cmake-deps-example-proxygen

An example showing how to handle dependencies with CMake, here using Proxygen. It goes with this blog post.

Warning: This is not trying to do anything useful with Proxygen! I just chose it as an example because it is not trivial to build its dependencies.

How to build

This project depends on Proxygen, which has a few dependencies (listed here).

With a package manager

It turns out that Proxygen is available in the Arch AUR repo. That means that it can be installed e.g. using yay.

It can be done like this:

1. Install the dependencies:

   yay -S proxygen
   

2. Build the project

   cmake -Bbuild -S.
   cmake --build build
   

The limitation here is that your package manager may not have Proxygen. For instance, it was outdated when I first tried it, and therefore unavailable.

With the helper script

1. Build the dependencies and install them into ./dependencies/install:

   cmake -DCMAKE_INSTALL_PREFIX=dependencies/install -DCMAKE_PREFIX_PATH=$(pwd)/dependencies/install -Bdependencies/build -Sdependencies
   cmake --build dependencies/build
   

Have a look into dependencies/install, and see that they were installed locally. Now we can tell CMake to look there when using find_package, by providing the path: -DCMAKE_PREFIX_PATH=/path/to/dependencies/install.

2. Build the project using the dependencies installed in step 1:

   cmake -DCMAKE_PREFIX_PATH=$(pwd)/dependencies/install -Bbuild -S.
   cmake --build build
   

About the CI

The CI runs the helper script. That's very convenient because as a result, it does not result in a custom package manager. Also it gets very useful for cross-compiling.

Finally, because the dependencies are installed locally, it's extremely easy to cache them:

- uses: actions/cache@v2
  id: cache
  with:
    path: ./install
    key: ${{ github.job }}-${{ hashFiles('./dependencies/**') }}

Here we tell the CI to cache all the files that are in ./install at the end of a successful build (note that ./install is where the CI installs them, instead of ./dependencies/install above).

Then we can just tell the CI to not build the dependencies if they are already in the cache:

if: steps.cache.outputs.cache-hit != 'true'