Return optional transaction ids when starting/ending a transaction

If the transaction was nested, we return None. Otherwise we return the transaction id in preparation for editors to maintain their own selection state.

crates/editor/src/editor.rs

@@ -25,11 +25,10 @@ use language::{
     BracketPair, Buffer, Diagnostic, DiagnosticSeverity, Language, Point, Selection, SelectionGoal,
     SelectionSetId,
 };
-use multi_buffer::{
-    Anchor, AnchorRangeExt, MultiBufferChunks, MultiBufferSnapshot,
-    SelectionSet, ToOffset, ToPoint,
-};
 pub use multi_buffer::MultiBuffer;
+use multi_buffer::{
+    Anchor, AnchorRangeExt, MultiBufferChunks, MultiBufferSnapshot, SelectionSet, ToOffset, ToPoint,
+};
 use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
 use smol::Timer;
@@ -3209,15 +3208,13 @@ impl Editor {
     fn start_transaction(&mut self, cx: &mut ViewContext<Self>) {
         self.end_selection(cx);
         self.buffer.update(cx, |buffer, cx| {
-            buffer
-                .start_transaction([self.selection_set_id], cx)
-                .unwrap()
+            buffer.start_transaction([self.selection_set_id], cx);
         });
     }
 
     fn end_transaction(&self, cx: &mut ViewContext<Self>) {
         self.buffer.update(cx, |buffer, cx| {
-            buffer.end_transaction([self.selection_set_id], cx).unwrap()
+            buffer.end_transaction([self.selection_set_id], cx);
         });
     }
 

crates/editor/src/multi_buffer.rs

@@ -8,7 +8,7 @@ use collections::HashMap;
 use gpui::{AppContext, Entity, ModelContext, ModelHandle, MutableAppContext, Task};
 use language::{
     Buffer, BufferChunks, BufferSnapshot, Chunk, DiagnosticEntry, Event, File, Language,
-    ToOffset as _, ToPoint as _,
+    ToOffset as _, ToPoint as _, TransactionId,
 };
 pub use selection::SelectionSet;
 use std::{
@@ -206,7 +206,7 @@ impl MultiBuffer {
         &mut self,
         selection_set_ids: impl IntoIterator<Item = SelectionSetId>,
         cx: &mut ModelContext<Self>,
-    ) -> Result<()> {
+    ) -> Option<TransactionId> {
         // TODO
         self.as_singleton()
             .unwrap()
@@ -217,7 +217,7 @@ impl MultiBuffer {
         &mut self,
         selection_set_ids: impl IntoIterator<Item = SelectionSetId>,
         cx: &mut ModelContext<Self>,
-    ) -> Result<()> {
+    ) -> Option<TransactionId> {
         // TODO
         self.as_singleton().unwrap().update(cx, |buffer, cx| {
             buffer.end_transaction(selection_set_ids, cx)