From 0fe954c28584169938e5c0738cfaa9930ce77577 Mon Sep 17 00:00:00 2001
From: David Rowley <drowley@postgresql.org>
Date: Fri, 7 Oct 2022 16:50:31 +1300
Subject: Add -Wshadow=compatible-local to the standard compilation flags

Since cd4e8caaa, we've been able to build the source tree with
-Wshadow=compatible-local without any warnings.  Lots of work was done by
Justin Pryzby and I (David) to get all our code to compile warning free
with that flag.  In that process, 2 bugs (16d69ec29 and af7d270dd) were
discovered and fixed.  Additionally, "git log --grep=shadow" shows that
there is no shortage of other bugs that have been fixed over the years
which were caused by variable shadowing.

In light of the above, it seems very much worthwhile to add at least
-Wshadow=compatible-local to our standard compilation flags.  We *may*
want to go further and take this to -Wshadow=local in the future, but
we're not ready for that today, so let's add -Wshadow=compatible-local now
to help make sure we don't introduce further local variable shadowing.

Author: Andres Freund
Discussion: https://postgr.es/m/20221006003920.6xlqaoccxwisza5k@awork3.anarazel.de
---
 configure    | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac |  2 ++
 meson.build  |  1 +
 3 files changed, 94 insertions(+)

diff --git a/configure b/configure
index 1caca21b62..a5a03f6cec 100755
--- a/configure
+++ b/configure
@@ -5852,6 +5852,97 @@ if test x"$pgac_cv_prog_CXX_cxxflags__Wcast_function_type" = x"yes"; then
 fi
 
 
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wshadow=compatible-local, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Wshadow=compatible-local, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Wshadow_compatible_local+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Wshadow=compatible-local"
+ac_save_c_werror_flag=$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__Wshadow_compatible_local=yes
+else
+  pgac_cv_prog_CC_cflags__Wshadow_compatible_local=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"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CC_cflags__Wshadow_compatible_local" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Wshadow_compatible_local" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Wshadow_compatible_local" = x"yes"; then
+  CFLAGS="${CFLAGS} -Wshadow=compatible-local"
+fi
+
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wshadow=compatible-local, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Wshadow=compatible-local, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CXXFLAGS=$CXXFLAGS
+pgac_save_CXX=$CXX
+CXX=${CXX}
+CXXFLAGS="${CXXFLAGS} -Wshadow=compatible-local"
+ac_save_cxx_werror_flag=$ac_cxx_werror_flag
+ac_cxx_werror_flag=yes
+ac_ext=cpp
+ac_cpp='$CXXCPP $CPPFLAGS'
+ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
+
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local=yes
+else
+  pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+ac_cxx_werror_flag=$ac_save_cxx_werror_flag
+CXXFLAGS="$pgac_save_CXXFLAGS"
+CXX="$pgac_save_CXX"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Wshadow=compatible-local"
+fi
+
+
   # This was included in -Wall/-Wformat in older GCC versions
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat-security, for CFLAGS" >&5
diff --git a/configure.ac b/configure.ac
index 10fa55dd15..c696566a7f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -508,6 +508,8 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CXX_CFLAGS_OPT([-Wimplicit-fallthrough=3])
   PGAC_PROG_CC_CFLAGS_OPT([-Wcast-function-type])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wcast-function-type])
+  PGAC_PROG_CC_CFLAGS_OPT([-Wshadow=compatible-local])
+  PGAC_PROG_CXX_CFLAGS_OPT([-Wshadow=compatible-local])
   # This was included in -Wall/-Wformat in older GCC versions
   PGAC_PROG_CC_CFLAGS_OPT([-Wformat-security])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wformat-security])
diff --git a/meson.build b/meson.build
index f0cb01c001..925db70c9d 100644
--- a/meson.build
+++ b/meson.build
@@ -1709,6 +1709,7 @@ common_warning_flags = [
   '-Wmissing-format-attribute',
   '-Wimplicit-fallthrough=3',
   '-Wcast-function-type',
+  '-Wshadow=compatible-local',
   # This was included in -Wall/-Wformat in older GCC versions
   '-Wformat-security',
 ]
-- 
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