Allow multiple base URLs in python_register_toolchains #964
Description
🚀 Allow multiple base URLs in python_register_toolchains
Relevant Rules
python_register_toolchains
Description
Currently, python_register_toolchains has a convenient tool_versions dictionary argument that the caller customize the mapping between Python versions and URLs from which to retrieve a build. However, the mapping is 1-to-1: a given Python version maps to a unique URL.
In my company's deployment, we have a monorepo that runs in multiple "environments" with strict firewalling rules. We are currently using a variant of thundergolfer's solution, passing a list of URLs for each Python version. The sha256 hash is the same but points to multiple URLs and repository_ctx.download_and_extract works "automatically": it tries to download from the first URL (say corp) and if it fails, tries to download from the next (say, public GitHub).
Describe the solution you'd like
Change the type of tool_versions (or introduce a new attribute) from str -> url to str -> list[url].
This is the simplest solution - Bazel will simply download each in turn and is a simple failure mechanism (to handle servers that are down).
Describe alternatives you've considered
Introducing additional configurability at the WORKSPACE level seems too complex. One design could be a different Python "version" for each environment, e.g., 3.9-corp and 3.9-github. But this is difficult to manage as both need to be declared in WORKSPACE and then pushed down via a select() on the requirements at each leaf in BUILD files.