Add "headerscheck" script to test header-file compilability under C.

We already had "cpluspluscheck", which served the dual purposes of
verifying that headers compile standalone and that they compile as C++.
However, C++ compilers don't have the exact same set of error conditions
as C compilers, so this doesn't really prove that a header will compile
standalone as C.

Hence, add a second script that's largely similar but runs the C
compiler not C++.

Also add a bit more documentation than the none-at-all we had before.

Discussion: https://postgr.es/m/14803.1566175851@sss.pgh.pa.us

GNUmakefile.in

@@ -128,7 +128,10 @@ distcheck: dist
 	rm -rf $(distdir) $(dummy)
 	@echo "Distribution integrity checks out."
 
+headerscheck: submake-generated-headers
+	$(top_srcdir)/src/tools/pginclude/headerscheck $(top_srcdir) $(abs_top_builddir)
+
 cpluspluscheck: submake-generated-headers
 	$(top_srcdir)/src/tools/pginclude/cpluspluscheck $(top_srcdir) $(abs_top_builddir)
 
-.PHONY: dist distdir distcheck docs install-docs world check-world install-world installcheck-world
+.PHONY: dist distdir distcheck docs install-docs world check-world install-world installcheck-world headerscheck cpluspluscheck

src/tools/pginclude/README

@@ -53,3 +53,51 @@ Another tools that does a similar task is at:
 An include file visualizer script is available at:
 
 	http://archives.postgresql.org/pgsql-hackers/2011-09/msg00311.php
+
+
+headerscheck
+============
+
+This script can be run to verify that all Postgres include files meet
+the project convention that they will compile "standalone", that is
+with no prerequisite headers other than postgres.h (or postgres_fe.h
+or c.h, as appropriate).
+
+A small number of header files are exempted from this requirement,
+and are whitelisted in the headerscheck script.
+
+The easy way to run the script is to say "make -s headerscheck" in
+the top-level build directory after completing a build.  You should
+have included "--with-perl --with-python" in your configure options,
+else you're likely to get errors about related headers not being found.
+
+A limitation of the current script is that it doesn't know which headers
+are for frontend or backend, so it tests everything with postgres.h
+as prerequisite, even if postgres_fe.h would be more appropriate.  Also
+note that the contents of macros are not checked; this is intentional.
+
+
+cpluspluscheck
+==============
+
+This script can be run to verify that all Postgres include files meet
+the project convention that they will compile as C++ code.  Although
+the project's coding language is C, some people write extensions in C++,
+so it's helpful for include files to be C++-clean.
+
+A small number of header files are exempted from this requirement,
+and are whitelisted in the cpluspluscheck script.
+
+The easy way to run the script is to say "make -s cpluspluscheck" in
+the top-level build directory after completing a build.  You should
+have included "--with-perl --with-python" in your configure options,
+else you're likely to get errors about related headers not being found.
+
+If you are using a non-g++-compatible C++ compiler, you may need to
+override the script's CXXFLAGS setting by setting a suitable environment
+value.
+
+A limitation of the current script is that it doesn't know which headers
+are for frontend or backend, so it tests everything with postgres.h
+as prerequisite, even if postgres_fe.h would be more appropriate.  Also
+note that the contents of macros are not checked; this is intentional.

src/tools/pginclude/cpluspluscheck

@@ -7,8 +7,13 @@
 # default to the current directory.
 #
 # Needs to be run after configuring and creating all generated headers.
+# It's advisable to configure --with-perl --with-python, else you're
+# likely to get errors from associated headers.
 #
 # No output if everything is OK, else compiler errors.
+#
+# src/tools/pginclude/cpluspluscheck
+# Copyright (c) 2009-2019, PostgreSQL Global Development Group
 
 if [ -z "$1" ]; then
     srcdir="."

src/tools/pginclude/headerscheck

@@ -0,0 +1,153 @@
+#!/bin/sh
+
+# Check (almost) all PostgreSQL include files for standalone build.
+#
+# Argument 1 is the top-level source directory, argument 2 the
+# top-level build directory (they might be the same). If not set, they
+# default to the current directory.
+#
+# Needs to be run after configuring and creating all generated headers.
+# It's advisable to configure --with-perl --with-python, else you're
+# likely to get errors from associated headers.
+#
+# No output if everything is OK, else compiler errors.
+#
+# src/tools/pginclude/headerscheck
+# Copyright (c) 2009-2019, PostgreSQL Global Development Group
+
+if [ -z "$1" ]; then
+    srcdir="."
+else
+    srcdir="$1"
+fi
+
+if [ -z "$2" ]; then
+    builddir="."
+else
+    builddir="$2"
+fi
+
+me=`basename $0`
+
+# Pull some info from configure's results.
+MGLOB="$builddir/src/Makefile.global"
+CPPFLAGS=`sed -n 's/^CPPFLAGS[ 	]*=[ 	]*//p' "$MGLOB"`
+CFLAGS=`sed -n 's/^CFLAGS[ 	]*=[ 	]*//p' "$MGLOB"`
+CC=`sed -n 's/^CC[ 	]*=[ 	]*//p' "$MGLOB"`
+PG_SYSROOT=`sed -n 's/^PG_SYSROOT[ 	]*=[ 	]*//p' "$MGLOB"`
+perl_includespec=`sed -n 's/^perl_includespec[ 	]*=[ 	]*//p' "$MGLOB"`
+python_includespec=`sed -n 's/^python_includespec[ 	]*=[ 	]*//p' "$MGLOB"`
+
+# needed on Darwin
+CPPFLAGS=`echo "$CPPFLAGS" | sed "s|\\\$(PG_SYSROOT)|$PG_SYSROOT|g"`
+
+# (EXTRAFLAGS is not set here, but user can pass it in if need be.)
+
+# Create temp directory.
+tmp=`mktemp -d /tmp/$me.XXXXXX`
+
+trap 'rm -rf $tmp' 0 1 2 3 15
+
+# Scan all of src/ and contrib/ for header files.
+for f in `cd "$srcdir" && find src contrib -name '*.h' -print`
+do
+	# Ignore files that are unportable or intentionally not standalone.
+
+	# These files are platform-specific, and c.h will include the
+	# one that's relevant for our current platform anyway.
+	test "$f" = src/include/port/aix.h && continue
+	test "$f" = src/include/port/cygwin.h && continue
+	test "$f" = src/include/port/darwin.h && continue
+	test "$f" = src/include/port/freebsd.h && continue
+	test "$f" = src/include/port/hpux.h && continue
+	test "$f" = src/include/port/linux.h && continue
+	test "$f" = src/include/port/netbsd.h && continue
+	test "$f" = src/include/port/openbsd.h && continue
+	test "$f" = src/include/port/solaris.h && continue
+	test "$f" = src/include/port/win32.h && continue
+
+	# Additional Windows-specific headers.
+	test "$f" = src/include/port/win32_port.h && continue
+	test "$f" = src/include/port/win32/sys/socket.h && continue
+	test "$f" = src/include/port/win32_msvc/dirent.h && continue
+	test "$f" = src/port/pthread-win32.h && continue
+
+	# Likewise, these files are platform-specific, and the one
+	# relevant to our platform will be included by atomics.h.
+	test "$f" = src/include/port/atomics/arch-arm.h && continue
+	test "$f" = src/include/port/atomics/arch-hppa.h && continue
+	test "$f" = src/include/port/atomics/arch-ia64.h && continue
+	test "$f" = src/include/port/atomics/arch-ppc.h && continue
+	test "$f" = src/include/port/atomics/arch-x86.h && continue
+	test "$f" = src/include/port/atomics/fallback.h && continue
+	test "$f" = src/include/port/atomics/generic.h && continue
+	test "$f" = src/include/port/atomics/generic-acc.h && continue
+	test "$f" = src/include/port/atomics/generic-gcc.h && continue
+	test "$f" = src/include/port/atomics/generic-msvc.h && continue
+	test "$f" = src/include/port/atomics/generic-sunpro.h && continue
+	test "$f" = src/include/port/atomics/generic-xlc.h && continue
+
+	# rusagestub.h is also platform-specific, and will be included
+	# by utils/pg_rusage.h if necessary.
+	test "$f" = src/include/rusagestub.h && continue
+
+	# sepgsql.h depends on headers that aren't there on most platforms.
+	test "$f" = contrib/sepgsql/sepgsql.h && continue
+
+	# These files are not meant to be included standalone, because
+	# they contain lists that might have multiple use-cases.
+	test "$f" = src/include/access/rmgrlist.h && continue
+	test "$f" = src/include/parser/kwlist.h && continue
+	test "$f" = src/pl/plpgsql/src/pl_reserved_kwlist.h && continue
+	test "$f" = src/pl/plpgsql/src/pl_unreserved_kwlist.h && continue
+	test "$f" = src/interfaces/ecpg/preproc/c_kwlist.h && continue
+	test "$f" = src/interfaces/ecpg/preproc/ecpg_kwlist.h && continue
+	test "$f" = src/include/regex/regerrs.h && continue
+	test "$f" = src/pl/plpgsql/src/plerrcodes.h && continue
+	test "$f" = src/pl/plpython/spiexceptions.h && continue
+	test "$f" = src/pl/tcl/pltclerrcodes.h && continue
+
+	# We can't make these Bison output files compilable standalone
+	# without using "%code require", which old Bison versions lack.
+	# parser/gram.h will be included by parser/gramparse.h anyway.
+	test "$f" = src/include/parser/gram.h && continue
+	test "$f" = src/backend/parser/gram.h && continue
+	test "$f" = src/pl/plpgsql/src/pl_gram.h && continue
+	test "$f" = src/interfaces/ecpg/preproc/preproc.h && continue
+
+	# This produces a "no previous prototype" warning.
+	test "$f" = src/include/storage/checksum_impl.h && continue
+
+	# ppport.h is not under our control, so we can't make it standalone.
+	test "$f" = src/pl/plperl/ppport.h && continue
+
+	# regression.h is not actually C, but ECPG code.
+	test "$f" = src/interfaces/ecpg/test/regression.h && continue
+	# printf_hack.h produces "unused function" warnings.
+	test "$f" = src/interfaces/ecpg/test/printf_hack.h && continue
+
+	# OK, create .c file to include this .h file.
+	{
+	    test "$f" != src/include/postgres_fe.h && echo '#include "postgres.h"'
+	    echo "#include \"$f\""
+	} >$tmp/test.c
+
+	# Some subdirectories need extra -I switches.
+	case "$f" in
+	    src/pl/plperl/*)
+		EXTRAINCLUDES="$perl_includespec" ;;
+	    src/pl/plpython/*)
+		EXTRAINCLUDES="$python_includespec" ;;
+	    src/interfaces/ecpg/*)
+		EXTRAINCLUDES="-I $builddir/src/interfaces/ecpg/include -I $srcdir/src/interfaces/ecpg/include" ;;
+	    *)
+		EXTRAINCLUDES="" ;;
+	esac
+
+	# Run the test.
+	${CC:-gcc} $CPPFLAGS $CFLAGS -I $builddir -I $srcdir \
+		-I $builddir/src/include -I $srcdir/src/include \
+		-I $builddir/src/interfaces/libpq -I $srcdir/src/interfaces/libpq \
+		$EXTRAINCLUDES $EXTRAFLAGS -c $tmp/test.c -o $tmp/test.o
+
+done