## Summary
The basic strategy:
- When the user does `uv tool run`, we resolve the `from` and `with`
requirements (always).
- After resolving, we generate a hash of the requirements. For now, I'm
just converting to a lockfile and hashing _that_, but that's an
implementation detail.
- Once we have a hash, we _also_ hash the interpreter.
- We then store environments in
`${CACHE_DIR}/${INTERPRETER_HASH}/${RESOLUTION_HASH}`.
Some consequences:
- We cache based on the interpreter, so if you request a different
Python, we'll create a new environment (even if they're compatible).
This has the nice side-effect of ensuring that we don't use environments
for interpreters that were later deleted.
- We cache the `from` and `with` together. In practice, we may want to
cache them separately, then layer them? But this is also an
implementation detail that we could change later.
- Because we use the lockfile as the cache key, we will invalidate the
cache when the format changes. That seems ok, but we could improve it in
the future by generating a stable hash from a lockfile that's
independent of the schema.
Closes https://github.com/astral-sh/uv/issues/4752.
This crate started off as generic caching utilities, but we started
adding a lot of Puffin-specific stuff (like the cache buckets
abstraction that knows about Git vs. direct URL vs. indexes and so on).
This PR moves the generic stuff into a new `cache-key` crate.
Charlie Marsh