Fix crash when cursor moves inside folded subtree

cove/src/ui/chat/renderer.rs

@@ -178,7 +178,7 @@ where
 }
 
 /// Expand blocks such that the screen is full for any offset where the
-/// specified block is visible.
+/// specified block is visible. The block must exist.
 pub async fn expand_to_fill_screen_around_block<Id, R>(r: &mut R, id: &Id) -> Result<(), R::Error>
 where
     Id: Eq,
@@ -196,6 +196,8 @@ where
     Ok(())
 }
 
+/// Scroll so that the top of the block is at the specified value. Returns
+/// `true` if successful, or `false` if the block could not be found.
 pub fn scroll_to_set_block_top<Id, R>(r: &mut R, id: &Id, top: i32) -> bool
 where
     Id: Eq,

cove/src/ui/chat/tree.rs

@@ -439,7 +439,7 @@ where
         let mut renderer = TreeRenderer::new(
             context,
             &self.state.store,
-            &self.state.folded,
+            &mut self.state.folded,
             self.cursor,
             self.editor,
             frame.widthdb(),

cove/src/ui/chat/tree/renderer.rs

@@ -80,7 +80,7 @@ pub struct TreeRenderer<'a, M: Msg, S: MsgStore<M>> {
     context: TreeContext<M::Id>,
 
     store: &'a S,
-    folded: &'a HashSet<M::Id>,
+    folded: &'a mut HashSet<M::Id>,
     cursor: &'a mut Cursor<M::Id>,
     editor: &'a mut EditorState,
     widthdb: &'a mut WidthDb,
@@ -107,7 +107,7 @@ where
     pub fn new(
         context: TreeContext<M::Id>,
         store: &'a S,
-        folded: &'a HashSet<M::Id>,
+        folded: &'a mut HashSet<M::Id>,
         cursor: &'a mut Cursor<M::Id>,
         editor: &'a mut EditorState,
         widthdb: &'a mut WidthDb,
@@ -279,12 +279,30 @@ where
         Ok(Some(path.into_first()))
     }
 
-    async fn prepare_initial_tree(&mut self, root_id: &Option<M::Id>) -> Result<(), S::Error> {
+    /// Render the tree containing the cursor to the blocks and set the top and
+    /// bottom root id accordingly. This function will always render a block
+    /// that has the cusor id.
+    async fn prepare_initial_tree(
+        &mut self,
+        cursor_id: &TreeBlockId<M::Id>,
+        root_id: &Option<M::Id>,
+    ) -> Result<(), S::Error> {
         self.top_root_id = root_id.clone();
         self.bottom_root_id = root_id.clone();
 
         let blocks = if let Some(root_id) = root_id {
             let tree = self.store.tree(root_id).await?;
+
+            // To ensure the cursor block will be rendered, all its parents must
+            // be unfolded.
+            if let TreeBlockId::Msg(id) | TreeBlockId::After(id) = cursor_id {
+                let mut id = id.clone();
+                while let Some(parent_id) = tree.parent(&id) {
+                    self.folded.remove(&parent_id);
+                    id = parent_id;
+                }
+            }
+
             self.layout_tree(tree)
         } else {
             self.layout_bottom()
@@ -318,9 +336,11 @@ where
         let cursor_id = TreeBlockId::from_cursor(self.cursor);
         let cursor_root_id = self.root_id(&cursor_id).await?;
 
-        // Render cursor and blocks around it until screen is filled as long as
-        // the cursor is visible, regardless of how the screen is scrolled.
-        self.prepare_initial_tree(&cursor_root_id).await?;
+        // Render cursor and blocks around it so that the screen will always be
+        // filled as long as the cursor is visible, regardless of how the screen
+        // is scrolled.
+        self.prepare_initial_tree(&cursor_id, &cursor_root_id)
+            .await?;
         renderer::expand_to_fill_screen_around_block(self, &cursor_id).await?;
 
         // Scroll based on last cursor position

cove/src/ui/chat/tree/scroll.rs

@@ -33,8 +33,14 @@ where
         delta: i32,
     ) -> Result<(), S::Error> {
         let context = self.last_context();
-        let mut renderer =
-            TreeRenderer::new(context, &self.store, &self.folded, cursor, editor, widthdb);
+        let mut renderer = TreeRenderer::new(
+            context,
+            &self.store,
+            &mut self.folded,
+            cursor,
+            editor,
+            widthdb,
+        );
         renderer.prepare_blocks_for_drawing().await?;
 
         renderer.scroll_by(delta).await?;
@@ -54,8 +60,14 @@ where
         widthdb: &mut WidthDb,
     ) -> Result<(), S::Error> {
         let context = self.last_context();
-        let mut renderer =
-            TreeRenderer::new(context, &self.store, &self.folded, cursor, editor, widthdb);
+        let mut renderer = TreeRenderer::new(
+            context,
+            &self.store,
+            &mut self.folded,
+            cursor,
+            editor,
+            widthdb,
+        );
         renderer.prepare_blocks_for_drawing().await?;
 
         renderer.center_cursor();