Ensure that builds within the cache aren't considered Git repositories

crates/uv-cache/src/lib.rs

@@ -236,11 +236,26 @@ impl Cache {
 
         // Add the .gitignore.
         let gitignore_path = root.join(".gitignore");
-        if !gitignore_path.exists() {
-            let mut file = fs::File::create(gitignore_path)?;
-            file.write_all(b"*")?;
+        match fs::OpenOptions::new()
+            .write(true)
+            .create_new(true)
+            .open(gitignore_path)
+        {
+            Ok(mut file) => file.write_all(b"*")?,
+            Err(err) if err.kind() == io::ErrorKind::AlreadyExists => (),
+            Err(err) => return Err(err),
         }
 
+        // Add a phony .git, if it doesn't exist, to ensure that the cache isn't considered to be
+        // part of a Git repository. (Some packages will include Git metadata (like a hash) in the
+        // built version if they're in a Git repository, but the cache should be viewed as an
+        // isolated store.)
+        let git_path = root.join(".git");
+        let _ = fs::OpenOptions::new()
+            .create(true)
+            .write(true)
+            .open(git_path);
+
         fs::canonicalize(root)
     }