Prevent an infinite loop in Text.onTextLayout

Summary:
Changelog: [internal]

# Problem
onTextLayout was called even if there was no change to text layout. This can cause an infinite loop with onTextLayout triggering commit which triggers onTextLayout.

# Fix
Do not call onTextLayout if there is nothing to layout.

Reviewed By: yungsters

Differential Revision: D23648430

fbshipit-source-id: 055dc34a9aca0edf2c78a5812b35b80df32c9e3e

ReactCommon/react/renderer/components/text/ParagraphShadowNode.cpp

@@ -164,6 +164,18 @@ void ParagraphShadowNode::layout(LayoutContext layoutContext) {
 
   updateStateIfNeeded(content);
 
+  if (content.attachments.empty()) {
+#ifndef ANDROID
+    if (getConcreteProps().onTextLayout) {
+      // `onTextLayout` needs to be called even if text is empty
+      // to be compatible with Paper.
+      getConcreteEventEmitter().onTextLayout({});
+    }
+#endif
+    // No attachments, nothing to layout.
+    return;
+  }
+
   auto measurement = textLayoutManager_->measure(
       AttributedStringBox{content.attributedString},
       content.paragraphAttributes,
@@ -179,11 +191,6 @@ void ParagraphShadowNode::layout(LayoutContext layoutContext) {
   }
 #endif
 
-  if (content.attachments.empty()) {
-    // No attachments, nothing to layout.
-    return;
-  }
-
   //  Iterating on attachments, we clone shadow nodes and moving
   //  `paragraphShadowNode` that represents clones of `this` object.
   auto paragraphShadowNode = static_cast<ParagraphShadowNode *>(this);