Automatically switch to unified diffs when diff view is narrower than a configurable "minimum split diff width" (#52781)

Release Notes:

- The git diff diff view now automatically switches from split mode to
unified mode when the pane is narrower than a configurable minimum
column count. You can configure this via the new
`minimum_split_diff_width` setting.

crates/editor/src/editor_settings.rs

@@ -60,6 +60,7 @@ pub struct EditorSettings {
     pub completion_menu_scrollbar: ShowScrollbar,
     pub completion_detail_alignment: CompletionDetailAlignment,
     pub diff_view_style: DiffViewStyle,
+    pub minimum_split_diff_width: f32,
 }
 #[derive(Debug, Clone)]
 pub struct Jupyter {
@@ -294,6 +295,7 @@ impl Settings for EditorSettings {
                 .unwrap(),
             completion_detail_alignment: editor.completion_detail_alignment.unwrap(),
             diff_view_style: editor.diff_view_style.unwrap(),
+            minimum_split_diff_width: editor.minimum_split_diff_width.unwrap(),
         }
     }
 }

crates/editor/src/split.rs

@@ -7,7 +7,8 @@ use buffer_diff::{BufferDiff, BufferDiffSnapshot};
 use collections::HashMap;
 
 use gpui::{
-    Action, AppContext as _, Entity, EventEmitter, Focusable, Font, Subscription, WeakEntity,
+    Action, AppContext as _, Entity, EventEmitter, Focusable, Font, Pixels, Subscription,
+    WeakEntity, canvas,
 };
 use itertools::Itertools;
 use language::{Buffer, Capability, HighlightedText};
@@ -17,7 +18,7 @@ use multi_buffer::{
 };
 use project::Project;
 use rope::Point;
-use settings::DiffViewStyle;
+use settings::{DiffViewStyle, Settings};
 use text::{Bias, BufferId, OffsetRangeExt as _, Patch, ToPoint as _};
 use ui::{
     App, Context, InteractiveElement as _, IntoElement as _, ParentElement as _, Render,
@@ -36,7 +37,7 @@ use workspace::{
 };
 
 use crate::{
-    Autoscroll, Editor, EditorEvent, RenderDiffHunkControlsFn, ToggleSoftWrap,
+    Autoscroll, Editor, EditorEvent, EditorSettings, RenderDiffHunkControlsFn, ToggleSoftWrap,
     actions::{DisableBreakpoint, EditLogBreakpoint, EnableBreakpoint, ToggleBreakpoint},
     display_map::Companion,
 };
@@ -377,6 +378,12 @@ pub struct SplittableEditor {
     workspace: WeakEntity<Workspace>,
     split_state: Entity<SplitEditorState>,
     searched_side: Option<SplitSide>,
+    /// The preferred diff style.
+    diff_view_style: DiffViewStyle,
+    /// True when the current width is below the minimum threshold for split
+    /// mode, regardless of the current diff view style setting.
+    too_narrow_for_split: bool,
+    last_width: Option<Pixels>,
     _subscriptions: Vec<Subscription>,
 }
 
@@ -396,6 +403,10 @@ impl SplittableEditor {
         self.lhs.as_ref().map(|s| &s.editor)
     }
 
+    pub fn diff_view_style(&self) -> DiffViewStyle {
+        self.diff_view_style
+    }
+
     pub fn is_split(&self) -> bool {
         self.lhs.is_some()
     }
@@ -499,12 +510,15 @@ impl SplittableEditor {
         });
         let split_state = cx.new(|cx| SplitEditorState::new(cx));
         Self {
+            diff_view_style: style,
             rhs_editor,
             rhs_multibuffer,
             lhs: None,
             workspace: workspace.downgrade(),
             split_state,
             searched_side: None,
+            too_narrow_for_split: false,
+            last_width: None,
             _subscriptions: subscriptions,
         }
     }
@@ -826,10 +840,19 @@ impl SplittableEditor {
         window: &mut Window,
         cx: &mut Context<Self>,
     ) {
-        if self.lhs.is_some() {
-            self.unsplit(window, cx);
-        } else {
-            self.split(window, cx);
+        match self.diff_view_style {
+            DiffViewStyle::Unified => {
+                self.diff_view_style = DiffViewStyle::Split;
+                if !self.too_narrow_for_split {
+                    self.split(window, cx);
+                }
+            }
+            DiffViewStyle::Split => {
+                self.diff_view_style = DiffViewStyle::Unified;
+                if self.is_split() {
+                    self.unsplit(window, cx);
+                }
+            }
         }
     }
 
@@ -1249,6 +1272,35 @@ impl SplittableEditor {
             }
         });
     }
+
+    fn width_changed(&mut self, width: Pixels, window: &mut Window, cx: &mut Context<Self>) {
+        self.last_width = Some(width);
+
+        let min_ems = EditorSettings::get_global(cx).minimum_split_diff_width;
+
+        let style = self.rhs_editor.read(cx).create_style(cx);
+        let font_id = window.text_system().resolve_font(&style.text.font());
+        let font_size = style.text.font_size.to_pixels(window.rem_size());
+        let em_advance = window
+            .text_system()
+            .em_advance(font_id, font_size)
+            .unwrap_or(font_size);
+        let min_width = em_advance * min_ems;
+        let is_split = self.lhs.is_some();
+
+        self.too_narrow_for_split = min_ems > 0.0 && width < min_width;
+
+        match self.diff_view_style {
+            DiffViewStyle::Unified => {}
+            DiffViewStyle::Split => {
+                if self.too_narrow_for_split && is_split {
+                    self.unsplit(window, cx);
+                } else if !self.too_narrow_for_split && !is_split {
+                    self.split(window, cx);
+                }
+            }
+        }
+    }
 }
 
 #[cfg(test)]
@@ -2042,30 +2094,23 @@ impl Focusable for SplittableEditor {
     }
 }
 
-// impl Item for SplittableEditor {
-//     type Event = EditorEvent;
-
-//     fn tab_content_text(&self, detail: usize, cx: &App) -> ui::SharedString {
-//         self.rhs_editor().tab_content_text(detail, cx)
-//     }
-
-//     fn as_searchable(&self, _this: &Entity<Self>, cx: &App) -> Option<Box<dyn workspace::searchable::SearchableItemHandle>> {
-//         Some(Box::new(self.last_selected_editor().clone()))
-//     }
-// }
-
 impl Render for SplittableEditor {
     fn render(
         &mut self,
         _window: &mut ui::Window,
         cx: &mut ui::Context<Self>,
     ) -> impl ui::IntoElement {
-        let inner = if self.lhs.is_some() {
+        let is_split = self.lhs.is_some();
+        let inner = if is_split {
             let style = self.rhs_editor.read(cx).create_style(cx);
             SplitEditorView::new(cx.entity(), style, self.split_state.clone()).into_any_element()
         } else {
             self.rhs_editor.clone().into_any_element()
         };
+
+        let this = cx.entity().downgrade();
+        let last_width = self.last_width;
+
         div()
             .id("splittable-editor")
             .on_action(cx.listener(Self::toggle_split))
@@ -2079,6 +2124,25 @@ impl Render for SplittableEditor {
             .capture_action(cx.listener(Self::toggle_soft_wrap))
             .size_full()
             .child(inner)
+            .child(
+                canvas(
+                    move |bounds, window, cx| {
+                        let width = bounds.size.width;
+                        if last_width == Some(width) {
+                            return;
+                        }
+                        window.defer(cx, move |window, cx| {
+                            this.update(cx, |this, cx| {
+                                this.width_changed(width, window, cx);
+                            })
+                            .ok();
+                        });
+                    },
+                    |_, _, _, _| {},
+                )
+                .absolute()
+                .size_full(),
+            )
     }
 }