Use Bitfield in YGLayout

Summary: Replaces the usage of C++ bitfields with our portable `Bitfield` class.

Reviewed By: SidharthGuglani

Differential Revision: D16656361

fbshipit-source-id: 05f679e2e994e109b2bd1090c879d6850fabdc40

yoga/YGLayout.h

@@ -5,6 +5,7 @@
  * file in the root directory of this source tree.
  */
 #pragma once
+#include "Bitfield.h"
 #include "YGFloatOptional.h"
 #include "Yoga-internal.h"
 
@@ -14,11 +15,16 @@ struct YGLayout {
   std::array<float, 4> margin = {};
   std::array<float, 4> border = {};
   std::array<float, 4> padding = {};
-  YGDirection direction : 2;
-  bool didUseLegacyFlag : 1;
-  bool doesLegacyStretchFlagAffectsLayout : 1;
-  bool hadOverflow : 1;
 
+private:
+  static constexpr size_t directionIdx = 0;
+  static constexpr size_t didUseLegacyFlagIdx = 1;
+  static constexpr size_t doesLegacyStretchFlagAffectsLayoutIdx = 2;
+  static constexpr size_t hadOverflowIdx = 3;
+  facebook::yoga::Bitfield<uint8_t, YGDirection, bool, bool, bool> flags_ =
+      {YGDirectionInherit, false, false, false};
+
+public:
   uint32_t computedFlexBasisGeneration = 0;
   YGFloatOptional computedFlexBasis = {};
 
@@ -34,11 +40,28 @@ struct YGLayout {
 
   YGCachedMeasurement cachedLayout = YGCachedMeasurement();
 
-  YGLayout()
-      : direction(YGDirectionInherit),
-        didUseLegacyFlag(false),
-        doesLegacyStretchFlagAffectsLayout(false),
-        hadOverflow(false) {}
+  YGDirection direction() const { return flags_.at<directionIdx>(); }
+  decltype(flags_)::Ref<directionIdx> direction() {
+    return flags_.at<directionIdx>();
+  }
+
+  bool didUseLegacyFlag() const { return flags_.at<didUseLegacyFlagIdx>(); }
+  decltype(flags_)::Ref<didUseLegacyFlagIdx> didUseLegacyFlag() {
+    return flags_.at<didUseLegacyFlagIdx>();
+  }
+
+  bool doesLegacyStretchFlagAffectsLayout() const {
+    return flags_.at<doesLegacyStretchFlagAffectsLayoutIdx>();
+  }
+  decltype(flags_)::Ref<doesLegacyStretchFlagAffectsLayoutIdx>
+  doesLegacyStretchFlagAffectsLayout() {
+    return flags_.at<doesLegacyStretchFlagAffectsLayoutIdx>();
+  }
+
+  bool hadOverflow() const { return flags_.at<hadOverflowIdx>(); }
+  decltype(flags_)::Ref<hadOverflowIdx> hadOverflow() {
+    return flags_.at<hadOverflowIdx>();
+  }
 
   bool operator==(YGLayout layout) const;
   bool operator!=(YGLayout layout) const { return !(*this == layout); }