Matthew Pickering authored Jan 13, 2023 and Marge Bot committed Jan 16, 2023

1. A python script in .gitlab/rel_eng/mk-ghcup-metadata which generates
   suitable metadata for consumption by GHCUp for the relevant
   pipelines.

  - The script generates the metadata just as the ghcup maintainers
    want, without taking into account platform/library combinations. It
    is updated manually when the mapping changes.

  - The script downloads the bindists which ghcup wants to distribute,
    calculates the hash and generates the yaml in the correct structure.

  - The script is documented in the .gitlab/rel_eng/mk-ghcup-metadata/README.mk file

1a. The script requires us to understand the mapping from platform ->
    job. To choose the preferred bindist for each platform the
    .gitlab/gen_ci.hs script is modified to allow outputting a metadata
    file which answers the question about which job produces the
    bindist which we want to distribute to users for a specific
    platform.

2. Pipelines to run on nightly and release jobs to generate metadata

  - ghcup-metadata-nightly: Generates metadata which points directly to
    artifacts in the nightly job.

  - ghcup-metadata-release: Generates metadata suitable for inclusion
    directly in ghcup by pointing to the downloads folder where the
    bindist will be uploaded to.

2a. Trigger jobs which test the generated metadata in the downstream
    `ghccup-ci` repo. See that repo for documentation about what is
    tested and how but essentially we test in a variety of clean images
    that ghcup can download and install the bindists we say exist in our
    metadata.