Still further rethinking of build changes for macOS Mojave.

To avoid the sorts of problems complained of by Jakob Egger, it'd be
best if configure didn't emit any references to the sysroot path at all.
In the case of PL/Tcl, we can do that just by keeping our hands off the
TCL_INCLUDE_SPEC string altogether.  In the case of PL/Perl, we need to
substitute -iwithsysroot for -I in the compile commands, which is easily
handled if we change to using a configure output variable that includes
the switch not only the directory name.  Since PL/Tcl and PL/Python
already do it like that, this seems like good consistency cleanup anyway.

Hence, this replaces the advice given to Perl-related extensions in commit
5e2217131; instead of writing "-I$(perl_archlibexp)/CORE", they should
just write "$(perl_includespec)".  (The old way continues to work, but not
on recent macOS.)

It's still the case that configure needs to be aware of the sysroot
path internally, but that's cleaner than what we had before.

As before, back-patch to all supported versions.

Discussion: https://postgr.es/m/20840.1537850987@sss.pgh.pa.us

configure

@@ -668,7 +668,7 @@ python_majorversion
 PYTHON
 perl_embed_ldflags
 perl_embed_ccflags
-perl_includedir
+perl_includespec
 perl_useshrplib
 perl_privlibexp
 perl_archlibexp
@@ -9549,11 +9549,12 @@ documentation for details.  Use --without-perl to disable building
 PL/Perl." "$LINENO" 5
   fi
   # On most platforms, archlibexp is also where the Perl include files live ...
-  perl_includedir="$perl_archlibexp"
-  # ... but on some macOS versions, we must look under $PG_SYSROOT instead
-  if test x"$PG_SYSROOT" != x"" ; then
+  perl_includespec="-I$perl_archlibexp/CORE"
+  # ... but on newer macOS versions, we must use -iwithsysroot to look
+  # under $PG_SYSROOT
+  if test \! -f "$perl_archlibexp/CORE/perl.h" ; then
     if test -f "$PG_SYSROOT$perl_archlibexp/CORE/perl.h" ; then
-      perl_includedir="$PG_SYSROOT$perl_archlibexp"
+      perl_includespec="-iwithsysroot $perl_archlibexp/CORE"
     fi
   fi
 
@@ -18135,11 +18136,6 @@ eval TCL_SHARED_BUILD=\"$TCL_SHARED_BUILD\"
       as_fn_error $? "cannot build PL/Tcl because Tcl is not a shared library
 Use --without-tcl to disable building PL/Tcl." "$LINENO" 5
     fi
-    # Some macOS versions report an include spec that uses -iwithsysroot.
-    # We don't really want to use -isysroot, so translate that if we can.
-    if test x"$PG_SYSROOT" != x"" ; then
-        TCL_INCLUDE_SPEC="`echo "$TCL_INCLUDE_SPEC" | sed "s|-iwithsysroot */|-I $PG_SYSROOT/|"`"
-    fi
     # now that we have TCL_INCLUDE_SPEC, we can check for <tcl.h>
     ac_save_CPPFLAGS=$CPPFLAGS
     CPPFLAGS="$TCL_INCLUDE_SPEC $CPPFLAGS"
@@ -18157,7 +18153,7 @@ fi
 # check for <perl.h>
 if test "$with_perl" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$CPPFLAGS -I$perl_includedir/CORE"
+  CPPFLAGS="$CPPFLAGS $perl_includespec"
   ac_fn_c_check_header_compile "$LINENO" "perl.h" "ac_cv_header_perl_h" "#include <EXTERN.h>
 "
 if test "x$ac_cv_header_perl_h" = xyes; then :

configure.in

@@ -1034,14 +1034,15 @@ documentation for details.  Use --without-perl to disable building
 PL/Perl.])
   fi
   # On most platforms, archlibexp is also where the Perl include files live ...
-  perl_includedir="$perl_archlibexp"
-  # ... but on some macOS versions, we must look under $PG_SYSROOT instead
-  if test x"$PG_SYSROOT" != x"" ; then
+  perl_includespec="-I$perl_archlibexp/CORE"
+  # ... but on newer macOS versions, we must use -iwithsysroot to look
+  # under $PG_SYSROOT
+  if test \! -f "$perl_archlibexp/CORE/perl.h" ; then
     if test -f "$PG_SYSROOT$perl_archlibexp/CORE/perl.h" ; then
-      perl_includedir="$PG_SYSROOT$perl_archlibexp"
+      perl_includespec="-iwithsysroot $perl_archlibexp/CORE"
     fi
   fi
-  AC_SUBST(perl_includedir)dnl
+  AC_SUBST(perl_includespec)dnl
   PGAC_CHECK_PERL_EMBED_CCFLAGS
   PGAC_CHECK_PERL_EMBED_LDFLAGS
 fi
@@ -2213,11 +2214,6 @@ if test "$with_tcl" = yes; then
       AC_MSG_ERROR([cannot build PL/Tcl because Tcl is not a shared library
 Use --without-tcl to disable building PL/Tcl.])
     fi
-    # Some macOS versions report an include spec that uses -iwithsysroot.
-    # We don't really want to use -isysroot, so translate that if we can.
-    if test x"$PG_SYSROOT" != x"" ; then
-        TCL_INCLUDE_SPEC="`echo "$TCL_INCLUDE_SPEC" | sed "s|-iwithsysroot */|-I $PG_SYSROOT/|"`"
-    fi
     # now that we have TCL_INCLUDE_SPEC, we can check for <tcl.h>
     ac_save_CPPFLAGS=$CPPFLAGS
     CPPFLAGS="$TCL_INCLUDE_SPEC $CPPFLAGS"
@@ -2228,7 +2224,7 @@ fi
 # check for <perl.h>
 if test "$with_perl" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$CPPFLAGS -I$perl_includedir/CORE"
+  CPPFLAGS="$CPPFLAGS $perl_includespec"
   AC_CHECK_HEADER(perl.h, [], [AC_MSG_ERROR([header file <perl.h> is required for Perl])],
                   [#include <EXTERN.h>])
   # While we're at it, check that we can link to libperl.

contrib/hstore_plperl/Makefile

@@ -35,8 +35,5 @@ rpathdir = $(perl_archlibexp)/CORE
 SHLIB_LINK += $(perl_embed_ldflags)
 endif
 
-# As with plperl we need to make sure that the CORE directory is included
-# last, probably because it sometimes contains some header files with names
-# that clash with some of ours, or with some that we include, notably on
-# Windows.
-override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) -I$(perl_includedir)/CORE
+# As with plperl we need to include the perl_includespec directory last.
+override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) $(perl_includespec)

contrib/jsonb_plperl/Makefile

@@ -35,8 +35,5 @@ rpathdir = $(perl_archlibexp)/CORE
 SHLIB_LINK += $(perl_embed_ldflags)
 endif
 
-# As with plperl we need to make sure that the CORE directory is included
-# last, probably because it sometimes contains some header files with names
-# that clash with some of ours, or with some that we include, notably on
-# Windows.
-override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) -I$(perl_includedir)/CORE
+# As with plperl we need to include the perl_includespec directory last.
+override CPPFLAGS := $(CPPFLAGS) $(perl_embed_ccflags) $(perl_includespec)

src/Makefile.global.in

@@ -331,7 +331,7 @@ else
 endif
 perl_archlibexp		= @perl_archlibexp@
 perl_privlibexp		= @perl_privlibexp@
-perl_includedir		= @perl_includedir@
+perl_includespec	= @perl_includespec@
 perl_embed_ccflags	= @perl_embed_ccflags@
 perl_embed_ldflags	= @perl_embed_ldflags@
 

src/pl/plperl/GNUmakefile

@@ -12,12 +12,13 @@ override CPPFLAGS += -DPLPERL_HAVE_UID_GID
 override CPPFLAGS += -Wno-comment
 endif
 
-# Note: we need to make sure that the CORE directory is included last,
+# Note: we need to include the perl_includespec directory last,
 # probably because it sometimes contains some header files with names
 # that clash with some of ours, or with some that we include, notably on
 # Windows.
-override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) $(perl_embed_ccflags) -I$(perl_includedir)/CORE
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) $(perl_embed_ccflags) $(perl_includespec)
 
+# this is often, but not always, the same directory named by perl_includespec
 rpathdir = $(perl_archlibexp)/CORE
 
 PGFILEDESC = "PL/Perl - procedural language"

src/template/darwin

@@ -3,9 +3,8 @@
 # Note: Darwin is the original code name for macOS, also known as OS X.
 # We still use "darwin" as the port name, partly because config.guess does.
 
-# Select where some include files should be sought.
-# We may eventually be forced to use "-isysroot" with this value,
-# but for now, it only affects Perl and Tcl include files.
+# Some configure tests require explicit knowledge of where the Xcode "sysroot"
+# is.  We try to avoid having this leak into configure's results, though.
 if test x"$PG_SYSROOT" = x"" ; then
   PG_SYSROOT=`xcodebuild -version -sdk macosx Path 2>/dev/null`
 fi