Fix extra space at the bottom of pull request status view (#2229) (#2761)

* notify delegate when manageButton's visibility changes

* calculate inset for manageButton dynamically

* compute threadInset using insetForManageButton

* update safe inset when manageButton's visibility changes

Author: Natalia Harateh

Classes/Issues/IssueManagingContextController.swift

@@ -12,6 +12,7 @@ import GitHubAPI
 
 protocol IssueManagingContextControllerDelegate: class {
     func willMutateModel(from controller: IssueManagingContextController)
+    func didUpdateManageButtonVisibility(_ manageButton: UIView)
 }
 
 final class IssueManagingContextController: NSObject, ContextMenuDelegate {
@@ -80,6 +81,7 @@ final class IssueManagingContextController: NSObject, ContextMenuDelegate {
 
     func updateButtonVisibility() {
         manageButton.isHidden = actions.count == 0
+        delegate?.didUpdateManageButtonVisibility(manageButton)
     }
 
     enum Action {

Classes/Issues/IssuesViewController.swift

@@ -45,12 +45,17 @@ IssueManagingContextControllerDelegate {
     private var bookmarkNavController: BookmarkNavigationController?
     private var autocompleteController: AutocompleteController!
     private let manageController: IssueManagingContextController
-    private let threadInset = UIEdgeInsets(
-        top: Styles.Sizes.rowSpacing / 2,
-        left: Styles.Sizes.gutter,
-        bottom: 2 * Styles.Sizes.rowSpacing + Styles.Sizes.tableCellHeight,
-        right: Styles.Sizes.gutter
-    )
+    private var insetForManageButton: CGFloat {
+        return manageController.manageButton.isHidden ? 0 : manageController.manageButton.frame.height
+    }
+    private var threadInset: UIEdgeInsets {
+        return UIEdgeInsets(
+            top: Styles.Sizes.rowSpacing / 2,
+            left: Styles.Sizes.gutter,
+            bottom: 2 * Styles.Sizes.rowSpacing + insetForManageButton,
+            right: Styles.Sizes.gutter
+        )
+    }
 
     private var needsScrollToBottom = false
     private var lastTimelineElement: ListDiffable?
@@ -639,4 +644,8 @@ IssueManagingContextControllerDelegate {
         needsScrollToBottom = true
     }
 
+    func didUpdateManageButtonVisibility(_ manageButton: UIView) {
+        feed.collectionView.updateSafeInset(container: view, base: threadInset)
+    }
+
 }