Preserve rename preview scroll through full details

crates/oa-desktop/src/app/source_rename.rs

@@ -49,6 +49,7 @@ pub enum Event {
     Line(Id, Id, bool),
     Segment(Id, Id, bool),
     Details(Id, bool),
+    PreviewScrolled(Id, Id, Id, f32),
     DetailSegment(Id, bool),
     ReadOnly(Id, text_editor::Action),
     Undo(Id),
@@ -112,6 +113,7 @@ struct Form {
     line: usize,
     segment: usize,
     preview_destination: Id,
+    preview_offset: f32,
     details: bool,
     detail_segment: usize,
     detail_editor: text_editor::Content,
@@ -170,6 +172,17 @@ impl App {
             return false;
         };
         match event {
+            Event::PreviewScrolled(invocation, approval, destination, offset) => {
+                *invocation == form.invocation
+                    && !form.details
+                    && form
+                        .approval
+                        .as_ref()
+                        .is_some_and(|ready| ready.id == *approval)
+                    && *destination == form.preview_destination
+                    && offset.is_finite()
+                    && *offset >= 0.
+            }
             Event::Preview(invocation, generation) => {
                 *invocation == form.invocation && *generation == form.generation
             }
@@ -435,11 +448,23 @@ impl App {
                 }
                 form.details = value;
                 // Leaving or returning to the preview ends the old visit. Keep
-                // its selected page and retained scroll; only retire delayed
+                // its selected page and scroll; the Details widget replaces the
-                // operations, without scheduling another return-to-top.
+                // preview subtree, so restore the reported offset on return.
                 form.preview_destination = Id::new_v4();
                 form.detail_segment = 0;
                 refresh_details(form);
+                if !value && let Some(ready) = &form.approval {
+                    return iced::widget::operation::scroll_to(
+                        preview_scroll_id(form, ready.id),
+                        iced::widget::scrollable::AbsoluteOffset {
+                            x: None,
+                            y: Some(form.preview_offset),
+                        },
+                    );
+                }
+            }
+            Event::PreviewScrolled(_, _, _, offset) => {
+                self.source_rename.form.as_mut().unwrap().preview_offset = offset;
             }
             Event::DetailSegment(_, next) => {
                 let form = self.source_rename.form.as_mut().unwrap();
@@ -516,6 +541,7 @@ impl App {
             line: 0,
             segment: 0,
             preview_destination: Id::new_v4(),
+            preview_offset: 0.,
             details: false,
             detail_segment: 0,
             detail_editor: text_editor::Content::new(),
@@ -953,6 +979,7 @@ fn input_id(invocation: Id) -> iced::widget::Id {
 // or changing a filter that leaves the page tuple unchanged (the ABA case).
 fn reset_preview_position(form: &mut Form) -> Task<Message> {
     form.preview_destination = Id::new_v4();
+    form.preview_offset = 0.;
     if !form.details
         && let Some(ready) = &form.approval
     {
@@ -1118,7 +1145,15 @@ where
             pager(format!("Row segments {}/{} · both sides", form.segment + 1, segments.max(1)),
                 (form.segment > 0).then(|| message(Event::Segment(invocation, preview_id, false))),
                 (form.segment + 1 < segments).then(|| message(Event::Segment(invocation, preview_id, true)))),
-            scrollable(displayed).id(preview_scroll_id(form, preview_id)).height(Fill).width(Fill).spacing(8),
+            scrollable(displayed)
+                .id(preview_scroll_id(form, preview_id))
+                .on_scroll({
+                    let destination = form.preview_destination;
+                    move |viewport| message(Event::PreviewScrolled(
+                        invocation, preview_id, destination, viewport.absolute_offset().y,
+                    ))
+                })
+                .height(Fill).width(Fill).spacing(8),
         ].spacing(6).height(Fill).into()
     } else {
         scrollable(column![

crates/oa-desktop/src/app/source_rename/preview_scroll_tests.rs

@@ -50,6 +50,7 @@ fn scroll_id(app: &App) -> widget::Id {
 struct Geometry {
     id: widget::Id,
     offset: Option<Vector>,
+    bounds: Option<Rectangle>,
 }
 impl widget::Operation for Geometry {
     fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn widget::Operation)) {
@@ -58,13 +59,14 @@ impl widget::Operation for Geometry {
     fn scrollable(
         &mut self,
         id: Option<&widget::Id>,
-        _: Rectangle,
+        bounds: Rectangle,
         _: Rectangle,
         offset: Vector,
         _: &mut dyn widget::operation::Scrollable,
     ) {
         if id == Some(&self.id) {
             self.offset = Some(offset);
+            self.bounds = Some(bounds);
         }
     }
 }
@@ -95,6 +97,7 @@ impl Mounted {
         let mut geometry = Geometry {
             id: scroll_id(app),
             offset: None,
+            bounds: None,
         };
         self.operate(app, &mut geometry);
         geometry.offset.expect("mounted preview scrollable").y
@@ -114,6 +117,41 @@ impl Mounted {
         assert!(offset > 10., "fixture must really be scrolled");
         offset
     }
+    fn wheel(&mut self, app: &App) -> Vec<Message> {
+        let mut geometry = Geometry {
+            id: scroll_id(app),
+            offset: None,
+            bounds: None,
+        };
+        self.operate(app, &mut geometry);
+        let position = geometry.bounds.expect("visible preview bounds").center();
+        let mut view = dialog_content(app, &self.editor);
+        self.tree.diff(view.as_widget());
+        let node = view.as_widget_mut().layout(
+            &mut self.tree,
+            &FontLayout,
+            &layout::Limits::new(Size::ZERO, HOST),
+        );
+        let mut messages = Vec::new();
+        let mut shell = iced::advanced::Shell::new(&mut messages);
+        view.as_widget_mut().update(
+            &mut self.tree,
+            &iced::Event::Mouse(iced::mouse::Event::WheelScrolled {
+                delta: iced::mouse::ScrollDelta::Pixels { x: 0., y: -120. },
+            }),
+            Layout::new(&node),
+            iced::mouse::Cursor::Available(position),
+            &FontLayout,
+            &mut iced::advanced::clipboard::Null,
+            &mut shell,
+            &Rectangle::with_size(HOST),
+        );
+        assert!(
+            shell.is_event_captured(),
+            "preview must consume wheel input"
+        );
+        messages
+    }
     async fn execute(&mut self, app: &App, task: Task<Message>) -> usize {
         let mut count = 0;
         if let Some(mut actions) = iced_runtime::task::into_stream(task) {
@@ -337,6 +375,7 @@ async fn details_round_trip_retires_held_reset_without_changing_page_or_repeated
             let mut hidden = Geometry {
                 id: old_preview.clone(),
                 offset: None,
+                bounds: None,
             };
             mounted.operate(&app, &mut hidden);
             assert!(
@@ -355,8 +394,8 @@ async fn details_round_trip_retires_held_reset_without_changing_page_or_repeated
         let show_preview = app.update(Message::SourceRename(Event::Details(invocation, false)));
         assert_eq!(
             mounted.execute(&app, show_preview).await,
-            0,
+            1,
-            "returning does not force a scroll reset"
+            "returning restores the reported offset in the new preview subtree"
         );
         let returned_visit = scroll_id(&app);
         assert_ne!(returned_visit, old_preview);
@@ -383,3 +422,82 @@ async fn details_round_trip_retires_held_reset_without_changing_page_or_repeated
         assert_eq!(evidence(&app), before);
     }
 }
+
+#[tokio::test]
+async fn details_remount_restores_wheel_offset_before_any_rescroll() {
+    for mount_details in [true, false] {
+        let mut app = paged_fixture();
+        let before = evidence(&app);
+        let form = app.source_rename.form.as_ref().unwrap();
+        let invocation = form.invocation;
+        let approval = form.approval.as_ref().unwrap().id;
+        let page = (form.file, form.hunk, form.line, form.segment);
+        let mut mounted = Mounted::new(&app);
+        let reports = mounted.wheel(&app);
+        assert_eq!(reports.len(), 1, "one actual preview scroll report");
+        assert!(matches!(
+            reports[0],
+            Message::SourceRename(Event::PreviewScrolled(..))
+        ));
+        let offset = mounted.offset(&app);
+        assert!(
+            offset > 10.,
+            "real wheel input must move the overflowing fixture"
+        );
+        for message in reports.iter().cloned() {
+            let task = app.update(message);
+            assert_eq!(mounted.execute(&app, task).await, 0);
+        }
+        assert_eq!(
+            app.source_rename.form.as_ref().unwrap().preview_offset,
+            offset
+        );
+
+        let details = app.update(Message::SourceRename(Event::Details(invocation, true)));
+        assert_eq!(mounted.execute(&app, details).await, 0);
+        if mount_details {
+            let mut hidden = Geometry {
+                id: scroll_id(&app),
+                offset: None,
+                bounds: None,
+            };
+            mounted.operate(&app, &mut hidden);
+            assert!(hidden.offset.is_none(), "Details replaced the Scrollable");
+        }
+        // A queued report from the hidden preview cannot overwrite its saved offset.
+        let Message::SourceRename(Event::PreviewScrolled(
+            old_invocation,
+            old_approval,
+            old_visit,
+            _,
+        )) = reports[0].clone()
+        else {
+            unreachable!()
+        };
+        let stale = Event::PreviewScrolled(old_invocation, old_approval, old_visit, offset + 100.);
+        assert!(!app.source_rename_envelope(&stale));
+        let task = app.update(Message::SourceRename(stale.clone()));
+        assert_eq!(mounted.execute(&app, task).await, 0);
+
+        let returned = app.update(Message::SourceRename(Event::Details(invocation, false)));
+        assert_eq!(mounted.execute(&app, returned).await, 1);
+        // This assertion precedes any new scroll: the former test scrolled again here.
+        assert_eq!(mounted.offset(&app), offset);
+        let form = app.source_rename.form.as_ref().unwrap();
+        assert_eq!((form.file, form.hunk, form.line, form.segment), page);
+        assert_eq!(form.approval.as_ref().unwrap().id, approval);
+        assert_eq!(form.preview_offset, offset);
+        assert!(!app.source_rename_envelope(&stale));
+        let task = app.update(Message::SourceRename(stale));
+        assert_eq!(mounted.execute(&app, task).await, 0);
+        assert_eq!(mounted.offset(&app), offset);
+
+        let next = app.update(Message::SourceRename(Event::File(
+            invocation, approval, true,
+        )));
+        assert_eq!(mounted.execute(&app, next).await, 1);
+        assert_eq!(mounted.offset(&app), 0.);
+        assert_eq!(app.source_rename.form.as_ref().unwrap().preview_offset, 0.);
+        assert_eq!(evidence(&app), before);
+    }
+}