[CMake] ExternalProject_Add - Automatic Incremental Rebuilds + Add Sources to IDE

[Aaron Nowack]

>
> You can structure the app CMakeLists such that it can reference the libs
> as part of a big "build everything" tree like this, or as something that
> has to be found with find_package, or as something you just point to with
> CMake variables.


Was the "parent" CMakeLists.txt an example of only how to combine the
sources, or should it be reasonably possible to do step-building? For
example, I attempted the following...

I've setup a "parent" CMakeLists.txt for the apps and libs as you described
with subdirectories for apps and libs. I build the libs first, and have it
set a variable of where the library will be installed to, named
apps_lib_path. apps_lib_path is set with PARENT_SCOPE so it is passed into
the apps/ directory.

Now, in the apps folder I must reference to the library that libs will
build. This seems to create a chicken-egg issue as I am trying to reference
a library that isn't yet created. I am using find_package(libs) which
checks several possible locations for the library, the first being
apps_lib_path for the library libApps. Since no libApps is present (hasn't
been built yet, still in the cmake stage) it is set to NOTFOUND and cmake
returns an error.

The best approach I've seen for this sort of thing so far is being used in
> the Open Cheimstry projects. They build and install everything as part of a
> "super build" into a known installation prefix in the "super build" build
> tree. Then, they use CMAKE_PREFIX_PATH and find_package to find
> *previously* built/installed sub-projects in subsequent sub-projects.
> Everything is built via ExternalProject there, but none of the individual
> projects build anything with ExternalProject -- they find everything with
> find_package. ( See their repos here: https://github.com/OpenChemistry --
> the super build is in: https://github.com/OpenChemistry/openchemistry )
>

This is a great example, so they install into a common place where each
project can use find_project(other_project) and link correctly. They force
incremental rebuilds by using ExternalProject_Add_Step.

Thanks for the help,
- Aaron

On Wed, Sep 18, 2013 at 8:51 AM, David Cole <dlrdave at aol.com> wrote:

> Ideally, for these rapid co-development phases I would like to
>> a) Be able to rebuild a project using ExternalProject_Add
>> whenever any source file changes.
>>
>
> ExternalProject is not well suited for handling source level changes.
>
>
>
>  b) Provide the mechanism for an IDE project to include all
>> the sources from another project specified by
>> ExternalProject_Add.
>>
>
> Because of my answer for "(a)", I still don't think it's a good idea.
>
>
>
>  For b) there was a bug open and closed here,
>> http://www.cmake.org/Bug/view.**php?id=12322<http://www.cmake.org/Bug/view.php?id=12322>
>>
>> I understand David's point about making bad assumptions, but I would
>> find it extremely useful if I was able to include the sources and
>>
> force a
>
>> rebuild as I'm describing.
>>
>
> I understand, and many others would also find it useful, but I doubt it
> can be done reliably. If somebody would like to prove me wrong, (on Windows
> with all supported versions of Visual Studio, and on the Mac with all
> versions of Xcode, and with Eclipse, and ...), I will gladly reverse my
> opinion.
>
>
>
>  Does anyone have any ideas? We're currently doing a lot of
>>
> refactoring on
>
>> both repositories so removing as much development overhead will really
>> help. When things get stable we will be using ExternalProject_Add on
>> tagged revisions.
>>
>
> The best solution for rapid co-development of multiple repositories is NOT
> to use ExternalProject. ExternalProject, as recently discussed in another
> mailing list thread here, is best suited for building static snapshots of
> repositories that do not change frequently.
>
> Does everything build with CMake? Good. Then you can make something like
> this work:
>
>    # CMakeLists.txt
>    cmake_minimum_required(VERSION 2.8.11)
>    project(GlueLibsAndApp)
>    add_subdirectory(libs)
>    add_subdirectory(app)
>
>     # Then, checkout the two separate repositories in "libs" and "app" and
> boom: all your sources for everything are all in the generated IDE project
>
> You can structure the app CMakeLists such that it can reference the libs
> as part of a big "build everything" tree like this, or as something that
> has to be found with find_package, or as something you just point to with
> CMake variables.
>
> Then later on, you can create a super build that builds both libs and app
> separately using ExternalProject, and have that app refer to the libs built
> in that manner, rather than as targets in the same CMakeLists directory
> structure.
>
>
> The best approach I've seen for this sort of thing so far is being used in
> the Open Cheimstry projects. They build and install everything as part of a
> "super build" into a known installation prefix in the "super build" build
> tree. Then, they use CMAKE_PREFIX_PATH and find_package to find
> *previously* built/installed sub-projects in subsequent sub-projects.
> Everything is built via ExternalProject there, but none of the individual
> projects build anything with ExternalProject -- they find everything with
> find_package. ( See their repos here: https://github.com/**OpenChemistry<https://github.com/OpenChemistry>-- the super build is in:
> https://github.com/**OpenChemistry/openchemistry<https://github.com/OpenChemistry/openchemistry>)
>
>
> HTH,
> David
>
>
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