# Travis CI

For many use cases, the
[Travis caching section of the user guide](GUIDE.md#travis-with-caching)
will be sufficient.

This page documents how to use Stack on [Travis CI](https://travis-ci.org/). We
assume you have basic familiarity with Travis.

*Note:* both Travis and Stack infrastructures are actively developed. We try to
 document best practices at the moment.

## Container infrastructure

For Stack on Travis to be practical, we must use caching. Otherwise build times
will take an incredibly long time, about 30 minutes versus 3-5. Caching is
currently available only for
[container-based Travis infrastructure](http://docs.travis-ci.com/user/workers/container-based-infrastructure/).
Shortly we have to add

```yaml
sudo: false

# Caching so the next build will be fast too.
cache:
  directories:
  - $HOME/.stack
```

To the `.travis.yml`. This however restricts how we can install GHC and Stack on
the Travis machines.

## Installing Stack

Currently there is only one reasonable way to install Stack: fetch precompiled
binary from the Github.

```yaml
before_install:
# Download and unpack the stack executable
- mkdir -p ~/.local/bin
- export PATH=$HOME/.local/bin:$PATH
- travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
```

Once Travis whitelists the stack .deb files, we'll be able to simply include
stack in the `addons` section, and automatically use the newest version of
stack, avoiding that complicated `before_install` section This is being
tracked in the
[apt-source-whitelist](https://github.com/travis-ci/apt-source-whitelist/pull/7)
and
[apt-package-whitelist](https://github.com/travis-ci/apt-package-whitelist/issues/379)
issue trackers.

## Installing GHC

There are two ways to install GHC:

- Let Stack download GHC
- Install GHC using [apt plugin](http://docs.travis-ci.com/user/apt/)

See the
[Travis caching section of the user guide](GUIDE.md#travis-with-caching) for
an example of the first option (letting Stack download GHC). Here, we will
explain the second option. With single GHC the situation is simple:

```yaml
before_install:
  - export PATH=/opt/ghc/7.10.2/bin:$PATH

addons:
  apt:
    sources:
    - hvr-ghc
    packages:
    - ghc-7.10.2
```

### Multiple GHC - parametrised builds

Travis apt plugin doesn't yet support installing apt packages dynamically
(https://github.com/travis-ci/travis-ci/issues/4291). That for we need to write
a bit repetitive `.travis.yml`.

Also for different GHC versions, you probably want to use different `stack.yaml`
files.

```yaml
# N.B. No top-level env: declaration!

matrix:
  include:
  - env: GHCVER=7.8.4 STACK_YAML=stack.yaml
    addons:
      apt:
        sources:
        - hvr-ghc
        packages:
        - ghc-7.8.4
  - env: GHCVER=7.10.1 STACK_YAML=stack-7.10.yaml
    addons:
      apt:
        sources:
        - hvr-ghc
        packages:
        - ghc-7.10.1
  - env: GHCVER=head STACK_YAML=stack-head.yaml
    addons:
      apt:
        sources:
        - hvr-ghc
        packages:
        - ghc-head
  allow_failures:
    - env: GHCVER=head STACK_YAML=stack-head.yaml

before_install:
  # ghc
  - export PATH=/opt/ghc/$GHCVER/bin:$PATH
```

Especially to use ghc `HEAD` you need to pass `--skip-ghc-check` option to Stack.

## Running tests

After the environment setup, actual test running is simple:

```yaml
script:
  - stack --no-terminal --skip-ghc-check test
```

## Other details

Some Stack commands will run for long time (when cache is cold) without
producing any output. For Travis not to timeout, one can wrap commands in
[a simple script](https://github.com/futurice/fum2github/blob/master/travis_long).

```yaml
install:
  - ./travis_long stack --no-terminal --skip-ghc-check setup
  - ./travis_long stack --no-terminal --skip-ghc-check test --only-snapshot
```

## Examples

- [futurice/fum2github](https://github.com/futurice/fum2github/blob/master/.travis.yml)
- [haskell-distributed/cloud-haskell](https://github.com/haskell-distributed/cloud-haskell/blob/master/.travis.yml)
- [simonmichael/hledger](https://github.com/simonmichael/hledger/blob/master/.travis.yml)
- [fpco/wai-middleware-crowd](https://github.com/fpco/wai-middleware-crowd/blob/master/.travis.yml)
- [commercialhaskell/all-cabal-hashes-tool](https://github.com/commercialhaskell/all-cabal-hashes-tool/blob/master/.travis.yml)