From e51e8fb9f43372bf78d2f34deeee2490912bdb46 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 12 Dec 2021 18:06:03 -0500
Subject: [PATCH] Clean up compilation warnings coming from PL/Perl with
 clang-12~

clang-12 has introduced -Wcompound-token-split-by-macro, that is causing
a large amount of warnings when building PL/Perl because of its
interactions with upstream Perl.  This commit adds one -Wno to CFLAGS at
./configure time if the flag is supported by the compiler to silence all
those warnings.

This back-patches commit 9ff47ea41 into out-of-support branches,
pursuant to newly-established project policy.  The point is to
suppress scary-looking warnings so that people building these
branches needn't expend brain cells verifying that it's safe
to ignore the warnings.

Discussion: https://postgr.es/m/d0316012-ece7-7b7e-2d36-9c38cb77cb3b@enterprisedb.com
---
 configure    | 42 ++++++++++++++++++++++++++++++++++++++++++
 configure.in |  8 ++++++++
 2 files changed, 50 insertions(+)

diff --git a/configure b/configure
index 18ec9423c6..5733793382 100755
--- a/configure
+++ b/configure
@@ -4775,6 +4775,48 @@ fi
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-unused-command-line-argument"
   fi
+  # Remove clang 12+'s compound-token-split-by-macro, as this causes a lot
+  # of warnings when building plperl because of Perl.  Like previously, test
+  # for the positive form and add the negative form
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -Wcompound-token-split-by-macro" >&5
+$as_echo_n "checking whether $CC supports -Wcompound-token-split-by-macro... " >&6; }
+if ${pgac_cv_prog_cc_cflags__Wcompound_token_split_by_macro+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -Wcompound-token-split-by-macro"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_cc_cflags__Wcompound_token_split_by_macro=yes
+else
+  pgac_cv_prog_cc_cflags__Wcompound_token_split_by_macro=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_cc_cflags__Wcompound_token_split_by_macro" >&5
+$as_echo "$pgac_cv_prog_cc_cflags__Wcompound_token_split_by_macro" >&6; }
+if test x"$pgac_cv_prog_cc_cflags__Wcompound_token_split_by_macro" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wcompound-token-split-by-macro"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    CFLAGS="$CFLAGS -Wno-compound-token-split-by-macro"
+  fi
   # Similarly disable useless truncation warnings from gcc 8+
   NOT_THE_CFLAGS=""
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -Wformat-truncation" >&5
diff --git a/configure.in b/configure.in
index 53c1f19fb5..a30904abc6 100644
--- a/configure.in
+++ b/configure.in
@@ -453,6 +453,14 @@ if test "$GCC" = yes -a "$ICC" = no; then
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-unused-command-line-argument"
   fi
+  # Remove clang 12+'s compound-token-split-by-macro, as this causes a lot
+  # of warnings when building plperl because of Perl.  Like previously, test
+  # for the positive form and add the negative form
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wcompound-token-split-by-macro])
+  if test -n "$NOT_THE_CFLAGS"; then
+    CFLAGS="$CFLAGS -Wno-compound-token-split-by-macro"
+  fi
   # Similarly disable useless truncation warnings from gcc 8+
   NOT_THE_CFLAGS=""
   PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wformat-truncation])