Opam and BSD Owl Support for Travis CI container-based infrastructure

This article is for users of Travis CI services interested in moving their OCaml, opam or BSD Owl projects to the new container-based infrastructure provided by Travis CI.

Travis, a continuous-integration service, introduced a new container-based infrastructure, promising more speed and reactivity than the old virtual-machine-based infrastructure, which is now deemed deprecated. Users willing to take the move to the new infrastructure are facing a major obstacle: the container-based infrastructure does not support the sudo command, which, in cascade, implies that the Travis users are not able any-more to install packages from random package sources. These dependencies now need to be installed from source until you arrange so that a repository containing these dependencies has been white-listed.
The script anvil_travisci_autoinstall.sh distributed with anvil will ease this operation for OCaml, opam and BSD Owl users!

Setting up Travis

We set up Travis to take advantage of its cache, which is not optional since a compilation matrices involving the three latest OCaml compilers needs about 15 minutes setup. For the purpose of the discussion, we consider the example of mixture, an OCaml library implementing common mixins. Let us walk through its .travis.yml file:

language: c
sudo: false
addons:
  apt:
    sources:
    - avsm
    packages:
    - ocaml
    - opam
    - ocaml-native-compilers
install: sh -ex ./Library/Ancillary/autoinstall bmake bsdowl opam
cache:
  directories:
  - ${HOME}/.local
  - ${HOME}/.opam
script: sh -ex ./Library/Ancillary/travisci
env:
  - TRAVIS_OCAML_VERSION=4.00.1
  - TRAVIS_OCAML_VERSION=4.01.0
  - TRAVIS_OCAML_VERSION=4.02.3

The first declarations, language, sudo and addons constitute the typical prelude of OCaml projects. The script ./Library/Ancillary/autoinstall installs dependencies from sources and initialises opam. The sources are installed to ${HOME}/.local and opam files are stored in ${HOME}/.opam, caching these files allows us to skip completely this step in case of a cache hit. We present the autoinstall script later, but right now we want to take a look at the last lines of .travis.yml: it defines the actual continuous integration script and a build environement matrix.
The continuous integration script is everything but fancy, it setups opam to target the compiler announced by TRAVIS_OCAML_VERSION and runs the traditional autoconf; ./configure; bmake all combo:

INSTALL_PREFIX="${HOME}/.local"
eval $(opam config env)
autoconf
./configure --prefix="${INSTALL_PREFIX}"
bmake -I "${INSTALL_PREFIX}/share/bsdowl" all

The autoinstall script

The script installing dependencies from sources actually delegates the job to anvil_travisci_autoinstall.sh. Theoretically, this script could be bundled in the distribution instead of being downloaded, but doing so eases updates. The autoinstall script is:

: ${local:=${HOME}/.local}
: ${srcdir:=${HOME}/.local/sources}

if [ -f "${local}/.anvil_autoinstall_cached" ]; then exit 0; fi

git clone 'https://github.com/michipili/anvil' "${srcdir}/anvil"
/bin/sh -ex "${srcdir}/anvil/subr/anvil_travisci_autoinstall.sh" "$@"\
    && touch "${local}/.anvil_autoinstall_cached"

When the installation is succeful, it leaves a cookie in the cache, whose existance guards an early exit condition. The autoinstall script supports three arguments, bmake, bsdowl and opam requiring the setup of the corresponding packages. When setting up opam the file .travis.opam is read to find out which compilers and packages need to be installed:

compiler:
  - 4.00.1
  - 4.01.0
  - 4.02.3
repository:
  - ocamlfind
git:
  - https://github.com/michipili/broken.git

The syntax of this file imitates the YaML format used in .travis.yml but it is converted to a tabular format with sed so that imaginative formatting is discouraged. There is two ways to specify a dependant package: either by reffering to a name in the official repository, or directly with a git repository supporting opam pinning.