Helping Travis catch the rustc train
I’ve been putting off configuring my continuous integration settings to match the Rust train model: it involves non-trivial branching on the configuration, and duplicating that over a pile of repos is not something I looked forward to. So, instead, I wrote travis-cargo to make things easier.
Branching on configuration?
One approach to developing Rust libraries once 1.0 is released will be to test by building with the latest stable compiler, to ensure that code is behaving as one hopes. I’m sure this will work well enough, but it’s missing an important part of the release model
Rust is adopting “trains” for releases, where features migrate from unstable to beta and then on to stable. That beta period is a big motivation for the approach: before releases become stable, there is 6 weeks of development for people to test their code and help ensure backwards compatibility isn’t accidentally broken. If there is a regression, it will be assessed and presumably fixed before the stable release. There is effort on going to incorporate this sort of checking into crates.io—brson has been posting regular regression reports recently—but this doesn’t cover all cases: at the very least, not all code is on crates.io.
The easiest way to get code to be tested is to have continuous integration infrastructure like Travis CI running tests against all configurations of interest: for a lot of code this is likely to mean running builds against the most recent stable release, the current beta, and the current nightly, and I forsee that some libraries may wish to compile against slightly older versions too. And having three builds for everything is just the start.
The nightly compilers offer unstable features that are fully
disallowed on the beta and stable channels, and libraries may wish to
offer or use functionality that is only enabled with unstable
compilers. At the moment, a big example is
#[bench], running them requires
importing the feature-gated
test crate: I configure my libraries to
unstable feature that has to be activated for
nightly-only features like benchmarks to be compiled in, so that the
library and its tests can be run with stable and beta compilers.
Unfortunately, all this means it is a little tricky to configure CI optimally so that nightly builders build with unstable features, and stable builds don’t. That said, It’s not that tricky, for example, using Travis’ Build Matrix functionality.
The final nail in the coffin is that I and others use CI to upload
rendered documentation for successful builds of the master branch:
method I usually use involves a big chunk of commands,
and requires manually inserting the library name. Having a separate
script allows me to use hoverbear’s code but abstracted out in a
DRY-er way. (The script even calls
cargo directly to extract the
true library name, straight from the horse’s mouth.)
Travis-cargo by example
Update 2015-05-01: the details of the code here has now changed but the explanation is still the same, see Travis on the train, part 2 for the up-to-date version of the code.
The interesting bit of the Travis configuration I’m now using for,
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 language: rust # run builds for both the nightly and beta branch rust: - nightly - beta # load travis-cargo before_script: - git clone --depth 1 https://github.com/huonw/travis-cargo # make a short alias (`alias` itself doesn't work) - ln -s ./travis-cargo/travis-cargo.py tc # the main build script: - | ./tc cargo build && ./tc cargo test && ./tc cargo bench && ./tc cargo doc after_success: # upload the documentation from the build with beta (automatically only actually # runs on the master branch) - ./tc --only beta doc-upload # ...
which makes builds look like (look at the two jobs!):
And, it’s exactly the same configuration that I’m using for my other
libraries, other than the chunk of
secure nonsense at the end (the
encrypted Github token).
tc cargo ... just runs cargo, but implicitly adds
unstable when running the
rust: nightly configuration (and
--verbose by default for all configurations). The command
doc-upload pushes the docs rendered by
cargo doc to the main repo,
but with multiple configuration this may result in “races”/displaying
documentation for an undesired or inconsistent configuration: the
--only beta argument ensures that it only runs in the
On the point of uploading docs: I imagine/hope there will be some sort of crates.io-based doc hosting in future which makes manually hosting docs less imperative. However, that day isn’t here yet, and that host will presumably only have docs for released crates, being able to easily host documentation for the cutting-edge master branch still seems handy.
Once we have a stable release, I intend to add
- stable to
--only stable; I believe these should be
the only changes necessary to get reliable testing against all three
Also, the manual passing of an unstable flag may become moot in
future, if the
compiler itself supports a
further reducing the necessity for this script.
The travis-cargo repo contains a README with more details, and the script itself.
(Thanks to hoverbear for their original code, and bluss for their similar shell script for inspiration.)