Add workaround for bug in iOS 11.1 beta around hit area of custom back buttons.

// FREEBIE

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -1106,27 +1106,29 @@ typedef NS_ENUM(NSInteger, MessagesRangeSizeMode) {
 - (void)createBackButton
 {
     UIBarButtonItem *backItem = [self createOWSBackButton];
-    // This method gets called multiple times, so it's important we re-layout the unread badge
-    // with respect to the new backItem.
-    [backItem.customView addSubview:_backButtonUnreadCountView];
-    // TODO: The back button assets are assymetrical.  There are strong reasons
-    // to use spacing in the assets to manipulate the size and positioning of
-    // bar button items, but it means we'll probably need separate RTL and LTR
-    // flavors of these assets.
-    [_backButtonUnreadCountView autoPinEdgeToSuperviewEdge:ALEdgeTop withInset:-6];
-    [_backButtonUnreadCountView autoPinLeadingToSuperviewWithMargin:1];
-    [_backButtonUnreadCountView autoSetDimension:ALDimensionHeight toSize:self.unreadCountViewDiameter];
-    // We set a min width, but we will also pin to our subview label, so we can grow to accommodate multiple digits.
-    [_backButtonUnreadCountView autoSetDimension:ALDimensionWidth
-                                          toSize:self.unreadCountViewDiameter
-                                        relation:NSLayoutRelationGreaterThanOrEqual];
-
-    [_backButtonUnreadCountView addSubview:_backButtonUnreadCountLabel];
-    [_backButtonUnreadCountLabel autoPinWidthToSuperviewWithMargin:4];
-    [_backButtonUnreadCountLabel autoPinHeightToSuperview];
-
-    // Initialize newly created unread count badge to accurately reflect the current unread count.
-    [self updateBackButtonUnreadCount];
+    if (backItem.customView) {
+        // This method gets called multiple times, so it's important we re-layout the unread badge
+        // with respect to the new backItem.
+        [backItem.customView addSubview:_backButtonUnreadCountView];
+        // TODO: The back button assets are assymetrical.  There are strong reasons
+        // to use spacing in the assets to manipulate the size and positioning of
+        // bar button items, but it means we'll probably need separate RTL and LTR
+        // flavors of these assets.
+        [_backButtonUnreadCountView autoPinEdgeToSuperviewEdge:ALEdgeTop withInset:-6];
+        [_backButtonUnreadCountView autoPinLeadingToSuperviewWithMargin:1];
+        [_backButtonUnreadCountView autoSetDimension:ALDimensionHeight toSize:self.unreadCountViewDiameter];
+        // We set a min width, but we will also pin to our subview label, so we can grow to accommodate multiple digits.
+        [_backButtonUnreadCountView autoSetDimension:ALDimensionWidth
+                                              toSize:self.unreadCountViewDiameter
+                                            relation:NSLayoutRelationGreaterThanOrEqual];
+
+        [_backButtonUnreadCountView addSubview:_backButtonUnreadCountLabel];
+        [_backButtonUnreadCountLabel autoPinWidthToSuperviewWithMargin:4];
+        [_backButtonUnreadCountLabel autoPinHeightToSuperview];
+
+        // Initialize newly created unread count badge to accurately reflect the current unread count.
+        [self updateBackButtonUnreadCount];
+    }
 
     self.navigationItem.leftBarButtonItem = backItem;
 }

Signal/src/util/UIViewController+OWS.m

@@ -53,6 +53,22 @@ NS_ASSUME_NONNULL_BEGIN
         = CGRectMake(0, 0, backImage.size.width + kExtraRightPadding, backImage.size.height + kExtraHeightPadding);
     backButton.frame = buttonFrame;
 
+    if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(11, 1)) {
+        // In iOS 11.1 beta, the hot area of custom bar button items is _only_
+        // the bounds of the custom view, making them very hard to hit.
+        //
+        // TODO: Remove this hack if the bug is fixed in iOS 11.1 by the time
+        //       it goes to production (or in a later release),
+        //       since it has two negative side effects: 1) the layout of the
+        //       back button isn't consistent with the iOS default back buttons
+        //       2) we can't add the unread count badge to the back button
+        //       with this hack.
+        return [[UIBarButtonItem alloc] initWithImage:backImage
+                                                style:UIBarButtonItemStylePlain
+                                               target:target
+                                               action:selector];
+    }
+
     UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithCustomView:backButton];
     backItem.width = buttonFrame.size.width;