Closes https://github.com/astral-sh/ruff/issues/12158
Hashing `Path` does not take into account path separators so `foo/bar`
is the same as `foobar` which is no good for our case. I'm guessing this
is an upstream bug, perhaps introduced by
45082b077b?
I'm investigating that further.
## Summary
Error if `tab-size` is set to zero (it is used as a divisor). Closes
#6423.
Also fixes a typo.
## Test Plan
Running ruff with a config
```toml
[tool.ruff]
tab-size = 0
```
returns an error message to the user saying that `tab-size` must be
greater than zero.
## Summary
This PR runs `rustfmt` with a few nightly options as a one-time fix to
catch some malformatted comments. I ended up just running with:
```toml
condense_wildcard_suffixes = true
edition = "2021"
max_width = 100
normalize_comments = true
normalize_doc_attributes = true
reorder_impl_items = true
unstable_features = true
use_field_init_shorthand = true
```
Since these all seem like reasonable things to fix, so may as well while
I'm here.
This PR introduces a new `CacheKey` trait for types that can be used as a cache key.
I'm not entirely sure if this is worth the "overhead", but I was surprised to find `HashableHashSet` and got scared when I looked at the time complexity of the `hash` function. These implementations must be extremely slow in hashed collections.
I then searched for usages and quickly realized that only the cache uses these `Hash` implementations, where performance is less sensitive.
This PR introduces a new `CacheKey` trait to communicate the difference between a hash and computing a key for the cache. The new trait can be implemented for types that don't implement `Hash` for performance reasons, and we can define additional constraints on the implementation: For example, we'll want to enforce portability when we add remote caching support. Using a different trait further allows us not to implement it for types without stable identities (e.g. pointers) or use other implementations than the standard hash function.
