Identify active buffer by id instead of index

So the active buffer doesn't change when buffers are reordered

src/app.rs

@@ -255,9 +255,9 @@ impl App {
               .buffers
               .set_active_index(self.buffers.active_index() as isize - 1)
           },
-          Action::ToBuffer(buffer_index) => {
+          Action::ToBuffer(buffer_id) => {
             changes_since_last_render = true;
-            self.buffers.set_active_index(buffer_index)
+            self.buffers.set_active_index(buffer_id)
           },
           Action::Resize(w, h) => {
             changes_since_last_render = true;

src/buffers/mod.rs

@@ -146,7 +146,7 @@ pub struct Buffers {
   /// steal them, even if they are also their child (or it would cause buffers to move
   /// every time we re-sort the buffer list)
   attached_to_parent: HashSet<BufferId>,
-  active_index: usize,
+  active_buffer: BufferId,
 }
 
 impl Buffers {
@@ -156,7 +156,7 @@ impl Buffers {
       children: HashMap::new(),
       parents: HashMap::new(),
       attached_to_parent: HashSet::new(),
-      active_index: 0,
+      active_buffer: BufferId::Log,
     }
   }
 
@@ -321,24 +321,40 @@ impl Buffers {
   }
 
   pub fn active_index(&self) -> usize {
-    self.active_index
+    self
+      .buffers
+      .iter()
+      .enumerate()
+      .find(|(_, buf)| buf.id() == self.active_buffer)
+      .map(|(i, _)| i)
+      .unwrap_or(0)
   }
 
   pub fn set_active_index(&mut self, index: isize) {
-    self.active_index = index.wrapping_rem_euclid(self.buffers.len() as isize) as usize;
+    self.active_buffer =
+      self.buffers[index.wrapping_rem_euclid(self.buffers.len() as isize) as usize].id();
+  }
+
+  pub fn set_active_id(&mut self, id: BufferId) {
+    self.active_buffer = id
   }
 
   pub fn active_buffer(&self) -> &dyn Buffer {
     &**self
       .buffers
-      .get(self.active_index)
-      .expect("Active buffer index does not exist")
+      .iter()
+      .find(|buf| buf.id() == self.active_buffer)
+      .unwrap_or(self.buffers.first().expect("No buffers"))
   }
 
   pub fn active_buffer_mut(&mut self) -> &mut Box<dyn Buffer> {
-    self
+    match self
       .buffers
-      .get_mut(self.active_index)
-      .expect("Active buffer index does not exist")
+      .iter()
+      .position(|buf| buf.id() == self.active_buffer)
+    {
+      Some(i) => self.buffers.get_mut(i).expect("Active buffer disappeared"),
+      None => self.buffers.first_mut().expect("No buffers"),
+    }
   }
 }

src/components/buflist.rs

@@ -88,24 +88,24 @@ impl Component for Buflist {
           return Ok(None);
         };
         let column = (x - last_area.x) / self.config.layout.buflist.column_width;
-        let mut buffer_id: isize =
+        let mut buffer_index: isize =
           (column as isize) * (last_area.height as isize) + ((y as isize) - (last_area.y as isize));
-        let buffer_id_usize: usize = buffer_id.try_into().expect("negative buffer_id");
-        if buffer_id_usize >= last_num_buffers {
+        let buffer_index_usize: usize = buffer_index.try_into().expect("negative buffer_index");
+        if buffer_index_usize >= last_num_buffers {
           if self.config.layout.buflist.penultimate_right_overflow {
             // Clicked on the overflow of the last-but-one column
-            buffer_id -= last_area.height as isize;
+            buffer_index -= last_area.height as isize;
           } else {
             // Clicked past the last buffer
             return Ok(None);
           }
         }
-        let buffer_id_usize: usize = buffer_id.try_into().expect("negative buffer_id");
-        if buffer_id_usize >= last_num_buffers {
+        let buffer_index_usize: usize = buffer_index.try_into().expect("negative buffer_index");
+        if buffer_index_usize >= last_num_buffers {
           tracing::error!("[BUG] Unexpected click past the last buffer");
           return Ok(None);
         }
-        Ok(Some(Action::ToBuffer(buffer_id)))
+        Ok(Some(Action::ToBuffer(buffer_index)))
       },
       _ => Ok(None),
     }