FilteredBackingStore: improve compareObjectsById when filters differ

Summary:
# This diff

Fixes a bug in compareObjectsById that causes two FilteredObjectIds to be considered different if their filters are not bytewise equal (despite being semantically equal).

Only one line of code needs to change -- we check if filters are identical rather than checking if they're bytewise equal.

Reviewed By: vilatto

Differential Revision: D87029066

fbshipit-source-id: 2ee80a9cdc49d148a9ab2569f131b522034261a1

Author: MichaelCuevas

eden/fs/store/FilteredBackingStore.cpp

@@ -163,7 +163,8 @@ ObjectComparison FilteredBackingStore::compareObjectsById(
       typeTwo == FilteredObjectIdType::OBJECT_TYPE_TREE) {
     // If the filters are the same, then we can simply check whether the
     // underlying ObjectIds resolve to equal.
-    if (filteredOne.filter() == filteredTwo.filter()) {
+    if (filter_->areFiltersIdentical(
+            filteredOne.filter(), filteredTwo.filter())) {
       return backingStore_->compareObjectsById(
           filteredOne.object(), filteredTwo.object());
     }

eden/fs/store/test/FilteredBackingStoreTest.cpp

@@ -826,13 +826,15 @@ TEST_F(FakeSubstringFilteredBackingStoreTest, testCompareTreeObjectsById) {
       filteredStore_->compareObjectsById(grandchildOID, grandchildOID2) ==
       ObjectComparison::Unknown);
 
-  // FIXME: These two trees have the same underlying tree (grandchildTreeId) and
-  // semantically identical filters. They should be Identical, but this will
-  // fail because compareObjectsById does a bytewise comparison instead of
-  // calling areFiltersIdentical.
+  // These two trees have the same underlying tree (grandchildTreeId) and
+  // bytewise different (but semantically identical) filters. They should
+  // be Identical despite the bytewise filter difference.
+  auto grandchildFIDLegacy = FilteredObjectId::fromObjectId(grandchildOID);
+  auto grandchildFIDV1 = FilteredObjectId::fromObjectId(grandchildOID1V1);
+  EXPECT_NE(grandchildFIDLegacy.filter(), grandchildFIDV1.filter());
   EXPECT_EQ(
       filteredStore_->compareObjectsById(grandchildOID, grandchildOID1V1),
-      ObjectComparison::Unknown);
+      ObjectComparison::Identical);
 }
 
 TEST_F(FakeSubstringFilteredBackingStoreTest, getGlobFiles) {