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

[David Cole]

> 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
>
> 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 -- the super build is in: 
https://github.com/OpenChemistry/openchemistry )


HTH,
David