Use warning option -Wshadow=local

Change the existing -Wshadow=compatible-local to -Wshadow=local.  This
covers more cases than before.  In particular, some types are
assignable to each other, such as char * and const char *, or bool and
some integer type, but they are not "compatible" in the C sense, so
they are missed by the previous warning setting, but they are really
the same basic problem.

The warnings were already fixed in commit f9fc9a78a3.  This just
enables the compiler option.

But: The LLVM headers are not clean for this option, so we need to
disable this option for those headers.  We do this by also detecting
in configure and meson the negative form of the warning option and
applying it when compiling the respective files, similar to how other
per-file warning disabling already works.

This technically loses the previous -Wshadow=compatible-local checking
of the LLVM-using files, but this worked only by accident anyway and
there is no guarantee that future LLVM versions wouldn't run afoul of
that warning level.

The variables are intentionally named "...shadow", not
"...shadow_local" or similar, so that other shadow warning option
variants could be substituted easily.

In the long run, a better solution might be to use -isystem for the
LLVM include directories, as was attempted in commit 704ef84ef2 but
then reverted in 7a0aa99e51, because porting that logic from meson
accurately to configure is complicated and fragile and hard to test
and maintain.

Discussion: https://www.postgresql.org/message-id/flat/84b6f128-91f5-480e-8a9e-7d0e8f538cea%40eisentraut.org

configure

@@ -749,6 +749,7 @@ CXXFLAGS_SL_MODULE
 CFLAGS_SL_MODULE
 CFLAGS_VECTORIZE
 CFLAGS_UNROLL_LOOPS
+PERMIT_CXX_SHADOW
 PERMIT_MISSING_VARIABLE_DECLARATIONS
 PERMIT_DECLARATION_AFTER_STATEMENT
 LLVM_BINPATH
@@ -5902,96 +5903,6 @@ 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 ${CC} supports -Wformat-security, for CFLAGS" >&5
@@ -6084,6 +5995,7 @@ if test x"$pgac_cv_prog_CXX_cxxflags__Wformat_security" = x"yes"; then
 fi
 
 
+
   # gcc 14+, clang for a while
   # (Supported in C++ by clang but not gcc.  For consistency, omit in C++.)
   save_CFLAGS=$CFLAGS
@@ -6132,6 +6044,107 @@ fi
     PERMIT_MISSING_VARIABLE_DECLARATIONS=-Wno-missing-variable-declarations
   fi
 
+
+  # We need to be able to disable shadow warnings for the LLVM
+  # includes.
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wshadow=local, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Wshadow=local, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Wshadow_local+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Wshadow=local"
+ac_save_c_werror_flag=$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_local=yes
+else
+  pgac_cv_prog_CC_cflags__Wshadow_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: $pgac_cv_prog_CC_cflags__Wshadow_local" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Wshadow_local" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Wshadow_local" = x"yes"; then
+  CFLAGS="${CFLAGS} -Wshadow=local"
+fi
+
+
+  save_CXXFLAGS=$CXXFLAGS
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wshadow=local, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Wshadow=local, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Wshadow_local+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CXXFLAGS=$CXXFLAGS
+pgac_save_CXX=$CXX
+CXX=${CXX}
+CXXFLAGS="${CXXFLAGS} -Wshadow=local"
+ac_save_cxx_werror_flag=$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_local=yes
+else
+  pgac_cv_prog_CXX_cxxflags__Wshadow_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: $pgac_cv_prog_CXX_cxxflags__Wshadow_local" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Wshadow_local" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Wshadow_local" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Wshadow=local"
+fi
+
+
+  PERMIT_CXX_SHADOW=
+  if test x"$save_CXXFLAGS" != x"$CXXFLAGS"; then
+    PERMIT_CXX_SHADOW=-Wno-shadow=local
+  fi
+
+
   # Disable strict-aliasing rules; needed for gcc 3.3+
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -fno-strict-aliasing, for CFLAGS" >&5

configure.ac

@@ -575,11 +575,11 @@ if test "$GCC" = yes -a "$ICC" = no; then
 
   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])
+
   # gcc 14+, clang for a while
   # (Supported in C++ by clang but not gcc.  For consistency, omit in C++.)
   save_CFLAGS=$CFLAGS
@@ -589,6 +589,18 @@ if test "$GCC" = yes -a "$ICC" = no; then
     PERMIT_MISSING_VARIABLE_DECLARATIONS=-Wno-missing-variable-declarations
   fi
   AC_SUBST(PERMIT_MISSING_VARIABLE_DECLARATIONS)
+
+  # We need to be able to disable shadow warnings for the LLVM
+  # includes.
+  PGAC_PROG_CC_CFLAGS_OPT([-Wshadow=local])
+  save_CXXFLAGS=$CXXFLAGS
+  PGAC_PROG_CXX_CFLAGS_OPT([-Wshadow=local])
+  PERMIT_CXX_SHADOW=
+  if test x"$save_CXXFLAGS" != x"$CXXFLAGS"; then
+    PERMIT_CXX_SHADOW=-Wno-shadow=local
+  fi
+  AC_SUBST(PERMIT_CXX_SHADOW)
+
   # Disable strict-aliasing rules; needed for gcc 3.3+
   PGAC_PROG_CC_CFLAGS_OPT([-fno-strict-aliasing])
   PGAC_PROG_CXX_CFLAGS_OPT([-fno-strict-aliasing])

meson.build

@@ -2209,7 +2209,6 @@ common_warning_flags = [
   '-Werror=unguarded-availability-new',
   '-Wmissing-format-attribute',
   '-Wcast-function-type',
-  '-Wshadow=compatible-local',
   # This was included in -Wall/-Wformat in older GCC versions
   '-Wformat-security',
 ]
@@ -2263,6 +2262,14 @@ if cc.has_argument('-Wmissing-variable-declarations')
   cflags_no_missing_var_decls += '-Wno-missing-variable-declarations'
 endif
 
+# We need to be able to disable shadow warnings for the LLVM includes.
+cflags_warn += cc.get_supported_arguments('-Wshadow=local')
+cxxflags_no_shadow = []
+if have_cxx and cxx.has_argument('-Wshadow=local')
+  cxxflags_warn += '-Wshadow=local'
+  cxxflags_no_shadow += '-Wno-shadow=local'
+endif
+
 # The following tests want to suppress various unhelpful warnings by adding
 # -Wno-foo switches.  But gcc won't complain about unrecognized -Wno-foo
 # switches, so we have to test for the positive form and if that works,

src/Makefile.global.in

@@ -279,6 +279,7 @@ CFLAGS_CRC = @CFLAGS_CRC@
 PERMIT_DECLARATION_AFTER_STATEMENT = @PERMIT_DECLARATION_AFTER_STATEMENT@
 PERMIT_MISSING_VARIABLE_DECLARATIONS = @PERMIT_MISSING_VARIABLE_DECLARATIONS@
 CXXFLAGS = @CXXFLAGS@
+PERMIT_CXX_SHADOW = @PERMIT_CXX_SHADOW@
 
 have_cxx = @have_cxx@
 

src/backend/jit/llvm/Makefile

@@ -24,7 +24,7 @@ NAME = llvmjit
 
 # All files in this directory use LLVM.
 CFLAGS += $(LLVM_CFLAGS)
-CXXFLAGS += $(LLVM_CXXFLAGS)
+CXXFLAGS += $(LLVM_CXXFLAGS) $(PERMIT_CXX_SHADOW)
 override CPPFLAGS += $(LLVM_CPPFLAGS)
 SHLIB_LINK += $(LLVM_LIBS)
 

src/backend/jit/llvm/meson.build

@@ -33,7 +33,7 @@ llvmjit = shared_module('llvmjit',
   llvmjit_sources,
   kwargs: pg_mod_args + {
     'dependencies': pg_mod_args['dependencies'] + [llvm],
-    'cpp_args': pg_mod_args['cpp_args'] + llvm.get_variable(configtool: 'cxxflags').split(),
+    'cpp_args': pg_mod_args['cpp_args'] + llvm.get_variable(configtool: 'cxxflags').split() + cxxflags_no_shadow,
   }
 )
 

src/makefiles/meson.build

@@ -102,6 +102,8 @@ pgxs_kv = {
     ' '.join(cflags_no_decl_after_statement),
   'PERMIT_MISSING_VARIABLE_DECLARATIONS':
     ' '.join(cflags_no_missing_var_decls),
+  'PERMIT_CXX_SHADOW':
+    ' '.join(cxxflags_no_shadow),
 
   'CFLAGS_CRC': ' '.join(cflags_crc),
   'CFLAGS_UNROLL_LOOPS': ' '.join(unroll_loops_cflags),