Add MarkerSection

Summary:
@public

Adds a class for triggering markers.

This calls `startMarker()` on construction, and `endMarker()` on destruction, thus being usable like a "scope guard": the object is instantiated, and automatically destroyed when going out of scope.

Reviewed By: SidharthGuglani

Differential Revision: D13817589

fbshipit-source-id: fd88884af970c1c0933d9ca6843f3f8f5d28b9e6

yoga/YGMarker.h

@@ -37,3 +37,25 @@ typedef struct {
 void YGConfigSetMarkerCallbacks(YGConfigRef, YGMarkerCallbacks);
 
 YG_EXTERN_C_END
+
+#ifdef __cplusplus
+
+namespace facebook {
+namespace yoga {
+namespace marker {
+namespace detail {
+
+template <YGMarker M>
+struct MarkerData;
+
+template <>
+struct MarkerData<YGMarkerLayout> {
+  using type = YGMarkerLayoutData;
+};
+
+} // namespace detail
+} // namespace marker
+} // namespace yoga
+} // namespace facebook
+
+#endif // __cplusplus

yoga/instrumentation.h

@@ -0,0 +1,44 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the LICENSE
+ * file in the root directory of this source tree.
+ */
+#include "YGConfig.h"
+#include "YGMarker.h"
+#include "YGNode.h"
+
+namespace facebook {
+namespace yoga {
+namespace marker {
+
+template <YGMarker MarkerType>
+class MarkerSection {
+public:
+  MarkerSection(YGNodeRef node) : MarkerSection{node, node->getConfig()} {}
+  ~MarkerSection() {
+    if (endMarker_) {
+      endMarker_(MarkerType, node_, {&data}, userData_);
+    }
+  }
+
+  typename detail::MarkerData<MarkerType>::type data = {};
+
+private:
+  decltype(YGMarkerCallbacks{}.endMarker) endMarker_;
+  YGNodeRef node_;
+  void* userData_;
+
+  MarkerSection(YGNodeRef node, YGConfigRef config)
+      : MarkerSection{node, config ? &config->markerCallbacks : nullptr} {}
+  MarkerSection(YGNodeRef node, YGMarkerCallbacks* callbacks)
+      : endMarker_{callbacks ? callbacks->endMarker : nullptr},
+        node_{node},
+        userData_{callbacks && callbacks->startMarker
+                      ? callbacks->startMarker(MarkerType, node, {&data})
+                      : nullptr} {}
+};
+
+} // namespace marker
+} // namespace yoga
+} // namespace facebook