Add support for dynamic cache keys (#7136)

## Summary

This PR adds a more flexible cache invalidation abstraction for uv, and
uses that new abstraction to improve support for dynamic metadata.

Specifically, instead of relying solely on a timestamp, we now pass
around a `CacheInfo` struct which (as of now) contains
`Option<Timestamp>` and `Option<Commit>`. The `CacheInfo` is saved in
`dist-info` as `uv_cache.json`, so we can test already-installed
distributions for cache validity (along with testing _cached_
distributions for cache validity).

Beyond the defaults (`pyproject.toml`, `setup.py`, and `setup.cfg`
changes), users can also specify additional cache keys, and it's easy
for us to extend support in the future. Right now, cache keys can either
be instructions to include the current commit (for `setuptools_scm` and
similar) or file paths (for `hatch-requirements-txt` and similar):

```toml
[tool.uv]
cache-keys = [{ file = "requirements.txt" }, { git = true }]
```

This change should be fully backwards compatible.

Closes https://github.com/astral-sh/uv/issues/6964.

Closes https://github.com/astral-sh/uv/issues/6255.

Closes https://github.com/astral-sh/uv/issues/6860.

crates/uv-configuration/Cargo.toml

@@ -13,12 +13,14 @@ license = { workspace = true }
 workspace = true
 
 [dependencies]
+cache-key = { workspace = true }
 distribution-types = { workspace = true }
 pep508_rs = { workspace = true, features = ["schemars"] }
 platform-tags = { workspace = true }
 pypi-types = { workspace = true }
 uv-auth = { workspace = true }
 uv-cache = { workspace = true }
+uv-cache-info = { workspace = true }
 uv-normalize = { workspace = true }
 
 clap = { workspace = true, features = ["derive"], optional = true }

crates/uv-configuration/src/config_settings.rs

@@ -1,3 +1,4 @@
+use cache_key::CacheKeyHasher;
 use std::{
     collections::{btree_map::Entry, BTreeMap},
     str::FromStr,
@@ -108,6 +109,16 @@ impl FromIterator<ConfigSettingEntry> for ConfigSettings {
 }
 
 impl ConfigSettings {
+    /// Returns the number of settings in the configuration.
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    /// Returns `true` if the configuration contains no settings.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
     /// Convert the settings to a string that can be passed directly to a PEP 517 build backend.
     pub fn escape_for_python(&self) -> String {
         serde_json::to_string(self).expect("Failed to serialize config settings")
@@ -150,6 +161,18 @@ impl ConfigSettings {
     }
 }
 
+impl cache_key::CacheKey for ConfigSettings {
+    fn cache_key(&self, state: &mut CacheKeyHasher) {
+        for (key, value) in &self.0 {
+            key.cache_key(state);
+            match value {
+                ConfigSettingValue::String(value) => value.cache_key(state),
+                ConfigSettingValue::List(values) => values.cache_key(state),
+            }
+        }
+    }
+}
+
 impl serde::Serialize for ConfigSettings {
     fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
         use serde::ser::SerializeMap;

crates/uv-configuration/src/package_options.rs

@@ -3,7 +3,8 @@ use pep508_rs::PackageName;
 
 use pypi_types::Requirement;
 use rustc_hash::FxHashMap;
-use uv_cache::{Refresh, Timestamp};
+use uv_cache::Refresh;
+use uv_cache_info::Timestamp;
 
 /// Whether to reinstall packages.
 #[derive(Debug, Default, Clone, serde::Serialize, serde::Deserialize)]