[network-manager-applet/nma-1-0: 3/6] build: disable warnings that trigger known clang problems

[Thomas Haller <thaller src gnome org>]

commit 3e472e152a85dadc2c58368c2fb9a7863f7de991
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Wed Mar 18 19:02:29 2015 +0100

    build: disable warnings that trigger known clang problems
    
    Fixes build with clang 3.5 on Fedora 21.
    
    Taken from NetworkManager, commit f0740aff88a83c228aa22cfd4c567e31e36bb504.
    
    (cherry picked from commit 440e8f59ea9b9ca4c3fae71606f6ff99751dcd88)

 m4/compiler_warnings.m4 |   80 +++++++++++++++++++++++++++++++++++++---------
 1 files changed, 64 insertions(+), 16 deletions(-)
---
diff --git a/m4/compiler_warnings.m4 b/m4/compiler_warnings.m4
index 97897e4..21e5c88 100644
--- a/m4/compiler_warnings.m4
+++ b/m4/compiler_warnings.m4
@@ -1,3 +1,24 @@
+dnl Check whether a particular compiler flag works with code provided,
+dnl disable it in CFLAGS if the check fails.
+AC_DEFUN([NM_COMPILER_WARNING], [
+       CFLAGS_SAVED="$CFLAGS"
+       CFLAGS="$CFLAGS -Werror -W$1"
+       AC_MSG_CHECKING(whether -W$1 works)
+
+       AC_COMPILE_IFELSE([AC_LANG_SOURCE([[]])], [
+               AC_COMPILE_IFELSE([AC_LANG_SOURCE([[$2]])], [
+                       AC_MSG_RESULT(yes)
+                       CFLAGS="$CFLAGS_SAVED -W$1"
+               ],[
+                       AC_MSG_RESULT(no)
+                       CFLAGS="$CFLAGS_SAVED -Wno-$1"
+               ])
+       ],[
+               AC_MSG_RESULT(not supported)
+               CFLAGS="$CFLAGS_SAVED"
+       ])
+])
+
 AC_DEFUN([NM_COMPILER_WARNINGS],
 [AC_ARG_ENABLE(more-warnings,
        AS_HELP_STRING([--enable-more-warnings], [Possible values: no/yes/error]),
@@ -5,22 +26,26 @@ AC_DEFUN([NM_COMPILER_WARNINGS],
 AC_MSG_CHECKING(for more warnings)
 if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
        AC_MSG_RESULT(yes)
+
+       dnl This is enabled in clang by default, makes little sense,
+       dnl and causes the build to abort with -Werror.
        CFLAGS_SAVED="$CFLAGS"
-       CFLAGS_MORE_WARNINGS="-Wall -std=gnu89"
+       CFLAGS="$CFLAGS -Qunused-arguments"
+       AC_COMPILE_IFELSE([AC_LANG_SOURCE([])], [], CFLAGS="$CFLAGS_SAVED")
+       unset CFLAGS_SAVED
 
        dnl clang only warns about unknown warnings, unless
        dnl called with "-Werror=unknown-warning-option"
        dnl Test if the compiler supports that, and if it does
        dnl attach it to the CFLAGS.
-       CFLAGS_EXTRA="-Werror=unknown-warning-option"
-       CFLAGS="$CFLAGS_MORE_WARNINGS $CFLAGS_EXTRA $CFLAGS_SAVED"
-       AC_TRY_COMPILE([], [],
-               has_option=yes,
-               has_option=no,)
-       if test $has_option = no; then
-               CFLAGS_EXTRA=
+       NM_COMPILER_WARNING([unknown-warning-option], [])
+
+       CFLAGS_SAVED="$CFLAGS"
+       CFLAGS_MORE_WARNINGS="-Wall -std=gnu89"
+
+       if test "x$set_more_warnings" = xerror; then
+               CFLAGS_MORE_WARNINGS="$CFLAGS_MORE_WARNINGS -Werror"
        fi
-       unset has_option
 
        for option in -Wshadow -Wmissing-declarations -Wmissing-prototypes \
                      -Wdeclaration-after-statement -Wformat-security \
@@ -31,8 +56,8 @@ if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
                      -Wpointer-arith -Winit-self \
                      -Wmissing-include-dirs -Waggregate-return; do
                dnl GCC 4.4 does not warn when checking for -Wno-* flags 
(https://gcc.gnu.org/wiki/FAQ#wnowarning)
-               CFLAGS="$CFLAGS_MORE_WARNINGS $CFLAGS_EXTRA $(printf '%s' "$option" | sed 's/^-Wno-/-W/')  
$CFLAGS_SAVED"
-               AC_MSG_CHECKING([whether gcc understands $option])
+               CFLAGS="$CFLAGS_MORE_WARNINGS $(printf '%s' "$option" | sed 's/^-Wno-/-W/')  $CFLAGS_SAVED"
+               AC_MSG_CHECKING([whether compiler understands $option])
                AC_TRY_COMPILE([], [],
                        has_option=yes,
                        has_option=no,)
@@ -43,12 +68,35 @@ if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
                unset has_option
        done
        unset option
-       unset CFLAGS_EXTRA
-       if test "x$set_more_warnings" = xerror; then
-               CFLAGS_MORE_WARNINGS="$CFLAGS_MORE_WARNINGS -Werror"
-       fi
-       CFLAGS="$CFLAGS_MORE_WARNINGS $CFLAGS_SAVED"
+
+       CFLAGS="$CFLAGS_SAVED"
        unset CFLAGS_SAVED
+
+       dnl Disable warnings triggered by known compiler problems
+
+       dnl https://bugzilla.gnome.org/show_bug.cgi?id=745821
+       NM_COMPILER_WARNING([unknown-attributes], [#include <glib.h>])
+
+       dnl https://llvm.org/bugs/show_bug.cgi?id=21614
+       NM_COMPILER_WARNING([array-bounds],
+               [#include <string.h>]
+               [void f () { strcmp ("something", "0"); }]
+       )
+
+       dnl https://llvm.org/bugs/show_bug.cgi?id=22949
+       NM_COMPILER_WARNING([parentheses-equality],
+               [#include <sys/wait.h>]
+               [void f () { if (WIFCONTINUED(0)) return; }]
+       )
+
+       dnl systemd-dhcp's log_internal macro and our handle_warn are sometimes
+       dnl used in void context,u sometimes in int. Makes clang unhappy.
+       NM_COMPILER_WARNING([unused-value],
+               [#define yolo ({ (666 + 666); })]
+               [int f () { int i = yolo; yolo; return i; }]
+       )
+
+       CFLAGS="$CFLAGS_MORE_WARNINGS $CFLAGS"
 else
        AC_MSG_RESULT(no)
 fi