merged_tree: micro-optimize Merge<Tree> entries iterator to return &T…

…reeValue

try_resolve_file_conflict() is also updated. It could be a generic function,
but there are only two callers, and the legacy tree one is used only in tests.

lib/src/merged_tree.rs

@@ -389,7 +389,7 @@ fn all_tree_entries(
 /// than `tree.entries_non_recursive()`.
 fn all_merged_tree_entries(
     trees: &Merge<Tree>,
-) -> impl Iterator<Item = (&RepoPathComponent, MergedTreeValue)> {
+) -> impl Iterator<Item = (&RepoPathComponent, Merge<Option<&TreeValue>>)> {
     let mut entries_iters = trees
         .iter()
         .map(|tree| tree.entries_non_recursive().peekable())
@@ -404,7 +404,7 @@ fn all_merged_tree_entries(
             .iter_mut()
             .map(|iter| {
                 let entry = iter.next_if(|entry| entry.name() == next_name)?;
-                Some(entry.value().clone())
+                Some(entry.value())
             })
             .collect();
         Some((next_name, values.build()))
@@ -456,7 +456,7 @@ fn merge_trees(merge: &Merge<Tree>) -> BackendResult<Merge<Tree>> {
     let mut conflicts = vec![];
     for (basename, path_merge) in all_merged_tree_entries(merge) {
         let path = dir.join(basename);
-        let path_merge = merge_tree_values(store, &path, path_merge)?;
+        let path_merge = merge_tree_values(store, &path, &path_merge)?;
         match path_merge.into_resolved() {
             Ok(value) => {
                 new_tree.set_or_remove(basename, value);
@@ -493,10 +493,10 @@ fn merge_trees(merge: &Merge<Tree>) -> BackendResult<Merge<Tree>> {
 fn merge_tree_values(
     store: &Arc<Store>,
     path: &RepoPath,
-    values: MergedTreeValue,
+    values: &Merge<Option<&TreeValue>>,
 ) -> BackendResult<MergedTreeValue> {
     if let Some(resolved) = values.resolve_trivial() {
-        return Ok(Merge::resolved(resolved.clone()));
+        return Ok(Merge::resolved(resolved.cloned()));
     }
 
     if let Some(trees) = values.to_tree_merge(store, path)? {
@@ -517,7 +517,7 @@ fn merge_tree_values(
             Ok(Merge::normal(resolved))
         } else {
             // Failed to merge the files, or the paths are not files
-            Ok(values)
+            Ok(values.map(|value| value.cloned()))
         }
     }
 }

lib/src/tree.rs

@@ -28,7 +28,7 @@ use crate::backend::{
 };
 use crate::files::MergeResult;
 use crate::matchers::{EverythingMatcher, Matcher};
-use crate::merge::{trivial_merge, Merge, MergedTreeValue};
+use crate::merge::{trivial_merge, Merge};
 use crate::object_id::ObjectId;
 use crate::repo_path::{RepoPath, RepoPathBuf, RepoPathComponent};
 use crate::store::Store;
@@ -382,8 +382,9 @@ fn merge_tree_value(
             match merge.into_resolved() {
                 Ok(value) => value,
                 Err(conflict) => {
+                    let conflict_borrowed = conflict.map(|value| value.as_ref());
                     if let Some(tree_value) =
-                        try_resolve_file_conflict(store, &filename, &conflict)?
+                        try_resolve_file_conflict(store, &filename, &conflict_borrowed)?
                     {
                         Some(tree_value)
                     } else {
@@ -403,7 +404,7 @@ fn merge_tree_value(
 pub fn try_resolve_file_conflict(
     store: &Store,
     filename: &RepoPath,
-    conflict: &MergedTreeValue,
+    conflict: &Merge<Option<&TreeValue>>,
 ) -> BackendResult<Option<TreeValue>> {
     // If there are any non-file or any missing parts in the conflict, we can't
     // merge it. We check early so we don't waste time reading file contents if