meson: Specify -Wformat as a common warning flag for extensions

From bce0f70f866bb0e3f8fb8eb14c05bbbdd27c51f2 Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Mon, 22 Jan 2024 13:51:58 +0900
Subject: [PATCH v2] Add -Wformat to common warning flags

We specify -Wformat-security as a common warning flag explicitly. GCC
requires -Wformat to be added for -Wformat-security to take effect. If
-Wformat-security is used without -Wformat, GCC shows the following
warning:

    cc1: warning: '-Wformat-security' ignored without '-Wformat' [-Wformat-security]

Co-authored-by: Sutou Kouhei <kou@clear-code.com>
---
 configure    | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac |  3 ++
 meson.build  |  2 ++
 3 files changed, 97 insertions(+)

diff --git a/configure b/configure
index 36feeafbb23..eafab247e1d 100755
--- a/configure
+++ b/configure
@@ -5985,6 +5985,98 @@ if test x"$pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local" = x"yes"; then
 fi
 
 
+  # -Wformat-security requires -Wformat, so check for it
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Wformat, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Wformat+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Wformat"
+ac_save_c_werror_flag=$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__Wformat=yes
+else
+  pgac_cv_prog_CC_cflags__Wformat=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: $pgac_cv_prog_CC_cflags__Wformat" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Wformat" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Wformat" = x"yes"; then
+  CFLAGS="${CFLAGS} -Wformat"
+fi
+
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wformat, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Wformat, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Wformat+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CXXFLAGS=$CXXFLAGS
+pgac_save_CXX=$CXX
+CXX=${CXX}
+CXXFLAGS="${CXXFLAGS} -Wformat"
+ac_save_cxx_werror_flag=$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__Wformat=yes
+else
+  pgac_cv_prog_CXX_cxxflags__Wformat=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: $pgac_cv_prog_CXX_cxxflags__Wformat" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Wformat" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Wformat" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Wformat"
+fi
+
+
   # This was included in -Wall/-Wformat in older GCC versions
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat-security, for CFLAGS" >&5
diff --git a/configure.ac b/configure.ac
index 57f734879e1..87a8860ecca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -527,6 +527,9 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CXX_CFLAGS_OPT([-Wcast-function-type])
   PGAC_PROG_CC_CFLAGS_OPT([-Wshadow=compatible-local])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wshadow=compatible-local])
+  # -Wformat-security requires -Wformat, so check for it
+  PGAC_PROG_CC_CFLAGS_OPT([-Wformat])
+  PGAC_PROG_CXX_CFLAGS_OPT([-Wformat])
   # 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 85788f9dd8f..717fdc4746b 100644
--- a/meson.build
+++ b/meson.build
@@ -1826,6 +1826,8 @@ common_warning_flags = [
   '-Wimplicit-fallthrough=3',
   '-Wcast-function-type',
   '-Wshadow=compatible-local',
+  # -Wformat-security requires -Wformat, so check for it
+  '-Wformat',
   # This was included in -Wall/-Wformat in older GCC versions
   '-Wformat-security',
 ]
-- 
Tristan Partin
Neon (https://neon.tech)

From 0ba2e6dd55b00ee8a57313a629a1e5fa8c9e40cc Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Wed, 13 Mar 2024 16:10:34 +0900
Subject: [PATCH v3] Add -Wformat to common warning flags

We specify -Wformat-security as a common warning flag explicitly. GCC
requires -Wformat to be added for -Wformat-security to take effect. If
-Wformat-security is used without -Wformat, GCC shows the following
warning:

    cc1: warning: '-Wformat-security' ignored without '-Wformat' [-Wformat-security]

Note that this is not needed for PostgreSQL itself because PostgreSQL
uses -Wall, which includes -Wformat=1. -Wformat is shorthand for
-Wformat=1. These flags without -Wall are persisted into "pg_config
--cflags", which is commonly used by PGXS-based extensions. So
PGXS-based extensions will get the warning without -Wformat.

Co-authored-by: Tristan Partin <tristan@neon.tech>
---
 configure    | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac | 10 ++++++
 meson.build  |  9 +++++
 3 files changed, 118 insertions(+)

diff --git a/configure b/configure
index 70a1968003..7b0fda3825 100755
--- a/configure
+++ b/configure
@@ -6013,6 +6013,105 @@ if test x"$pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local" = x"yes"; then
 fi
 
 
+  # -Wformat-security requires -Wformat. We compile with -Wall in
+  # PostgreSQL, which includes -Wformat=1. -Wformat is shorthand for
+  # -Wformat=1. The set of flags which includes -Wformat-security is
+  # persisted into pg_config --cflags, which is commonly used by
+  # PGXS-based extensions. The lack of -Wformat in the persisted flags
+  # will produce a warning on many GCC versions, so even though adding
+  # -Wformat here is a no-op for PostgreSQL, it silences other use
+  # cases., so check for it.
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Wformat, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Wformat+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Wformat"
+ac_save_c_werror_flag=$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__Wformat=yes
+else
+  pgac_cv_prog_CC_cflags__Wformat=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: $pgac_cv_prog_CC_cflags__Wformat" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Wformat" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Wformat" = x"yes"; then
+  CFLAGS="${CFLAGS} -Wformat"
+fi
+
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wformat, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Wformat, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Wformat+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CXXFLAGS=$CXXFLAGS
+pgac_save_CXX=$CXX
+CXX=${CXX}
+CXXFLAGS="${CXXFLAGS} -Wformat"
+ac_save_cxx_werror_flag=$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__Wformat=yes
+else
+  pgac_cv_prog_CXX_cxxflags__Wformat=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: $pgac_cv_prog_CXX_cxxflags__Wformat" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Wformat" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Wformat" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Wformat"
+fi
+
+
   # This was included in -Wall/-Wformat in older GCC versions
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat-security, for CFLAGS" >&5
diff --git a/configure.ac b/configure.ac
index 52fd7af446..e4776b9963 100644
--- a/configure.ac
+++ b/configure.ac
@@ -533,6 +533,16 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CXX_CFLAGS_OPT([-Wcast-function-type])
   PGAC_PROG_CC_CFLAGS_OPT([-Wshadow=compatible-local])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wshadow=compatible-local])
+  # -Wformat-security requires -Wformat. We compile with -Wall in
+  # PostgreSQL, which includes -Wformat=1. -Wformat is shorthand for
+  # -Wformat=1. The set of flags which includes -Wformat-security is
+  # persisted into pg_config --cflags, which is commonly used by
+  # PGXS-based extensions. The lack of -Wformat in the persisted flags
+  # will produce a warning on many GCC versions, so even though adding
+  # -Wformat here is a no-op for PostgreSQL, it silences other use
+  # cases., so check for it.
+  PGAC_PROG_CC_CFLAGS_OPT([-Wformat])
+  PGAC_PROG_CXX_CFLAGS_OPT([-Wformat])
   # 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 55184db248..732cb59b1f 100644
--- a/meson.build
+++ b/meson.build
@@ -1822,6 +1822,15 @@ common_warning_flags = [
   '-Wimplicit-fallthrough=3',
   '-Wcast-function-type',
   '-Wshadow=compatible-local',
+  # -Wformat-security requires -Wformat. We compile with -Wall in
+  # PostgreSQL, which includes -Wformat=1. -Wformat is shorthand for
+  # -Wformat=1. The set of flags which includes -Wformat-security is
+  # persisted into pg_config --cflags, which is commonly used by
+  # PGXS-based extensions. The lack of -Wformat in the persisted flags
+  # will produce a warning on many GCC versions, so even though adding
+  # -Wformat here is a no-op for PostgreSQL, it silences other use
+  # cases., so check for it.
+  '-Wformat',
   # This was included in -Wall/-Wformat in older GCC versions
   '-Wformat-security',
 ]
-- 
2.43.0

From a515720338dc49e764f598021200316c6d01ddf9 Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Fri, 15 Mar 2024 18:27:30 +0900
Subject: [PATCH v4] meson: Restore implicit warning/debug/optimize flags for
 extensions

Meson specifies warning/debug/optimize flags such as "-Wall", "-g" and
"-O2" automatically based on "--warnlevel" and "--buildtype"
options. And we use "--warning_level=1" and
"--buildtype=debugoptimized" by default.

We don't specify warning/debug/optimize flags explicitly to build
PostgreSQL with Meson. Because Meson does it automatically as we said.
But Meson doesn't care about flags in Makefile.global and
pg_config. So we need to care about them manually.

This changes do it. They detect warning/debug/optimize flags based on
warning_level/debug/optimization option values because Meson doesn't
tell us flags Meson guessed.
---
 meson.build             | 40 ++++++++++++++++++++++++++++++++++++++++
 src/include/meson.build |  4 ++--
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/meson.build b/meson.build
index c8fdfeb0ec..3c5c449a0a 100644
--- a/meson.build
+++ b/meson.build
@@ -1824,6 +1824,46 @@ endif
 vectorize_cflags = cc.get_supported_arguments(['-ftree-vectorize'])
 unroll_loops_cflags = cc.get_supported_arguments(['-funroll-loops'])
 
+# They aren't used for building PostgreSQL itself because Meson does
+# everything internally. They are used by extensions via pg_config or
+# Makefile.global.
+common_builtin_flags = []
+
+warning_level = get_option('warning_level')
+# See https://mesonbuild.com/Builtin-options.html#details-for-warning_level for
+# warning_level values.
+if warning_level == '1'
+  common_builtin_flags += ['-Wall', '/W2']
+elif warning_level == '2'
+  common_builtin_flags += ['-Wall', '-Wextra', '/W3']
+elif warning_level == '3'
+  common_builtin_flags += ['-Wall', '-Wextra', '-Wpedantic', '/W4']
+elif warning_level == 'everything'
+  common_builtin_flags += ['-Weverything', '/Wall']
+endif
+
+if get_option('debug')
+  common_builtin_flags += ['-g']
+endif
+
+optimization = get_option('optimization')
+if optimization == '0'
+  common_builtin_flags += ['-O0']
+elif optimization == '1'
+  common_builtin_flags += ['-O1']
+elif optimization == '2'
+  common_builtin_flags += ['-O2']
+elif optimization == '3'
+  common_builtin_flags += ['-O3']
+elif optimization == 's'
+  common_builtin_flags += ['-Os']
+endif
+
+cflags_builtin = cc.get_supported_arguments(common_builtin_flags)
+if llvm.found()
+  cxxflags_builtin = cpp.get_supported_arguments(common_builtin_flags)
+endif
+
 common_warning_flags = [
   '-Wmissing-prototypes',
   '-Wpointer-arith',
diff --git a/src/include/meson.build b/src/include/meson.build
index a28f115d86..58b7a9c1e7 100644
--- a/src/include/meson.build
+++ b/src/include/meson.build
@@ -44,9 +44,9 @@ config_paths_data.set_quoted('MANDIR', dir_prefix / dir_man)
 
 var_cc = ' '.join(cc.cmd_array())
 var_cpp = ' '.join(cc.cmd_array() + ['-E'])
-var_cflags = ' '.join(cflags + cflags_warn + get_option('c_args'))
+var_cflags = ' '.join(cflags + cflags_builtin + cflags_warn + get_option('c_args'))
 if llvm.found()
-  var_cxxflags = ' '.join(cxxflags + cxxflags_warn + get_option('cpp_args'))
+  var_cxxflags = ' '.join(cxxflags + cxxflags_builtin + cxxflags_warn + get_option('cpp_args'))
 else
   var_cxxflags = ''
 endif
-- 
2.43.0

From 205ef88c66cf1050eedfc1e72d951de93a02e53a Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Fri, 15 Mar 2024 18:27:30 +0900
Subject: [PATCH v5] meson: Restore implicit warning/debug/optimize flags for
 extensions

Meson specifies warning/debug/optimize flags such as "-Wall", "-g" and
"-O2" automatically based on "--warnlevel" and "--buildtype"
options. And we use "--warning_level=1" and
"--buildtype=debugoptimized" by default.

We don't specify warning/debug/optimize flags explicitly to build
PostgreSQL with Meson. Because Meson does it automatically as we said.
But Meson doesn't care about flags in Makefile.global and
pg_config. So we need to care about them manually.

This changes do it. They detect warning/debug/optimize flags based on
warning_level/debug/optimization option values because Meson doesn't
tell us flags Meson guessed.
---
 meson.build             | 41 +++++++++++++++++++++++++++++++++++++++++
 src/include/meson.build |  4 ++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/meson.build b/meson.build
index 5acf083ce3c..11bd56f79a7 100644
--- a/meson.build
+++ b/meson.build
@@ -1848,6 +1848,47 @@ endif
 vectorize_cflags = cc.get_supported_arguments(['-ftree-vectorize'])
 unroll_loops_cflags = cc.get_supported_arguments(['-funroll-loops'])
 
+# They aren't used for building PostgreSQL itself because Meson does
+# everything internally. They are used by extensions via pg_config or
+# Makefile.global.
+common_builtin_flags = []
+
+warning_level = get_option('warning_level')
+# See https://mesonbuild.com/Builtin-options.html#details-for-warning_level for
+# warning_level values.
+#
+# We don't use "/W*" flags here because we don't need to care about MSVC here.
+#
+# We don't have "warning_level == 3" and "warning_level ==
+# 'everything'" here because we don't use these warning levels.
+if warning_level == '1'
+  common_builtin_flags += ['-Wall']
+elif warning_level == '2'
+  common_builtin_flags += ['-Wall', '-Wextra']
+endif
+
+if get_option('debug')
+  common_builtin_flags += ['-g']
+endif
+
+optimization = get_option('optimization')
+if optimization == '0'
+  common_builtin_flags += ['-O0']
+elif optimization == '1'
+  common_builtin_flags += ['-O1']
+elif optimization == '2'
+  common_builtin_flags += ['-O2']
+elif optimization == '3'
+  common_builtin_flags += ['-O3']
+elif optimization == 's'
+  common_builtin_flags += ['-Os']
+endif
+
+cflags_builtin = cc.get_supported_arguments(common_builtin_flags)
+if llvm.found()
+  cxxflags_builtin = cpp.get_supported_arguments(common_builtin_flags)
+endif
+
 common_warning_flags = [
   '-Wmissing-prototypes',
   '-Wpointer-arith',
diff --git a/src/include/meson.build b/src/include/meson.build
index a28f115d867..58b7a9c1e7e 100644
--- a/src/include/meson.build
+++ b/src/include/meson.build
@@ -44,9 +44,9 @@ config_paths_data.set_quoted('MANDIR', dir_prefix / dir_man)
 
 var_cc = ' '.join(cc.cmd_array())
 var_cpp = ' '.join(cc.cmd_array() + ['-E'])
-var_cflags = ' '.join(cflags + cflags_warn + get_option('c_args'))
+var_cflags = ' '.join(cflags + cflags_builtin + cflags_warn + get_option('c_args'))
 if llvm.found()
-  var_cxxflags = ' '.join(cxxflags + cxxflags_warn + get_option('cpp_args'))
+  var_cxxflags = ' '.join(cxxflags + cxxflags_builtin + cxxflags_warn + get_option('cpp_args'))
 else
   var_cxxflags = ''
 endif
-- 
2.43.0

From 8238adba3f3fc96d4a9e50af611b1cb3566abc0e Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Fri, 15 Mar 2024 18:27:30 +0900
Subject: [PATCH v6] meson: Restore implicit warning/debug/optimize flags for
 extensions

Meson specifies warning/debug/optimize flags such as "-Wall", "-g" and
"-O2" automatically based on "--warnlevel" and "--buildtype"
options. And we use "--warning_level=1" and
"--buildtype=debugoptimized" by default.

We don't specify warning/debug/optimize flags explicitly to build
PostgreSQL with Meson. Because Meson does it automatically as we said.
But Meson doesn't care about flags in Makefile.global and
pg_config. So we need to care about them manually.

This changes do it. They detect debug/optimize flags based on
debug/optimization option values because Meson doesn't tell us flags
Meson guessed. We always use -Wall for warning flags.
---
 meson.build             | 27 +++++++++++++++++++++++++++
 src/include/meson.build |  4 ++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/meson.build b/meson.build
index d6401fb8e30..d7239dbb114 100644
--- a/meson.build
+++ b/meson.build
@@ -1851,6 +1851,33 @@ endif
 vectorize_cflags = cc.get_supported_arguments(['-ftree-vectorize'])
 unroll_loops_cflags = cc.get_supported_arguments(['-funroll-loops'])
 
+# They aren't used for building PostgreSQL itself because Meson does
+# everything internally. They are used by extensions via pg_config or
+# Makefile.global.
+common_builtin_flags = ['-Wall']
+
+if get_option('debug')
+  common_builtin_flags += ['-g']
+endif
+
+optimization = get_option('optimization')
+if optimization == '0'
+  common_builtin_flags += ['-O0']
+elif optimization == '1'
+  common_builtin_flags += ['-O1']
+elif optimization == '2'
+  common_builtin_flags += ['-O2']
+elif optimization == '3'
+  common_builtin_flags += ['-O3']
+elif optimization == 's'
+  common_builtin_flags += ['-Os']
+endif
+
+cflags_builtin = cc.get_supported_arguments(common_builtin_flags)
+if llvm.found()
+  cxxflags_builtin = cpp.get_supported_arguments(common_builtin_flags)
+endif
+
 common_warning_flags = [
   '-Wmissing-prototypes',
   '-Wpointer-arith',
diff --git a/src/include/meson.build b/src/include/meson.build
index a28f115d867..58b7a9c1e7e 100644
--- a/src/include/meson.build
+++ b/src/include/meson.build
@@ -44,9 +44,9 @@ config_paths_data.set_quoted('MANDIR', dir_prefix / dir_man)
 
 var_cc = ' '.join(cc.cmd_array())
 var_cpp = ' '.join(cc.cmd_array() + ['-E'])
-var_cflags = ' '.join(cflags + cflags_warn + get_option('c_args'))
+var_cflags = ' '.join(cflags + cflags_builtin + cflags_warn + get_option('c_args'))
 if llvm.found()
-  var_cxxflags = ' '.join(cxxflags + cxxflags_warn + get_option('cpp_args'))
+  var_cxxflags = ' '.join(cxxflags + cxxflags_builtin + cxxflags_warn + get_option('cpp_args'))
 else
   var_cxxflags = ''
 endif
-- 
2.43.0