fix(data-service): don't abort the transaction from 'outside' the tra…

…nsaction COMPASS-7368 (#5107)

* don't abort the transaction from 'outside' the transaction

* clarify a bit

packages/data-service/src/data-service.ts

@@ -2391,10 +2391,8 @@ class DataServiceImpl extends WithLogContext implements DataService {
                 .sort({ _id: 1 })
                 .toArray();
 
-              if (session.inTransaction()) {
-                await session.abortTransaction();
-                await session.endSession();
-              }
+              await session.abortTransaction();
+              await session.endSession();
 
               const changes = docsToPreview.map((before, idx) => ({
                 before,
@@ -2409,10 +2407,14 @@ class DataServiceImpl extends WithLogContext implements DataService {
         } catch (err: any) {
           if (isTransactionAbortError(err)) {
             // The transaction was aborted while it was still calculating the
-            // preview. Just return something here rather than erroring.
+            // preview. Just return something here rather than erroring. No
+            // reason to abort the transaction or end the session again because
+            // we only got here because that already happened.
             return { changes: [] };
           }
 
+          // The only way this if statement would be true is if aborting the
+          // transaction and ending the session itself failed above. Unlikely.
           if (session.inTransaction()) {
             await session.abortTransaction();
             await session.endSession();
@@ -2421,11 +2423,13 @@ class DataServiceImpl extends WithLogContext implements DataService {
           throw err;
         }
       },
-      async (session) => {
-        if (session.inTransaction()) {
-          await session.abortTransaction();
-          await session.endSession();
-        }
+      async () => {
+        // Rely on the session being killed when we cancel the operation. It can
+        // take a few seconds before the driver reacts, but the Promise.race()
+        // against the abort signal should cause the UI to immediately be
+        // notified that the operation was cancelled. We don't abort the
+        // transaction or end the session as well because the code we run inside
+        // session.withTransaction() above would experience race conditions.
       },
       abortSignal
     );