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sheaf authored
In configureRequiredProgram, we would unconditionally configure the
program, even if it was configured already. To explain why this is
problematic:

  - The programs we try to configure in this function are those that
    arise from a "build-tool-depends" field of a package.
  - If the program is not in the "unconfigured" state, we would
    unconditionally treat it as a simpleProgram.
    This means that if such a program is builtin but is not a
    simpleProgram, we might fail to configure it properly.

This problem arises when we configure programs more eagerly: when, in
the past, we might have gone looking up an unconfigured program and
successfully configured it, now we might find the program is already
configured.

One example in which this would cause an issue is when we have

   build-tool-depends: hsc2hs

If we end up re-configuring hsc2hs in configureRequiredProgram, we would
treat it as a simple program, which would cause us to be unable to
determine its version.
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Cabal

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This Cabal Git repository contains the following main packages:

The canonical upstream repository is located at https://github.com/haskell/cabal.

Ways to get the cabal-install binary

  1. GHCup (preferred): get GHCup using the directions on its website and run:

    ghcup install --set cabal latest
  2. Download from official website: the cabal-install binary download for your platform should contain the cabal executable.

Preview Releases

Getting unreleased versions of cabal-install: gives you a chance to try out yet-unreleased features. Currently, we only provide binaries for x86_64 platforms.

  1. GitHub preview release built from the tip of the master branch: download from GitHub or use this GHCup command to install:

    ghcup install cabal -u https://github.com/haskell/cabal/releases/download/cabal-head/cabal-head-Linux-x86_64.tar.gz head

    Replace "Linux" with "Windows" or "macOS" as appropriate.

    The default Linux build is dynamically linked against zlib, gmp and glibc. You will need to have appropriate versions of these libraries installed to use it. Alternatively a statically linked "Linux-static" binary is also provided.

    You might need to add the following to your cabal.project file if your build fails because of an out-of-date Cabal library:

    allow-newer:
      *:Cabal,
      *:Cabal-syntax
    
    source-repository-package
        type: git
        location: https://github.com/haskell/cabal.git
        subdir: Cabal Cabal-syntax
  2. Even more cutting-edge binaries built from pull requests are always available from the Validate worklow page on GitHub, at the very bottom of the page, or from the build-alpine workflow for statically linked Linux builds.

Ways to build cabal-install for everyday use

  1. With cabal-install: if you have a pre-existing version of cabal-install, run:

    cabal install cabal-install

    to get the latest version of cabal-install. (You may want to cabal update first.)

  2. From Git: again with a pre-existing version of cabal-install, you can install the latest version from the Git repository. Clone the Git repository, move to its root, and run:

    cabal install --project-file=cabal.release.project cabal-install
  3. Bootstrapping: if you don't have a pre-existing version of cabal-install, look into the bootstrap directory.

Learn how to use cabal and get support

cabal comes with a thorough User Manual. If you are new to cabal and want to quickly learn the basics, check Getting Started With Haskell and Cabal.

Got questions? Ask in Haskell Matrix (online chat) or Haskell Discourse.

Build for hacking and contributing to cabal

Refer to CONTRIBUTING.md.