Add file dependencies to a custom target - cmake

Question

I would like to set up CMake to build qresource files when the contents of files referenced in the .qrc file change. For example I have some qml files that are packaged into a qrc file and the qrc needs to be recompiled if the qml files are changed.
I have the following macro to run the resource compiler but it will only rebuild it if the resource file itself changes.
MACRO(PYQT5_WRAP_RC outfiles)
FOREACH(it ${ARGN})
GET_FILENAME_COMPONENT(outfile ${it} NAME_WE)
GET_FILENAME_COMPONENT(infile ${it} ABSOLUTE)
SET(outfile ${CMAKE_CURRENT_SOURCE_DIR}/${outfile}_rc.py)
ADD_CUSTOM_TARGET(${it} ALL
DEPENDS ${outfile}
)
ADD_CUSTOM_COMMAND(OUTPUT ${outfile}
COMMAND ${PYRCC5BINARY} ${infile} -o ${outfile}
MAIN_DEPENDENCY ${infile}
)
SET(${outfiles} ${${outfiles}} ${outfile})
ENDFOREACH(it)
ENDMACRO (PYQT5_WRAP_RC)
The macro is used like this:
PYQT5_WRAP_RC(rc_gen file1.qrc file2.qrc ...)
How can I make it so the qrc file gets recompiled if one of files that it refers to changes?
Do I need to do something convoluted like this?

Answer 1

It seems to me that the command you are looking for is add_custom_command:
This defines a command to generate specified OUTPUT file(s). A target
created in the same directory (CMakeLists.txt file) that specifies any
output of the custom command as a source file is given a rule to
generate the file using the command at build time.
Configuring the dependencies correctly you should be able to get the file recompiled only when it is really needed.

Answer 2

If I understand correctly your situation, the problem is that CMake does not know anything about what qrc file is and it does not know, that qrc file references some other files. This dependency is implicit for CMake (compare with C++ includes; but for those cmake have special mechanisms to detect dependencies).
So, as I understand, what you can do is to use add_custom_target (which is executed always) but not only add qrc file to its depends, but also write some script, which whould check that files referenced in qrc are also up to date and if they are not, then touch qrc file).
Of course you can use methods from the other answer, which you reference above, to touch qrc file, but you have to develop your own script to extract paths of files referenced in qrc files. Then you can use CMake scripting facilities to check if they are up to date and to touch qrc file.