How do we test fixes?

Suppose there's some upstream change that requires an update to the downstream libraries to fix (we'll pick dask-cudf for the example). How do we ensure that the fix actually fixes the issue (and doesn't introduce any new ones)?

The PR to rapidsai/cudf will test in an environment against a released version of Dask and the PR, which will ensure we don't have a regression but doesn't test against dask main. So that's good, but doesn't actually test the fix.

I'd lightly suggest a workflow like:

1. We identify an issue through nightly testing
2. We fix the issue in the downstream library

• The developer working on the fix can manually / temporarily install dask @ main to verify it works as they develop the fix
• The developer makes a PR to the downstream library with the fix. This triggers a wheel build / upload to http://downloads.rapids.ai/ci/ (behind the NVIDIA VPN).

3. The developer triggers a workflow here, and indicates that

• Just the specific downstream tests should run
• That downstream library (and its dependencies?) should be installed from http://downloads.rapids.ai/ci/{project}/pull-request/{PR}/{sha}

That manual workflow run will use an environment with Dask main and the PR's commit.

This will require some adjustments to the workfow here. cron.yaml includes a workflow_dispatch trigger so it can run manually. We'll need to

• add an input to control which version of downstream libraries to install (one per library?). This will default to nightly, the current behavior
• update our install logic to be able to download and install artifacts from that downloads.rapids.ai. That's not a package index, and the artifacts are gzipped wheels.

Start with cron.yaml and its workflow_dispatch trigger, then trace the current install logic for nightly downstream libraries. Implement inputs for selecting downstream versions and support installing gzipped wheels from the specified downloads.rapids.ai pull-request path; done means manual runs can target downstream tests while defaulting to nightly.