bpo-26317: Support OBJC and OBJCXX configure command line variables (GH-20176)

Add support to the configure script for OBJC and OBJCXX command line options so that the macOS builds can use the clang compiler for the macOS-specific Objective C source files. This allows third-party compilers, like GNU gcc, to be used to build the rest of the project since some of the Objective C system header files are not compilable by GNU gcc.

Co-authored-by: Jeffrey Kintscher <websurfer@surf2c.net>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Doc/whatsnew/3.9.rst

@@ -892,6 +892,14 @@ Build Changes
   functions are now required to build Python.
   (Contributed by Victor Stinner in :issue:`39395`.)
 
+* The ``OBJC`` and ``OBJCXX`` standard command line options for the configure
+  script are now supported. This allows building fot macOS with a third-party
+  compiler, like GNU `gcc`, for everything except for the several
+  system-specific source files that need system headers that require the
+  Apple-supplied compile chain (e.g. the ``_scproxy`` helper module and
+  ``PythonLauncher.app``).
+  (Contributed by Jeffrey Kintscher in :issue:`26317`.)
+
 
 C API Changes
 =============

Mac/Makefile.in

@@ -21,6 +21,7 @@ PYTHONFRAMEWORK=@PYTHONFRAMEWORK@
 PYTHONFRAMEWORKIDENTIFIER=@PYTHONFRAMEWORKIDENTIFIER@
 LIPO_32BIT_FLAGS=@LIPO_32BIT_FLAGS@
 CC=@CC@
+OBJC=@OBJC@
 MACOSX_DEPLOYMENT_TARGET=@CONFIGURE_MACOSX_DEPLOYMENT_TARGET@
 export MACOSX_DEPLOYMENT_TARGET
 

Mac/PythonLauncher/Makefile.in

@@ -1,5 +1,7 @@
 CC=@CC@
 LD=@CC@
+OBJC=@OBJC@
+OBJCFLAFS=@OBJCFLAGS@
 BASECFLAGS=@BASECFLAGS@
 OPT=@OPT@
 CFLAGS=@CFLAGS@ $(BASECFLAGS) $(OPT)
@@ -52,25 +54,25 @@ Python\ Launcher.app:  Info.plist \
 	cp -R $(srcdir)/English.lproj "Python Launcher.app/Contents/Resources"
 
 FileSettings.o: $(srcdir)/FileSettings.m
-	$(CC) $(CFLAGS) -o $@ -c $(srcdir)/FileSettings.m
+	$(OBJC) $(CFLAGS) -o $@ -c $(srcdir)/FileSettings.m
 
 MyAppDelegate.o: $(srcdir)/MyAppDelegate.m
-	$(CC) $(CFLAGS) -o $@ -c $(srcdir)/MyAppDelegate.m
+	$(OBJC) $(CFLAGS) -o $@ -c $(srcdir)/MyAppDelegate.m
 
 MyDocument.o: $(srcdir)/MyDocument.m
-	$(CC) $(CFLAGS) -o $@ -c $(srcdir)/MyDocument.m
+	$(OBJC) $(CFLAGS) -o $@ -c $(srcdir)/MyDocument.m
 
 PreferencesWindowController.o: $(srcdir)/PreferencesWindowController.m
-	$(CC) $(CFLAGS) -o $@ -c $(srcdir)/PreferencesWindowController.m
+	$(OBJC) $(CFLAGS) -o $@ -c $(srcdir)/PreferencesWindowController.m
 
 doscript.o: $(srcdir)/doscript.m
-	$(CC) $(CFLAGS) -o $@ -c $(srcdir)/doscript.m
+	$(OBJC) $(CFLAGS) -o $@ -c $(srcdir)/doscript.m
 
 main.o: $(srcdir)/main.m
-	$(CC) $(CFLAGS) -o $@ -c $(srcdir)/main.m
+	$(OBJC) $(CFLAGS) -o $@ -c $(srcdir)/main.m
 
 Python\ Launcher: $(OBJECTS)
-	$(CC) $(LDFLAGS) -o "Python Launcher" $(OBJECTS) -framework AppKit -framework Carbon
+	$(OBJC) $(LDFLAGS) -o "Python Launcher" $(OBJECTS) -framework AppKit -framework Carbon
 
 Info.plist: $(srcdir)/Info.plist.in
 	sed 's/%VERSION%/'"`$(RUNSHARED) $(BUILDPYTHON) -c 'import platform; print(platform.python_version())'`"'/g' < $(srcdir)/Info.plist.in > Info.plist

Makefile.pre.in

@@ -35,6 +35,7 @@ abs_builddir=	@abs_builddir@
 
 CC=		@CC@
 CXX=		@CXX@
+OBJC=		@OBJC@
 MAINCC=		@MAINCC@
 LINKCC=		@LINKCC@
 AR=		@AR@
@@ -613,12 +614,22 @@ $(srcdir)/Modules/_blake2/blake2s_impl.c: $(srcdir)/Modules/_blake2/blake2b_impl
 	$(PYTHON_FOR_REGEN) $(srcdir)/Modules/_blake2/blake2b2s.py
 	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/clinic/clinic.py -f $@
 
+# _scproxy.o needs to be built outside of setup.py so that we can force
+# the use of the OBJC compiler when the CC compiler is different. For
+# example, it allows _scproxy.c to be compiled using the clang compiler
+# while the rest of the project uses the GNU C compiler.
+#
+# see issue #26317 for details
+@SCPROXY@Modules/_scproxy.o:	$(srcdir)/Modules/_scproxy.c $(srcdir)/Include/Python.h
+@SCPROXY@	$(OBJC) -c $(CCSHARED) $(PY_CORE_CFLAGS) -o $@ $<
+@NOSCPROXY@.PHONY:	Modules/_scproxy.o
+
 # Build the shared modules
 # Under GNU make, MAKEFLAGS are sorted and normalized; the 's' for
 # -s, --silent or --quiet is always the first char.
 # Under BSD make, MAKEFLAGS might be " -s -v x=y".
 # Ignore macros passed by GNU make, passed after --
-sharedmods: $(BUILDPYTHON) pybuilddir.txt Modules/_math.o
+sharedmods: $(BUILDPYTHON) pybuilddir.txt Modules/_math.o Modules/_scproxy.o
 	@case "`echo X $$MAKEFLAGS | sed 's/^X //;s/ -- .*//'`" in \
 	    *\ -s*|s*) quiet="-q";; \
 	    *) quiet="";; \

Misc/ACKS

@@ -882,6 +882,7 @@ Sam Kimbrel
 Tomohiko Kinebuchi
 James King
 W. Trevor King
+Jeffrey Kintscher
 Paul Kippes
 Steve Kirsch
 Sebastian Kirsche

Misc/NEWS.d/next/Build/2019-05-14-05-35-14.bpo-26317.no8mw-.rst

@@ -0,0 +1 @@
+The OBJC and OBJCXX standard command line options for the configure script are now supported. This allows building fot macOS with a third-party compiler, like GNU gcc, for everything except for the several system-specific source files that need system headers that require the Apple-supplied compile chain (e.g. the _scproxy helper module and PythonLauncher.app).  Patch by Jeffrey Kintscher.

aclocal.m4

@@ -55,7 +55,7 @@ dnl
 dnl See the "Since" comment for each macro you use to see what version
 dnl of the macros you require.
 m4_defun([PKG_PREREQ],
-[m4_define([PKG_MACROS_VERSION], [0.29.1])
+[m4_define([PKG_MACROS_VERSION], [0.29.2])
 m4_if(m4_version_compare(PKG_MACROS_VERSION, [$1]), -1,
     [m4_fatal([pkg.m4 version $1 or higher is required but ]PKG_MACROS_VERSION[ found])])
 ])dnl PKG_PREREQ
@@ -156,7 +156,7 @@ AC_ARG_VAR([$1][_CFLAGS], [C compiler flags for $1, overriding pkg-config])dnl
 AC_ARG_VAR([$1][_LIBS], [linker flags for $1, overriding pkg-config])dnl
 
 pkg_failed=no
-AC_MSG_CHECKING([for $1])
+AC_MSG_CHECKING([for $2])
 
 _PKG_CONFIG([$1][_CFLAGS], [cflags], [$2])
 _PKG_CONFIG([$1][_LIBS], [libs], [$2])
@@ -166,11 +166,11 @@ and $1[]_LIBS to avoid the need to call pkg-config.
 See the pkg-config man page for more details.])
 
 if test $pkg_failed = yes; then
-   	AC_MSG_RESULT([no])
+        AC_MSG_RESULT([no])
         _PKG_SHORT_ERRORS_SUPPORTED
         if test $_pkg_short_errors_supported = yes; then
 	        $1[]_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "$2" 2>&1`
-        else 
+        else
 	        $1[]_PKG_ERRORS=`$PKG_CONFIG --print-errors --cflags --libs "$2" 2>&1`
         fi
 	# Put the nasty error message in config.log where it belongs
@@ -187,7 +187,7 @@ installed software in a non-standard prefix.
 _PKG_TEXT])[]dnl
         ])
 elif test $pkg_failed = untried; then
-     	AC_MSG_RESULT([no])
+        AC_MSG_RESULT([no])
 	m4_default([$4], [AC_MSG_FAILURE(
 [The pkg-config script could not be found or is too old.  Make sure it
 is in your PATH or set the PKG_CONFIG environment variable to the full

configure.ac

@@ -663,6 +663,25 @@ AC_PROG_SED
 
 AC_SUBST(CXX)
 AC_SUBST(MAINCC)
+
+if test "$ac_sys_system" = "Darwin"
+then
+	# MacOSX requires an Objective C compiler to
+	# build some Mac-specific code.
+	AC_PROG_OBJC
+	AC_PROG_OBJCXX
+	AC_SUBST(OBJC)
+	AC_SUBST(OBJCXX)
+	SCPROXY=
+	NOSCPROXY=#
+else
+	SCPROXY=#
+	NOSCPROXY=
+fi
+
+AC_SUBST(SCPROXY)
+AC_SUBST(NOSCPROXY)
+
 AC_MSG_CHECKING(for --with-cxx-main=<compiler>)
 AC_ARG_WITH(cxx_main,
             AS_HELP_STRING([--with-cxx-main@<:@=COMPILER@:>@],

setup.py

@@ -1583,10 +1583,11 @@ class PyBuildExt(build_ext):
             self.missing.append('ossaudiodev')
 
         if MACOS:
-            self.add(Extension('_scproxy', ['_scproxy.c'],
+            self.add(Extension('_scproxy', [],
                                extra_link_args=[
                                    '-framework', 'SystemConfiguration',
-                                   '-framework', 'CoreFoundation']))
+                                   '-framework', 'CoreFoundation'],
+                               extra_objects=['Modules/_scproxy.o']))
 
     def detect_compress_exts(self):
         # Andrew Kuchling's zlib module.  Note that some versions of zlib