Fixed bug in changesSinceV2 where to and from in CommitTransitions we…

…re swapped

Summary:
# Context

We are introducing EdenFS notifications to support scalable and ergonomic file system notifications for EdenFS mounts.

# This Diff

* Because we process the journal from back to front there was confusion on which commit id is `from` and which is `to`. We got it backwards. This diff fixes that.
* Updated the integration tests (there are no .t tests here).
* We have put in a hack in the buck2 integration code that will need to be addressed when this change is rolled out fully.

# Next Steps

* Add suffix (extension) filters - inclusion and exclusion.
* Investigate best performance data structures for modeling inclusion and exclusion path filters (Watchman uses a radix tree search).
* Change the journal walking code to scan for position then walk forwards - current implemantion walks backward.
* .t tests, Python integration tests, C++ unit tests

# Discussion Points

None

Differential Revision: D67552308

fbshipit-source-id: 972e1581fd896acc57d9e77d198ccd5a4946ac33

eden/fs/service/EdenServiceHandler.cpp

@@ -2425,9 +2425,9 @@ void EdenServiceHandler::sync_changesSinceV2(
         },
         [&](const RootUpdateJournalDelta& current) -> void {
           CommitTransition commitTransition;
-          commitTransition.from_ref() = rootIdCodec.renderRootId(currentHash);
-          commitTransition.to_ref() =
+          commitTransition.from_ref() =
               rootIdCodec.renderRootId(current.fromHash);
+          commitTransition.to_ref() = rootIdCodec.renderRootId(currentHash);
           currentHash = current.fromHash;
 
           LargeChangeNotification largeChange;

eden/integration/changes_test.py

@@ -182,8 +182,8 @@ def test_commit_transition(self):
             # For CommitTransition, from_bytes is the current hash and to_bytes is the previous hash
             buildLargeChange(
                 LargeChangeNotification.COMMITTRANSITION,
-                from_bytes=bytes.fromhex(commit1),
-                to_bytes=bytes.fromhex(self.commit0),
+                from_bytes=bytes.fromhex(self.commit0),
+                to_bytes=bytes.fromhex(commit1),
             ),
         ]
         self.assertTrue(self.check_changes(changes1.changes, expected_changes1))
@@ -193,8 +193,8 @@ def test_commit_transition(self):
         expected_changes2 = [
             buildLargeChange(
                 LargeChangeNotification.COMMITTRANSITION,
-                from_bytes=bytes.fromhex(self.commit0),
-                to_bytes=bytes.fromhex(commit1),
+                from_bytes=bytes.fromhex(commit1),
+                to_bytes=bytes.fromhex(self.commit0),
             ),
         ]
         self.assertTrue(self.check_changes(changes2.changes, expected_changes2))