Correctly allow components to return different top-level nodes during different renderings

sky/framework/fn.dart

Index: sky/framework/fn.dart
diff --git a/sky/framework/fn.dart b/sky/framework/fn.dart
index fc6ef99bbd974e84918e8c736dfef6b88fda846a..1811a705f272c90890aea66523766214d949b23c 100644
--- a/sky/framework/fn.dart
+++ b/sky/framework/fn.dart
@@ -615,8 +615,13 @@ abstract class Component extends Node {
 
     _dirty = false;
 
-    if (oldRendered != null && _rendered.runtimeType != oldRendered.runtimeType)
+    // TODO(rafaelw): This eagerly removes the old VDOM. It may be that a

[Hixie, 2015/03/06 21:32:52]

Do you mean VDOM here, or DOM? _remove() seems to do both (though I can't quite
tell what it means to remove things from the VDOM, I thought that was an
immutable structure).

[rafaelw, 2015/03/06 21:37:29]

You are correct, it is actually both (concretely, sky DOM nodes must be removed
and any components should get the didUnmount() signal).
Logically yes, though that's not how it's implemented.

+    // new component was rendered that could re-use some of it. Consider
+    // syncing the new VDROM against the old one.

[Hixie, 2015/03/06 21:32:52]

s/VDROM/VDOM/?

[rafaelw, 2015/03/06 21:37:29]

Yeah, I fixed that before landing.

+    if (oldRendered != null && _rendered.runtimeType != oldRendered.runtimeType) {
+      oldRendered._remove();
       oldRendered = null;
+    }
 
     if (_rendered._sync(oldRendered, host, insertBefore)) {
       _rendered = oldRendered; // retain stateful component