## Summary
This PR adds support for resolving and installing dependencies via
direct URLs, like:
```
werkzeug @ 960bb4017c/Werkzeug-2.0.0-py3-none-any.whl
```
These are fairly common (e.g., with `torch`), but you most often see
them as Git dependencies.
Broadly, structs like `RemoteDistribution` and friends are now enums
that can represent either registry-based dependencies or URL-based
dependencies:
```rust
/// A built distribution (wheel) that exists as a remote file (e.g., on `PyPI`).
#[derive(Debug, Clone)]
#[allow(clippy::large_enum_variant)]
pub enum RemoteDistribution {
/// The distribution exists in a registry, like `PyPI`.
Registry(PackageName, Version, File),
/// The distribution exists at an arbitrary URL.
Url(PackageName, Url),
}
```
In the resolver, we now allow packages to take on an extra, optional
`Url` field:
```rust
#[derive(Debug, Clone, Eq, Derivative)]
#[derivative(PartialEq, Hash)]
pub enum PubGrubPackage {
Root,
Package(
PackageName,
Option<DistInfoName>,
#[derivative(PartialEq = "ignore")]
#[derivative(PartialOrd = "ignore")]
#[derivative(Hash = "ignore")]
Option<Url>,
),
}
```
However, for the purpose of version satisfaction, we ignore the URL.
This allows for the URL dependency to satisfy the transitive request in
cases like:
```
flask==3.0.0
werkzeug @ 254c3e9b5f/werkzeug-3.0.1-py3-none-any.whl
```
There are a couple limitations in the current approach:
- The caching for remote URLs is done separately in the resolver vs. the
installer. I decided not to sweat this too much... We need to figure out
caching holistically.
- We don't support any sort of time-based cache for remote URLs -- they
just exist forever. This will be a problem for URL dependencies, where
we need some way to evict and refresh them. But I've deferred it for
now.
- I think I need to redo how this is modeled in the resolver, because
right now, we don't detect a variety of invalid cases, e.g., providing
two different URLs for a dependency, asking for a URL dependency and a
_different version_ of the same dependency in the list of first-party
dependencies, etc.
- (We don't yet support VCS dependencies.)
2652caa3e3