Fabric: EmptyLayoutMetrics does not contain invalid values anymore

Summary:
Before this change, fields of EmptyLayoutMetrics have some "invalid" values to allow us to compare equal them individually and get `false`. Turned out that having invalid values there might break some serialization layers, which is no good.
This change fixes that and adds explicit check for EmptyLayoutMetrics before running a comparison of individual fields.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: mdvacca

Differential Revision: D20324881

fbshipit-source-id: ab8e2a402f6bdfb393fc9b6789decb526fa94dfa

React/Fabric/Mounting/UIView+ComponentViewProtocol.mm

@@ -63,7 +63,9 @@ - (void)handleCommand:(NSString *)commandName args:(NSArray *)args
 - (void)updateLayoutMetrics:(LayoutMetrics const &)layoutMetrics
            oldLayoutMetrics:(LayoutMetrics const &)oldLayoutMetrics
 {
-  if (layoutMetrics.frame != oldLayoutMetrics.frame) {
+  bool forceUpdate = oldLayoutMetrics == EmptyLayoutMetrics;
+
+  if (forceUpdate || (layoutMetrics.frame != oldLayoutMetrics.frame)) {
     CGRect frame = RCTCGRectFromRect(layoutMetrics.frame);
 
     if (!std::isfinite(frame.origin.x) || !std::isfinite(frame.origin.y) || !std::isfinite(frame.size.width) ||
@@ -86,13 +88,13 @@ - (void)updateLayoutMetrics:(LayoutMetrics const &)layoutMetrics
     self.bounds = CGRect{CGPointZero, frame.size};
   }
 
-  if (layoutMetrics.layoutDirection != oldLayoutMetrics.layoutDirection) {
+  if (forceUpdate || (layoutMetrics.layoutDirection != oldLayoutMetrics.layoutDirection)) {
     self.semanticContentAttribute = layoutMetrics.layoutDirection == LayoutDirection::RightToLeft
         ? UISemanticContentAttributeForceRightToLeft
         : UISemanticContentAttributeForceLeftToRight;
   }
 
-  if (layoutMetrics.displayType != oldLayoutMetrics.displayType) {
+  if (forceUpdate || (layoutMetrics.displayType != oldLayoutMetrics.displayType)) {
     self.hidden = layoutMetrics.displayType == DisplayType::None;
   }
 }

ReactCommon/fabric/core/layout/LayoutMetrics.h

@@ -57,29 +57,10 @@ struct LayoutMetrics {
  * Represents some undefined, not-yet-computed or meaningless value of
  * `LayoutMetrics` type.
  * The value is comparable by equality with any other `LayoutMetrics` value.
- * All individual sub-properties of `EmptyLayoutMetrics` have the most possible
- * "invalid" values; this is useful when we compare them with some valid values.
  */
-static const LayoutMetrics EmptyLayoutMetrics = {
-    /* .frame = */ {
-        /* .origin = */ {std::numeric_limits<Float>::min(),
-                         std::numeric_limits<Float>::min()},
-        /* .size = */
-        {std::numeric_limits<Float>::min(), std::numeric_limits<Float>::min()},
-    },
-    /* .contentInsets = */
-    {std::numeric_limits<Float>::min(),
-     std::numeric_limits<Float>::min(),
-     std::numeric_limits<Float>::min(),
-     std::numeric_limits<Float>::min()},
-    /* .borderWidth = */
-    {std::numeric_limits<Float>::min(),
-     std::numeric_limits<Float>::min(),
-     std::numeric_limits<Float>::min(),
-     std::numeric_limits<Float>::min()},
-    /* .displayType = */ (DisplayType)-1,
-    /* .layoutDirection = */ (LayoutDirection)-1,
-    /* .pointScaleFactor = */ std::numeric_limits<Float>::min()};
+static LayoutMetrics const EmptyLayoutMetrics = {
+    /* .frame = */ {{0, 0}, {-1.0, -1.0}}
+};
 
 } // namespace react
 } // namespace facebook