Remove allocation in Git SHA truncation (#10801)

crates/uv-distribution/src/index/built_wheel_index.rs

@@ -170,7 +170,7 @@ impl<'a> BuiltWheelIndex<'a> {
 
         let cache_shard = self.cache.shard(
             CacheBucket::SourceDistributions,
-            WheelCache::Git(&source_dist.url, &git_sha.to_short_string()).root(),
+            WheelCache::Git(&source_dist.url, git_sha.as_short_str()).root(),
         );
 
         // If there are build settings, we need to scope to a cache shard.

crates/uv-distribution/src/source/mod.rs

@@ -1426,7 +1426,7 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
         let git_sha = fetch.git().precise().expect("Exact commit after checkout");
         let cache_shard = self.build_context.cache().shard(
             CacheBucket::SourceDistributions,
-            WheelCache::Git(resource.url, &git_sha.to_short_string()).root(),
+            WheelCache::Git(resource.url, git_sha.as_short_str()).root(),
         );
         let metadata_entry = cache_shard.entry(METADATA);
 
@@ -1564,7 +1564,7 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
         let git_sha = fetch.git().precise().expect("Exact commit after checkout");
         let cache_shard = self.build_context.cache().shard(
             CacheBucket::SourceDistributions,
-            WheelCache::Git(resource.url, &git_sha.to_short_string()).root(),
+            WheelCache::Git(resource.url, git_sha.as_short_str()).root(),
         );
         let metadata_entry = cache_shard.entry(METADATA);
 

crates/uv-git/src/sha.rs

@@ -8,9 +8,14 @@ use thiserror::Error;
 pub struct GitSha(GitOid);
 
 impl GitSha {
-    /// Convert the SHA to a truncated representation, i.e., the first 16 characters of the SHA.
-    pub fn to_short_string(&self) -> String {
-        self.0.to_string()[0..16].to_string()
+    /// Return the Git SHA as a string.
+    pub fn as_str(&self) -> &str {
+        self.0.as_str()
+    }
+
+    /// Return a truncated representation, i.e., the first 16 characters of the SHA.
+    pub fn as_short_str(&self) -> &str {
+        &self.0.as_str()[..16]
     }
 }