files: use borrowed Merge iterator in merge()

Since the underlying Merge data type is no longer (Vec<T>, Vec<T>), it doesn't
make sense to build removes/adds Vecs and concatenate them.

cli/src/merge_tools/builtin.rs

@@ -516,7 +516,7 @@ pub fn edit_merge_builtin(
     content: Merge<ContentHunk>,
 ) -> Result<MergedTreeId, BuiltinToolError> {
     let slices = content.map(|ContentHunk(v)| v.as_slice());
-    let merge_result = files::merge(slices);
+    let merge_result = files::merge(&slices);
     let sections = make_merge_sections(merge_result)?;
     let recorder = scm_record::Recorder::new(
         scm_record::RecordState {
@@ -731,7 +731,7 @@ mod tests {
         );
         let content = extract_as_single_hunk(&merge, store, &path).block_on();
         let slices = content.map(|ContentHunk(buf)| buf.as_slice());
-        let merge_result = files::merge(slices);
+        let merge_result = files::merge(&slices);
         let sections = make_merge_sections(merge_result).unwrap();
         insta::assert_debug_snapshot!(sections, @r###"
         [

lib/src/conflicts.rs

@@ -109,7 +109,7 @@ pub fn materialize_merge_result(
     output: &mut dyn Write,
 ) -> std::io::Result<()> {
     let slices = single_hunk.map(|content| content.0.as_slice());
-    let merge_result = files::merge(slices);
+    let merge_result = files::merge(&slices);
     match merge_result {
         MergeResult::Resolved(content) => {
             output.write_all(&content.0)?;

lib/src/files.rs

@@ -167,14 +167,12 @@ struct SyncRegion {
     right: Range<usize>,
 }
 
-pub fn merge(slices: Merge<&[u8]>) -> MergeResult {
-    let (removes, adds) = slices.take();
-    let num_diffs = removes.len();
+pub fn merge(slices: &Merge<&[u8]>) -> MergeResult {
     // TODO: Using the first remove as base (first in the inputs) is how it's
     // usually done for 3-way conflicts. Are there better heuristics when there are
     // more than 3 parts?
-    let mut diff_inputs = removes.to_vec();
-    diff_inputs.extend(adds);
+    let num_diffs = slices.removes().len();
+    let diff_inputs = slices.removes().chain(slices.adds()).copied().collect_vec();
 
     let diff = Diff::for_tokenizer(&diff_inputs, &diff::find_line_ranges);
     let mut resolved_hunk = ContentHunk(vec![]);
@@ -226,7 +224,7 @@ mod tests {
     }
 
     fn merge(removes: &[&[u8]], adds: &[&[u8]]) -> MergeResult {
-        super::merge(Merge::new(removes.to_vec(), adds.to_vec()))
+        super::merge(&Merge::new(removes.to_vec(), adds.to_vec()))
     }
 
     #[test]

lib/src/tree.rs

@@ -453,7 +453,7 @@ pub fn try_resolve_file_conflict(
             Ok(content)
         })?;
     let slices = contents.map(|content| content.as_slice());
-    let merge_result = files::merge(slices);
+    let merge_result = files::merge(&slices);
     match merge_result {
         MergeResult::Resolved(merged_content) => {
             let id = store.write_file(filename, &mut merged_content.0.as_slice())?;

lib/tests/test_merged_tree.rs

@@ -1305,7 +1305,7 @@ fn test_merge_simplify_file_conflict() {
         ],
     );
     assert!(matches!(
-        jj_lib::files::merge(text_merge.flatten()),
+        jj_lib::files::merge(&text_merge.flatten()),
         MergeResult::Conflict(_)
     ));
 }