[cmake-developers] Extracting target metadata, IDE integration

[Tobias Hunger]

Hi Aleix,

thank you for the ping:-)

Since I am not fully fluent with cmake (have not really used it in a
couple of years) and sometimes have a bit of trouble following the
discussion about the details of this patch, I took the liberty to
copy/paste (and part of) one of the example files you put up on KDEs
codepaster, commenting on what I understood each section to mean. I
think that is the best way for me to contribute to this discussion at
this point.

What are you actually building here? /home/kde-devel/tmp/llvm/CMakeLists.txt?

> {

How about adding some information on what this is you are actually
building here? CMake has the PROJECT command that does provide quite a
bit of information that could go here.

Where are the sources this thing here is building? How were those
sources configured? CMake supports quite a few generators, so which
ones where used? Do I need to run ninja or make to build this (or
should I use "cmake build" anyway)?

Creator does allow existing qmake builds to be imported and that kind
of information does help a lot with that functionality.

> "dependencies" :
> [ "/home/kde-devel/tmp/llvm/build/CMakeFiles/3.2.20150306-g139588/CMakeSystem.cmake", "/lots/more/files", ... ]

So these are all the files I need to watch for changes? If they change
then I should re-run cmake?

> "targets" :
> [

So now comes a list of the possible things I can build...

>   {
>     "backtrace" :
>     [
>       "/home/kde-devel/tmp/llvm/cmake/modules/AddLLVM.cmake:312",
>       "/home/kde-devel/tmp/llvm/cmake/modules/AddLLVM.cmake:399",
>       "/home/kde-devel/tmp/llvm/lib/Target/PowerPC/TargetInfo/CMakeLists.txt:1"
>     ],

That backtrace is nice!

>    "configs" :
>    [
>        {
>            "name" : "",

Why is the name empty?

>            "output" : "/home/kde-devel/tmp/llvm/build/lib/libLLVMPowerPCInfo.a",

Can this be a list?

>            "sources" : [ "/list/of/cpp/files, ]

Any way to also get the headers? Do you see any option to hint where
new sources would need to be added to make them a part of this target?

>        }
>    ],
>    "installed" : "true",

I guess this means "make install" will install it. Where will this file end up?

>    "name" : "LLVMPowerPCInfo",
>    "output_directory" : "/home/kde-devel/tmp/llvm/build/lib/Target/PowerPC/TargetInfo",

For what is the output directory relevant? The output above does
implicitly list that already, doesn't it?

>    "type" : "STATIC_LIBRARY"

Which types are possible here?

> },


There is a lot of useful information here! Thanks for pushing into
this direction. I am sure this will help a lot.

Ideally this file would be enough to provide all information we need
as an IDE to:

* Present the project structure as seen by the build system.
* Generate the code model
* Build the project
* Deploy the project
* Run and debug parts of the project
* Adding and removing files to a project

For the project structure this does help: It provides us with a list
of all the build targets, which is already nice. CMake does support
more structure with Projects and subprojects IIRC and that information
is lost. Would it be much work to get that information back?

For the code model this is not much help at all: There is no
information on compiler used, include directories nor Defines or
compiler flags. Where am I supposed to get that information from? Do I
need to generate and parse the list of commands run and extract that
information from there? Having that information available right in the
sources array of each target would be so much more convenient and
would also make IDE integration so much easier: You would need to know
about one file only and won't need to figure out several.

Building the project should be fine with the information provided.
Explicitly stating the generators used would help a little bit (even
better just giving the command necessary to build, e.g. make or ninja
or whatnot. Then we would not need to hard-code the mapping of
generators->build tools, which makes it much easier for you to support
new things:-)

Running/Debugging is a bit tricky again: All the information used for
linking the binaries is gone. So there is no way to figure out which
LD_LIBRARY_PATH needs to be set or anything. There also seems to be no
information where files are going to get installed to. Would it be
possible to add that information?

I do not see any way to provide a reliable automatic way to add
sources to a cmake build system (the others are unfortunately not
better:-). For removing the files it would be nice to know where in
which file/line the sources were added to the target. Not sure whether
it is even possible to get that information... The backtrace you have
is already great piece of information: At least that way we should be
able to open the right file and have the user edit that manually.

Does this help?

Best Regards,
Tobias