From 0767f4d10522677a0254613b8fe6466bc3b29534 Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Tue, 14 Jul 2020 15:20:24 -0700
Subject: [PATCH] Using `YGPositionTypeAbsolute` value where we compare
 `absolute` vs `relative`

Summary:
Now Yoga.cpp does not use the `YGPositionTypeRelative` value/constant, it uses `YGPositionTypeAbsolute` instead.
Now `YGPositionType` can only be `YGPositionTypeRelative` or `YGPositionTypeAbsolute`, so expressions `x == YGPositionTypeRelative` and `x != YGPositionTypeAbsolute` are equivalent.
The reasoning behind the change is that in all cases we actually check a node to be (or not to be) `absolute`, not `relative`. This will make a difference in the coming diffs in the stack when we will introduce a new value for the type: `static`.

We need to differentiate `static` and `relative` values t implement the `stacking context` feature in the W3C-compliant way (to fix bugs and avoid developer confusion). Read more here:
https://developer.mozilla.org/en-US/docs/Web/CSS/position

Changelog: [Internal] Internal change in Yoga.

Reviewed By: SidharthGuglani

Differential Revision: D22386733

fbshipit-source-id: 8e2c2b88b404660639f845783c8f93f0c62c0fbb
---
 yoga/YGNode.cpp |  5 ++++-
 yoga/Yoga.cpp   | 12 ++++++------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/yoga/YGNode.cpp b/yoga/YGNode.cpp
index 23d5c40b..1ee1bde6 100644
--- a/yoga/YGNode.cpp
+++ b/yoga/YGNode.cpp
@@ -307,6 +307,9 @@ void YGNode::setPosition(
   const YGFlexDirection crossAxis =
       YGFlexDirectionCross(mainAxis, directionRespectingRoot);
 
+  // Here we should check for `YGPositionTypeStatic` and in this case zero inset
+  // properties (left, right, top, bottom, begin, end).
+  // https://www.w3.org/TR/css-position-3/#valdef-position-static
   const YGFloatOptional relativePositionMain =
       relativePosition(mainAxis, mainSize);
   const YGFloatOptional relativePositionCross =
@@ -440,7 +443,7 @@ float YGNode::resolveFlexShrink() const {
 
 bool YGNode::isNodeFlexible() {
   return (
-      (style_.positionType() == YGPositionTypeRelative) &&
+      (style_.positionType() != YGPositionTypeAbsolute) &&
       (resolveFlexGrow() != 0 || resolveFlexShrink() != 0));
 }
 
diff --git a/yoga/Yoga.cpp b/yoga/Yoga.cpp
index cb06c10e..97e64075 100644
--- a/yoga/Yoga.cpp
+++ b/yoga/Yoga.cpp
@@ -1131,7 +1131,7 @@ static bool YGIsBaselineLayout(const YGNodeRef node) {
   const uint32_t childCount = YGNodeGetChildCount(node);
   for (uint32_t i = 0; i < childCount; i++) {
     const YGNodeRef child = YGNodeGetChild(node, i);
-    if (child->getStyle().positionType() == YGPositionTypeRelative &&
+    if (child->getStyle().positionType() != YGPositionTypeAbsolute &&
         child->getStyle().alignSelf() == YGAlignBaseline) {
       return true;
     }
@@ -2505,7 +2505,7 @@ static void YGJustifyMainAxis(
        i < collectedFlexItemsValues.endOfLineIndex;
        i++) {
     const YGNodeRef child = node->getChild(i);
-    if (child->getStyle().positionType() == YGPositionTypeRelative) {
+    if (child->getStyle().positionType() != YGPositionTypeAbsolute) {
       if (child->marginLeadingValue(mainAxis).unit == YGUnitAuto) {
         numberOfAutoMarginsOnCurrentLine++;
       }
@@ -2589,7 +2589,7 @@ static void YGJustifyMainAxis(
       // Now that we placed the element, we need to update the variables.
       // We need to do that only for relative elements. Absolute elements do not
       // take part in that phase.
-      if (childStyle.positionType() == YGPositionTypeRelative) {
+      if (childStyle.positionType() != YGPositionTypeAbsolute) {
         if (child->marginLeadingValue(mainAxis).unit == YGUnitAuto) {
           collectedFlexItemsValues.mainDim +=
               collectedFlexItemsValues.remainingFreeSpace /
@@ -3311,7 +3311,7 @@ static void YGNodelayoutImpl(
         if (child->getStyle().display() == YGDisplayNone) {
           continue;
         }
-        if (child->getStyle().positionType() == YGPositionTypeRelative) {
+        if (child->getStyle().positionType() != YGPositionTypeAbsolute) {
           if (child->getLineIndex() != i) {
             break;
           }
@@ -3353,7 +3353,7 @@ static void YGNodelayoutImpl(
           if (child->getStyle().display() == YGDisplayNone) {
             continue;
           }
-          if (child->getStyle().positionType() == YGPositionTypeRelative) {
+          if (child->getStyle().positionType() != YGPositionTypeAbsolute) {
             switch (YGNodeAlignItem(node, child)) {
               case YGAlignFlexStart: {
                 child->setLayoutPosition(
@@ -3544,7 +3544,7 @@ static void YGNodelayoutImpl(
   if (performLayout && node->getStyle().flexWrap() == YGWrapWrapReverse) {
     for (uint32_t i = 0; i < childCount; i++) {
       const YGNodeRef child = YGNodeGetChild(node, i);
-      if (child->getStyle().positionType() == YGPositionTypeRelative) {
+      if (child->getStyle().positionType() != YGPositionTypeAbsolute) {
         child->setLayoutPosition(
             node->getLayout().measuredDimensions[dim[crossAxis]] -
                 child->getLayout().position[pos[crossAxis]] -