[ASPagerNode] Fix content insets are wrong in pager node if root node of ASViewController and transition back (#2736)

* Fix content insets are wrong in pager node if root node of ASViewController and transition back

* Add unit test

* Improve test

* Fix test

* Move tests to ASPagerNodeTests

AsyncDisplayKit/ASCollectionView.mm

@@ -1232,10 +1232,6 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
 
 - (void)layoutSubviews
 {
-  if (_zeroContentInsets) {
-    self.contentInset = UIEdgeInsetsZero;
-  }
-  
   // Flush any pending invalidation action if needed.
   ASCollectionViewInvalidationStyle invalidationStyle = _nextLayoutInvalidationStyle;
   _nextLayoutInvalidationStyle = ASCollectionViewInvalidationStyleNone;
@@ -1254,6 +1250,10 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   
   // To ensure _maxSizeForNodesConstrainedSize is up-to-date for every usage, this call to super must be done last
   [super layoutSubviews];
+    
+  if (_zeroContentInsets) {
+    self.contentInset = UIEdgeInsetsZero;
+  }
   
   // Update range controller immediately if possible & needed.
   // Calling -updateIfNeeded in here with self.window == nil (early in the collection view's life)

AsyncDisplayKitTests/ASPagerNodeTests.m

@@ -7,8 +7,7 @@
 //
 
 #import <XCTest/XCTest.h>
-#import "ASPagerNode.h"
-#import "ASCellNode.h"
+#import <AsyncDisplayKit/AsyncDisplayKit.h>
 
 @interface ASPagerNodeTestDataSource : NSObject <ASPagerDataSource>
 @end
@@ -94,4 +93,72 @@
   return testController;
 }
 
+- (void)testThatRootPagerNodeDoesGetTheRightInsetWhilePoppingBack
+{
+  UICollectionViewCell *cell = nil;
+  
+  UIWindow *window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
+  ASDisplayNode *node = [[ASDisplayNode alloc] init];
+  node.automaticallyManagesSubnodes = YES;
+  
+  ASPagerNodeTestDataSource *dataSource = [[ASPagerNodeTestDataSource alloc] init];
+  ASPagerNode *pagerNode = [[ASPagerNode alloc] init];
+  pagerNode.dataSource = dataSource;
+  node.layoutSpecBlock = ^(ASDisplayNode *node, ASSizeRange constrainedSize){
+    return [ASInsetLayoutSpec insetLayoutSpecWithInsets:UIEdgeInsetsZero child:pagerNode];
+  };
+  ASViewController *vc = [[ASViewController alloc] initWithNode:node];
+  UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:vc];
+  window.rootViewController = nav;
+  [window makeKeyAndVisible];
+  [window layoutIfNeeded];
+  
+  // Wait until view controller is visible
+  XCTestExpectation *e = [self expectationWithDescription:@"Transition completed"];
+  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
+    [e fulfill];
+  });
+  [self waitForExpectationsWithTimeout:2 handler:nil];
+  
+  // Test initial values
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+  cell = [pagerNode.view cellForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
+#pragma clang diagnostic pop
+  XCTAssertEqualObjects(NSStringFromCGRect(window.bounds), NSStringFromCGRect(node.frame));
+  XCTAssertEqualObjects(NSStringFromCGRect(window.bounds), NSStringFromCGRect(cell.frame));
+  XCTAssertEqual(pagerNode.view.contentOffset.y, 0);
+  XCTAssertEqual(pagerNode.view.contentInset.top, 0);
+  
+  e = [self expectationWithDescription:@"Transition completed"];
+  // Push another view controller
+  UIViewController *vc2 = [[UIViewController alloc] init];
+  vc2.view.frame = nav.view.bounds;
+  vc2.view.backgroundColor = [UIColor blueColor];
+  [nav pushViewController:vc2 animated:YES];
+  
+  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.505 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
+    [e fulfill];
+  });
+  [self waitForExpectationsWithTimeout:2 handler:nil];
+  
+  // Pop view controller
+  e = [self expectationWithDescription:@"Transition completed"];
+  [vc2.navigationController popViewControllerAnimated:YES];
+  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 0.505 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
+    [e fulfill];
+  });
+  [self waitForExpectationsWithTimeout:2 handler:nil];
+  
+  // Test values again after popping the view controller
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+  cell = [pagerNode.view cellForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];
+#pragma clang diagnostic pop
+  XCTAssertEqualObjects(NSStringFromCGRect(window.bounds), NSStringFromCGRect(node.frame));
+  XCTAssertEqualObjects(NSStringFromCGRect(window.bounds), NSStringFromCGRect(cell.frame));
+  XCTAssertEqual(pagerNode.view.contentOffset.y, 0);
+  XCTAssertEqual(pagerNode.view.contentInset.top, 0);
+}
+
 @end