DIY External Project

With dep you can download, build, and install projects using the familiar ExternalProject syntax at configuration time.

But why?

FetchContent - https://cmake.org/cmake/help/latest/module/FetchContent.html

CMake 3.11 introduced the module FetchContent which at a first glance does exactly what this project aims at. However, instead of building and installing libraries it makes other (CMake) projects available to be built as part of your own build setup. Obviously, this does not work for non-cmake projects.
ExternalProject - https://cmake.org/cmake/help/latest/module/ExternalProject.html

When CMake was kind of new and very awkward to use, it at least had the module ExternalProject. It is great except it does everything at build time which is a huge flaw since what you should be using CMake for is to detect dependencies at configure time. This project fixes that flaw.

Alternatives?

Hunter - https://github.com/cpp-pm/hunter

A package manager that has been around since 2013 (give or take).

Examples!

option(BUILD_PREBUILTLIB "Build a prebuilt lib" ON)
if(BUILD_PREBUILTLIB)
   dep_build(libprebuilt
      DOWNLOAD_STEP
      URL "https://no.virus.promiz/releases/prebuiltlib.zip"
      TIMEOUT 10

      INSTALL_STEP
      INSTALL_COMMAND ${CMAKE_COMMAND} -E copy_if_different "\$\{_source_dir\}/prebuilt.h" "\$\{_install_prefix\}/include/dumb_directory"
      Linux_x86_64
      COMMAND ${CMAKE_COMMAND} -E copy_if_different "\$\{_source_dir\}/liblin64.a" "\$\{_install_prefix\}/lib"
      Windows_AMD64
      COMMAND ${CMAKE_COMMAND} -E copy_if_different "\$\{_source_dir\}/libwin64.lib" "\$\{_install_prefix\}/lib"
      )
endif()

dep_package(libprebuilt my_prebuilt_target
   FILES
   IN_DIRECTORY dumb_directory
   prebuilt.h

   LIBS
   Linux_x86_64 liblin64.a
   Windows_AMD64 libwin64.lib
   )

option(BUILD_SOMECMAKEPROJECT "Build some CMake project that I need" ON)
if(BUILD_SOMECMAKEPROJECT)
   dep_build(somename
      SUPPORTS_DEBUG

      DOWNLOAD_STEP
      GIT_REPOSITORY "https://github.com/myfavoritedeveloper/someproject.git"
      GIT_TAG "1.2.3"
      GIT_SHALLOW True

      CMAKE_OPTIONS
      -DSOME_SETTING=OFF
      -DBUT_I_DO_NEED_THIS=ON
      )
endif()

dep_package(somename my_cmake_dependency
   SUPPORTS_DEBUG

   DEPENDS
   my_prebuilt_target

   FILES
   somedir/someheader1.h
   somedir/someheader2.h

   LIBS
   debug somelibd
   optimized somelib
   )

target_link_libraries(myproject INTERFACE my_cmake_dependency)

Customization

There are three properties that can be set in order to modify the functionality of dep.

DEP_DIRECTORY - of type DIRECTORY

The path to where dep will put all the stuff. This directory serves as both a working directory (where downloads, source unpacking, and build data is located) as well as the install directory (where the dependencies are all installed to). Unless explicitly set, it will default to "${CMAKE_SOURCE_DIR}/dep".

Protip: If you build your project with multiple compilers (e.g. gcc and clang), or if you are on Windows and want to use both msvc and your favorite compiler under wsl, do something like the following
```
set_property(DIRECTORY PROPERTY DEP_DIRECTORY "${CMAKE_SOURCE_DIR}/dep/${CMAKE_CXX_COMPILER_ID}-${CMAKE_CXX_COMPILER_VERSION}")
```
That way, the dependencies will not collide between your various build setups.
DEP_NONDEBUG_CONFIG - of type DIRECTORY

The build type that should be used for non-debug builds. This is the version of the dependency that will be used by default. Unless explicitly set, it will default to Release.
DEP_DEBUG_CONFIG - of type DIRECTORY

The build type that should be used for debug builds. This is the version of the dependency that will be used whenever the dependency is marked with SUPPORTS_DEBUG and your project is built with a build type that is listed in the GLOBAL property DEBUG_CONFIGURATIONS. Unless explicitly set, it will default to Debug.

Quirks