How to build cmake ExternalProject while configurating main one?

Question

It can be a pain to refrence ExternalProjects when their install targets are messed up. So one may want to build and install ExternalProjects once before generating main pro

Answer 1

You may use cmake call within execute_process for configure and build CMake project, which contains ExternalProject:

other_project/CMakeLists.txt:

project(other_project)
include(ExternalProject)

ExternalProject_Add(<project_name> <options...>)

CMakeLists.txt:

execute_process(
    COMMAND ${CMAKE_COMMAND} --build . ${CMAKE_SOURCE_DIR}/other_project
    WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/other_project
)

Such a way other_project will be configured and built (because of --build option) in directory ${CMAKE_BINARY_DIR}/other_project. If you do not disable installation in ExternalProject_Add call, then it will performed when building other_project.

Normally, you want some options to ExternalProject, like SOURCE_DIR, BINARY_DIR, INSTALL_DIR, to be deduced from variables in the main project. You have two ways for achive that:

1. Create CMakeLists.txt for other_project with configure_file, called from main project (before execute_process command).

2. Pass variables from main project as -D parameters to ${CMAKE_COMMAND}.