When buffer closes, focus on parent buffer (helix-editor#4766)

helix-view/src/tree.rs

@@ -219,7 +219,7 @@ impl Tree {
 
         if self.focus == index {
             // focus on something else
-            self.focus = self.next();
+            self.focus = self.prev();
         }
 
         stack.push(index);
@@ -521,6 +521,26 @@ impl Tree {
         Some(child_id)
     }
 
+    pub fn prev(&self) -> ViewId {
+        // This function is very dumb, but that's because we don't store any parent links.
+        // (we'd be able to go parent.prev_sibling() recursively until we find something)
+        // For now that's okay though, since it's unlikely you'll be able to open a large enough
+        // number of splits to notice.
+
+        let mut views = self
+            .traverse()
+            .rev()
+            .skip_while(|&(id, _view)| id != self.focus)
+            .skip(1); // Skip focused value
+        if let Some((id, _)) = views.next() {
+            id
+        } else {
+            // extremely crude, take the last item
+            let (key, _) = self.traverse().rev().next().unwrap();
+            key
+        }
+    }
+
     pub fn next(&self) -> ViewId {
         // This function is very dumb, but that's because we don't store any parent links.
         // (we'd be able to go parent.next_sibling() recursively until we find something)
@@ -661,6 +681,23 @@ impl<'a> Iterator for Traverse<'a> {
     }
 }
 
+impl<'a> DoubleEndedIterator for Traverse<'a> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        loop {
+            let key = self.stack.pop()?;
+
+            let node = &self.tree.nodes[key];
+
+            match &node.content {
+                Content::View(view) => return Some((key, view)),
+                Content::Container(container) => {
+                    self.stack.extend(container.children.iter());
+                }
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;