editor: Restore selections to positions after last edit (#28527)

Closes #22692

Makes it so when undoing a format operation, the selections are set to
where they were at the last edit.

Release Notes:

- Made it so the cursor position is reset to where it was after the last
edit when undoing a format operation. This will only result in different
behavior when you make an edit, scroll away, initiate formatting (either
by saving or manually) and then undo the format.

---------

Co-authored-by: Zed AI <ai@zed.dev>

crates/editor/src/editor.rs

@@ -14175,12 +14175,28 @@ impl Editor {
             }
         };
 
+        let transaction_id_prev = buffer.read_with(cx, |b, cx| b.last_transaction_id(cx));
+        let selections_prev = transaction_id_prev
+            .and_then(|transaction_id_prev| {
+                // default to selections as they were after the last edit, if we have them,
+                // instead of how they are now.
+                // This will make it so that editing, moving somewhere else, formatting, then undoing the format
+                // will take you back to where you made the last edit, instead of staying where you scrolled
+                self.selection_history
+                    .transaction(transaction_id_prev)
+                    .map(|t| t.0.clone())
+            })
+            .unwrap_or_else(|| {
+                log::info!("Failed to determine selections from before format. Falling back to selections when format was initiated");
+                self.selections.disjoint_anchors()
+            });
+
         let mut timeout = cx.background_executor().timer(FORMAT_TIMEOUT).fuse();
         let format = project.update(cx, |project, cx| {
             project.format(buffers, target, true, trigger, cx)
         });
 
-        cx.spawn_in(window, async move |_, cx| {
+        cx.spawn_in(window, async move |editor, cx| {
             let transaction = futures::select_biased! {
                 transaction = format.log_err().fuse() => transaction,
                 () = timeout => {
@@ -14200,6 +14216,19 @@ impl Editor {
                 })
                 .ok();
 
+            if let Some(transaction_id_now) =
+                buffer.read_with(cx, |b, cx| b.last_transaction_id(cx))?
+            {
+                let has_new_transaction = transaction_id_prev != Some(transaction_id_now);
+                if has_new_transaction {
+                    _ = editor.update(cx, |editor, _| {
+                        editor
+                            .selection_history
+                            .insert_transaction(transaction_id_now, selections_prev);
+                    });
+                }
+            }
+
             Ok(())
         })
     }