Triggering rebuild after changing a *.json file

[Kevin Funk]

On Sunday 23 November 2014 17:54:21 Milian Wolff wrote:
> On Sunday 23 November 2014 10:39:02 Andreas Pakulat wrote:
> > Hi,
> > 
> > On Sun, Nov 23, 2014 at 4:36 AM, Milian Wolff <mail at milianw.de> wrote:
> > > Hey all,
> > > 
> > > in my quest for better *.json support in KF5 based applications, I
> > > noticed
> > > that we currently do not rebuild properly on changes to the *.desktop or
> > > *.json files.
> > > 
> > > For KDevelop, I'm thus playing around with something like this
> > > currently:
> > > 
> > > ~~~~~~~~~~~~~~~+
> > > function(kdevplatform_add_plugin plugin)
> > > 
> > >     set(options )
> > >     set(oneValueArgs JSON)
> > >     set(multiValueArgs SOURCES)
> > >     cmake_parse_arguments(KDEV_ADD_PLUGIN "${options}" "${oneValueArgs}"
> > > 
> > > "${multiValueArgs}" ${ARGN})
> > > 
> > >     string(REGEX REPLACE "\\.cmake$" "" json_out
> > >     ${KDEV_ADD_PLUGIN_JSON})
> > >     configure_file(${KDEV_ADD_PLUGIN_JSON}
> > > 
> > > ${CMAKE_CURRENT_BINARY_DIR}/${json_out})
> > > 
> > >     # ensure we recompile the corresponding object files when the json
> > >     file
> > > 
> > > changes
> > > 
> > >     set(dependent_sources )
> > >     foreach(header ${KDEV_ADD_PLUGIN_SOURCES})
> > >     
> > >         file(STRINGS "${header}" match REGEX
> > >         "K_PLUGIN_FACTORY_WITH_JSON")
> > >         if(match)
> > >         
> > >             list(APPEND dependent_sources "${header}")
> > >         
> > >         endif()
> > >     
> > >     endforeach()
> > >     if(NOT dependent_sources)
> > >     
> > >         # fallback to all sources - better safe than sorry...
> > >         set(dependent_sources ${KDEV_ADD_PLUGIN_SOURCES})
> > >     
> > >     endif()
> > >     set_property(SOURCE ${dependent_sources} APPEND PROPERTY
> > >     OBJECT_DEPENDS
> > > 
> > > ${CMAKE_CURRENT_BINARY_DIR}/${json_out})
> > > 
> > >     add_library(${plugin} MODULE ${KDEV_ADD_PLUGIN_SOURCES})
> > >     set_property(TARGET ${plugin} APPEND PROPERTY AUTOGEN_TARGET_DEPENDS
> > > 
> > > ${CMAKE_CURRENT_BINARY_DIR}/${json_out})
> > > endfunction()
> > > ~~~~~~~~~~~~~~~+
> > > 
> > > 
> > > To be used like this:
> > > 
> > > kdevplatform_add_plugin(kdevgit JSON kdevgit.json.cmake SOURCES
> > > ${kdevgit_PART_SRCS})
> > > 
> > > This does trigger a rebuild, but the strings are still not updated
> > > properly.
> > > I'm quite confused actually, does anyone know where the code comes from
> > > that
> > > is embedded into the *.o that uses Q_PLUGIN_METADATA? I suspect CMake
> > > AUTOGEN?
> > > But where does that put its generated binary JSON representation? How
> > > can
> > > I
> > > make sure that it gets updated properly when the source file changes?
> > > 
> > > To reproduce this, you can just change any *.desktop file that is piped
> > > through desktop_to_json. The change will be picked up by CMake and a
> > > reconfigure is triggered, which is pretty slow as well. But nothing is
> > > rebuilt. With the macro above, I trigger the build but still, the *.o
> > > file
> > > that uses K_PLUGIN_FACTORY_WITH_JSON is still containing the "old"
> > > strings...
> > > I'm at loss - can someone help me please? <http://milianw.de>
> > 
> > Is there a particular reason why you run the to-json part during cmake
> > time? If you setup a simple cmake script you could easily switch the
> > generation to be a custom target and then have the plugin depend on that
> > custom target (or rather its json output file).
> 
> That was apparently a side-effect of KDevelop using configure_file to embed
> the version number in the *.desktop file. This is not required anymore with
> the JSON-based plugin loading mechanism, as we install plugins into a
> versioned directory path. I've changed this now and the CMake configure step
> when changing a file is gone. Note that desktop_to_json already uses a
> custom target internally.
> 
> > I also think you're misunderstanding the AUTOGEN_TARGET_DEPENDS property,
> > according to the documentation it is to be set on an auto-generator target
> > and not on a 'standard' one like the library. As far as I can see you know
> > the input and output files of the desktop-to-json conversion so a custom
> > target should be easily doable (unlike automoc).
> 
> This might be true, yes. Note that I just copied that line from
> desktop_to_json. But note that in the ideal case, we wouldn't have any
> desktop-to-json. Rather, we just have a *.json file, a *.cpp file that uses
> K_PLUGIN_FACTORY_WITH_JSON. Currently, when the *.json file is changed, the
> *.cpp.o is not updated, nor the plugin *.so rebuilt and thus the new strings
> are not available at runtime.
> 
> This is what we need to fix somehow, and I still don't know how. Will we
> have to fix this inside CMake?

Seems like a job for OBJECT_DEPENDS... That would require you to explicitly 
name the .cpp containing the K_PLUGIN_FACTORY_WITH_JSON(...) use, though.

Something along:
  SET_SOURCE_FILES_PROPERTIES(myplugin.cpp
    PROPERTIES OBJECT_DEPENDS myplugin.json)

  http://www.cmake.org/cmake/help/v2.8.12/cmake.html#prop_sf%3aOBJECT_DEPENDS

Greets

PS: Thanks for providing a kdevplatform_add_plugin macro (awesome!)

-- 
Kevin Funk | kfunk at kde.org | http://kfunk.org