[ASDisplayNode+Layout] Ensure a pending layout is applied once (#695)

Before:
  - Even if a pending layout was applied before, it'll be unnecessarily applied again in next layout passes and cause `-calculatedLayoutDidChange` being called multiple times.

After:
  - If a pending layout was applied, the calculated layout will not be ignored but reused, if possible, in next layout passes.

Test plan: testSetNeedsLayoutAndNormalLayoutPass in #424.

CHANGELOG.md

@@ -11,6 +11,7 @@
 - [API CHANGES] `ASPerformMainThreadDeallocation` and `ASPerformBackgroundDeallocation` functions take `id *` instead of `id` and they're now more reliable. Also, in Swift, `ASDeallocQueue.sharedDeallocationQueue() -> ASDeallocQueue.sharedDeallocationQueue`. [Adlai Holler](https://github.com/Adlai-Holler) [#651](https://github.com/TextureGroup/Texture/pull/651)
 - [Collection/Table] Added direct support for mapping section indexes between data spaces. [Adlai Holler](https://github.com/Adlai-Holler) [#651](https://github.com/TextureGroup/Texture/pull/660)
 - [ASCornerLayoutSpec] New layout spec class for declarative corner element layout. [#657](https://github.com/TextureGroup/Texture/pull/657) [huangkun](https://github.com/huang-kun)
+- [Layout] Fix an issue that causes a pending layout to be applied multiple times.  [Huy Nguyen](https://github.com/nguyenhuy) [#695](https://github.com/TextureGroup/Texture/pull/695)
 
 ## 2.6
 - [Xcode 9] Updated to require Xcode 9 (to fix warnings) [Garrett Moon](https://github.com/garrettmoon)

Source/ASDisplayNode+Layout.mm

@@ -300,14 +300,16 @@ - (void)_u_measureNodeWithBoundsIfNecessary:(CGRect)bounds
 
   CGSize boundsSizeForLayout = ASCeilSizeValues(bounds.size);
 
-  // Prefer _pendingDisplayNodeLayout over _calculatedDisplayNodeLayout (if exists, it's the newest)
-  // If there is no _pending, check if _calculated is valid to reuse (avoiding recalculation below).
-  if (_pendingDisplayNodeLayout == nullptr || _pendingDisplayNodeLayout->version < _layoutVersion) {
-    if (_calculatedDisplayNodeLayout->version >= _layoutVersion
-        && (_calculatedDisplayNodeLayout->requestedLayoutFromAbove == YES
-            || CGSizeEqualToSize(_calculatedDisplayNodeLayout->layout.size, boundsSizeForLayout))) {
-      return;
-    }
+  // Prefer a newer and not yet applied _pendingDisplayNodeLayout over _calculatedDisplayNodeLayout
+  // If there is no such _pending, check if _calculated is valid to reuse (avoiding recalculation below).
+  BOOL pendingLayoutIsPreferred = (_pendingDisplayNodeLayout != nullptr
+                                   && _pendingDisplayNodeLayout->version >= _layoutVersion
+                                   && _pendingDisplayNodeLayout->version > _calculatedDisplayNodeLayout->version); // _pending is not yet applied
+  BOOL calculatedLayoutIsReusable = (_calculatedDisplayNodeLayout->version >= _layoutVersion
+                                     && (_calculatedDisplayNodeLayout->requestedLayoutFromAbove
+                                         || CGSizeEqualToSize(_calculatedDisplayNodeLayout->layout.size, boundsSizeForLayout)));
+  if (!pendingLayoutIsPreferred && calculatedLayoutIsReusable) {
+    return;
   }
 
   as_activity_create_for_scope("Update node layout for current bounds");