[CMake] How to execute an external project target as part of a standard target.

[Bill Somerville]

On 24/03/2015 18:31, David Cole wrote:
Hi David,
> How about:
>
>      add_custom_target(custom-install DEPENDS xxx-install)
>
> and
>
>      cmake --build . --target custom-install
>
> ??
OK that does work but I wanted the project to have a normal set of 
targets. The issue is that the ExternalProject in question is the actual 
purpose of the outer project but the outer project has some special 
targets that do extra stuff. For example it has a 'source' target that 
transforms the whole lot into a source tarball suitable for running on 
an isolated build machine like those used for building Linux packages. 
The same outer project CMakeLists.txt doubles as the CMakeLists.txt for 
that source package and build servers expect the "usual" targets to 
build the package contents.

I don't want to dump the whole of the real project CMakeLists.txt into 
this superbuild script and that is a maintenance hazard due to the 
duplication.

The other ExternalProjects that build required components rather neatly 
fetch from their respective repos unless the source tar ball is there 
already so they "just work" in this dual phase build process.
>
> The problem is that you are adding a custom target with the name
> "install" which is one that CMake generates for you. (Names to be
> avoided are all, clean, install, package, help ... (maybe a few
> others?))
I understand that but it works without complaint before recent CMake 
versions.
>
> I think this whole process should be unnecessary anyway, because the
> install step of the ExternalProject runs as part of the overall build,
> even with just a "cmake --build ." -- doesn't it?
Maybe, but I need to have the 'install' target run when I am running the 
custom 'source' target of the outer project.

To get this all to hang together I had to set the EXCLUDE_FROM_ALL 
property to '1' of the ExternalProject in question so it doesn't install 
when running the default target. This is necessary because we don't want 
the install phase to run when running our custom targets as 
CMAKE_INSTALL_PREFIX is set to the outer project CMAKE_INSTALL_PREFIX 
i.e. we only want this ExternalProject to install when we run the outer 
'install' target.

Sorry this is a bit complex and I may not have been clear enough. The 
basic idea works beautifully with a relatively simple low maintenance 
superbuild project that wraps a cross platform project that cannot make 
a kit suitable for Linux packaging and cannot have conventional 
ExternalProjects for the prerequisites on Windows and Mac. All was well 
until CMake started complaining about something that works.
>
>
> HTH,
> David C.
Regards
Bill Somerville.
>
> On Tue, Mar 24, 2015 at 2:21 PM, Bill Somerville <bill at classdesign.com> wrote:
>> On 13/03/2015 14:06, Bill Somerville wrote:
>>> Hi All,
>>>
>>> I have a superbuild style project consisting of a few external projects. I
>>> wish to build the install target of one of them as part of the install
>>> target of the parent project. I had it working by adding a step target
>>> called install and adding a custom target to the parent project that depends
>>> on the child step target. E.g.
>>>
>>> ExternalProject_Add (xxx
>>>    SVN_REPOSITORY ${xxx_repo}
>>>    CMAKE_ARGS
>>>      -D CMAKE_INSTALL_PATH=<INSTALL_DIR>
>>>    INSTALL_DIR ${CMAKE_INSTALL_PREFIX}
>>>    STEP_TARGETS install)
>>>
>>> add_custom_target (install DEPENDS xxx-install)
>>>
>>> This arrangement allowed me to 'cmake --build . --target install' and have
>>> the child project install target run.
>>>
>>> Now CMake complains about policy CMP0037, because I cannot define a
>>> reserved target name, so it seems I cannot abuse the 'install' target by
>>> adding extra dependencies any more.
>>>
>>> Is there a better way to link child and parent targets that doesn't invoke
>>> this error?
>> No replies on this one. Am I asking something that can't be done or am I
>> missing something obvious?
>>>
>>> Regards
>>> Bill Somerville.
>>
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