R Dev Container: Multi-platform build of the Docker container

[hturner]

The R Dev Container was primarily built for use with GitHub Codespaces (now extended to Gitpod Workspaces), so the underlying Docker container is built for linux/amd64 architecture. This means that it doesn't work well on M+ macOS or Windows as discussed in issue 112 of the R Dev Container repo.

@StarTrooper08 has attempted to use buildx to build a linux/amd64 image but got stuck.

If anyone with experience in this area can help us make progress on this issue it would be appreciated!

[hturner]

Notes from RSECon24 added to https://github.com/r-devel/r-dev-env/issues/112. t

To summarise: The dockerfile uses the Ubuntu r-project repo to install r-base-core when building the container, but this doesn't have a recent arm build (most recent when we tried was 4.1.2). There may be a more recent arm build in the debian r-project repo, so that may be a potential solution.

[sjimellor-jr]

A few findings from looking into this issue.

• GitHub Actions do not support ARM for non-Enterprise customers (reference: https://github.com/github/roadmap/issues/970). We will not be able to natively build ARM containers in GitHub Hosted Actions for now.
• The Debian OS packages do not include ARM builds of R (same issue as Ubuntu) - the ARM reference in the CRAN documentation is for some R packages available via Debian repos only. (tested with FROM mcr.microsoft.com/devcontainers/cpp:dev-debian-12 and suitable deb reference changes)
• The dev container contains everything needed to build R if you stop just after apt -y build-dep r-base-dev, you just don't have any version of R installed to initially test with, and don't have the language server R packages installed yet. But once a build has completed within the container, you can continue - this avoids the missing r-base-dev dependency on ARM completely.
• Docker builds can emulate ARM using QEMU via binfmt on x86_64 (reference: https://github.com/docker/buildx?tab=readme-ov-file#building-multi-platform-images). apt-src can be used to build r-base-dev instead of installing it, but this was extremely slow on non-ARM hardware although may complete if given ~24 hours (about 15 times the build time).
• Cross compiling with https://github.com/tonistiigi/xx may provide native performance for a build, suitable for use in a GitHub Action, to provide R within a dev container. (about twice the build time)
• Attempts to use apt-src in combination with xx to cross compile the r-base-dev Debian package source have not succeeded (dpkg-buildpackage fails with missing dependencies, because we used the x86 package source, or "No such file or directory", "clang: error: no input files" if we ignore missing dependencies)
• A combination of using xx to build the source binary, and buildx to create an ARM container (copying in the stable build), may provide a fully functional dev container.

Current status:

• An ARM native dev container can be built on non-ARM if an existing R build is not required within it.
• An ARM native dev container with an R build inside it may be built if we had ARM hardware to do the build.
• An ARM native dev container may be cross compiled with additional research, or emulated with a very long build time.

[hturner]

Thanks @sjimellor-jr for digging into this! Your (off GitHub) comment about "why there isn't an ARM build of the Debian/Ubuntu package in the first place" got me wondering and after some searching around I found from the rocker/r-ubuntu Dockerfile that they use "ppa:marutter/rrutter4.0" as the repository vs "https://cloud.r-project.org/bin/linux/ubuntu jammy-cran40/". I tried building from the R Dev Container Dockerfile with Michael Rutter's base R PPA as the R repository and the build was successful on my ARM machine!

I think we will now be able to get this working with buildx. I'll leave this issue open for the moment and hopefully update it when we've got that working!