Add YGErrata Enum (#1256)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1256

X-link: https://github.com/facebook/react-native/pull/37076

This adds a `YGErrata` bitset enum matching the API and guarantees described in https://github.com/facebook/yoga/issues/1247.

It is hooked up in later diffs. There are a couple of `YGExperimentalFeature` values that belong here, but keeping the current options means that the default `YGErrataNone` corresponds to existing default behavior, letting us stage the series of changes as:
1. Implement errata API
2. Update internal Yoga users we want to de-risk to `YGErrataClassic` or `YGErrataAll` (if setting `UseLegacyStretchBehaviour`)
3. Add new errata, changing Yoga defaults to be conformant, while letting internal apps opt into compatibility modes pending experimentation.

I also added a macro to let C++ users of Yoga perform bitwise operations on the enum without casting (already available for C users).

Reviewed By: rshest

Differential Revision: D45254098

fbshipit-source-id: d4b61271a8018f548f2d9d8c953db4b121a502d1

yoga/YGEnums.cpp

@@ -87,6 +87,20 @@ const char* YGEdgeToString(const YGEdge value) {
   return "unknown";
 }
 
+const char* YGErrataToString(const YGErrata value) {
+  switch (value) {
+    case YGErrataNone:
+      return "none";
+    case YGErrataStretchFlexBasis:
+      return "stretch-flex-basis";
+    case YGErrataAll:
+      return "all";
+    case YGErrataClassic:
+      return "classic";
+  }
+  return "unknown";
+}
+
 const char* YGExperimentalFeatureToString(const YGExperimentalFeature value) {
   switch (value) {
     case YGExperimentalFeatureWebFlexBasis:

yoga/YGEnums.h

@@ -54,6 +54,14 @@ YG_ENUM_SEQ_DECL(
     YGEdgeVertical,
     YGEdgeAll)
 
+YG_ENUM_DECL(
+    YGErrata,
+    YGErrataNone = 0,
+    YGErrataStretchFlexBasis = 1,
+    YGErrataAll = 2147483647,
+    YGErrataClassic = 2147483646)
+YG_DEFINE_ENUM_FLAG_OPERATORS(YGErrata)
+
 YG_ENUM_SEQ_DECL(
     YGExperimentalFeature,
     YGExperimentalFeatureWebFlexBasis,

yoga/YGMacros.h

@@ -7,6 +7,10 @@
 
 #pragma once
 
+#ifdef __cplusplus
+#include <type_traits>
+#endif
+
 #ifdef __cplusplus
 #define YG_EXTERN_C_BEGIN extern "C" {
 #define YG_EXTERN_C_END }
@@ -40,6 +44,48 @@
 #define YG_ENUM_END(name) name
 #endif
 
+#ifdef __cplusplus
+#define YG_DEFINE_ENUM_FLAG_OPERATORS(name)                       \
+  extern "C++" {                                                  \
+  constexpr inline name operator~(name a) {                       \
+    return static_cast<name>(                                     \
+        ~static_cast<std::underlying_type<name>::type>(a));       \
+  }                                                               \
+  constexpr inline name operator|(name a, name b) {               \
+    return static_cast<name>(                                     \
+        static_cast<std::underlying_type<name>::type>(a) |        \
+        static_cast<std::underlying_type<name>::type>(b));        \
+  }                                                               \
+  constexpr inline name operator&(name a, name b) {               \
+    return static_cast<name>(                                     \
+        static_cast<std::underlying_type<name>::type>(a) &        \
+        static_cast<std::underlying_type<name>::type>(b));        \
+  }                                                               \
+  constexpr inline name operator^(name a, name b) {               \
+    return static_cast<name>(                                     \
+        static_cast<std::underlying_type<name>::type>(a) ^        \
+        static_cast<std::underlying_type<name>::type>(b));        \
+  }                                                               \
+  inline name& operator|=(name& a, name b) {                      \
+    return reinterpret_cast<name&>(                               \
+        reinterpret_cast<std::underlying_type<name>::type&>(a) |= \
+        static_cast<std::underlying_type<name>::type>(b));        \
+  }                                                               \
+  inline name& operator&=(name& a, name b) {                      \
+    return reinterpret_cast<name&>(                               \
+        reinterpret_cast<std::underlying_type<name>::type&>(a) &= \
+        static_cast<std::underlying_type<name>::type>(b));        \
+  }                                                               \
+  inline name& operator^=(name& a, name b) {                      \
+    return reinterpret_cast<name&>(                               \
+        reinterpret_cast<std::underlying_type<name>::type&>(a) ^= \
+        static_cast<std::underlying_type<name>::type>(b));        \
+  }                                                               \
+  }
+#else
+#define YG_DEFINE_ENUM_FLAG_OPERATORS(name)
+#endif
+
 #ifdef __cplusplus
 namespace facebook {
 namespace yoga {