travis.yml

# The Travis docs (https://docs.travis-ci.com/user/languages/haskell)
# suggest that we use `language: haskell` and `ghc:` to specify GHC versions.
# However, as of this writing, Travis only supported versions up to 7.8.
# If Travis supports all versions we would like to test, then we could switch.
# Until then, we use the https://github.com/haskell-CI/haskell-ci setup.
language: c
addons:
  apt: &apt
    sources:
      - hvr-ghc
matrix:
  # Cabal version selection:
  # In all cases, need 2.0 for new-test.
  # Note which versions each https://www.haskell.org/cabal/download.html indicates.
  # Using an older version will still allow build to succeed but will warn:
  # "Warning: Unknown/unsupported 'ghc' version detected (Cabal 2.4.1.0 supports
  # 'ghc' version < 8.7): /opt/ghc/bin/ghc-8.8.1 is version 8.8.1"
  include:
    # All development machines are >= this version.
    - compiler: ghc-8.10.1
      addons:
        apt:
          <<: *apt
          packages: [ghc-8.10.1, cabal-install-3.0]
    # Lowest version that the overall project will work on.
    # NumericUnderscores added in 8.6.1
    # No attempt will be made at backwards compatibility.
    - compiler: ghc-8.6.1
      addons:
        apt:
          <<: *apt
          packages: [ghc-8.6.1, cabal-install-2.4]
    # To prove that it doesn't work on older versions:
    - compiler: ghc-8.4.4
      addons:
        apt:
          <<: *apt
          packages: [ghc-8.4.4, cabal-install-2.2]
  allow_failures:
    - compiler: ghc-8.6.1
    - compiler: ghc-8.4.4
cache:
  directories:
    - $HOME/.cabal/packages
    - $HOME/.cabal/store
before_cache:
  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/build-reports.log
  # remove files that are regenerated by 'cabal update'
  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/00-index.*
  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/*.json
  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/01-index.cache
  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/01-index.tar
  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/01-index.tar.idx

  - rm -rfv $HOME/.cabal/packages/head.hackage
before_install:
  - HC=${CC}
  - unset CC
install:
  - export PATH=$(ls -d /opt/cabal/*)/bin:/opt/ghc/bin:$PATH
  - echo $PATH
  - ghc --version
  - ${HC} --version
  - cabal --version
  # I don't know why this is update and not new-update but okay
  - travis_retry cabal update -v
  # Container environment reports 16 cores when it has 2.
  # Causes slight slowdowns on `cabal build`,
  # for versions where jobs defaults to $ncpus.
  # See https://ghc.haskell.org/trac/ghc/ticket/9221
  # We fix this by explicitly changing it back to 2.
  # Still relevant as of 2019, but the difference is 4 mins vs 5 mins.
  - "sed -i.bak 's/^jobs:.*/jobs: 2/' ${HOME}/.cabal/config"
script:
  - cabal new-build -w ${HC}
  - ghc-pkg list # to debug