qt - qmake pre-build step before ANY compilation

Question

There are several questions on SO regarding how to create a pre-build step for qmake, I can do that with this in my .pro file:

versionTarget.target = ../VersionData/versioning.h
versionTarget.depends = FORCE
win32: versionTarget.commands = cd $$PWD; python.exe ./version_getter.py -p $$TARGET
else:  versionTarget.commands = cd $$PWD; python ./version_getter.py -p $$TARGET

PRE_TARGETDEPS += ../VersionData/versioning.h
QMAKE_EXTRA_TARGETS += versionTarget

Now, the problem is that this approach is not a build step per se but just another build target, so if I have the -j flag configured for make it runs my script in parallel with the other build jobs. This is very bad, because my script creates/updates a header file - having it change part way through the compilation is not acceptable.

So, is there anyway I can have this script executed before any compilation is ran? I know I can create another script and call the version_getter.py and qmake in sequence from that, but this is not desirable as I would have to compile from the command line rather than from within Qt Creator.

---

Update

The complete .pri file that is included by every one of my sub-projects is below:

CONFIG += thread
QT += core 
      gui

versionTarget.target = ../VersionData/versioning.h
versionTarget.depends = FORCE
win32: versionTarget.commands = cd $$PWD; python.exe ./version_getter.py -p $$TARGET
else:  versionTarget.commands = cd $$PWD; python ./version_getter.py -p $$TARGET

PRE_TARGETDEPS += ../VersionData/versioning.h
QMAKE_EXTRA_TARGETS += versionTarget

DEPENDPATH += ../VersionData
INCLUDEPATH += ../VersionData
HEADERS += ../VersionData/versioning.h

UI_HEADERS_DIR = $${_PRO_FILE_PWD_}/include/Qui
DESTDIR = $(SYREN_PATH)

!win32-msvc {
    QMAKE_CXXFLAGS += -std=c++0x
}

But this still results in the same parallel behaviour. I thought it may have been due to my use of ccache, but turning it off made no difference (other than being much slower of course).

Answer 1

Another option would be to start with the project file snippet in your original question, and also ensure that qmake is aware that versioning.h is a dependency for the other build targets in your project file —

• Add the full path to versioning.h to your HEADERS variable.
• Add the folder in which versioning.h resides to your DEPENDPATH variable.

(Caveat: if you run qmake when versioning.h doesn't exist, it will emit "WARNING: Failure to find: versioning.h" — the only workaround for that warning is to use the system() command, as I described in my other answer.)

Example

Create test.pro containing the following:

versionTarget.target = ../versioning.h
versionTarget.depends = FORCE
versionTarget.commands = sleep 5s ; touch ../versioning.h
PRE_TARGETDEPS += ../versioning.h
QMAKE_EXTRA_TARGETS += versionTarget

SOURCES = test.c
HEADERS = ../versioning.h
DEPENDPATH = ..

Create test.c containing the following:

#include "../versioning.h"

Run qmake. It will output WARNING: Failure to find: ../versioning.h.

Run make -j9. It will run versionTarget.commands (which sleeps for 5 seconds to exaggerate any multiprocessing problems), and, after that is done, run the command to compile test.c.

(And if you examine the generated Makefile, you'll see that test.o depends on both test.c and ../versioning.h, so Make should correctly figure out that it can't run the command to compile test.c before the command to create/update ../versioning.h.)