Overflow detection in Yoga

Summary:
We need to provide Yoga clients with means of detecting overflow in flexbox layout. This information can be used later to identify a non-overflowing layout variant among others.

Flexbox layout considered overflown if (this is *not* an exhaustive list):

- if any child node overflows
- [no-wrap] total flex basis of all child nodes is greater than available space in parent and there are no flexible children
- [no-wrap] after flexing there is still not enough space to layout all child nodes

Reviewed By: gkassabli

Differential Revision: D5336645

fbshipit-source-id: c4f87d1754d7bac848e8d347b31d619393b94d2c

yoga/Yoga.c

@@ -54,6 +54,7 @@ typedef struct YGLayout {
 
   uint32_t computedFlexBasisGeneration;
   float computedFlexBasis;
+  bool hadOverflow;
 
   // Instead of recomputing the entire layout every single time, we
   // cache some information to break early when nothing changed
@@ -192,6 +193,7 @@ static YGNode gYGNodeDefaults = {
             .lastParentDirection = (YGDirection) -1,
             .nextCachedMeasurementsIndex = 0,
             .computedFlexBasis = YGUndefined,
+            .hadOverflow = false,
             .measuredDimensions = YG_DEFAULT_DIMENSION_VALUES,
 
             .cachedLayout =
@@ -782,6 +784,7 @@ YG_NODE_LAYOUT_PROPERTY_IMPL(float, Bottom, position[YGEdgeBottom]);
 YG_NODE_LAYOUT_PROPERTY_IMPL(float, Width, dimensions[YGDimensionWidth]);
 YG_NODE_LAYOUT_PROPERTY_IMPL(float, Height, dimensions[YGDimensionHeight]);
 YG_NODE_LAYOUT_PROPERTY_IMPL(YGDirection, Direction, direction);
+YG_NODE_LAYOUT_PROPERTY_IMPL(bool, HadOverflow, hadOverflow);
 
 YG_NODE_LAYOUT_RESOLVED_PROPERTY_IMPL(float, Margin, margin);
 YG_NODE_LAYOUT_RESOLVED_PROPERTY_IMPL(float, Border, border);
@@ -2574,12 +2577,14 @@ static void YGNodelayoutImpl(const YGNodeRef node,
                              performLayout && !requiresStretchLayout,
                              "flex",
                              config);
+        node->layout.hadOverflow = node->layout.hadOverflow || currentRelativeChild->layout.hadOverflow;
 
         currentRelativeChild = currentRelativeChild->nextChild;
       }
     }
 
     remainingFreeSpace = originalRemainingFreeSpace + deltaFreeSpace;
+    node->layout.hadOverflow = node->layout.hadOverflow || (remainingFreeSpace < 0);
 
     // STEP 6: MAIN-AXIS JUSTIFICATION & CROSS-AXIS SIZE DETERMINATION
 

yoga/Yoga.h

@@ -215,6 +215,7 @@ YG_NODE_LAYOUT_PROPERTY(float, Bottom);
 YG_NODE_LAYOUT_PROPERTY(float, Width);
 YG_NODE_LAYOUT_PROPERTY(float, Height);
 YG_NODE_LAYOUT_PROPERTY(YGDirection, Direction);
+YG_NODE_LAYOUT_PROPERTY(bool, HadOverflow);
 
 // Get the computed values for these nodes after performing layout. If they were set using
 // point values then the returned value will be the same as YGNodeStyleGetXXX. However if