From 93eb005f74d31ae0b1d805da7fc0c67774884ddd Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@zed.dev>
Date: Thu, 10 Feb 2022 09:26:20 -0700
Subject: [PATCH] Correctly redo all undone edits after undoing in multi-buffer

When undoing edits performed in the multi-buffer, we also undo subsequent edits that may have occurred outside of the multi-buffer. This commit makes us redo those edits as well.

Co-Authored-By: Antonio Scandurra <me@as-cii.com>
---
 crates/editor/src/multi_buffer.rs | 28 ++++++++++++++++++----------
 crates/text/src/text.rs           |  8 ++++++++
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/crates/editor/src/multi_buffer.rs b/crates/editor/src/multi_buffer.rs
index ed3d67f8b3..acc7b22183 100644
--- a/crates/editor/src/multi_buffer.rs
+++ b/crates/editor/src/multi_buffer.rs
@@ -557,10 +557,14 @@ impl MultiBuffer {
 
         while let Some(transaction) = self.history.pop_undo() {
             let mut undone = false;
-            for (buffer_id, buffer_transaction_id) in &transaction.buffer_transactions {
+            for (buffer_id, buffer_transaction_id) in &mut transaction.buffer_transactions {
                 if let Some(BufferState { buffer, .. }) = self.buffers.borrow().get(&buffer_id) {
-                    undone |= buffer.update(cx, |buf, cx| {
-                        buf.undo_to_transaction(*buffer_transaction_id, cx)
+                    undone |= buffer.update(cx, |buffer, cx| {
+                        let undo_to = *buffer_transaction_id;
+                        if let Some(entry) = buffer.peek_undo_stack() {
+                            *buffer_transaction_id = entry.transaction_id();
+                        }
+                        buffer.undo_to_transaction(undo_to, cx)
                     });
                 }
             }
@@ -580,10 +584,14 @@ impl MultiBuffer {
 
         while let Some(transaction) = self.history.pop_redo() {
             let mut redone = false;
-            for (buffer_id, buffer_transaction_id) in &transaction.buffer_transactions {
+            for (buffer_id, buffer_transaction_id) in &mut transaction.buffer_transactions {
                 if let Some(BufferState { buffer, .. }) = self.buffers.borrow().get(&buffer_id) {
-                    redone |= buffer.update(cx, |buf, cx| {
-                        buf.redo_to_transaction(*buffer_transaction_id, cx)
+                    redone |= buffer.update(cx, |buffer, cx| {
+                        let redo_to = *buffer_transaction_id;
+                        if let Some(entry) = buffer.peek_redo_stack() {
+                            *buffer_transaction_id = entry.transaction_id();
+                        }
+                        buffer.redo_to_transaction(redo_to, cx)
                     });
                 }
             }
@@ -2274,21 +2282,21 @@ impl History {
         }
     }
 
-    fn pop_undo(&mut self) -> Option<&Transaction> {
+    fn pop_undo(&mut self) -> Option<&mut Transaction> {
         assert_eq!(self.transaction_depth, 0);
         if let Some(transaction) = self.undo_stack.pop() {
             self.redo_stack.push(transaction);
-            self.redo_stack.last()
+            self.redo_stack.last_mut()
         } else {
             None
         }
     }
 
-    fn pop_redo(&mut self) -> Option<&Transaction> {
+    fn pop_redo(&mut self) -> Option<&mut Transaction> {
         assert_eq!(self.transaction_depth, 0);
         if let Some(transaction) = self.redo_stack.pop() {
             self.undo_stack.push(transaction);
-            self.undo_stack.last()
+            self.undo_stack.last_mut()
         } else {
             None
         }
diff --git a/crates/text/src/text.rs b/crates/text/src/text.rs
index 20f0e422c8..9b7f8dd230 100644
--- a/crates/text/src/text.rs
+++ b/crates/text/src/text.rs
@@ -84,6 +84,10 @@ pub struct Transaction {
 }
 
 impl HistoryEntry {
+    pub fn transaction_id(&self) -> TransactionId {
+        self.transaction.id
+    }
+
     fn push_edit(&mut self, edit: &EditOperation) {
         self.transaction.edit_ids.push(edit.timestamp.local());
         self.transaction.end.observe(edit.timestamp.local());
@@ -1150,6 +1154,10 @@ impl Buffer {
         self.history.undo_stack.last()
     }
 
+    pub fn peek_redo_stack(&self) -> Option<&HistoryEntry> {
+        self.history.redo_stack.last()
+    }
+
     pub fn start_transaction(&mut self) -> Option<TransactionId> {
         self.start_transaction_at(Instant::now())
     }