rust-pathauditor: use interior mutability for use in multi-threaded contexts The usual recommendation for using `RwLock` or `Mutex` is that if there are about as many write as there are reads, use `Mutex`, and if there are more reads than writes, use `RwLock`. If after the main bottleneck (i.e. parallel traversal) is removed this shows up on profiles, we should investigate using the `parking_lot` since we don't need a poisoning API, or maybe move to different types of caches entirely. Differential Revision: https://phab.mercurial-scm.org/D8213

--- a/rust/hg-core/src/utils/files.rs	Wed Mar 04 15:12:08 2020 +0100
+++ b/rust/hg-core/src/utils/files.rs	Wed Mar 04 15:10:11 2020 +0100
@@ -210,7 +210,7 @@
     } else {
         name.to_owned()
     };
-    let mut auditor = PathAuditor::new(&root);
+    let auditor = PathAuditor::new(&root);
     if name != root && name.starts_with(&root) {
         let name = name.strip_prefix(&root).unwrap();
         auditor.audit_path(path_to_hg_path_buf(name)?)?;