Add a default_diff_view setting

assets/settings/default.json

@@ -1450,6 +1450,11 @@
     // Should the name or path be displayed first in the git view.
     // "path_style": "file_name_first" or "file_path_first"
     "path_style": "file_name_first",
+    // Whether the project diff view opens in stacked or side-by-side mode.
+    //
+    // Choices: stacked, side_by_side
+    // Default: stacked
+    "default_diff_view": "stacked",
   },
   // The list of custom Git hosting providers.
   "git_hosting_providers": [

crates/editor/src/split.rs

@@ -467,16 +467,25 @@ impl SplittableEditor {
     }
 
     fn split(&mut self, _: &SplitDiff, window: &mut Window, cx: &mut Context<Self>) {
+        let Some(workspace) = self.workspace.upgrade() else {
+            return;
+        };
+        let project = workspace.read(cx).project().clone();
+        self.do_split(project, window, cx);
+    }
+
+    pub fn do_split(
+        &mut self,
+        project: Entity<Project>,
+        window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
         if !cx.has_flag::<SplitDiffFeatureFlag>() {
             return;
         }
         if self.lhs.is_some() {
             return;
         }
-        let Some(workspace) = self.workspace.upgrade() else {
-            return;
-        };
-        let project = workspace.read(cx).project().clone();
 
         let lhs_multibuffer = cx.new(|cx| {
             let mut multibuffer = MultiBuffer::new(Capability::ReadOnly);

crates/git_ui/src/project_diff.rs

@@ -26,14 +26,15 @@ use gpui::{
 };
 use language::{Anchor, Buffer, Capability, OffsetRangeExt};
 use multi_buffer::{MultiBuffer, PathKey};
+use project::project_settings::ProjectSettings;
 use project::{
     Project, ProjectPath,
     git_store::{
         Repository,
         branch_diff::{self, BranchDiffEvent, DiffBase},
     },
 };
-use settings::{Settings, SettingsStore};
+use settings::{DefaultDiffView, Settings, SettingsStore};
 use smol::future::yield_now;
 use std::any::{Any, TypeId};
 use std::sync::Arc;
@@ -300,7 +301,7 @@ impl ProjectDiff {
         });
 
         let editor = cx.new(|cx| {
-            let diff_display_editor = SplittableEditor::new_unsplit(
+            let mut diff_display_editor = SplittableEditor::new_unsplit(
                 multibuffer.clone(),
                 project.clone(),
                 workspace.clone(),
@@ -332,6 +333,12 @@ impl ProjectDiff {
                     }
                 }
             });
+
+            if ProjectSettings::get_global(cx).git.default_diff_view == DefaultDiffView::SideBySide
+            {
+                diff_display_editor.do_split(project.clone(), window, cx);
+            }
+
             diff_display_editor
         });
         let editor_subscription = cx.subscribe_in(&editor, window, Self::handle_editor_event);
@@ -2727,4 +2734,73 @@ mod tests {
         assert_eq!(paths_b.len(), 1);
         assert_eq!(*paths_b[0], *"b.txt");
     }
+
+    #[gpui::test]
+    async fn test_default_diff_view_is_stacked_when_no_setting_specified(cx: &mut TestAppContext) {
+        init_test(cx);
+        assert_default_diff_view(None, false, cx).await;
+    }
+
+    #[gpui::test]
+    async fn test_default_diff_view_is_stacked_when_set_to_stacked(cx: &mut TestAppContext) {
+        init_test(cx);
+        assert_default_diff_view(Some(settings::DefaultDiffView::Stacked), false, cx).await;
+    }
+
+    #[gpui::test]
+    async fn test_default_diff_view_is_split_when_set_to_side_by_side(cx: &mut TestAppContext) {
+        init_test(cx);
+        assert_default_diff_view(Some(settings::DefaultDiffView::SideBySide), true, cx).await;
+    }
+
+    async fn assert_default_diff_view(
+        default_diff_view: Option<settings::DefaultDiffView>,
+        expect_split: bool,
+        cx: &mut TestAppContext,
+    ) {
+        if let Some(default_diff_view) = default_diff_view {
+            cx.update(|cx| {
+                let mut settings = ProjectSettings::get_global(cx).clone();
+                settings.git.default_diff_view = default_diff_view;
+                ProjectSettings::override_global(settings, cx);
+            });
+        }
+
+        let fs = FakeFs::new(cx.executor());
+        fs.insert_tree(
+            path!("/project"),
+            json!({
+                ".git": {},
+                "foo.txt": "dominate\n",
+            }),
+        )
+        .await;
+        let project = Project::test(fs.clone(), [path!("/project").as_ref()], cx).await;
+
+        fs.set_head_and_index_for_repo(
+            Path::new(path!("/project/.git")),
+            &[("foo.txt", "intimidate\n".to_string())],
+        );
+
+        let (workspace, cx) =
+            cx.add_window_view(|window, cx| Workspace::test_new(project.clone(), window, cx));
+        cx.run_until_parked();
+
+        cx.focus(&workspace);
+        cx.update(|window, cx| {
+            window.dispatch_action(project_diff::Diff.boxed_clone(), cx);
+        });
+        cx.run_until_parked();
+
+        let diff_item = workspace.update(cx, |workspace, cx| {
+            workspace.active_item_as::<ProjectDiff>(cx).unwrap()
+        });
+        diff_item.read_with(cx, |diff, cx| {
+            assert_eq!(
+                diff.editor.read(cx).is_split(),
+                expect_split,
+                "Expected is_split() to be {expect_split}"
+            );
+        });
+    }
 }

crates/project/src/project_settings.rs

@@ -454,6 +454,10 @@ pub struct GitSettings {
     ///
     /// Default: file_name_first
     pub path_style: GitPathStyle,
+    /// Whether the project diff view opens in stacked or side-by-side mode.
+    ///
+    /// Default: stacked
+    pub default_diff_view: settings::DefaultDiffView,
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -643,6 +647,7 @@ impl Settings for ProjectSettings {
             },
             hunk_style: git.hunk_style.unwrap(),
             path_style: git.path_style.unwrap().into(),
+            default_diff_view: git.default_diff_view.unwrap(),
         };
         Self {
             context_servers: project

crates/settings_content/src/project.rs

@@ -9,8 +9,8 @@ use settings_macros::{MergeFrom, with_fallible_options};
 use util::serde::default_true;
 
 use crate::{
-    AllLanguageSettingsContent, DelayMs, ExtendingVec, ParseStatus, ProjectTerminalSettingsContent,
-    RootUserSettings, SlashCommandSettings, fallible_options,
+    AllLanguageSettingsContent, DefaultDiffView, DelayMs, ExtendingVec, ParseStatus,
+    ProjectTerminalSettingsContent, RootUserSettings, SlashCommandSettings, fallible_options,
 };
 
 #[with_fallible_options]
@@ -468,6 +468,10 @@ pub struct GitSettings {
     ///
     /// Default: file_name_first
     pub path_style: Option<GitPathStyle>,
+    /// Whether the project diff view opens in stacked or side-by-side mode.
+    ///
+    /// Default: stacked
+    pub default_diff_view: Option<DefaultDiffView>,
 }
 
 #[with_fallible_options]

crates/settings_content/src/settings_content.rs

@@ -584,6 +584,29 @@ pub struct GitPanelSettingsContent {
     pub tree_view: Option<bool>,
 }
 
+#[derive(
+    Default,
+    Copy,
+    Clone,
+    Debug,
+    Serialize,
+    Deserialize,
+    JsonSchema,
+    MergeFrom,
+    PartialEq,
+    Eq,
+    strum::VariantArray,
+    strum::VariantNames,
+)]
+#[serde(rename_all = "snake_case")]
+pub enum DefaultDiffView {
+    /// Show the old and new content in a single editor, interleaved.
+    #[default]
+    Stacked,
+    /// Show the old and new content in side-by-side editors.
+    SideBySide,
+}
+
 #[derive(
     Default,
     Copy,

crates/settings_ui/src/settings_ui.rs

@@ -516,6 +516,7 @@ fn init_renderers(cx: &mut App) {
         .add_basic_renderer::<settings::NotifyWhenAgentWaiting>(render_dropdown)
         .add_basic_renderer::<settings::ImageFileSizeUnit>(render_dropdown)
         .add_basic_renderer::<settings::StatusStyle>(render_dropdown)
+        .add_basic_renderer::<settings::DefaultDiffView>(render_dropdown)
         .add_basic_renderer::<settings::EncodingDisplayOptions>(render_dropdown)
         .add_basic_renderer::<settings::PaneSplitDirectionHorizontal>(render_dropdown)
         .add_basic_renderer::<settings::PaneSplitDirectionVertical>(render_dropdown)