Is there a possibility to pass includes via -isystem when using qmake

I just added this to my macx-clang/qmake.conf:

QMAKE_CXXFLAGS += $$join(QMAKE_INCDIR_QT, " -isystem", "-isystem")

works nicely now.

Since many settings are hardcoded into spec files, I think you need to create your own. Start with reading mkspecs/linux-g++/qmake.conf or mkspecs/win32-g++/qmake.conf

You will see that by default CONFIG uses warn_on setting. and in mkspecs/common/g++ you have

QMAKE_CFLAGS_WARN_ON += -Wall -W QMAKE_CFLAGS_WARN_OFF += -w QMAKE_CXXFLAGS_WARN_ON += $$QMAKE_CFLAGS_WARN_ON QMAKE_CXXFLAGS_WARN_OFF += $$QMAKE_CFLAGS_WARN_OFF 

so you can change the spec file and make new settings default for every project, or you can set this variables in your project file.

CONFIG += warn_on QMAKE_CFLAGS_WARN_ON = -Wall -Werror -Wundef -Wextra -pedantic QMAKE_CXXFLAGS_WARN_ON = $$QMAKE_CFLAGS_WARN_ON 

qt include path is hardcoded in mkspecs/features/qt.prf as

#handle includes INCLUDEPATH = $$QMAKE_INCDIR_QT $$INCLUDEPATH #prepending prevents us from picking up "stale" includes 

You don't want QMAKE_INCDIR_QT to be a part of INCLUDEPATH since its components are joined with -I. You want to expand it as $$join(QMAKE_INCDIR_QT, " -isystem", "-isystem") somewhere else...

Came up with a workaround: manually changing Makefile.

Add this line to .pro file

system(./suppress_system_warnings.sh) 

And then create an executable file suppress_system_warnings.sh

#!/bin/bash run_in_background() { pidof qmake > /dev/null while [ $? -eq 0 ] do sleep 0.2 pidof qmake > /dev/null done file=Makefile new_line=$( grep ^INCPATH $file | sed 's:-I\/:-isystem\/:g' | sed 's:-I\$:-isystem\$:' ) line_num=$( grep -n ^INCPATH $file | cut -d':' -f1 ) head -n $(expr $line_num - 1) $file > __tmp echo $new_line >> __tmp tail -n +$(expr $line_num + 1) $file >> __tmp mv __tmp $file exit 0; } run_in_background & exit 0;