Port FSTDocumentKeySet to C++ DocumentKeySet (#1229)

* Define a Comparator for DocumentKey

* Automated migration from FSTDocumentKeySet to DocumentKeySet

* Manual fixups for DocumentKeySet

* Delete FSTDocumentKeySet

9 files changed, 91 insertions, 93 deletions

diff --git a/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm b/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm
index 0454152..7ae9704 100644
--- a/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm
+++ b/Firestore/Example/Tests/Core/FSTQueryListenerTests.mm
@@ -27,6 +27,8 @@
 
 #import "Firestore/Example/Tests/Util/FSTHelpers.h"
 
+using firebase::firestore::model::DocumentKeySet;
+
 NS_ASSUME_NONNULL_BEGIN
 
 @interface FSTQueryListenerTests : XCTestCase
@@ -53,7 +55,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQueryListener *listener = [self listenToQuery:query accumulatingSnapshots:accum];
   FSTQueryListener *otherListener = [self listenToQuery:query accumulatingSnapshots:otherAccum];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1, doc2 ], nil);
   FSTViewSnapshot *snap2 = FSTTestApplyChanges(view, @[ doc2prime ], nil);
 
@@ -107,7 +109,7 @@ NS_ASSUME_NONNULL_BEGIN
 
   FSTQueryListener *listener = [self listenToQuery:query accumulatingSnapshots:accum];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[], nil);
 
   FSTTargetChange *ackTarget =
@@ -136,7 +138,7 @@ NS_ASSUME_NONNULL_BEGIN
               [listener mute];
             }];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *viewSnapshot1 = FSTTestApplyChanges(view, @[ doc1 ], nil);
   FSTViewSnapshot *viewSnapshot2 = FSTTestApplyChanges(view, @[ doc2 ], nil);
 
@@ -178,7 +180,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQueryListener *fullListener =
       [self listenToQuery:query options:options accumulatingSnapshots:fullAccum];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1 ], nil);
 
   FSTTargetChange *ackTarget =
@@ -218,7 +220,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQueryListener *fullListener =
       [self listenToQuery:query options:options accumulatingSnapshots:fullAccum];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1, doc2 ], nil);
   FSTViewSnapshot *snap2 = FSTTestApplyChanges(view, @[ doc1Prime ], nil);
   FSTViewSnapshot *snap3 = FSTTestApplyChanges(view, @[ doc3 ], nil);
@@ -265,7 +267,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQueryListener *fullListener =
       [self listenToQuery:query options:options accumulatingSnapshots:fullAccum];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1, doc2 ], nil);
   FSTViewSnapshot *snap2 = FSTTestApplyChanges(view, @[ doc1Prime ], nil);
   FSTViewSnapshot *snap3 = FSTTestApplyChanges(view, @[ doc3 ], nil);
@@ -298,7 +300,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQueryListener *filteredListener =
       [self listenToQuery:query accumulatingSnapshots:filteredAccum];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1, doc2 ], nil);
   FSTViewSnapshot *snap2 = FSTTestApplyChanges(view, @[ doc1Prime, doc3 ], nil);
 
@@ -331,7 +333,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                                         waitForSyncWhenOnline:YES]
           accumulatingSnapshots:events];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1 ], nil);
   FSTViewSnapshot *snap2 = FSTTestApplyChanges(view, @[ doc2 ], nil);
   FSTViewSnapshot *snap3 =
@@ -374,7 +376,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                                         waitForSyncWhenOnline:YES]
           accumulatingSnapshots:events];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[ doc1 ], nil);
   FSTViewSnapshot *snap2 = FSTTestApplyChanges(view, @[ doc2 ], nil);
 
@@ -415,7 +417,7 @@ NS_ASSUME_NONNULL_BEGIN
                                            options:[FSTListenOptions defaultOptions]
                              accumulatingSnapshots:events];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[], nil);
 
   [listener applyChangedOnlineState:FSTOnlineStateOnline];   // no event
@@ -441,7 +443,7 @@ NS_ASSUME_NONNULL_BEGIN
                                            options:[FSTListenOptions defaultOptions]
                              accumulatingSnapshots:events];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTViewSnapshot *snap1 = FSTTestApplyChanges(view, @[], nil);
 
   [listener applyChangedOnlineState:FSTOnlineStateOffline];  // no event
diff --git a/Firestore/Example/Tests/Core/FSTViewTests.mm b/Firestore/Example/Tests/Core/FSTViewTests.mm
index 63ce711..ec62d82 100644
--- a/Firestore/Example/Tests/Core/FSTViewTests.mm
+++ b/Firestore/Example/Tests/Core/FSTViewTests.mm
@@ -34,6 +34,7 @@
 
 namespace testutil = firebase::firestore::testutil;
 using firebase::firestore::model::ResourcePath;
+using firebase::firestore::model::DocumentKeySet;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -49,7 +50,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)testAddsDocumentsBasedOnQuery {
   FSTQuery *query = [self queryForMessages];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{@"text" : @"msg1"}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{@"text" : @"msg2"}, NO);
@@ -77,7 +78,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)testRemovesDocuments {
   FSTQuery *query = [self queryForMessages];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{@"text" : @"msg1"}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{@"text" : @"msg2"}, NO);
@@ -108,7 +109,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)testReturnsNilIfThereAreNoChanges {
   FSTQuery *query = [self queryForMessages];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{@"text" : @"msg1"}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{@"text" : @"msg2"}, NO);
@@ -123,7 +124,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)testDoesNotReturnNilForFirstChanges {
   FSTQuery *query = [self queryForMessages];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTViewSnapshot *snapshot = FSTTestApplyChanges(view, @[], nil);
   XCTAssertNotNil(snapshot);
@@ -137,7 +138,7 @@ NS_ASSUME_NONNULL_BEGIN
                                    value:[FSTDoubleValue doubleValue:2]];
   query = [query queryByAddingFilter:filter];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{ @"sort" : @1 }, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{ @"sort" : @2 }, NO);
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/3", 0, @{ @"sort" : @3 }, NO);
@@ -169,7 +170,7 @@ NS_ASSUME_NONNULL_BEGIN
                                    value:[FSTDoubleValue doubleValue:2]];
   query = [query queryByAddingFilter:filter];
 
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{ @"sort" : @1 }, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{ @"sort" : @3 }, NO);
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/3", 0, @{ @"sort" : @2 }, NO);
@@ -205,7 +206,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (void)testRemovesDocumentsForQueryWithLimit {
   FSTQuery *query = [self queryForMessages];
   query = [query queryBySettingLimit:2];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{@"text" : @"msg1"}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{@"text" : @"msg2"}, NO);
@@ -239,7 +240,7 @@ NS_ASSUME_NONNULL_BEGIN
   query = [query queryByAddingSortOrder:[FSTSortOrder sortOrderWithFieldPath:testutil::Field("num")
                                                                    ascending:YES]];
   query = [query queryBySettingLimit:2];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/1", 0, @{ @"num" : @1 }, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/2", 0, @{ @"num" : @2 }, NO);
@@ -283,7 +284,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)testKeepsTrackOfLimboDocuments {
   FSTQuery *query = [self queryForMessages];
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
@@ -339,8 +340,8 @@ NS_ASSUME_NONNULL_BEGIN
 
   // Unlike other cases, here the view is initialized with a set of previously synced documents
   // which happens when listening to a previously listened-to query.
-  FSTView *view = [[FSTView alloc] initWithQuery:query
-                                 remoteDocuments:FSTTestDocKeySet(@[ doc1.key, doc2.key ])];
+  FSTView *view =
+      [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{doc1.key, doc2.key}];
 
   FSTTargetChange *markCurrent =
       [FSTTargetChange changeWithDocuments:@[]
@@ -361,7 +362,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQuery *query = [[self queryForMessages] queryBySettingLimit:2];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
@@ -394,7 +395,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{ @"order" : @1 }, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{ @"order" : @2 }, NO);
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/2", 0, @{ @"order" : @3 }, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
@@ -430,7 +431,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/2", 0, @{ @"order" : @3 }, NO);
   FSTDocument *doc4 = FSTTestDoc("rooms/eros/messages/3", 0, @{ @"order" : @4 }, NO);
   FSTDocument *doc5 = FSTTestDoc("rooms/eros/messages/4", 0, @{ @"order" : @5 }, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
@@ -460,7 +461,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/2", 0, @{ @"order" : @3 }, NO);
   FSTDocument *doc4 = FSTTestDoc("rooms/eros/messages/3", 0, @{ @"order" : @4 }, NO);
   FSTDocument *doc5 = FSTTestDoc("rooms/eros/messages/4", 0, @{ @"order" : @5 }, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
@@ -483,7 +484,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQuery *query = [[self queryForMessages] queryBySettingLimit:2];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
@@ -506,7 +507,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQuery *query = [[self queryForMessages] queryBySettingLimit:20];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   FSTViewDocumentChanges *changes =
       [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc1, doc2 ])];
@@ -528,7 +529,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQuery *query = [[self queryForMessages] queryBySettingLimit:2];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
@@ -551,69 +552,69 @@ NS_ASSUME_NONNULL_BEGIN
   FSTQuery *query = [self queryForMessages];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
       [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc1, doc2 ])];
   [view applyChangesToDocuments:changes];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[]));
+  XCTAssertEqual(changes.mutatedKeys, DocumentKeySet{});
 
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/2", 0, @{}, YES);
   changes = [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc3 ])];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[ doc3.key ]));
+  XCTAssertEqual(changes.mutatedKeys, DocumentKeySet{doc3.key});
 }
 
 - (void)testRemovesKeysFromMutatedKeysWhenNewDocHasNoLocalChanges {
   FSTQuery *query = [self queryForMessages];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, YES);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
       [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc1, doc2 ])];
   [view applyChangesToDocuments:changes];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[ doc2.key ]));
+  XCTAssertEqual(changes.mutatedKeys, (DocumentKeySet{doc2.key}));
 
   FSTDocument *doc2Prime = FSTTestDoc("rooms/eros/messages/1", 0, @{}, NO);
   changes = [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc2Prime ])];
   [view applyChangesToDocuments:changes];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[]));
+  XCTAssertEqual(changes.mutatedKeys, DocumentKeySet{});
 }
 
 - (void)testRemembersLocalMutationsFromPreviousSnapshot {
   FSTQuery *query = [self queryForMessages];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, YES);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
       [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc1, doc2 ])];
   [view applyChangesToDocuments:changes];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[ doc2.key ]));
+  XCTAssertEqual(changes.mutatedKeys, (DocumentKeySet{doc2.key}));
 
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/2", 0, @{}, NO);
   changes = [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc3 ])];
   [view applyChangesToDocuments:changes];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[ doc2.key ]));
+  XCTAssertEqual(changes.mutatedKeys, (DocumentKeySet{doc2.key}));
 }
 
 - (void)testRemembersLocalMutationsFromPreviousCallToComputeChangesWithDocuments {
   FSTQuery *query = [self queryForMessages];
   FSTDocument *doc1 = FSTTestDoc("rooms/eros/messages/0", 0, @{}, NO);
   FSTDocument *doc2 = FSTTestDoc("rooms/eros/messages/1", 0, @{}, YES);
-  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:[FSTDocumentKeySet keySet]];
+  FSTView *view = [[FSTView alloc] initWithQuery:query remoteDocuments:DocumentKeySet{}];
 
   // Start with a full view.
   FSTViewDocumentChanges *changes =
       [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc1, doc2 ])];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[ doc2.key ]));
+  XCTAssertEqual(changes.mutatedKeys, (DocumentKeySet{doc2.key}));
 
   FSTDocument *doc3 = FSTTestDoc("rooms/eros/messages/2", 0, @{}, NO);
   changes = [view computeChangesWithDocuments:FSTTestDocUpdates(@[ doc3 ]) previousChanges:changes];
-  XCTAssertEqualObjects(changes.mutatedKeys, FSTTestDocKeySet(@[ doc2.key ]));
+  XCTAssertEqual(changes.mutatedKeys, (DocumentKeySet{doc2.key}));
 }
 
 @end
diff --git a/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm b/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm
index 421f244..0e160c0 100644
--- a/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm
+++ b/Firestore/Example/Tests/Local/FSTLocalSerializerTests.mm
@@ -125,7 +125,7 @@ NS_ASSUME_NONNULL_BEGIN
   XCTAssertEqual(decoded.batchID, model.batchID);
   XCTAssertEqualObjects(decoded.localWriteTime, model.localWriteTime);
   XCTAssertEqualObjects(decoded.mutations, model.mutations);
-  XCTAssertEqualObjects([decoded keys], [model keys]);
+  XCTAssertEqual([decoded keys], [model keys]);
 }
 
 - (void)testEncodesDocumentAsMaybeDocument {
diff --git a/Firestore/Example/Tests/Local/FSTLocalStoreTests.mm b/Firestore/Example/Tests/Local/FSTLocalStoreTests.mm
index 4175118..c417646 100644
--- a/Firestore/Example/Tests/Local/FSTLocalStoreTests.mm
+++ b/Firestore/Example/Tests/Local/FSTLocalStoreTests.mm
@@ -46,6 +46,7 @@
 namespace testutil = firebase::firestore::testutil;
 using firebase::firestore::auth::User;
 using firebase::firestore::model::SnapshotVersion;
+using firebase::firestore::model::DocumentKeySet;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -230,8 +231,8 @@ FSTDocumentVersionDictionary *FSTVersionDictionary(FSTMutation *mutation,
   FSTMutationBatch *batch = [[FSTMutationBatch alloc] initWithBatchID:1
                                                        localWriteTime:[FIRTimestamp timestamp]
                                                             mutations:@[ set1, set2 ]];
-  FSTDocumentKeySet *keys = [batch keys];
-  XCTAssertEqual(keys.count, 2);
+  DocumentKeySet keys = [batch keys];
+  XCTAssertEqual(keys.size(), 2u);
 }
 
 - (void)testHandlesSetMutation {
@@ -856,13 +857,14 @@ FSTDocumentVersionDictionary *FSTVersionDictionary(FSTMutation *mutation,
 
   [self.localStore locallyWriteMutations:@[ FSTTestSetMutation(@"foo/bonk", @{@"a" : @"b"}) ]];
 
-  FSTDocumentKeySet *keys = [self.localStore remoteDocumentKeysForTarget:2];
-  FSTAssertEqualSets(keys, (@[ FSTTestDocKey(@"foo/bar"), FSTTestDocKey(@"foo/baz") ]));
+  DocumentKeySet keys = [self.localStore remoteDocumentKeysForTarget:2];
+  DocumentKeySet expected{testutil::Key("foo/bar"), testutil::Key("foo/baz")};
+  XCTAssertEqual(keys, expected);
 
   [self restartWithNoopGarbageCollector];
 
   keys = [self.localStore remoteDocumentKeysForTarget:2];
-  FSTAssertEqualSets(keys, (@[ FSTTestDocKey(@"foo/bar"), FSTTestDocKey(@"foo/baz") ]));
+  XCTAssertEqual(keys, (DocumentKeySet{testutil::Key("foo/bar"), testutil::Key("foo/baz")}));
 }
 
 @end
diff --git a/Firestore/Example/Tests/Local/FSTQueryCacheTests.mm b/Firestore/Example/Tests/Local/FSTQueryCacheTests.mm
index 5d07516..44b49de 100644
--- a/Firestore/Example/Tests/Local/FSTQueryCacheTests.mm
+++ b/Firestore/Example/Tests/Local/FSTQueryCacheTests.mm
@@ -32,6 +32,7 @@
 namespace testutil = firebase::firestore::testutil;
 using firebase::firestore::model::DocumentKey;
 using firebase::firestore::model::SnapshotVersion;
+using firebase::firestore::model::DocumentKeySet;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -278,12 +279,12 @@ NS_ASSUME_NONNULL_BEGIN
     [self addMatchingKey:key2 forTargetID:1];
     [self addMatchingKey:key3 forTargetID:2];
 
-    FSTAssertEqualSets([self.queryCache matchingKeysForTargetID:1], (@[ key1, key2 ]));
-    FSTAssertEqualSets([self.queryCache matchingKeysForTargetID:2], @[ key3 ]);
+    XCTAssertEqual([self.queryCache matchingKeysForTargetID:1], (DocumentKeySet{key1, key2}));
+    XCTAssertEqual([self.queryCache matchingKeysForTargetID:2], (DocumentKeySet{key3}));
 
     [self addMatchingKey:key1 forTargetID:2];
-    FSTAssertEqualSets([self.queryCache matchingKeysForTargetID:1], (@[ key1, key2 ]));
-    FSTAssertEqualSets([self.queryCache matchingKeysForTargetID:2], (@[ key1, key3 ]));
+    XCTAssertEqual([self.queryCache matchingKeysForTargetID:1], (DocumentKeySet{key1, key2}));
+    XCTAssertEqual([self.queryCache matchingKeysForTargetID:2], (DocumentKeySet{key1, key3}));
   });
 }
 
@@ -428,14 +429,12 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 - (void)addMatchingKey:(const DocumentKey &)key forTargetID:(FSTTargetID)targetID {
-  FSTDocumentKeySet *keys = [FSTDocumentKeySet keySet];
-  keys = [keys setByAddingObject:key];
+  DocumentKeySet keys{key};
   [self.queryCache addMatchingKeys:keys forTargetID:targetID];
 }
 
 - (void)removeMatchingKey:(const DocumentKey &)key forTargetID:(FSTTargetID)targetID {
-  FSTDocumentKeySet *keys = [FSTDocumentKeySet keySet];
-  keys = [keys setByAddingObject:key];
+  DocumentKeySet keys{key};
   [self.queryCache removeMatchingKeys:keys forTargetID:targetID];
 }
 
diff --git a/Firestore/Example/Tests/Remote/FSTRemoteEventTests.mm b/Firestore/Example/Tests/Remote/FSTRemoteEventTests.mm
index e2cb8cc..84d0fa1 100644
--- a/Firestore/Example/Tests/Remote/FSTRemoteEventTests.mm
+++ b/Firestore/Example/Tests/Remote/FSTRemoteEventTests.mm
@@ -33,6 +33,7 @@
 
 namespace testutil = firebase::firestore::testutil;
 using firebase::firestore::model::DocumentKey;
+using firebase::firestore::model::DocumentKeySet;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -575,7 +576,7 @@ NS_ASSUME_NONNULL_BEGIN
   FSTDeletedDocument *expected =
       [FSTDeletedDocument documentWithKey:synthesized version:event.snapshotVersion];
   XCTAssertEqualObjects(expected, event.documentUpdates.at(synthesized));
-  XCTAssertTrue([event.limboDocumentChanges containsObject:synthesized]);
+  XCTAssertTrue(event.limboDocumentChanges.contains(synthesized));
 }
 
 - (void)testDoesntSynthesizeDeletesForWrongState {
@@ -590,7 +591,7 @@ NS_ASSUME_NONNULL_BEGIN
   DocumentKey notSynthesized = DocumentKey::FromPathString("docs/no1");
   [event synthesizeDeleteForLimboTargetChange:event.targetChanges[@2] key:notSynthesized];
   XCTAssertEqual(event.documentUpdates.find(notSynthesized), event.documentUpdates.end());
-  XCTAssertFalse([event.limboDocumentChanges containsObject:notSynthesized]);
+  XCTAssertFalse(event.limboDocumentChanges.contains(notSynthesized));
 }
 
 - (void)testDoesntSynthesizeDeletesForExistingDoc {
@@ -609,7 +610,7 @@ NS_ASSUME_NONNULL_BEGIN
   [event synthesizeDeleteForLimboTargetChange:event.targetChanges[@3] key:doc.key];
   FSTMaybeDocument *docData = event.documentUpdates.at(doc.key);
   XCTAssertFalse([docData isKindOfClass:[FSTDeletedDocument class]]);
-  XCTAssertFalse([event.limboDocumentChanges containsObject:doc.key]);
+  XCTAssertFalse(event.limboDocumentChanges.contains(doc.key));
 }
 
 - (void)testFilterUpdates {
@@ -631,24 +632,24 @@ NS_ASSUME_NONNULL_BEGIN
                       outstanding:_noPendingResponses
                           changes:@[ newDocChange, existingDocChange ]];
   FSTRemoteEvent *event = [aggregator remoteEvent];
-  FSTDocumentKeySet *existingKeys = [[FSTDocumentKeySet keySet] setByAddingObject:existingDoc.key];
+  DocumentKeySet existingKeys = DocumentKeySet{existingDoc.key};
 
   FSTTargetChange *updateChange = event.targetChanges[@1];
   XCTAssertTrue([updateChange.mapping isKindOfClass:[FSTUpdateMapping class]]);
   FSTUpdateMapping *update = (FSTUpdateMapping *)updateChange.mapping;
   FSTDocumentKey *existingDocKey = existingDoc.key;
   FSTDocumentKey *newDocKey = newDoc.key;
-  XCTAssertTrue([update.addedDocuments containsObject:existingDocKey]);
+  XCTAssertTrue(update.addedDocuments.contains(existingDocKey));
 
   [update filterUpdatesUsingExistingKeys:existingKeys];
   // Now it's been filtered, since it already existed.
-  XCTAssertFalse([update.addedDocuments containsObject:existingDocKey]);
-  XCTAssertTrue([update.addedDocuments containsObject:newDocKey]);
+  XCTAssertFalse(update.addedDocuments.contains(existingDocKey));
+  XCTAssertTrue(update.addedDocuments.contains(newDocKey));
 }
 
 - (void)testDoesntFilterResets {
   FSTDocument *existingDoc = FSTTestDoc("docs/existing", 1, @{@"some" : @"data"}, NO);
-  FSTDocumentKey *existingDocKey = existingDoc.key;
+  const DocumentKey &existingDocKey = existingDoc.key;
   FSTWatchTargetChange *resetTargetChange =
       [FSTWatchTargetChange changeWithState:FSTWatchTargetChangeStateReset
                                   targetIDs:@[ @2 ]
@@ -663,16 +664,16 @@ NS_ASSUME_NONNULL_BEGIN
                       outstanding:_noPendingResponses
                           changes:@[ resetTargetChange, existingDocChange ]];
   FSTRemoteEvent *event = [aggregator remoteEvent];
-  FSTDocumentKeySet *existingKeys = [[FSTDocumentKeySet keySet] setByAddingObject:existingDocKey];
+  DocumentKeySet existingKeys = DocumentKeySet{existingDocKey};
 
   FSTTargetChange *resetChange = event.targetChanges[@2];
   XCTAssertTrue([resetChange.mapping isKindOfClass:[FSTResetMapping class]]);
   FSTResetMapping *resetMapping = (FSTResetMapping *)resetChange.mapping;
-  XCTAssertTrue([resetMapping.documents containsObject:existingDocKey]);
+  XCTAssertTrue(resetMapping.documents.contains(existingDocKey));
 
   [resetMapping filterUpdatesUsingExistingKeys:existingKeys];
   // Document is still there, even though it already exists. Reset mappings don't get filtered.
-  XCTAssertTrue([resetMapping.documents containsObject:existingDocKey]);
+  XCTAssertTrue(resetMapping.documents.contains(existingDocKey));
 }
 
 - (void)testTracksLimboDocuments {
@@ -715,13 +716,13 @@ NS_ASSUME_NONNULL_BEGIN
   [aggregator addWatchChanges:@[ docChange1, docChange2, docChange3, targetsChange ]];
 
   FSTRemoteEvent *event = [aggregator remoteEvent];
-  FSTDocumentKeySet *limboDocChanges = event.limboDocumentChanges;
+  DocumentKeySet limboDocChanges = event.limboDocumentChanges;
   // Doc1 is in both limbo and non-limbo targets, therefore not tracked as limbo
-  XCTAssertFalse([limboDocChanges containsObject:doc1.key]);
+  XCTAssertFalse(limboDocChanges.contains(doc1.key));
   // Doc2 is only in the limbo target, so is tracked as a limbo document
-  XCTAssertTrue([limboDocChanges containsObject:doc2.key]);
+  XCTAssertTrue(limboDocChanges.contains(doc2.key));
   // Doc3 is only in the non-limbo target, therefore not tracked as limbo
-  XCTAssertFalse([limboDocChanges containsObject:doc3.key]);
+  XCTAssertFalse(limboDocChanges.contains(doc3.key));
 }
 
 @end
diff --git a/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm b/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm
index 12be590..5a7cb72 100644
--- a/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm
+++ b/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm
@@ -603,10 +603,13 @@ static NSString *const kNoIOSTag = @"no-ios";
     // XCTAssertEqualObjects(actualTargets[targetID], queryData);
 
     FSTQueryData *actual = actualTargets[targetID];
-    XCTAssertEqualObjects(actual.query, queryData.query);
-    XCTAssertEqual(actual.targetID, queryData.targetID);
-    XCTAssertEqual(actual.snapshotVersion, queryData.snapshotVersion);
-    XCTAssertEqualObjects(actual.resumeToken, queryData.resumeToken);
+    XCTAssertNotNil(actual);
+    if (actual) {
+      XCTAssertEqualObjects(actual.query, queryData.query);
+      XCTAssertEqual(actual.targetID, queryData.targetID);
+      XCTAssertEqual(actual.snapshotVersion, queryData.snapshotVersion);
+      XCTAssertEqualObjects(actual.resumeToken, queryData.resumeToken);
+    }
 
     [actualTargets removeObjectForKey:targetID];
   }];
diff --git a/Firestore/Example/Tests/Util/FSTHelpers.h b/Firestore/Example/Tests/Util/FSTHelpers.h
index f80f163..ccc01ca 100644
--- a/Firestore/Example/Tests/Util/FSTHelpers.h
+++ b/Firestore/Example/Tests/Util/FSTHelpers.h
@@ -21,7 +21,6 @@
 
 #import "Firestore/Source/Core/FSTTypes.h"
 #import "Firestore/Source/Model/FSTDocumentDictionary.h"
-#import "Firestore/Source/Model/FSTDocumentKeySet.h"
 
 #include "Firestore/core/src/firebase/firestore/model/field_path.h"
 #include "Firestore/core/src/firebase/firestore/model/field_value.h"
@@ -181,9 +180,6 @@ FSTObjectValue *FSTTestObjectValue(NSDictionary<NSString *, id> *data);
 /** A convenience method for creating document keys for tests. */
 FSTDocumentKey *FSTTestDocKey(NSString *path);
 
-/** A convenience method for creating a document key set for tests. */
-FSTDocumentKeySet *FSTTestDocKeySet(NSArray<FSTDocumentKey *> *keys);
-
 /** Allow tests to just use an int literal for versions. */
 typedef int64_t FSTTestSnapshotVersion;
 
diff --git a/Firestore/Example/Tests/Util/FSTHelpers.mm b/Firestore/Example/Tests/Util/FSTHelpers.mm
index 92eb730..dbd19aa 100644
--- a/Firestore/Example/Tests/Util/FSTHelpers.mm
+++ b/Firestore/Example/Tests/Util/FSTHelpers.mm
@@ -44,6 +44,7 @@
 
 #include "Firestore/core/src/firebase/firestore/model/database_id.h"
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
+#include "Firestore/core/src/firebase/firestore/model/document_key_set.h"
 #include "Firestore/core/src/firebase/firestore/model/field_mask.h"
 #include "Firestore/core/src/firebase/firestore/model/field_transform.h"
 #include "Firestore/core/src/firebase/firestore/model/field_value.h"
@@ -66,6 +67,7 @@ using firebase::firestore::model::Precondition;
 using firebase::firestore::model::ResourcePath;
 using firebase::firestore::model::ServerTimestampTransform;
 using firebase::firestore::model::TransformOperation;
+using firebase::firestore::model::DocumentKeySet;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -146,14 +148,6 @@ FSTDocumentKey *FSTTestDocKey(NSString *path) {
   return [FSTDocumentKey keyWithPathString:path];
 }
 
-FSTDocumentKeySet *FSTTestDocKeySet(NSArray<FSTDocumentKey *> *keys) {
-  FSTDocumentKeySet *result = [FSTDocumentKeySet keySet];
-  for (FSTDocumentKey *key in keys) {
-    result = [result setByAddingObject:key];
-  }
-  return result;
-}
-
 FSTDocument *FSTTestDoc(const absl::string_view path,
                         FSTTestSnapshotVersion version,
                         NSDictionary<NSString *, id> *data,
@@ -343,17 +337,17 @@ NSData *_Nullable FSTTestResumeTokenFromSnapshotVersion(FSTTestSnapshotVersion s
 FSTLocalViewChanges *FSTTestViewChanges(FSTQuery *query,
                                         NSArray<NSString *> *addedKeys,
                                         NSArray<NSString *> *removedKeys) {
-  FSTDocumentKeySet *added = [FSTDocumentKeySet keySet];
+  DocumentKeySet added;
   for (NSString *keyPath in addedKeys) {
-    FSTDocumentKey *key = FSTTestDocKey(keyPath);
-    added = [added setByAddingObject:key];
+    added = added.insert(testutil::Key(util::MakeStringView(keyPath)));
   }
-  FSTDocumentKeySet *removed = [FSTDocumentKeySet keySet];
+  DocumentKeySet removed;
   for (NSString *keyPath in removedKeys) {
-    FSTDocumentKey *key = FSTTestDocKey(keyPath);
-    removed = [removed setByAddingObject:key];
+    removed = removed.insert(testutil::Key(util::MakeStringView(keyPath)));
   }
-  return [FSTLocalViewChanges changesForQuery:query addedKeys:added removedKeys:removed];
+  return [FSTLocalViewChanges changesForQuery:query
+                                    addedKeys:std::move(added)
+                                  removedKeys:std::move(removed)];
 }
 
 NS_ASSUME_NONNULL_END