an extensible project to build (or copy pre-built) external (3rd-party) projects
externpro supports options for 4 steps: mkpatch (make patch), download, patch, build -- with patch being the default option
externpro makes heavy use of cmake's ExternalProject module
for each project in the projects directory which implements a mkpatch_project-name cmake function, the mkpatch step: clones a repository, does a checkout of a specified branch or hash, and creates a patch -- this is how the patches directory is populated and updated
this is typically a task done by a single maintainer - others developers who wish to use externpro aren't usually doing this step
for each project in the projects directory which implements a download_project-name cmake function, the download step: downloads and/or verifies the md5 of a compressed archive of a specified URL -- this is how the externpkg directory is populated and updated
we are also maintaining externpkg as a git submodule (separate repository) to reduce how often we're downloading from the internet
executing this step produces a directory structure suitable for light transport - burn to media to take into a closed environment or disconnect from the internet and you'll still be able to execute the next steps
for each project in the projects directory which implements a patch_project-name cmake function, the patch step: downloads the compressed archive (if it hasn't already been downloaded), verfies the md5, expands the compressed archive, and applies the patch (made by mkpatch, if one exists)
executing this step produces the source code in a patched state, suitable for debugging and stepping into the source
if a developer already has externpro installed (using the installer produced by the build step below), they can simply run the patch step (on an externpro revision that matches their installed revision) and are now able to debug and step into third party code
for each project in the projects directory which implements a build_project-name cmake function, the build step: makes sure the patch step has been executed, then builds the project with the compiler (aka cmake generator) detected or specified at cmake-time of externpro
externpro also contains cmake options to specify different build platforms (32, 64 bit) and configurations (release, debug, multiple release runtime support with MSVC) - all of these platforms and configurations are built at build-time of externpro
the package target of externpro will build an installer suitable for the OS on which you're building
- compiler choice and compatibility - build third-party projects with the same compiler you're using with your project
- version choice - choose the exact version of a third-party project you want to employ in your project (can be bleeding edge or trailing what's available via other means)
- patch - apply fixes or tweaks you've found to be necessary or easily cherry-pick a fix from a version you're not ready to move to yet
- consistency across platforms - every OS can be using the same (perhaps patched) version of third-party code
- platform choice - build for the OS and architecture you support
- build configuration choice - support debug builds for stepping into code (and gaining understanding) and release configurations that utilize different runtimes (DLL or static)
- compiler flags - consistency across all third-party libraries and your project(s) is often required (c++11, fpic, libumem on Solaris)