Use gitoxide merge-trees for when applying and unapplying branches.

While at it, check make it a thing to check for clean merges easily.

crates/gitbutler-branch-actions/src/branch_manager/branch_creation.rs

@@ -8,6 +8,7 @@ use gitbutler_error::error::Marker;
 use gitbutler_oplog::SnapshotExt;
 use gitbutler_project::access::WorktreeWritePermission;
 use gitbutler_reference::{Refname, RemoteRefname};
+use gitbutler_repo::GixRepositoryExt;
 use gitbutler_repo::{
     rebase::{cherry_rebase_group, gitbutler_merge_commits},
     LogUntil, RepositoryExt,
@@ -301,29 +302,27 @@ impl BranchManager<'_> {
             ))?;
 
         // Branch is out of date, merge or rebase it
-        let merge_base_tree = repo
+        let merge_base_tree_id = repo
             .find_commit(merge_base)
             .context(format!("failed to find merge base commit {}", merge_base))?
             .tree()
-            .context("failed to find merge base tree")?;
-
-        let branch_tree = repo
-            .find_tree(branch.tree)
-            .context("failed to find branch tree")?;
+            .context("failed to find merge base tree")?
+            .id();
+        let branch_tree_id = branch.tree;
 
         // We don't support having two branches applied that conflict with each other
         {
-            let uncommited_changes_tree = repo.create_wd_tree()?;
-            let branch_merged_with_other_applied_branches = repo
-                .merge_trees(
-                    &merge_base_tree,
-                    &branch_tree,
-                    &uncommited_changes_tree,
-                    None,
+            let uncommited_changes_tree_id = repo.create_wd_tree()?.id();
+            let gix_repo = self.ctx.gix_repository_for_merging_non_persisting()?;
+            let merges_cleanly = gix_repo
+                .merges_cleanly_compat(
+                    merge_base_tree_id,
+                    branch_tree_id,
+                    uncommited_changes_tree_id,
                 )
                 .context("failed to merge trees")?;
 
-            if branch_merged_with_other_applied_branches.has_conflicts() {
+            if !merges_cleanly {
                 for branch in vb_state
                     .list_branches_in_workspace()?
                     .iter()

crates/gitbutler-branch-actions/src/branch_manager/branch_removal.rs

@@ -5,12 +5,16 @@ use git2::Commit;
 use gitbutler_branch::BranchExt;
 use gitbutler_commit::commit_headers::CommitHeadersV2;
 use gitbutler_oplog::SnapshotExt;
+use gitbutler_oxidize::git2_to_gix_object_id;
+use gitbutler_oxidize::gix_to_git2_oid;
 use gitbutler_project::access::WorktreeWritePermission;
 use gitbutler_reference::{normalize_branch_name, ReferenceName, Refname};
+use gitbutler_repo::GixRepositoryExt;
 use gitbutler_repo::RepositoryExt;
 use gitbutler_repo::SignaturePurpose;
 use gitbutler_repo_actions::RepoActionsExt;
 use gitbutler_stack::{Stack, StackId};
+use gix::objs::Write;
 use tracing::instrument;
 
 use super::BranchManager;
@@ -79,7 +83,10 @@ impl BranchManager<'_> {
 
         let repo = self.ctx.repository();
 
-        let base_tree = target_commit.tree().context("failed to get target tree")?;
+        let base_tree_id = target_commit
+            .tree()
+            .context("failed to get target tree")?
+            .id();
 
         let applied_statuses = get_applied_status(self.ctx, None)
             .context("failed to get status by branch")?
@@ -98,13 +105,14 @@ impl BranchManager<'_> {
                 num_branches = applied_statuses.len() - 1
             )
             .entered();
-            applied_statuses
+            let gix_repo = self.ctx.gix_repository()?;
+            let merge_options = gix_repo.tree_merge_options()?;
+            let final_tree_id = applied_statuses
                 .into_iter()
                 .filter(|(branch, _)| branch.id != branch_id)
-                .fold(
-                    target_commit.tree().context("failed to get target tree"),
-                    |final_tree, status| {
-                        let final_tree = final_tree?;
+                .try_fold(
+                    git2_to_gix_object_id(target_commit.tree_id()),
+                    |final_tree_id, status| -> Result<_> {
                         let branch = status.0;
                         let files = status
                             .1
@@ -113,14 +121,21 @@ impl BranchManager<'_> {
                             .collect::<Vec<(PathBuf, Vec<VirtualBranchHunk>)>>();
                         let tree_oid =
                             gitbutler_diff::write::hunks_onto_oid(self.ctx, branch.head(), files)?;
-                        let branch_tree = repo.find_tree(tree_oid)?;
-                        let mut result =
-                            repo.merge_trees(&base_tree, &final_tree, &branch_tree, None)?;
-                        let final_tree_oid = result.write_tree_to(repo)?;
-                        repo.find_tree(final_tree_oid)
-                            .context("failed to find tree")
+                        let mut merge = gix_repo.merge_trees(
+                            git2_to_gix_object_id(base_tree_id),
+                            final_tree_id,
+                            git2_to_gix_object_id(tree_oid),
+                            gix_repo.default_merge_labels(),
+                            merge_options.clone(),
+                        )?;
+                        let final_tree_id = merge
+                            .tree
+                            .write(|tree| gix_repo.write(tree))
+                            .map_err(|err| anyhow::anyhow!("Could not write merged tree: {err}"))?;
+                        Ok(final_tree_id)
                     },
-                )?
+                )?;
+            repo.find_tree(gix_to_git2_oid(final_tree_id))?
         };
 
         let _span = tracing::debug_span!("checkout final tree").entered();

crates/gitbutler-branch-actions/src/integration.rs

@@ -9,10 +9,12 @@ use gitbutler_command_context::CommandContext;
 use gitbutler_commit::commit_ext::CommitExt;
 use gitbutler_error::error::Marker;
 use gitbutler_operating_modes::OPEN_WORKSPACE_REFS;
+use gitbutler_oxidize::{git2_to_gix_object_id, gix_to_git2_oid};
 use gitbutler_project::access::WorktreeWritePermission;
-use gitbutler_repo::SignaturePurpose;
+use gitbutler_repo::{GixRepositoryExt, SignaturePurpose};
 use gitbutler_repo::{LogUntil, RepositoryExt};
 use gitbutler_stack::{Stack, VirtualBranchesHandle};
+use gix::objs::Write;
 use tracing::instrument;
 
 use crate::{branch_manager::BranchManagerExt, conflicts, VirtualBranchesExt};
@@ -41,6 +43,7 @@ pub(crate) fn get_workspace_head(ctx: &CommandContext) -> Result<git2::Oid> {
 
     let target_commit = repo.find_commit(target.sha)?;
     let mut workspace_tree = repo.find_real_tree(&target_commit, Default::default())?;
+    let mut workspace_tree_id = git2_to_gix_object_id(workspace_tree.id());
 
     if conflicts::is_conflicting(ctx, None)? {
         let merge_parent = conflicts::merge_parent(ctx)?.ok_or(anyhow!("No merge parent"))?;
@@ -49,22 +52,37 @@ pub(crate) fn get_workspace_head(ctx: &CommandContext) -> Result<git2::Oid> {
         let merge_base = repo.merge_base(first_branch.head(), merge_parent)?;
         workspace_tree = repo.find_commit(merge_base)?.tree()?;
     } else {
+        let gix_repo = ctx.gix_repository_for_merging()?;
+        let mut merge_options_fail_fast = gix_repo.tree_merge_options()?;
+        let conflict_kind = gix::merge::tree::UnresolvedConflict::Renames;
+        merge_options_fail_fast.fail_on_conflict = Some(conflict_kind);
+        let merge_tree_id = git2_to_gix_object_id(repo.find_commit(target.sha)?.tree_id());
         for branch in virtual_branches.iter_mut() {
-            let merge_tree = repo.find_commit(target.sha)?.tree()?;
-            let branch_tree = repo.find_commit(branch.head())?;
-            let branch_tree = repo.find_real_tree(&branch_tree, Default::default())?;
-
-            let mut index = repo.merge_trees(&merge_tree, &workspace_tree, &branch_tree, None)?;
+            let branch_head = repo.find_commit(branch.head())?;
+            let branch_tree_id =
+                git2_to_gix_object_id(repo.find_real_tree(&branch_head, Default::default())?.id());
+
+            let mut merge = gix_repo.merge_trees(
+                merge_tree_id,
+                workspace_tree_id,
+                branch_tree_id,
+                gix_repo.default_merge_labels(),
+                merge_options_fail_fast.clone(),
+            )?;
 
-            if !index.has_conflicts() {
-                workspace_tree = repo.find_tree(index.write_tree_to(repo)?)?;
+            if !merge.has_unresolved_conflicts(conflict_kind) {
+                workspace_tree_id = merge
+                    .tree
+                    .write(|tree| gix_repo.write(tree))
+                    .map_err(|err| anyhow!("{err}"))?;
             } else {
                 // This branch should have already been unapplied during the "update" command but for some reason that failed
                 tracing::warn!("Merge conflict between base and {:?}", branch.name);
                 branch.in_workspace = false;
                 vb_state.set_branch(branch.clone())?;
             }
         }
+        workspace_tree = repo.find_tree(gix_to_git2_oid(workspace_tree_id))?;
     }
 
     let committer = gitbutler_repo::signature(SignaturePurpose::Committer)?;

crates/gitbutler-branch-actions/src/stack.rs

@@ -7,7 +7,6 @@ use gitbutler_oplog::entry::{OperationKind, SnapshotDetails};
 use gitbutler_oplog::{OplogExt, SnapshotExt};
 use gitbutler_project::Project;
 use gitbutler_reference::normalize_branch_name;
-use gitbutler_repo::GixRepositoryExt;
 use gitbutler_repo_actions::RepoActionsExt;
 use gitbutler_stack::{
     CommitOrChangeId, ForgeIdentifier, PatchReference, PatchReferenceUpdate, Series,
@@ -192,10 +191,7 @@ pub fn push_stack(project: &Project, branch_id: StackId, with_force: bool) -> Re
 
     // First fetch, because we dont want to push integrated series
     ctx.fetch(&default_target.push_remote_name(), None)?;
-    let gix_repo = ctx
-        .gix_repository()?
-        .for_tree_diffing()?
-        .with_object_memory();
+    let gix_repo = ctx.gix_repository_for_merging_non_persisting()?;
     let cache = gix_repo.commit_graph_if_enabled()?;
     let mut graph = gix_repo.revision_graph(cache.as_ref());
     let mut check_commit = IsCommitIntegrated::new(ctx, &default_target, &gix_repo, &mut graph)?;

crates/gitbutler-branch-actions/src/virtual.rs

@@ -25,7 +25,7 @@ use gitbutler_project::access::WorktreeWritePermission;
 use gitbutler_reference::{normalize_branch_name, Refname, RemoteRefname};
 use gitbutler_repo::{
     rebase::{cherry_rebase, cherry_rebase_group},
-    GixRepositoryExt, LogUntil, RepositoryExt,
+    LogUntil, RepositoryExt,
 };
 use gitbutler_repo_actions::RepoActionsExt;
 use gitbutler_stack::{
@@ -302,10 +302,7 @@ pub fn list_virtual_branches_cached(
     let branches_span =
         tracing::debug_span!("handle branches", num_branches = status.branches.len()).entered();
     let repo = ctx.repository();
-    let gix_repo = ctx
-        .gix_repository()?
-        .for_tree_diffing()?
-        .with_object_memory();
+    let gix_repo = ctx.gix_repository_for_merging_non_persisting()?;
     // We will perform virtual merges, no need to write them to the ODB.
     let cache = gix_repo.commit_graph_if_enabled()?;
     let mut graph = gix_repo.revision_graph(cache.as_ref());

crates/gitbutler-command-context/src/lib.rs

@@ -86,6 +86,26 @@ impl CommandContext {
         Ok(gix::open(self.repository().path())?)
     }
 
+    /// Return a newly opened `gitoxide` repository, with all configuration available
+    /// to correctly figure out author and committer names (i.e. with most global configuration loaded),
+    /// *and* which will perform diffs quickly thanks to an adequate object cache.
+    pub fn gix_repository_for_merging(&self) -> Result<gix::Repository> {
+        let mut repo = gix::open(self.repository().path())?;
+        let bytes = repo.compute_object_cache_size_for_tree_diffs(&***repo.index_or_empty()?);
+        repo.object_cache_size_if_unset(bytes);
+        Ok(repo)
+    }
+
+    /// Return a newly opened `gitoxide` repository, with all configuration available
+    /// to correctly figure out author and committer names (i.e. with most global configuration loaded),
+    /// *and* which will perform diffs quickly thanks to an adequate object cache, *and*
+    /// which **writes all objects into memory**.
+    ///
+    /// This means *changes are non-persisting*.
+    pub fn gix_repository_for_merging_non_persisting(&self) -> Result<gix::Repository> {
+        Ok(self.gix_repository_for_merging()?.with_object_memory())
+    }
+
     /// Return a newly opened `gitoxide` repository with only the repository-local configuration
     /// available. This is a little faster as it has to open less files upon startup.
     ///

crates/gitbutler-repo/src/repository_ext.rs

@@ -699,6 +699,38 @@ pub trait GixRepositoryExt: Sized {
     /// Configure the repository for diff operations between trees.
     /// This means it needs an object cache relative to the amount of files in the repository.
     fn for_tree_diffing(self) -> Result<Self>;
+
+    /// Returns `true` if the merge between `our_tree` and `their_tree` is free of conflicts.
+    /// Conflicts entail content merges with conflict markers, or anything else that doesn't merge cleanly in the tree.
+    ///
+    /// # Important
+    ///
+    /// Make sure the repository is configured [`with_object_memory()`](gix::Repository::with_object_memory()).
+    fn merges_cleanly_compat(
+        &self,
+        ancestor_tree: git2::Oid,
+        our_tree: git2::Oid,
+        their_tree: git2::Oid,
+    ) -> Result<bool>;
+
+    /// Just like the above, but with `gix` types.
+    fn merges_cleanly(
+        &self,
+        ancestor_tree: gix::ObjectId,
+        our_tree: gix::ObjectId,
+        their_tree: gix::ObjectId,
+    ) -> Result<bool>;
+
+    /// Return default lable names when merging trees.
+    ///
+    /// Note that these should probably rather be branch names, but that's for another day.
+    fn default_merge_labels(&self) -> gix::merge::blob::builtin_driver::text::Labels<'static> {
+        gix::merge::blob::builtin_driver::text::Labels {
+            ancestor: Some("base".into()),
+            current: Some("ours".into()),
+            other: Some("theirs".into()),
+        }
+    }
 }
 
 impl GixRepositoryExt for gix::Repository {
@@ -707,6 +739,40 @@ impl GixRepositoryExt for gix::Repository {
         self.object_cache_size_if_unset(bytes);
         Ok(self)
     }
+
+    fn merges_cleanly_compat(
+        &self,
+        ancestor_tree: git2::Oid,
+        our_tree: git2::Oid,
+        their_tree: git2::Oid,
+    ) -> Result<bool> {
+        self.merges_cleanly(
+            git2_to_gix_object_id(ancestor_tree),
+            git2_to_gix_object_id(our_tree),
+            git2_to_gix_object_id(their_tree),
+        )
+    }
+
+    fn merges_cleanly(
+        &self,
+        ancestor_tree: gix::ObjectId,
+        our_tree: gix::ObjectId,
+        their_tree: gix::ObjectId,
+    ) -> Result<bool> {
+        let mut options = self.tree_merge_options()?;
+        let conflict_kind = gix::merge::tree::UnresolvedConflict::Renames;
+        options.fail_on_conflict = Some(conflict_kind);
+        let merge_outcome = self
+            .merge_trees(
+                ancestor_tree,
+                our_tree,
+                their_tree,
+                Default::default(),
+                options,
+            )
+            .context("failed to merge trees")?;
+        Ok(!merge_outcome.has_unresolved_conflicts(conflict_kind))
+    }
 }
 
 type OidFilter = dyn Fn(&git2::Commit) -> Result<bool>;