Coordinate dismiss of ComposeVC with presentation of ConversationVC

Signal/src/ViewControllers/RecipientPicker/ComposeViewController.swift

@@ -47,28 +47,20 @@ class ComposeViewController: RecipientPickerContainerViewController {
 
     /// Presents the conversation for the given thread and dismisses this
     /// controller such that the conversation is visible.
-    ///
-    /// - Note
-    /// In practice, the view controller dismissing us here is the same one
-    /// (a ``ConversationSplitViewController``) that will ultimately present the
-    /// conversation. To that end, there be dragons in potential races between
-    /// the two actions, which seem to particularly be prominent when this
-    /// method is called from a `DispatchQueue.main` block. (This happens, for
-    /// example, when doing some asynchronous work, such as a lookup, which
-    /// completes in a `DispatchQueue.main` block that calls this method.)
-    ///
-    /// Some example dragons found at the time of writing include user
-    /// interaction being disabled on the nav bar, incorrect nav bar layout,
-    /// keyboards refusing to pop, and the conversation input toolbar being
-    /// hidden behind the keyboard if it does pop.
-    ///
-    /// Ensuring that the presentation and dismissal are in separate dispatch
-    /// blocks seems to dodge the dragons.
     func newConversation(thread: TSThread) {
-        SignalApp.shared.presentConversationForThread(thread, action: .compose, animated: false)
-
-        DispatchQueue.main.async { [weak self] in
-            self?.presentingViewController?.dismiss(animated: true)
+        presentingViewController?.dismiss(animated: true)
+        if let transitionCoordinator = presentingViewController?.transitionCoordinator {
+            // When transitionCoordinator is present, coordinate the immediate presentation of
+            // the conversationVC with the animated dismissal of the compose VC
+            transitionCoordinator.animate { _ in
+                UIView.performWithoutAnimation {
+                    SignalApp.shared.presentConversationForThread(thread, action: .compose, animated: false)
+                }
+            }
+        } else {
+            // There isn't a transition coordinator present for some reason, revert to displaying
+            // the conversation VC in parallel with the animated dismissal of the compose VC
+            SignalApp.shared.presentConversationForThread(thread, action: .compose, animated: false)
         }
     }