs-devel@gnu.org>]

> On 8 May 2021, at 9:21 pm, Alan Third <alan@idiocy.org> wrote:
>> src/nsterm.m: use NSWindowTabbingModeAutomatic to respect user choice.
>> Tabbed window managers are now widely available for free systems.
> 
> For the record the tabbing being enabled here is not Emacs's own
> tabbing, it's a macOS method of combining multiple OS windows into
> one. Emacs's tabbing has still to be implemented on the NS port (I've
> no interest as I think tabbed windows are an abomination that should
> be burnt on sight, but would happily let someone else implement it).

I think all the more reason not to hobble the macOS window manager! But 
yes it should be noted that tabs here are in the context of window 
management (i.e. Emacs frames) not tab-bar-mode. A Linux counterpart 
would be https://tools.suckless.org/tabbed/

> Paul, is this still the absolute disaster it was when it first
> appeared where some random Emacs frames would get combined but not
> others, not to mention the crashes? Also there was no "user choice" as
> I recall, it just happened without any warning or input from the user,
> at random.
> 
> Is it actually stable and usable now?

I've been building Emacs with this change applied for several years now 
across a few different macOS versions and I've never experienced a crash 
or unexpected behaviour. But it depends on what you might be doing that 
I'm not; can you provide a step-by-step?

The user choice I refer to resides in the odd place of System 
Preferences > Dock > Prefer tabs when opening documents: [Always | In 
Full Screen Only | Manually]. The behaviour I've experienced with each 
of these is:

- Always: invoking `make-new-frame' will always create a frame in a new 
tab
- In Full Screen Only: invoking `make-new-frame' will create a frame in 
a new tab only when `(frame-parameter nil 'fullscreen)' is non-nil
- Manually: `make-new-frame' will never create new tabs

(Off topic but it would be nice if there were some mention in the docs 
that tab-bar-mode does not function at all on macOS rather than silently 
failing.)