Fix mutating array datasource bug

CHANGELOG.md

@@ -12,6 +12,7 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 - 5x improvement to diffing performance when result is only inserts or deletes. [Ryan Nystrom](https://github.com/rnystrom) [(tbd)](tbd)
 
 ### Fixes
+- Copy objects when retrieving from datasource to prevent modification of models in binding section controller. [Kashish Goel](https://github.com/kashishgoel) [(#1109)](https://github.com/Instagram/IGListKit/pull/1109)
 
 3.2.0
 -----

Source/IGListBindingSectionController.m

@@ -114,7 +114,7 @@ - (void)didUpdateToObject:(id)object {
  self.object = object;
 
  if (oldObject == nil) {
- self.viewModels = [self.dataSource sectionController:self viewModelsForObject:object];
+ self.viewModels = [[self.dataSource sectionController:self viewModelsForObject:object] copy];
  } else {
  IGAssert([oldObject isEqualToDiffableObject:object],
  @"Unequal objects %@ and %@ will cause IGListBindingSectionController to reload the entire section",

Tests/IGListBindingSectionControllerTests.m

@@ -296,5 +296,24 @@ - (void)test_whenUpdatingManually_with2Updates_thatBothCompletionBlocksCalled {
  [self waitForExpectationsWithTimeout:30 handler:nil];
 }
 
+- (void)test_whenUpdating_withMutableArrayObject_thatViewModelsDontMutate {
+ NSArray *objects = @[
+ @"foo",
+ @"bar"
+ ];
+ NSMutableArray *initObjects = [NSMutableArray arrayWithArray:objects];
+
+ [self setupWithObjects:@[
+ [[IGTestDiffingObject alloc] initWithKey:@1 objects:initObjects]
+ ]];
+
+ IGTestDiffingSectionController *section = [self.adapter sectionControllerForObject:self.dataSource.objects.firstObject];
+
+ NSArray *oldModels = [section.viewModels copy];
+ [initObjects removeAllObjects];
+
+ XCTAssertEqual(oldModels, section.viewModels);
+}
+
 @end