Re: macOS/GCC support policy

[Philipp Stephani <p.stephani2@gmail.com>]

Am Fr., 2. Aug. 2019 um 16:59 Uhr schrieb Philipp Stephani
<p.stephani2@gmail.com>:
>
> Am Fr., 2. Aug. 2019 um 16:55 Uhr schrieb Philipp Stephani
> <p.stephani2@gmail.com>:
> >
> > Am Fr., 2. Aug. 2019 um 13:51 Uhr schrieb Eli Zaretskii <eliz@gnu.org>:
> > >
> > > > From: Philipp Stephani <p.stephani2@gmail.com>
> > > > Date: Fri, 2 Aug 2019 12:08:35 +0200
> > > > Cc: Alan Third <alan@idiocy.org>, pcr910303@icloud.com,
> > > >       Emacs developers <emacs-devel@gnu.org>
> > > >
> > > > > What exactly prevents building with GCC on macOS?
> > > > >
> > > >
> > > > I haven't investigated in detail, but when I try to run configure with
> > > > GCC 9 from Homebrew, I get the error message
> > > >
> > > > checking AppKit/AppKit.h usability... no
> > > > checking AppKit/AppKit.h presence... yes
> > > > configure: WARNING: AppKit/AppKit.h: present but cannot be compiled
> > > > configure: WARNING: AppKit/AppKit.h:     check for missing prerequisite headers?
> > > > configure: WARNING: AppKit/AppKit.h: see the Autoconf documentation
> > > > configure: WARNING: AppKit/AppKit.h:     section "Present But Cannot
> > > > Be Compiled"
> > > > configure: WARNING: AppKit/AppKit.h: proceeding with the compiler's result
> > > > configure: WARNING:     ## ------------------------------------ ##
> > > > configure: WARNING:     ## Report this to bug-gnu-emacs@gnu.org ##
> > > > configure: WARNING:     ## ------------------------------------ ##
> > > > checking for AppKit/AppKit.h... no
> > > > configure: error: The include files (AppKit/AppKit.h etc) that
> > > > are required for a Nextstep build are missing or cannot be compiled.
> > > > Either fix this, or re-configure with the option '--without-ns'.
> > >
> > > Thanks.  It would be good if someone could investigate what is the
> > > problem here (and any other problems, if there are any).
> >
> > Excerpt from config.log:
> >
> > configure:10941: checking AppKit/AppKit.h usability
> > configure:10941: gcc-9 -c -g3 -O1 -fsanitize=address
> > -fsanitize=undefined -fno-omit-frame-pointer -x objective-c     -x
> > objective-c  conftest.c >&5
> > In file included from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/os/object.h:101,
> >                  from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/dispatch/dispatch.h:48,
> >                  from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreFoundation.framework/Headers/CFStream.h:20,
> >                  from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreFoundation.framework/Headers/CFPropertyList.h:17,
> >                  from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreFoundation.framework/Headers/CoreFoundation.h:60,
> >                  from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/Foundation.framework/Headers/Foundation.h:6,
> >                  from
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks/AppKit.framework/Headers/AppKit.h:10,
> >                  from conftest.c:142:
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/objc/NSObject.h:22:4:
> > error: unknown type name 'instancetype'
> >    22 | - (instancetype)self;
> >       |    ^~~~~~~~~~~~
> >
> > (lots of similar errors follow)
> >
> > This indicates that GCC treats the header as C instead of Objective C.
> > Which is interesting because -x objective-c is given explicitly. Does
> > GCC need some other flag to force compilation as Objective C?
>
> The behavior difference is indeed trivial to reproduce:
>
> p@p:/tmp$ cat appkit.c
> #include <AppKit/AppKit.h>
> p@p:/tmp$ clang -c -x objective-c appkit.c 2> /dev/null ; echo $?
> 0
> p@p:/tmp$ gcc-9 -c -x objective-c appkit.c 2> /dev/null ; echo $?
> 1
>
> Without the redirection GCC prints tons of similar errors.

OK, I guess this is a red herring and the problem has nothing to do
with -x. The Objective C dialect supported by GCC is simply different
from the Objective C dialect used by Apple, and until GCC supports the
Apple dialect it can't be used to build any macOS app.