Publish events for layout pass

Summary:
Adds `LayoutPassStart` and `LayoutPassEnd` events.

The existing `NodeLayout` event in isolation is not as useful as it could be. Having events that mark start and end of a layout pass are a useful addition.

Differential Revision: D15305467

fbshipit-source-id: 14af6f65e698fb1e3112eb2ffd87a74d31df4840

tests/EventsTest.cpp

@@ -127,6 +127,10 @@ void EventTest::listen(const YGNode& node, Event::Type type, Event::Data data) {
     case Event::NodeLayout:
       events.push_back(createArgs<Event::NodeLayout>(node, data));
       break;
+    case Event::LayoutPassStart:
+      break;
+    case Event::LayoutPassEnd:
+      break;
   }
 }
 

yoga/Yoga.cpp

@@ -9,6 +9,7 @@
 #include <float.h>
 #include <string.h>
 #include <algorithm>
+#include <memory>
 #include "Utils.h"
 #include "YGNode.h"
 #include "YGNodePrint.h"
@@ -4002,7 +4003,13 @@ void YGNodeCalculateLayoutWithContext(
     const float ownerHeight,
     const YGDirection ownerDirection,
     void* layoutContext) {
-  marker::MarkerSection<YGMarkerLayout> marker{node};
+
+#ifdef YG_ENABLE_EVENTS
+  Event::publish<Event::LayoutPassStart>(node);
+#endif
+  // unique pointer to allow ending the marker early
+  std::unique_ptr<marker::MarkerSection<YGMarkerLayout>> marker{
+      new marker::MarkerSection<YGMarkerLayout>{node}};
 
   // Increment the generation count. This will force the recursive routine to
   // visit all dirty nodes at least once. Subsequent visits will be skipped if
@@ -4061,7 +4068,7 @@ void YGNodeCalculateLayoutWithContext(
           true,
           "initial",
           node->getConfig(),
-          marker.data,
+          marker->data,
           layoutContext)) {
     node->setPosition(
         node->getLayout().direction, ownerWidth, ownerHeight, ownerWidth);
@@ -4078,6 +4085,13 @@ void YGNodeCalculateLayoutWithContext(
 #endif
   }
 
+  // end marker here
+  marker = nullptr;
+
+#ifdef YG_ENABLE_EVENTS
+  Event::publish<Event::LayoutPassEnd>(node);
+#endif
+
   // We want to get rid off `useLegacyStretchBehaviour` from YGConfig. But we
   // aren't sure whether client's of yoga have gotten rid off this flag or not.
   // So logging this in YGLayout would help to find out the call sites depending

yoga/event/event.h

@@ -15,7 +15,13 @@ namespace facebook {
 namespace yoga {
 
 struct Event {
-  enum Type { NodeAllocation, NodeDeallocation, NodeLayout };
+  enum Type {
+    NodeAllocation,
+    NodeDeallocation,
+    NodeLayout,
+    LayoutPassStart,
+    LayoutPassEnd
+  };
   class Data;
   using Subscriber = void(const YGNode&, Type, Data);