macOS fullscreen crashes

[Alan Third <alan@idiocy.org>]

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We still occasionally receive bug reports about crashes on macOS
10.12+ caused by macOS turning fullscreen windows into ‘tabbed’
windows. I’ve also seen it discussed in a few places round the web.

We currently have a compile‐time check to include code that fixes this
on 10.12+, and it can be over‐ridden if Emacs is being built on an
older version of macOS but is expected to run on 10.12+, however it is
clearly not doing the job.

I propose for Emacs 26.2 (and the master branch) that we remove the
compile‐time check and just use a run‐time check. This will result in
a compiler warning on macOS 10.11 and below, but will prevent crashes
everywhere.

Any thoughts?

Patch attached.
-- 
Alan Third

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From 4df81ee31f0f2cf9ca4f906d753cf7dd134cf64d Mon Sep 17 00:00:00 2001
From: Alan Third <alan@idiocy.org>
Date: Fri, 30 Nov 2018 10:50:44 +0000
Subject: [PATCH] Remove macOS version checks for tabbed frames (bug#33118)

* src/nsterm.m ([EmacsView initFrameFromEmacs:]) [NS_IMPL_COCOA]:
Remove compile-time version checks.
---
 src/nsterm.m | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/nsterm.m b/src/nsterm.m
index 948dd1da2e..7a751b3868 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -7397,14 +7397,16 @@ - (instancetype) initFrameFromEmacs: (struct frame *)f
   [NSApp registerServicesMenuSendTypes: ns_send_types
                            returnTypes: [NSArray array]];
 
+#if defined (NS_IMPL_COCOA)
   /* macOS Sierra automatically enables tabbed windows.  We can't
      allow this to be enabled until it's available on a Free system.
-     Currently it only happens by accident and is buggy anyway. */
-#if defined (NS_IMPL_COCOA) \
-  && MAC_OS_X_VERSION_MAX_ALLOWED >= 101200
-#if MAC_OS_X_VERSION_MIN_REQUIRED < 101200
+     Currently it only happens by accident and is buggy anyway.
+
+     This will cause a build warning on older versions of macOS, but
+     limiting it to just 10.12+ has resulted in a number of crash
+     reports where Emacs was built on an older version of macOS than
+     it's being used on.  */
   if ([win respondsToSelector: @selector(setTabbingMode:)])
-#endif
     [win setTabbingMode: NSWindowTabbingModeDisallowed];
 #endif
 
-- 
2.19.1