From 498b7d472823748bdeb19cc6494ba22e1fd5e13d Mon Sep 17 00:00:00 2001
From: Caleb Owens <hello@calebowens.com>
Date: Fri, 5 Dec 2025 17:10:47 +0100
Subject: [PATCH] Implement reword_commit as an example of rebase engine usage

---
 .../ExperimentalSettings.svelte               | 22 ++++-
 apps/desktop/src/lib/config/uiFeatureFlags.ts |  1 +
 .../src/lib/stacks/stackService.svelte.ts     | 21 ++++-
 crates/but-api/Cargo.toml                     | 38 ++++----
 crates/but-api/src/commit.rs                  | 44 +++++++++
 crates/but-api/src/lib.rs                     |  3 +
 .../src/graph_rebase/materialize.rs           | 15 +++-
 .../src/{commit.rs => commit/mod.rs}          |  3 +
 crates/but-workspace/src/commit/reword.rs     | 35 ++++++++
 crates/but-workspace/src/lib.rs               |  2 +-
 .../fixtures/scenario/reword-three-commits.sh | 30 +++++++
 .../workspace/{commit.rs => commit/mod.rs}    |  2 +
 .../tests/workspace/commit/reword.rs          | 89 +++++++++++++++++++
 crates/gitbutler-tauri/src/main.rs            |  3 +-
 14 files changed, 283 insertions(+), 25 deletions(-)
 create mode 100644 crates/but-api/src/commit.rs
 rename crates/but-workspace/src/{commit.rs => commit/mod.rs} (99%)
 create mode 100644 crates/but-workspace/src/commit/reword.rs
 create mode 100644 crates/but-workspace/tests/fixtures/scenario/reword-three-commits.sh
 rename crates/but-workspace/tests/workspace/{commit.rs => commit/mod.rs} (99%)
 create mode 100644 crates/but-workspace/tests/workspace/commit/reword.rs

diff --git a/apps/desktop/src/components/profileSettings/ExperimentalSettings.svelte b/apps/desktop/src/components/profileSettings/ExperimentalSettings.svelte
index 5f3f1355f3..c4d66c299f 100644
--- a/apps/desktop/src/components/profileSettings/ExperimentalSettings.svelte
+++ b/apps/desktop/src/components/profileSettings/ExperimentalSettings.svelte
@@ -1,6 +1,11 @@
 <script lang="ts">
 	import { SETTINGS_SERVICE } from '$lib/config/appSettingsV2';
-	import { ircEnabled, ircServer, fModeEnabled } from '$lib/config/uiFeatureFlags';
+	import {
+		ircEnabled,
+		ircServer,
+		fModeEnabled,
+		useNewRebaseEngine
+	} from '$lib/config/uiFeatureFlags';
 	import { USER } from '$lib/user/user';
 	import { inject } from '@gitbutler/core/context';
 	import { CardGroup, Textbox, Toggle } from '@gitbutler/ui';
@@ -83,6 +88,21 @@
 			/>
 		{/snippet}
 	</CardGroup.Item>
+	<CardGroup.Item labelFor="new-rebase-engine">
+		{#snippet title()}
+			New rebase engine
+		{/snippet}
+		{#snippet caption()}
+			Use the new graph-based rebase engine for stack operations.
+		{/snippet}
+		{#snippet actions()}
+			<Toggle
+				id="new-rebase-engine"
+				checked={$useNewRebaseEngine}
+				onclick={() => useNewRebaseEngine.set(!$useNewRebaseEngine)}
+			/>
+		{/snippet}
+	</CardGroup.Item>
 
 	{#if $user?.role === 'admin'}
 		<CardGroup.Item labelFor="single-branch">
diff --git a/apps/desktop/src/lib/config/uiFeatureFlags.ts b/apps/desktop/src/lib/config/uiFeatureFlags.ts
index 2947048e06..1aa67203fd 100644
--- a/apps/desktop/src/lib/config/uiFeatureFlags.ts
+++ b/apps/desktop/src/lib/config/uiFeatureFlags.ts
@@ -15,3 +15,4 @@ export type StagingBehavior = 'all' | 'selection' | 'none';
 export const stagingBehaviorFeature = persisted<StagingBehavior>('all', 'feature-staging-behavior');
 export const fModeEnabled = persisted(true, 'f-mode');
 export const newlineOnEnter = persisted(false, 'feature-newline-on-enter');
+export const useNewRebaseEngine = persisted(false, 'feature-use-new-rebase-engine');
diff --git a/apps/desktop/src/lib/stacks/stackService.svelte.ts b/apps/desktop/src/lib/stacks/stackService.svelte.ts
index ac837e5163..d3128d6ca9 100644
--- a/apps/desktop/src/lib/stacks/stackService.svelte.ts
+++ b/apps/desktop/src/lib/stacks/stackService.svelte.ts
@@ -1,3 +1,4 @@
+import { useNewRebaseEngine } from '$lib/config/uiFeatureFlags';
 import { ConflictEntries, type ConflictEntriesObj } from '$lib/files/conflicts';
 import { sortLikeFileTree } from '$lib/files/filetreeV3';
 import { showToast } from '$lib/notifications/toasts';
@@ -28,6 +29,7 @@ import {
 	type ThunkDispatch,
 	type UnknownAction
 } from '@reduxjs/toolkit';
+import { get } from 'svelte/store';
 import type { StackOrder } from '$lib/branches/branch';
 import type { Commit, CommitDetails, UpstreamCommit } from '$lib/branches/v3';
 import type { MoveCommitIllegalAction } from '$lib/commits/commit';
@@ -630,7 +632,11 @@ export class StackService {
 	}
 
 	get updateCommitMessage() {
-		return this.api.endpoints.updateCommitMessage.useMutation();
+		if (get(useNewRebaseEngine)) {
+			return this.api.endpoints.updateCommitMessage.useMutation();
+		} else {
+			return this.api.endpoints.legacyUpdateCommitMessage.useMutation();
+		}
 	}
 
 	get newBranch() {
@@ -1181,7 +1187,7 @@ function injectEndpoints(api: ClientState['backendApi'], uiState: UiState) {
 					};
 				}
 			}),
-			updateCommitMessage: build.mutation<
+			legacyUpdateCommitMessage: build.mutation<
 				string,
 				{ projectId: string; stackId: string; commitId: string; message: string }
 			>({
@@ -1192,6 +1198,17 @@ function injectEndpoints(api: ClientState['backendApi'], uiState: UiState) {
 				query: (args) => args,
 				invalidatesTags: () => [invalidatesList(ReduxTag.HeadSha)]
 			}),
+			updateCommitMessage: build.mutation<
+				string,
+				{ projectId: string; commitId: string; message: string }
+			>({
+				extraOptions: {
+					command: 'reword_commit',
+					actionName: 'Update Commit Message'
+				},
+				query: (args) => args,
+				invalidatesTags: () => [invalidatesList(ReduxTag.HeadSha)]
+			}),
 			newBranch: build.mutation<
 				void,
 				{ projectId: string; stackId: string; request: { targetPatch?: string; name: string } }
diff --git a/crates/but-api/Cargo.toml b/crates/but-api/Cargo.toml
index 8461ff6e3e..45e17b45fd 100644
--- a/crates/but-api/Cargo.toml
+++ b/crates/but-api/Cargo.toml
@@ -20,7 +20,7 @@ default = []
 tauri = ["dep:tauri", "legacy"]
 ## When paths are turned into strings they are lossy. Also provide a `_bytes` variant of such fields with the original value
 ## for lossless use.
-path-bytes = ["dep:bstr"]
+path-bytes = []
 ## Make legacy functionality available.
 legacy = [
     "but-ctx/legacy",
@@ -86,25 +86,27 @@ but-rules = { workspace = true, optional = true }
 but-gerrit = { workspace = true, optional = true }
 but-worktrees = { workspace = true, optional = true }
 
-gitbutler-user = {workspace = true, optional = true}
-gitbutler-project = {workspace = true, optional = true}
-gitbutler-branch = {workspace = true, optional = true}
-gitbutler-branch-actions = {workspace = true, optional = true}
-gitbutler-commit = {workspace = true, optional = true}
-gitbutler-reference = {workspace = true, optional = true}
-gitbutler-stack = {workspace = true, optional = true}
-gitbutler-repo = {workspace = true, optional = true}
-gitbutler-repo-actions = {workspace = true, optional = true}
-gitbutler-edit-mode = {workspace = true, optional = true}
-gitbutler-operating-modes = {workspace = true, optional = true}
-gitbutler-sync = {workspace = true, optional = true}
-gitbutler-oplog = {workspace = true, optional = true}
-gitbutler-git = {workspace = true, optional = true}
+gitbutler-user = { workspace = true, optional = true }
+gitbutler-project = { workspace = true, optional = true }
+gitbutler-branch = { workspace = true, optional = true }
+gitbutler-branch-actions = { workspace = true, optional = true }
+gitbutler-commit = { workspace = true, optional = true }
+gitbutler-reference = { workspace = true, optional = true }
+gitbutler-stack = { workspace = true, optional = true }
+gitbutler-repo = { workspace = true, optional = true }
+gitbutler-repo-actions = { workspace = true, optional = true }
+gitbutler-edit-mode = { workspace = true, optional = true }
+gitbutler-operating-modes = { workspace = true, optional = true }
+gitbutler-sync = { workspace = true, optional = true }
+gitbutler-oplog = { workspace = true, optional = true }
+gitbutler-git = { workspace = true, optional = true }
 
-tauri = { version = "^2.9.3", features = ["unstable"], optional = true } # For the #[tauri::command(async)] macro only
+tauri = { version = "^2.9.3", features = [
+    "unstable",
+], optional = true } # For the #[tauri::command(async)] macro only
 
 boolean-enums = { version = "0.4.1", features = ["serde"] }
-bstr = { workspace = true, optional = true }
+bstr = { workspace = true }
 schemars.workspace = true
 serde.workspace = true
 tokio = { workspace = true, features = ["full"] }
@@ -112,7 +114,7 @@ anyhow.workspace = true
 serde_json.workspace = true
 tracing.workspace = true
 serde-error = "0.1.3"
-gix = { workspace = true, features = ["worktree-mutation" ] }
+gix = { workspace = true, features = ["worktree-mutation"] }
 git2.workspace = true
 open.workspace = true
 url = { version = "2.5", optional = true }
diff --git a/crates/but-api/src/commit.rs b/crates/but-api/src/commit.rs
new file mode 100644
index 0000000000..f73d61cf14
--- /dev/null
+++ b/crates/but-api/src/commit.rs
@@ -0,0 +1,44 @@
+use bstr::{BString, ByteSlice};
+use but_api_macros::but_api;
+use but_oplog::legacy::{OperationKind, SnapshotDetails};
+use tracing::instrument;
+
+/// Rewords a commit, but without updating the oplog.
+///
+/// Returns the ID of the newly renamed commit
+#[but_api]
+#[instrument(err(Debug))]
+pub fn reword_commit_only(
+    ctx: &but_ctx::Context,
+    commit_id: gix::ObjectId,
+    message: BString,
+) -> anyhow::Result<gix::ObjectId> {
+    let mut guard = ctx.exclusive_worktree_access();
+    let (repo, _, graph) = ctx.graph_and_meta_mut_and_repo_from_head(guard.write_permission())?;
+
+    but_workspace::commit::reword(&graph, &repo, commit_id, message.as_bstr())
+}
+
+/// Apply `existing_branch` to the workspace in the repository that `ctx` refers to, or create the workspace with default name.
+///
+/// Returns the ID of the newly renamed commit
+#[but_api]
+#[instrument(err(Debug))]
+pub fn reword_commit(
+    ctx: &but_ctx::Context,
+    commit_id: gix::ObjectId,
+    message: BString,
+) -> anyhow::Result<gix::ObjectId> {
+    // NOTE: since this is optional by nature, the same would be true if snapshotting/undo would be disabled via `ctx` app settings, for instance.
+    let maybe_oplog_entry = but_oplog::UnmaterializedOplogSnapshot::from_details(
+        ctx,
+        SnapshotDetails::new(OperationKind::UpdateCommitMessage),
+    )
+    .ok();
+
+    let res = reword_commit_only(ctx, commit_id, message);
+    if let Some(snapshot) = maybe_oplog_entry.filter(|_| res.is_ok()) {
+        snapshot.commit(ctx).ok();
+    };
+    res
+}
diff --git a/crates/but-api/src/lib.rs b/crates/but-api/src/lib.rs
index 143feca79a..c91ae292be 100644
--- a/crates/but-api/src/lib.rs
+++ b/crates/but-api/src/lib.rs
@@ -16,6 +16,9 @@ pub mod github;
 /// Functions that take a branch as input.
 pub mod branch;
 
+/// Functions that operate commits
+pub mod commit;
+
 /// Functions that show what changed in various Git entities, like trees, commits and the worktree.
 pub mod diff;
 
diff --git a/crates/but-rebase/src/graph_rebase/materialize.rs b/crates/but-rebase/src/graph_rebase/materialize.rs
index a07bbb6345..46c99a439e 100644
--- a/crates/but-rebase/src/graph_rebase/materialize.rs
+++ b/crates/but-rebase/src/graph_rebase/materialize.rs
@@ -1,4 +1,6 @@
 //! Functions for materializing a rebase
+use std::collections::HashMap;
+
 use crate::graph_rebase::{Checkouts, rebase::SuccessfulRebase};
 use anyhow::Result;
 use but_core::{
@@ -9,9 +11,16 @@ use but_core::{
     },
 };
 
+/// The outcome of a materialize
+#[derive(Debug, Clone)]
+pub struct MaterializeOutcome {
+    /// A mapping of any commits that were rewritten as part of the rebase
+    pub commit_mapping: HashMap<gix::ObjectId, gix::ObjectId>,
+}
+
 impl SuccessfulRebase {
     /// Materializes a history rewrite
-    pub fn materialize(mut self) -> Result<()> {
+    pub fn materialize(mut self) -> Result<MaterializeOutcome> {
         let repo = self.repo.clone();
         if let Some(memory) = self.repo.objects.take_object_memory() {
             memory.persist(self.repo)?;
@@ -40,6 +49,8 @@ impl SuccessfulRebase {
 
         repo.edit_references(self.ref_edits.clone())?;
 
-        Ok(())
+        Ok(MaterializeOutcome {
+            commit_mapping: self.commit_mapping,
+        })
     }
 }
diff --git a/crates/but-workspace/src/commit.rs b/crates/but-workspace/src/commit/mod.rs
similarity index 99%
rename from crates/but-workspace/src/commit.rs
rename to crates/but-workspace/src/commit/mod.rs
index 84965db4cb..b44bec39f7 100644
--- a/crates/but-workspace/src/commit.rs
+++ b/crates/but-workspace/src/commit/mod.rs
@@ -4,6 +4,9 @@ use but_core::ref_metadata::MaybeDebug;
 
 use crate::WorkspaceCommit;
 
+pub mod reword;
+pub use reword::function::reword;
+
 /// A minimal stack for use by [WorkspaceCommit::new_from_stacks()].
 #[derive(Clone)]
 pub struct Stack {
diff --git a/crates/but-workspace/src/commit/reword.rs b/crates/but-workspace/src/commit/reword.rs
new file mode 100644
index 0000000000..50efa4c802
--- /dev/null
+++ b/crates/but-workspace/src/commit/reword.rs
@@ -0,0 +1,35 @@
+//! An action to perform a reword of a commit
+
+pub(crate) mod function {
+    use anyhow::Result;
+    use bstr::BStr;
+    use but_rebase::{
+        commit::DateMode,
+        graph_rebase::{GraphExt, Step},
+    };
+
+    /// This action will rewrite a commit and any relevant history so it uses
+    /// the new name.
+    ///
+    /// Returns the ID of the newly renamed commit
+    pub fn reword(
+        graph: &but_graph::Graph,
+        repo: &gix::Repository,
+        commit_id: gix::ObjectId,
+        new_message: &BStr,
+    ) -> Result<gix::ObjectId> {
+        let mut editor = graph.to_editor(repo)?;
+        let target_selector = editor.select_commit(commit_id)?;
+
+        let mut commit = editor.find_commit(commit_id)?;
+        commit.message = new_message.to_owned();
+        let new_id = editor.write_commit(commit, DateMode::CommitterUpdateAuthorKeep)?;
+
+        editor.replace(&target_selector, Step::new_pick(new_id));
+
+        let outcome = editor.rebase()?;
+        outcome.materialize()?;
+
+        Ok(new_id)
+    }
+}
diff --git a/crates/but-workspace/src/lib.rs b/crates/but-workspace/src/lib.rs
index 169d4b86b6..ae6c4bd2ad 100644
--- a/crates/but-workspace/src/lib.rs
+++ b/crates/but-workspace/src/lib.rs
@@ -47,7 +47,7 @@ pub mod branch;
 mod changeset;
 
 /// Utility types for the [`WorkspaceCommit`].
-pub(crate) mod commit;
+pub mod commit;
 
 /// Types used only when obtaining head-information.
 ///
diff --git a/crates/but-workspace/tests/fixtures/scenario/reword-three-commits.sh b/crates/but-workspace/tests/fixtures/scenario/reword-three-commits.sh
new file mode 100644
index 0000000000..8753861fa6
--- /dev/null
+++ b/crates/but-workspace/tests/fixtures/scenario/reword-three-commits.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+
+set -eu -o pipefail
+
+echo "/remote/" > .gitignore
+mkdir remote
+pushd remote
+git init
+popd
+
+git init
+
+git remote add origin ./remote
+
+git checkout -b one
+echo "foo" > one.txt
+git add .
+git commit -m "commit one"
+
+git checkout -b two
+echo "foo" > two.txt
+git add .
+git commit -m "commit two"
+
+git push -u origin two
+
+git checkout -b three
+echo "foo" > three.txt
+git add .
+git commit -m "commit three"
diff --git a/crates/but-workspace/tests/workspace/commit.rs b/crates/but-workspace/tests/workspace/commit/mod.rs
similarity index 99%
rename from crates/but-workspace/tests/workspace/commit.rs
rename to crates/but-workspace/tests/workspace/commit/mod.rs
index e9e3f879b0..cbaa1c7560 100644
--- a/crates/but-workspace/tests/workspace/commit.rs
+++ b/crates/but-workspace/tests/workspace/commit/mod.rs
@@ -1,3 +1,5 @@
+mod reword;
+
 mod from_new_merge_with_metadata {
     use bstr::ByteSlice;
     use but_graph::init::{Options, Overlay};
diff --git a/crates/but-workspace/tests/workspace/commit/reword.rs b/crates/but-workspace/tests/workspace/commit/reword.rs
new file mode 100644
index 0000000000..8a1dd84ed2
--- /dev/null
+++ b/crates/but-workspace/tests/workspace/commit/reword.rs
@@ -0,0 +1,89 @@
+use anyhow::Result;
+use but_testsupport::{assure_stable_env, visualize_commit_graph_all};
+use but_workspace::commit::reword;
+
+use crate::ref_info::with_workspace_commit::utils::named_writable_scenario_with_description_and_graph as writable_scenario;
+
+#[test]
+fn reword_head_commit() -> Result<()> {
+    assure_stable_env();
+    let (_tmp, graph, repo, mut _meta, _description) =
+        writable_scenario("reword-three-commits", |_| {})?;
+    insta::assert_snapshot!(visualize_commit_graph_all(&repo)?, @r"
+    * c9f444c (HEAD -> three) commit three
+    * 16fd221 (origin/two, two) commit two
+    * 8b426d0 (one) commit one
+    ");
+
+    let head_tree = repo.head_tree_id()?;
+    let id = repo.rev_parse_single("three")?;
+    reword(&graph, &repo, id.detach(), b"New name".into())?;
+
+    insta::assert_snapshot!(visualize_commit_graph_all(&repo)?, @r"
+    * 7580b8e (HEAD -> three) New name
+    * 16fd221 (origin/two, two) commit two
+    * 8b426d0 (one) commit one
+    ");
+
+    assert_eq!(head_tree, repo.head_tree_id()?);
+
+    Ok(())
+}
+
+#[test]
+fn reword_middle_commit() -> Result<()> {
+    assure_stable_env();
+    let (_tmp, graph, repo, mut _meta, _description) =
+        writable_scenario("reword-three-commits", |_| {})?;
+    insta::assert_snapshot!(visualize_commit_graph_all(&repo)?, @r"
+    * c9f444c (HEAD -> three) commit three
+    * 16fd221 (origin/two, two) commit two
+    * 8b426d0 (one) commit one
+    ");
+
+    let head_tree = repo.head_tree_id()?;
+    let id = repo.rev_parse_single("two")?;
+    reword(&graph, &repo, id.detach(), b"New name".into())?;
+
+    insta::assert_snapshot!(visualize_commit_graph_all(&repo)?, @r"
+    * 086ad49 (HEAD -> three) commit three
+    * d9cea5b (two) New name
+    | * 16fd221 (origin/two) commit two
+    |/  
+    * 8b426d0 (one) commit one
+    ");
+
+    assert_eq!(head_tree, repo.head_tree_id()?);
+
+    Ok(())
+}
+
+#[test]
+fn reword_base_commit() -> Result<()> {
+    assure_stable_env();
+    let (_tmp, graph, repo, mut _meta, _description) =
+        writable_scenario("reword-three-commits", |_| {})?;
+    insta::assert_snapshot!(visualize_commit_graph_all(&repo)?, @r"
+    * c9f444c (HEAD -> three) commit three
+    * 16fd221 (origin/two, two) commit two
+    * 8b426d0 (one) commit one
+    ");
+
+    let head_tree = repo.head_tree_id()?;
+    let id = repo.rev_parse_single("one")?;
+    reword(&graph, &repo, id.detach(), b"New name".into())?;
+
+    // We end up with two divergent histories here. This is to be expected if we
+    // rewrite the very bottom commit in a repoository.
+    insta::assert_snapshot!(visualize_commit_graph_all(&repo)?, @r"
+    * 33b56b8 (HEAD -> three) commit three
+    * 2548c60 (two) commit two
+    * b8c5693 (one) New name
+    * 16fd221 (origin/two) commit two
+    * 8b426d0 commit one
+    ");
+
+    assert_eq!(head_tree, repo.head_tree_id()?);
+
+    Ok(())
+}
diff --git a/crates/gitbutler-tauri/src/main.rs b/crates/gitbutler-tauri/src/main.rs
index 98b3af5164..a0fbfa8ed7 100644
--- a/crates/gitbutler-tauri/src/main.rs
+++ b/crates/gitbutler-tauri/src/main.rs
@@ -14,7 +14,7 @@
 use std::sync::Arc;
 
 use anyhow::bail;
-use but_api::{diff, github, legacy};
+use but_api::{commit, diff, github, legacy};
 use but_claude::{Broadcaster, Claude};
 use but_settings::AppSettingsWithDiskSync;
 use gitbutler_tauri::{
@@ -383,6 +383,7 @@ fn main() -> anyhow::Result<()> {
                 claude::claude_cancel_session,
                 claude::claude_is_stack_active,
                 claude::claude_compact_history,
+                commit::tauri_reword_commit::reword_commit
             ])
             .menu(move |handle| menu::build(handle, &app_settings_for_menu))
             .on_window_event(|window, event| match event {