Support transforms forming containing blocks (#1539)

Summary:
X-link: https://github.com/facebook/react-native/pull/42191

Pull Request resolved: https://github.com/facebook/yoga/pull/1539

React native supports transforms and if a node has a transform it will [form a containing block for absolute descendants regardless of position type](https://developer.mozilla.org/en-US/docs/Web/CSS/Containing_block#identifying_the_containing_block). So we need to pass that information into Yoga to ensure this happens.

The verbiage for the field "alwaysFormsContainingBlock" is very specific. In a vacuum a node cannot simply "form a containing block". It only forms a containing block in reference to a different node. This can be illustrated in a scenario where we have a static node that is a flex container which has 1 absolute child and 1 relative child. This static node will form a containing block for the relative child but not the absolute one. We could just pass the information on rather something has a transform or not but Yoga is not supposed to know about transforms in general. As a result we have a notion of "always" forming a containing block. Since Yoga is a flexbox spec, non-absolute nodes' containing blocks will ways be their parent. If we add something like a transform to a node then that will also apply to absolute nodes - hence we can say the node will **always** form a CB, no matter who is the descendant.

Changelog: [Internal]

Reviewed By: NickGerleman

Differential Revision: D52521160

fbshipit-source-id: bab9319ffddec617f5281823930f2a00cc2967f2

yoga/YGNode.cpp

@@ -328,6 +328,12 @@ void YGNodeSetPrintFunc(YGNodeRef node, YGPrintFunc printFunc) {
   resolveRef(node)->setPrintFunc(printFunc);
 }
 
+void YGNodeSetAlwaysFormsContainingBlock(
+    YGNodeRef node,
+    bool alwaysFormsContainingBlock) {
+  resolveRef(node)->setAlwaysFormsContainingBlock(alwaysFormsContainingBlock);
+}
+
 #ifdef DEBUG
 void YGNodePrint(const YGNodeConstRef node, const YGPrintOptions options) {
   yoga::print(resolveRef(node), scopedEnum(options));

yoga/YGNode.h

@@ -270,6 +270,17 @@ typedef void (*YGPrintFunc)(YGNodeConstRef node);
  */
 YG_EXPORT void YGNodeSetPrintFunc(YGNodeRef node, YGPrintFunc printFunc);
 
+/**
+ * Make it so that this node will always form a containing block for any
+ * descendant nodes. This is useful for when a node has a property outside of
+ * of Yoga that will form a containing block. For example, transforms or some of
+ * the others listed in
+ * https://developer.mozilla.org/en-US/docs/Web/CSS/Containing_block
+ */
+YG_EXPORT void YGNodeSetAlwaysFormsContainingBlock(
+    YGNodeRef node,
+    bool alwaysFormsContainingBlock);
+
 /**
  * Print a node to log output.
  */

yoga/algorithm/AbsoluteLayout.cpp

@@ -528,7 +528,9 @@ void layoutAbsoluteDescendants(
       if (needsTrailingPosition(crossAxis)) {
         setChildTrailingPosition(currentNode, child, crossAxis);
       }
-    } else if (child->getStyle().positionType() == PositionType::Static) {
+    } else if (
+        child->getStyle().positionType() == PositionType::Static &&
+        !child->alwaysFormsContainingBlock()) {
       const Direction childDirection =
           child->resolveDirection(currentNodeDirection);
       const float childMainOffsetFromContainingBlock =

yoga/algorithm/CalculateLayout.cpp

@@ -2034,7 +2034,7 @@ static void calculateLayoutImpl(
       // Let the containing block layout its absolute descendants. By definition
       // the containing block will not be static unless we are at the root.
       if (node->getStyle().positionType() != PositionType::Static ||
-          depth == 1) {
+          node->alwaysFormsContainingBlock() || depth == 1) {
         layoutAbsoluteDescendants(
             node,
             node,

yoga/node/Node.h

@@ -48,6 +48,10 @@ class YG_EXPORT Node : public ::YGNode {
     return context_;
   }
 
+  bool alwaysFormsContainingBlock() const {
+    return alwaysFormsContainingBlock_;
+  }
+
   void print();
 
   bool getHasNewLayout() const {
@@ -242,6 +246,10 @@ class YG_EXPORT Node : public ::YGNode {
     context_ = context;
   }
 
+  void setAlwaysFormsContainingBlock(bool alwaysFormsContainingBlock) {
+    alwaysFormsContainingBlock_ = alwaysFormsContainingBlock;
+  }
+
   void setPrintFunc(YGPrintFunc printFunc) {
     printFunc_ = printFunc;
   }
@@ -369,6 +377,7 @@ class YG_EXPORT Node : public ::YGNode {
   bool hasNewLayout_ : 1 = true;
   bool isReferenceBaseline_ : 1 = false;
   bool isDirty_ : 1 = false;
+  bool alwaysFormsContainingBlock_ : 1 = false;
   NodeType nodeType_ : bitCount<NodeType>() = NodeType::Default;
   void* context_ = nullptr;
   YGMeasureFunc measureFunc_ = {nullptr};