## Summary
This PR adds support for local path dependencies. The approach mostly
just falls out of our existing approach and infrastructure for Git and
URL dependencies.
Closes https://github.com/astral-sh/puffin/issues/436. (We'll open a
separate issue for editable installs.)
## Test Plan
Added `pip-compile` tests that pre-download a wheel or source
distribution, then install it via local path.
This PR massively speeds up the case in which you need to install wheels
that already exist in the global cache.
The new strategy is as follows:
- Download the wheel into the content-addressed cache.
- Unzip the wheel into the cache, but ignore content-addressing. It
turns out that writing to `cacache` for every file in the zip added a
ton of overhead, and I don't see any actual advantages to doing so.
Instead, we just unzip the contents into a directory at, e.g.,
`~/.cache/puffin/django-4.1.5`.
- (The unzip itself is now parallelized with Rayon.)
- When installing the wheel, we now support unzipping from a directory
instead of a zip archive. This required duplicating and tweaking a few
functions.
- When installing the wheel, we now use reflinks (or copy-on-write
links). These have a few fantastic properties: (1) they're extremely
cheap to create (on macOS, they are allegedly faster than hard links);
(2) they minimize disk space, since we avoid copying files entirely in
the vast majority of cases; and (3) if the user then edits a file
locally, the cache doesn't get polluted. Orogene, Bun, and soon pnpm all
use reflinks.
Puffin is now ~15x faster than `pip` for the common case of installing
cached data into a fresh environment.
Closes https://github.com/astral-sh/puffin/issues/21.
Closes https://github.com/astral-sh/puffin/issues/39.
