[cmake-developers] ExternalProject can't have interface library as a dependency

[Brad King]

On 04/21/2015 03:34 AM, Andrey Pokrovskiy wrote:
> CMake Error at /usr/share/cmake/share/cmake-3.2/Modules/ExternalProject.cmake:2031
> (get_property):
>   INTERFACE_LIBRARY targets may only have whitelisted properties.  The
>   property "_EP_IS_EXTERNAL_PROJECT" is not allowed.
> Call Stack (most recent call first):
>   /usr/share/cmake/share/cmake-3.2/Modules/ExternalProject.cmake:2328
> (_ep_add_configure_command)
>   src/libwebsockets/CMakeLists.txt:21 (ExternalProject_Add)

Fixed:

 ExternalProject: Allow dependencies on INTERFACE libraries
 http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=4bce6c5d

> My first idea was that having a whitelist for get_property() is
> probably not that good idea.

The idea is to restrict INTERFACE libraries as much as possible to
intended use cases so we can expand later without breaking projects
depending on undefined behavior.

> Why there is a special case when dependency is also an external project?

When one external project depends on another then we add both
the target-level ordering dependencies (add_dependencies) and
add file-level dependencies on the stamp files so that things
re-run when needed.

-Brad