This folder is where we put BUILD.bazel files for external (e.g. third party) dependencies.

If a dependency supports Bazel, we should use those rules, but if the dependency does not, we need to create our own rules in a subdirectory.

We generally compile third_party deps from source. If we do, we clone the repository and use the given BUILD.bazel file to build it. This is specified in the WORKSPACE.bazel (e.g. new_local_repository or new_git_repository) and we refer to those targets using labels like @freetype, or @libpng.

Some third_party deps we only link against prebuilt versions. For those, we do not involve WORKSPACE.bazel and link to them directly, e.g. //bazel/external/fontconfig.