tree merge with tree-related auto-resolution

crate-status.md

@@ -352,8 +352,11 @@ Check out the [performance discussion][gix-diff-performance] as well.
     - [ ] a way to control inter-hunk merging based on proximity (maybe via `gix-diff` feature which could use the same)
 * [x] **tree**-diff-heuristics match Git for its test-cases
     - [x] a way to generate an index with stages, mostly conforming with Git.
+    - [ ] resolve to be *ours* or the *ancestors* version of the tree.
     - [ ] submodule merges (*right now they count as conflicts if they differ*)
     - [ ] assure sparse indices are handled correctly during application - right now we refuse.
+    - [ ] rewrite so that the whole logic can be proven to be correct - it's too insane now and probably has way 
+          more possible states than are tested, despite best attempts.
 * [x] **commits** - with handling of multiple merge bases by recursive merge-base merge
 * [x] API documentation
     * [ ] Examples

gitoxide-core/src/query/engine/update.rs

@@ -139,7 +139,12 @@ pub fn update(
         });
 
         let rewrites = {
-            let mut r = gix::diff::new_rewrites(&repo.config_snapshot(), true)?.unwrap_or_default();
+            // These are either configured, or we set them to the default. There is no turning them off.
+            let (r, was_configured) = gix::diff::new_rewrites(&repo.config_snapshot(), true)?;
+            if was_configured && r.is_none() {
+                gix::trace::warn!("Rename tracking is disabled by configuration, but we enable it using the default");
+            }
+            let mut r = r.unwrap_or_default();
             r.copies = Some(gix::diff::rewrites::Copies {
                 source: if find_copies_harder {
                     CopySource::FromSetOfModifiedFilesAndAllSources

gitoxide-core/src/repository/merge/commit.rs

@@ -17,6 +17,7 @@ pub fn commit(
     Options {
         format,
         file_favor,
+        tree_favor,
         in_memory,
         debug,
     }: Options,
@@ -31,7 +32,10 @@ pub fn commit(
     let (ours_ref, ours_id) = refname_and_commit(&repo, ours)?;
     let (theirs_ref, theirs_id) = refname_and_commit(&repo, theirs)?;
 
-    let options = repo.tree_merge_options()?.with_file_favor(file_favor);
+    let options = repo
+        .tree_merge_options()?
+        .with_file_favor(file_favor)
+        .with_tree_favor(tree_favor);
     let ours_id_str = ours_id.to_string();
     let theirs_id_str = theirs_id.to_string();
     let labels = gix::merge::blob::builtin_driver::text::Labels {
@@ -49,7 +53,7 @@ pub fn commit(
         .merge_commits(ours_id, theirs_id, labels, options.into())?
         .tree_merge;
     let has_conflicts = res.conflicts.is_empty();
-    let has_unresolved_conflicts = res.has_unresolved_conflicts(TreatAsUnresolved::Renames);
+    let has_unresolved_conflicts = res.has_unresolved_conflicts(TreatAsUnresolved::default());
     {
         let _span = gix::trace::detail!("Writing merged tree");
         let mut written = 0;

gitoxide-core/src/repository/merge/tree.rs

@@ -3,6 +3,7 @@ use crate::OutputFormat;
 pub struct Options {
     pub format: OutputFormat,
     pub file_favor: Option<gix::merge::tree::FileFavor>,
+    pub tree_favor: Option<gix::merge::tree::TreeFavor>,
     pub in_memory: bool,
     pub debug: bool,
 }
@@ -29,6 +30,7 @@ pub(super) mod function {
         Options {
             format,
             file_favor,
+            tree_favor,
             in_memory,
             debug,
         }: Options,
@@ -44,7 +46,10 @@ pub(super) mod function {
         let (ours_ref, ours_id) = refname_and_tree(&repo, ours)?;
         let (theirs_ref, theirs_id) = refname_and_tree(&repo, theirs)?;
 
-        let options = repo.tree_merge_options()?.with_file_favor(file_favor);
+        let options = repo
+            .tree_merge_options()?
+            .with_file_favor(file_favor)
+            .with_tree_favor(tree_favor);
         let base_id_str = base_id.to_string();
         let ours_id_str = ours_id.to_string();
         let theirs_id_str = theirs_id.to_string();
@@ -64,7 +69,7 @@ pub(super) mod function {
         };
         let res = repo.merge_trees(base_id, ours_id, theirs_id, labels, options)?;
         let has_conflicts = res.conflicts.is_empty();
-        let has_unresolved_conflicts = res.has_unresolved_conflicts(TreatAsUnresolved::Renames);
+        let has_unresolved_conflicts = res.has_unresolved_conflicts(TreatAsUnresolved::default());
         {
             let _span = gix::trace::detail!("Writing merged tree");
             let mut written = 0;

gitoxide-core/src/repository/status.rs

@@ -81,6 +81,7 @@ pub fn show(
                 copies: None,
                 percentage: Some(percentage),
                 limit: 0,
+                track_empty: false,
             });
             if opts.rewrites.is_some() {
                 if let Some(opts) = opts.dirwalk_options.as_mut() {

gix-diff/src/lib.rs

@@ -37,6 +37,11 @@ pub struct Rewrites {
     /// If the limit would not be enough to test the entire set of combinations, the algorithm will trade in precision and not
     /// run the fuzzy version of identity tests at all. That way results are never partial.
     pub limit: usize,
+
+    /// If `true`, empty blobs will be tracked. If `false`, they do not participate in rename tracking.
+    ///
+    /// Leaving this off usually leads to better results as empty files don't have a unique-enough identity.
+    pub track_empty: bool,
 }
 
 /// Contains a [Tracker](rewrites::Tracker) to detect rewrites.

gix-diff/src/rewrites/mod.rs

@@ -70,6 +70,7 @@ impl Default for Rewrites {
             copies: None,
             percentage: Some(0.5),
             limit: 1000,
+            track_empty: false,
         }
     }
 }

gix-diff/src/rewrites/tracker.rs

@@ -286,12 +286,10 @@ impl<T: Change> Tracker<T> {
                 CopySource::FromSetOfModifiedFiles => {}
                 CopySource::FromSetOfModifiedFilesAndAllSources => {
                     push_source_tree(&mut |change, location| {
-                        assert!(
-                            self.try_push_change(change, location).is_none(),
-                            "we must accept every change"
-                        );
-                        // make sure these aren't viable to be emitted anymore.
-                        self.items.last_mut().expect("just pushed").emitted = true;
+                        if self.try_push_change(change, location).is_none() {
+                            // make sure these aren't viable to be emitted anymore.
+                            self.items.last_mut().expect("just pushed").emitted = true;
+                        }
                     })
                     .map_err(|err| emit::Error::GetItemsForExhaustiveCopyDetection(Box::new(err)))?;
                     self.items.sort_by(by_id_and_location);
@@ -341,6 +339,10 @@ impl<T: Change> Tracker<T> {
     ) -> Result<(), emit::Error> {
         // we try to cheaply reduce the set of possibilities first, before possibly looking more exhaustively.
         let needs_second_pass = !needs_exact_match(percentage);
+
+        // https://github.com/git/git/blob/cc01bad4a9f566cf4453c7edd6b433851b0835e2/diffcore-rename.c#L350-L369
+        // We would need a hashmap to be OK to not use the limit here, otherwise the performance is too bad.
+        // This also means we don't find all renames if we hit the rename limit.
         if self.match_pairs(cb, None /* by identity */, kind, out, diff_cache, objects, filter)? == Action::Cancel {
             return Ok(());
         }
@@ -384,10 +386,35 @@ impl<T: Change> Tracker<T> {
         filter: Option<fn(&T) -> bool>,
     ) -> Result<Action, emit::Error> {
         let mut dest_ofs = 0;
+        let mut num_checks = 0;
+        let max_checks = {
+            let limit = self.rewrites.limit.saturating_pow(2);
+            // There can be trees with a lot of entries and pathological search behaviour, as they can be repeated
+            // and then have a lot of similar hashes. This also means we have to search a lot of candidates which
+            // can be too slow despite best attempts. So play it save and detect such cases 'roughly' by amount of items.
+            if self.items.len() < 100_000 {
+                0
+            } else {
+                limit
+            }
+        };
+
         while let Some((mut dest_idx, dest)) = self.items[dest_ofs..].iter().enumerate().find_map(|(idx, item)| {
             (!item.emitted
                 && matches!(item.change.kind(), ChangeKind::Addition)
-                && filter.map_or(true, |f| f(&item.change)))
+                && filter.map_or_else(
+                    || {
+                        self.rewrites.track_empty
+                            // We always want to keep track of entries that are involved of a directory rename.
+                            // Note that this may still match them up arbitrarily if empty, but empty is empty.
+                            || matches!(item.change.relation(), Some(Relation::ChildOfParent(_)))
+                            || {
+                                let id = item.change.id();
+                                id != gix_hash::ObjectId::empty_blob(id.kind())
+                            }
+                    },
+                    |f| f(&item.change),
+                ))
             .then_some((idx, item))
         }) {
             dest_idx += dest_ofs;
@@ -403,6 +430,7 @@ impl<T: Change> Tracker<T> {
                 objects,
                 diff_cache,
                 &self.path_backing,
+                &mut num_checks,
             )?
             .map(|(src_idx, src, diff)| {
                 let (id, entry_mode) = src.change.id_and_entry_mode();
@@ -420,6 +448,12 @@ impl<T: Change> Tracker<T> {
                     src_idx,
                 )
             });
+            if max_checks != 0 && num_checks > max_checks {
+                gix_trace::warn!(
+                    "Cancelled rename matching as there were too many iterations ({num_checks} > {max_checks})"
+                );
+                return Ok(Action::Cancel);
+            }
             let Some((src, src_idx)) = src else {
                 continue;
             };
@@ -631,6 +665,7 @@ fn find_match<'a, T: Change>(
     objects: &impl gix_object::FindObjectOrHeader,
     diff_cache: &mut crate::blob::Platform,
     path_backing: &[u8],
+    num_checks: &mut usize,
 ) -> Result<Option<SourceTuple<'a, T>>, emit::Error> {
     let (item_id, item_mode) = item.change.id_and_entry_mode();
     if needs_exact_match(percentage) || item_mode.is_link() {
@@ -651,6 +686,7 @@ fn find_match<'a, T: Change>(
         }
         let res = items[range.clone()].iter().enumerate().find_map(|(mut src_idx, src)| {
             src_idx += range.start;
+            *num_checks += 1;
             (src_idx != item_idx && src.is_source_for_destination_of(kind, item_mode)).then_some((src_idx, src, None))
         });
         if let Some(src) = res {
@@ -685,6 +721,7 @@ fn find_match<'a, T: Change>(
             )?;
             let prep = diff_cache.prepare_diff()?;
             stats.num_similarity_checks += 1;
+            *num_checks += 1;
             match prep.operation {
                 Operation::InternalDiff { algorithm } => {
                     let tokens =

gix-diff/tests/diff/rewrites/tracker.rs

@@ -27,6 +27,7 @@ fn rename_by_id() -> crate::Result {
             copies: None,
             percentage: None,
             limit,
+            track_empty: false,
         };
         let mut track = util::new_tracker(rewrites);
         assert!(
@@ -80,6 +81,7 @@ fn copy_by_similarity_reports_limit_if_encountered() -> crate::Result {
         }),
         percentage: None,
         limit: 1,
+        track_empty: false,
     };
     let mut track = util::new_tracker(rewrites);
     let odb = util::add_retained_blobs(
@@ -132,6 +134,7 @@ fn copy_by_id() -> crate::Result {
             }),
             percentage: None,
             limit,
+            track_empty: false,
         };
         let mut track = util::new_tracker(rewrites);
         let odb = util::add_retained_blobs(
@@ -206,6 +209,7 @@ fn copy_by_id_search_in_all_sources() -> crate::Result {
             }),
             percentage: None,
             limit,
+            track_empty: false,
         };
         let mut track = util::new_tracker(rewrites);
         let odb = util::add_retained_blobs(
@@ -284,6 +288,7 @@ fn copy_by_50_percent_similarity() -> crate::Result {
         }),
         percentage: None,
         limit: 0,
+        track_empty: false,
     };
     let mut track = util::new_tracker(rewrites);
     let odb = util::add_retained_blobs(
@@ -363,6 +368,7 @@ fn copy_by_id_in_additions_only() -> crate::Result {
         }),
         percentage: None,
         limit: 0,
+        track_empty: false,
     };
     let mut track = util::new_tracker(rewrites);
     let odb = util::add_retained_blobs(
@@ -413,6 +419,7 @@ fn rename_by_similarity_reports_limit_if_encountered() -> crate::Result {
         copies: None,
         percentage: Some(0.5),
         limit: 1,
+        track_empty: false,
     };
     let mut track = util::new_tracker(rewrites);
     let odb = util::add_retained_blobs(
@@ -458,6 +465,7 @@ fn rename_by_50_percent_similarity() -> crate::Result {
         copies: None,
         percentage: Some(0.5),
         limit: 0,
+        track_empty: false,
     };
     let mut track = util::new_tracker(rewrites);
     let odb = util::add_retained_blobs(
@@ -547,6 +555,7 @@ fn directory_renames_by_id_can_fail_gracefully() -> crate::Result {
         copies: None,
         percentage: Some(0.5),
         limit: 0,
+        track_empty: false,
     };
     let mut track = util::new_tracker(rename_by_similarity);
     let tree_dst_id = 1;
@@ -638,6 +647,7 @@ fn simple_directory_rename_by_id() -> crate::Result {
         copies: None,
         percentage: None,
         limit: 0,
+        track_empty: false,
     };
     let mut track = util::new_tracker(renames_by_identity);
     let tree_dst_id = 1;