Sunday, February 7, 2021

Configuring Cabal Build Flags

*markdown-output*

Configuring Cabal build flags

It’s always an emergency when I go looking for this information!

Suppose you are building HLint.

mkdir ~/tmp && cd ~/tmp
curl -o hlint-3.2.7.tar.gz https://hackage.haskell.org/package/hlint-3.2.7/hlint-3.2.7.tar.gz
gunzip  hlint-3.2.7.tar.gz && tar xvf  hlint-3.2.7.tar

Left to their own devices, HLint and ghc-lib-parser-ex will default to auto mode meaning, they will decide for themselves if they should depend on ghc-lib-parser or native ghc libraries.

Sometimes it’s desirable to force the situation though and explicitly make them do one or the other. How you do that? The answer is of course package Cabal flags. There are two scenarios: building with stack or building with cabal.

  • stack.yaml

    • Force link with ghc-lib-parser

        flags:
          hlint:
            ghc-lib: true
          ghc-lib-parser-ex:
            auto: false
            no-ghc-lib: false
    • Force link with native ghc

        flags:
          hlint:
            ghc-lib: false
          ghc-lib-parser-ex:
            auto: false
            no-ghc-lib: true
  • cabal.project

    • Force link with ghc-lib-parser

        packages: hlint-3.2.7
        package hlint
          flags: +ghc-lib
        package ghc-lib-parser-ex
          flags: -auto -no-ghc-lib
    • Force link with native ghc

        packages: hlint-3.2.7
        package hlint
          flags: -ghc-lib
        package ghc-lib-parser-ex
          flags: -auto +no-ghc-lib