Travis ships with an older version of ghc (I think its 7.8) and cabal. But many projects either rely on newer versions of ghc, such as elm-init or want to be compatible with older ghc, such as ja-base-extra. This requires building with either a different version of ghc or multiple ghc/base library versions.
There’s a wonderful project by a github user named @hvr. The project itself is called multi-ghc-travis and provides an example .travis.yml which configures a matrix of build environments for travis based on as many ghc and cabal versions as you require by manually downloading and installing the necessary ghc ppa’s on the build VM.
This is great and all, however bears a downside as it requires root privileges in the VM to add ppa’s and install packages, which prohibits use of the new and faster, container based travis architecture.
There has been some nice development in container customization lately and as a result there’s now a container compatible way of customizing your Haskell build environment on travis as this section of the README shows.
The even nicer thing is that the repository also provides you with a Haskell script that automatically creates the new-style .travis.yml from your tested-with section in your .cabal file. Simply provide the script with a .cabal file and pipe the output into a file called .travis.yml and you’re pretty much set.
Now I found it rather difficult to find information on how the tested-with section in a .cabal file should look. The cabal documentation simply states that it contain list compiler.
Searching further I found that compiler is supposed to be the short name of a compiler, such as ghc version bounds for that compiler. Those version bounds are very similar to those of dependencies. Resulting in a field which looks something like this:
tested-with: GHC >= 7.0 && < 7.10, LHC >= 0.6 && < 0.8
That’s all I’ve got for now. If you’ve got something to add catch me on twitter.