Adding custom compiler to qmake project file and parallel compilation

Hi

The title already says what my question is about: I want to add a custom compiler which produces output another target depends on.

This is my code:

Code:

---

!equals(ffmpegpath, "") {
    WINDOWS_ICONS = resources/icons/hicolor/128x128/apps/$${projectname}.png
    windowsicon.name = windowsicon
    windowsicon.input = WINDOWS_ICONS
    windowsicon.output = "$${OUT_PWD}/res/windowsicon_${QMAKE_FILE_BASE}.ico"
    windowsicon.commands = $${ffmpegpath} -y -i ${QMAKE_FILE_IN} -vf crop=iw-20:ih-20:10:10,scale=64:64 "$${OUT_PWD}/res/windowsicon_${QMAKE_FILE_BASE}.ico"
    windowsicon.CONFIG = no_link target_predeps
    QMAKE_EXTRA_COMPILERS += windowsicon
    PRE_TARGETDEPS += compiler_windowsicon_make_all # I added this line because the configuration "target_predeps" somehow doesn't work
    RC_ICONS = $${OUT_PWD}/res/windowsicon_$${projectname}.ico
}

---

As you can see, this code generates the Windows icon with ffmpeg. This actually works.

The problem comes when trying to compile with the -j option for parallel execution of jobs.

The compilation fails here

Code:

---

Makefile.Release:135: recipe for target 'obj/passwordmanager_resource_res.o' failed
make[1]: *** [obj/passwordmanager_resource_res.o] Error 1

---

because

Code:

---

i686-w64-mingw32-windres: can't open icon file `/build/mingw-w64-passwordmanager/src/passwordmanager/build-i686-w64-mingw32/res/windowsic
co': No such file or directory

---

Obviously the build order is important and make tries to do the target 'obj/passwordmanager_resource_res.o' before the target of the additional compiler is done (which seems to be called 'compiler_windowsicon_make_all').
How can I add 'compiler_windowsicon_make_all' as a dependency of 'obj/passwordmanager_resource_res.o' so make knows the right order?

I've already fiddled some time with qmake but had no success.

Thanks for your help.