Add experiment to ensure ASCollectionView's range controller updates on changeset updates

This experiment makes sure a ASCollectionView's `rangeController` updates when
a changeset WITH updates is applied. Currently it is possible for nodes
inserted into the preload range to not get preloaded when performing a batch
update.

For example, suppose a collection node has:
- Tuning parameters with a preload range of 1 screenful for the given range
  mode.
- Nodes A and B where A is visible and B is off screen.
Currently if node B is deleted and a new node C is inserted in its place, node
C will not get preloaded until the collection node is scrolled.

Author: rqueue

Source/ASCollectionView.mm

@@ -2311,7 +2311,11 @@ - (void)rangeController:(ASRangeController *)rangeController updateWithChangeSet
 
       // Flush any range changes that happened as part of submitting the update.
       as_activity_scope(changeSet.rootActivity);
-      [self->_rangeController updateIfNeeded];
+      if (numberOfUpdates > 0 && ASActivateExperimentalFeature(ASExperimentalRangeUpdateOnChangesetUpdate)) {
+        [self->_rangeController setNeedsUpdate];
+      } else {
+        [self->_rangeController updateIfNeeded];
+      }
     }
   });
 }

Source/ASExperimentalFeatures.h

@@ -30,6 +30,7 @@ typedef NS_OPTIONS(NSUInteger, ASExperimentalFeatures) {
   ASExperimentalOptimizeDataControllerPipeline = 1 << 9,                    // exp_optimize_data_controller_pipeline
   ASExperimentalDisableGlobalTextkitLock = 1 << 10,                         // exp_disable_global_textkit_lock
   ASExperimentalMainThreadOnlyDataController = 1 << 11,                     // exp_main_thread_only_data_controller
+  ASExperimentalRangeUpdateOnChangesetUpdate = 1 << 12,                     // exp_range_update_on_changeset_update
   ASExperimentalFeatureAll = 0xFFFFFFFF
 };
 

Source/ASExperimentalFeatures.mm

@@ -23,7 +23,8 @@
                                       @"exp_drawing_global",
                                       @"exp_optimize_data_controller_pipeline",
                                       @"exp_disable_global_textkit_lock",
-                                      @"exp_main_thread_only_data_controller"]));
+                                      @"exp_main_thread_only_data_controller",
+                                      @"exp_range_update_on_changeset_update"]));
   if (flags == ASExperimentalFeatureAll) {
     return allNames;
   }

Tests/ASCollectionViewTests.mm

@@ -24,6 +24,7 @@ @interface ASTextCellNodeWithSetSelectedCounter : ASTextCellNode
 
 @property (nonatomic) NSUInteger setSelectedCounter;
 @property (nonatomic) NSUInteger applyLayoutAttributesCount;
+@property (nonatomic) NSUInteger didEnterPreloadStateCount;
 
 @end
 
@@ -40,6 +41,12 @@ - (void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttribut
   _applyLayoutAttributesCount++;
 }
 
+- (void)didEnterPreloadState
+{
+  [super didEnterPreloadState];
+  _didEnterPreloadStateCount++;
+}
+
 @end
 
 @interface ASTestSectionContext : NSObject <ASSectionContext>
@@ -177,7 +184,8 @@ - (void)setUp
 {
   [super setUp];
   ASConfiguration *config = [ASConfiguration new];
-  config.experimentalFeatures = ASExperimentalOptimizeDataControllerPipeline;
+  config.experimentalFeatures = ASExperimentalOptimizeDataControllerPipeline
+                              | ASExperimentalRangeUpdateOnChangesetUpdate;
   [ASConfigurationManager test_resetWithConfiguration:config];
 }
 
@@ -518,6 +526,81 @@ - (void)testThatDeletingAndReloadingASectionThrowsAnException
   } completion:nil]);
 }
 
+- (void)testItemsInsertedIntoThePreloadRangeGetPreloaded
+{
+  updateValidationTestPrologue
+  
+  ASRangeTuningParameters minimumPreloadParams = { .leadingBufferScreenfuls = 1, .trailingBufferScreenfuls = 1 };
+  [cn setTuningParameters:minimumPreloadParams forRangeMode:ASLayoutRangeModeMinimum rangeType:ASLayoutRangeTypePreload];
+  [cn updateCurrentRangeWithMode:ASLayoutRangeModeMinimum];
+
+  __weak ASCollectionViewTestController *weakController = testController;
+  NSIndexPath *lastVisibleIndex = [cv indexPathsForVisibleItems].lastObject;
+  
+  NSInteger itemCount = weakController.asyncDelegate->_itemCounts[lastVisibleIndex.section];
+  BOOL isLastItemInSection = lastVisibleIndex.row == itemCount - 1;
+  NSInteger nextItemSection = isLastItemInSection ? lastVisibleIndex.section + 1 : lastVisibleIndex.section;
+  NSInteger nextItemRow = isLastItemInSection ? 0 : lastVisibleIndex.row + 1;
+  
+  XCTAssertTrue(weakController.asyncDelegate->_itemCounts.size() > nextItemSection, @"There is no items after the last visible item. Update the section/row counts so that there is one for this test to work properly.");
+  XCTAssertTrue(weakController.asyncDelegate->_itemCounts[nextItemSection] > nextItemRow, @"There is no items after the last visible item. Update the section/row counts so that there is one for this test to work properly.");
+  
+  NSIndexPath *nextItemIndexPath = [NSIndexPath indexPathForRow:nextItemRow inSection:nextItemSection];
+  ASTextCellNodeWithSetSelectedCounter *nodeBeforeUpdate = (ASTextCellNodeWithSetSelectedCounter *)[cv nodeForItemAtIndexPath:nextItemIndexPath];
+
+  XCTestExpectation *noChangeDone = [self expectationWithDescription:@"Batch update with no changes done and completion block has been called. Tuning params set to 1 screenful."];
+  
+  __block ASTextCellNodeWithSetSelectedCounter *nodeAfterUpdate;
+  [cv performBatchUpdates:^{
+  } completion:^(BOOL finished) {
+    nodeAfterUpdate = (ASTextCellNodeWithSetSelectedCounter *)[cv nodeForItemAtIndexPath:nextItemIndexPath];
+    [noChangeDone fulfill];
+  }];
+  
+  [self waitForExpectations:@[ noChangeDone ] timeout:1];
+  
+  XCTAssertTrue(nodeBeforeUpdate == nodeAfterUpdate, @"Node should not have changed since no updates were made.");
+  XCTAssertTrue(nodeAfterUpdate.didEnterPreloadStateCount == 1, @"Node should have been preloaded.");
+
+  XCTestExpectation *changeDone = [self expectationWithDescription:@"Batch update with changes done and completion block has been called. Tuning params set to 1 screenful."];
+  
+  [cv performBatchUpdates:^{
+    NSArray *indexPaths = @[ nextItemIndexPath ];
+    [cv deleteItemsAtIndexPaths:indexPaths];
+    [cv insertItemsAtIndexPaths:indexPaths];
+  } completion:^(BOOL finished) {
+    nodeAfterUpdate = (ASTextCellNodeWithSetSelectedCounter *)[cv nodeForItemAtIndexPath:nextItemIndexPath];
+    [changeDone fulfill];
+  }];
+  
+  [self waitForExpectations:@[ changeDone ] timeout:1];
+  
+  XCTAssertTrue(nodeBeforeUpdate != nodeAfterUpdate, @"Node should have changed after updating.");
+  XCTAssertTrue(nodeAfterUpdate.didEnterPreloadStateCount == 1, @"New node should have been preloaded.");
+  
+  minimumPreloadParams = { .leadingBufferScreenfuls = 0, .trailingBufferScreenfuls = 0 };
+  [cn setTuningParameters:minimumPreloadParams forRangeMode:ASLayoutRangeModeMinimum rangeType:ASLayoutRangeTypePreload];
+  [cn updateCurrentRangeWithMode:ASLayoutRangeModeMinimum];
+
+  XCTestExpectation *changeDoneZeroSreenfuls = [self expectationWithDescription:@"Batch update with changes done and completion block has been called. Tuning params set to 0 screenful."];
+  
+  nodeBeforeUpdate = nodeAfterUpdate;
+  __block ASTextCellNodeWithSetSelectedCounter *nodeAfterUpdateZeroSreenfuls;
+  [cv performBatchUpdates:^{
+    NSArray *indexPaths = @[ nextItemIndexPath ];
+    [cv deleteItemsAtIndexPaths:indexPaths];
+    [cv insertItemsAtIndexPaths:indexPaths];
+  } completion:^(BOOL finished) {
+    nodeAfterUpdateZeroSreenfuls = (ASTextCellNodeWithSetSelectedCounter *)[cv nodeForItemAtIndexPath:nextItemIndexPath];
+    [changeDoneZeroSreenfuls fulfill];
+  }];
+  
+  [self waitForExpectations:@[ changeDoneZeroSreenfuls ] timeout:1];
+  
+  XCTAssertTrue(nodeBeforeUpdate != nodeAfterUpdateZeroSreenfuls, @"Node should have changed after updating.");
+  XCTAssertTrue(nodeAfterUpdateZeroSreenfuls.didEnterPreloadStateCount == 0, @"New node should NOT have been preloaded.");
+}
+
 - (void)testCellNodeLayoutAttributes
 {
   updateValidationTestPrologue

Tests/ASConfigurationTests.mm

@@ -30,6 +30,7 @@
   ASExperimentalOptimizeDataControllerPipeline,
   ASExperimentalDisableGlobalTextkitLock,
   ASExperimentalMainThreadOnlyDataController,
+  ASExperimentalRangeUpdateOnChangesetUpdate,
 };
 
 @interface ASConfigurationTests : ASTestCase <ASConfigurationDelegate>
@@ -53,7 +54,8 @@ + (NSArray *)names {
     @"exp_drawing_global",
     @"exp_optimize_data_controller_pipeline",
     @"exp_disable_global_textkit_lock",
-    @"exp_main_thread_only_data_controller"
+    @"exp_main_thread_only_data_controller",
+    @"exp_range_update_on_changeset_update"
   ];
 }