copies-rust: pre-introduce a PathToken type and use it where applicable

Handling string all the time is quite slow. So we are about to use more
efficient "token". We do some of the churn early to clarify the next changesets.

Differential Revision: https://phab.mercurial-scm.org/D9492

rust/hg-core/src/copy_tracing.rs

@@ -11,17 +11,19 b' use std::convert::TryInto;'
 
 pub type PathCopies = HashMap<HgPathBuf, HgPathBuf>;
 
+type PathToken = HgPathBuf;
+
 #[derive(Clone, Debug, PartialEq)]
 struct TimeStampedPathCopy {
     /// revision at which the copy information was added
     rev: Revision,
     /// the copy source, (Set to None in case of deletion of the associated
     /// key)
-    path: Option<HgPathBuf>,
+    path: Option<PathToken>,
 }
 
 /// maps CopyDestination to Copy Source (+ a "timestamp" for the operation)
-type TimeStampedPathCopies = OrdMap<HgPathBuf, TimeStampedPathCopy>;
+type TimeStampedPathCopies = OrdMap<PathToken, TimeStampedPathCopy>;
 
 /// hold parent 1, parent 2 and relevant files actions.
 pub type RevInfo<'a> = (Revision, Revision, ChangedFiles<'a>);
@@ -467,7 +469,7 b' fn merge_copies_dict<A: Fn(Revision, Rev'
     // actively working on this code. Feel free to re-inline it once this
     // code is more settled.
     let mut cmp_value =
-        |dest: &HgPathBuf,
+        |dest: &PathToken,
          src_minor: &TimeStampedPathCopy,
          src_major: &TimeStampedPathCopy| {
             compare_value(changes, oracle, dest, src_minor, src_major)
@@ -525,10 +527,10 b' fn merge_copies_dict<A: Fn(Revision, Rev'
         let mut override_minor = Vec::new();
         let mut override_major = Vec::new();
 
-        let mut to_major = |k: &HgPathBuf, v: &TimeStampedPathCopy| {
+        let mut to_major = |k: &PathToken, v: &TimeStampedPathCopy| {
             override_major.push((k.clone(), v.clone()))
         };
-        let mut to_minor = |k: &HgPathBuf, v: &TimeStampedPathCopy| {
+        let mut to_minor = |k: &PathToken, v: &TimeStampedPathCopy| {
             override_minor.push((k.clone(), v.clone()))
         };
 
@@ -602,7 +604,7 b' enum MergePick {'
 fn compare_value<A: Fn(Revision, Revision) -> bool>(
     changes: &ChangedFiles,
     oracle: &mut AncestorOracle<A>,
-    dest: &HgPathBuf,
+    dest: &PathToken,
     src_minor: &TimeStampedPathCopy,
     src_major: &TimeStampedPathCopy,
 ) -> MergePick {