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depot/pkgs/development/haskell-modules/HACKING.md
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Maintainer Workflow

The goal of the @NixOS/haskell team is to keep the Haskell packages in Nixpkgs up-to-date, while making sure there are no Haskell-related evaluation errors or build errors that get into the Nixpkgs master branch.

We do this by periodically merging an updated set of Haskell packages on the haskell-updates branch into the master branch. Each member of the team takes a two week period where they are in charge of merging the haskell-updates branch into master. This is the documentation for this workflow.

The workflow generally proceeds in three main steps:

  1. create the initial haskell-updates PR, and update Stackage and Hackage snapshots
  2. wait for contributors to fix newly broken Haskell packages
  3. merge haskell-updates into master

Each of these steps is described in a separate section.

There is a script that automates the workflow for merging the currently open haskell-updates PR into master and opening the next PR. It is described at the end of this document.

Initial haskell-updates PR

In this section we create the PR for merging haskell-updates into master.

  1. Make sure the haskell-updates branch is up-to-date with master.

  2. Update the Stackage Nightly resolver used by Nixpkgs and create a commit:

    $ ./maintainers/scripts/haskell/update-stackage.sh --do-commit

  3. Update the Hackage package set used by Nixpkgs and create a commit:

    $ ./maintainers/scripts/haskell/update-hackage.sh --do-commit

  4. Regenerate the Haskell package set used in Nixpkgs and create a commit:

    $ ./maintainers/scripts/haskell/regenerate-hackage-packages.sh --do-commit

  5. Push these commits to the haskell-updates branch of the NixOS/nixpkgs repository.

  6. Open a PR on Nixpkgs for merging haskell-updates into master. The recommended PR title and body text are described in the merge-and-open-pr.sh section.

Notify Maintainers and Fix Broken Packages

After you've done the previous steps, Hydra will start building the new and updated Haskell packages. You can see the progress Hydra is making at https://hydra.nixos.org/jobset/nixpkgs/haskell-updates. This Hydra jobset is defined in the file release-haskell.nix.

Notify Maintainers

When Hydra finishes building all the updated packages for the haskell-updates jobset, you should generate a build report to notify maintainers of their newly broken packages. You can do that with the following commands:

$ ./maintainers/scripts/haskell/hydra-report.hs get-report
$ ./maintainers/scripts/haskell/hydra-report.hs ping-maintainers

The hydra-report.hs ping-maintainers command generates a Markdown document that you can paste in a GitHub comment on the PR opened above. This comment describes which Haskell packages are now failing to build. It also pings the maintainers so that they know to fix up their packages.

It may be helpful to pipe hydra-report.hs ping-maintainers into xclip (XOrg) or wl-copy (Wayland) in order to post on GitHub.

This build report can be fetched and re-generated for new Hydra evaluations. It may help contributors to try to keep the GitHub comment updated with the most recent build report.

Maintainers should be given at least 7 days to fix up their packages when they break. If maintainers don't fix up their packages within 7 days, then they may be marked broken before merging haskell-updates into master.

Fix Broken Packages

After getting the build report, you can see which packages and Hydra jobs are failing to build. The most important jobs are the maintained and mergeable jobs. These are both defined in release-haskell.nix.

mergeable is a set of the most important Haskell packages, including things like Pandoc and XMonad. These packages are widely used. We would like to always keep these building.

maintained is a set of Haskell packages that have maintainers in Nixpkgs. We should be proactive in working with maintainers to keep their packages building.

Steps to fix Haskell packages that are failing to build is out of scope for this document, but it usually requires fixing up dependencies that are now out-of-bounds.

Mark Broken Packages

Packages that do not get fixed can be marked broken with the following commands. First check which packages are broken:

$ ./maintainers/scripts/haskell/hydra-report.hs get-report
$ ./maintainers/scripts/haskell/hydra-report.hs mark-broken-list

This shows a list of packages that reported a build failure on x86_64-linux on Hydra.

Next, run the following command:

$ ./maintainers/scripts/haskell/mark-broken.sh --do-commit

This first opens up an editor with the broken package list. Some of these packages may have a maintainer in Nixpkgs. If these maintainers have not been given 7 days to fix up their package, then make sure to remove those packages from the list before continuing. After saving and exiting the editor, the following will happen:

  • Packages from the list will be added to configuration-hackage2nix/broken.yaml. This is a list of Haskell packages that are known to be broken.

  • hackage-packages.nix will be regenerated. This will mark all Haskell packages in configuration-hackage2nix/broken.yaml as broken.

  • The configuration-hackage2nix/transitive-broken.yaml file will be updated. This is a list of Haskell packages that depend on a package in configuration-hackage2nix/broken.yaml or configuration-hackage2nix/transitive-broken.yaml

  • hackage-packages.nix will be regenerated again. This will set hydraPlatforms = none for all the packages in configuration-hackage2nix/transitive-broken.yaml. This makes sure that Hydra does not try to build any of these packages.

  • All updated files will be committed.

Merge haskell-updates into master

Now it is time to merge the haskell-updates PR you opened above.

Before doing this, make sure of the following:

  • All Haskell packages that fail to build are correctly marked broken or transitively broken.

  • The maintained and mergeable jobs are passing on Hydra.

  • The maintainers for any maintained Haskell packages that are newly broken have been pinged on GitHub and given at least a week to fix their packages. This is especially important for widely-used packages like cachix.

  • Make sure you first merge the master branch into haskell-updates. Wait for Hydra to evaluate the new haskell-updates jobset. Make sure you only merge haskell-updates into master when there are no evaluation errors.

  • Due to Hydra having only a small number of Darwin build machines, the haskell-updates jobset on Hydra often has many queued Darwin jobs. In order to not have these queued Darwin jobs prevent the haskell-updates branch from being merged to master in a timely manner, we have special rules for Darwin jobs.

    • It is alright to merge the haskell-updates branch to master if there are remaining queued Darwin jobs on Hydra.

    • We would like to keep GHC and the mergeable job building on Darwin. Do not merge the haskell-updates branch to master if GHC is failing to build, or the mergeable job has failing Darwin constituent jobs.

      If GHC and the mergeable job are not failing, but merely queued, it is alright to merge the haskell-updates branch to master.

    • We do not need to keep the maintained job building on Darwin. If maintained packages are failing on Darwin, it is helpful to mark them as broken on that platform.

When you've double-checked these points, go ahead and merge the haskell-updates PR. After merging, make sure not to delete the haskell-updates branch, since it causes all currently open Haskell-related pull-requests to be automatically closed on GitHub.

Script for Merging haskell-updates and Opening a New PR

There is a script that automates merging the current haskell-updates PR and opening the next one. When you want to merge the currently open haskell-updates PR, you can run the script with the following steps:

  1. Make sure you have previously authenticated with the gh command. The script uses the gh command to merge the current PR and open a new one. You should only need to do this once.

    This command can be used to authenticate:

    $ gh auth login

    This command can be used to confirm that you have already authenticated:

    $ gh auth status

  2. Make sure you have setup your ~/.cabal/config file for authentication for uploading the NixOS package versions to Hackage. See the following section for details on how to do this.

  3. Make sure you have correctly marked packages broken. One of the previous sections explains how to do this.

    In short:

    $ ./maintainers/scripts/haskell/hydra-report.hs get-report
$ ./maintainers/scripts/haskell/hydra-report.hs mark-broken-list
$ ./maintainers/scripts/haskell/mark-broken.sh --do-commit

  4. Merge master into haskell-updates and make sure to push to the haskell-updates branch. (This can be skipped if master has recently been merged into haskell-updates.)

  5. Go to https://hydra.nixos.org/jobset/nixpkgs/haskell-updates and force an evaluation of the haskell-updates jobset. See one of the following sections for how to do this. Make sure there are no evaluation errors. If there are remaining evaluation errors, fix them before continuing with this merge.

  6. Run the script to merge haskell-updates:

    $ ./maintainers/scripts/haskell/merge-and-open-pr.sh PR_NUM_OF_CURRENT_HASKELL_UPDATES_PR

    Find the PR number easily here

    This does the following things:

    1. Fetches origin, makes sure you currently have the haskell-updates branch checked out, and makes sure your currently checked-out haskell-updates branch is on the same commit as origin/haskell-updates.

    2. Merges the currently open haskell-updates PR.

    3. Updates the version of Haskell packages in NixOS on Hackage.

    4. Updates Stackage and Hackage snapshots. Regenerates the Haskell package set.

    5. Pushes the commits updating Stackage and Hackage and opens a new haskell-updates PR on Nixpkgs. If you'd like to do this by hand, look in the script for the recommended PR title and body text.

Update Hackage Version Information

After merging into master you can update what Hackage displays as the current version in NixOS for every individual package. To do this you run maintainers/scripts/haskell/upload-nixos-package-list-to-hackage.sh. See the script for how to provide credentials. Once you have configured credentials, running this takes only a few seconds.

Additional Info

Here are some additional tips that didn't fit in above.