Fix stale layout when a child switches to display: contents after insertion

[cipolleschi]

Summary:
Each node caches how many of its children use display: contents (contentsChildrenCount_, added in react/yoga#1726). The count is updated in insertChild, removeChild, replaceChild and setChildren, but not when the display of a child that is already attached changes.

So if YGNodeStyleSetDisplay(child, YGDisplayContents) is called after the child was inserted, the owner still reports hasContentsChildren() == false. The layout algorithm then skips cleanupContentsNodesRecursively for it, and the contents node keeps isDirty == true after layout. When a descendant of that node changes later, markDirtyAndPropagate stops at the contents node because it is already dirty, the root is never marked dirty, and the next YGNodeCalculateLayout returns the cached layout.

Minimal repro:

YGNodeRef root = YGNodeNew();
YGNodeStyleSetWidth(root, 100);
YGNodeStyleSetHeight(root, 100);
YGNodeRef child = YGNodeNew();
YGNodeInsertChild(root, child, 0);
YGNodeRef grandchild = YGNodeNew();
YGNodeStyleSetWidth(grandchild, 10);
YGNodeStyleSetHeight(grandchild, 10);
YGNodeInsertChild(child, grandchild, 0);

YGNodeStyleSetDisplay(child, YGDisplayContents);
YGNodeCalculateLayout(root, YGUndefined, YGUndefined, YGDirectionLTR);
// YGNodeIsDirty(child) is still true

YGNodeStyleSetWidth(grandchild, 20);
// YGNodeIsDirty(root) is false
YGNodeCalculateLayout(root, YGUndefined, YGUndefined, YGDirectionLTR);
// YGNodeLayoutGetWidth(grandchild) is 10, expected 20

This affects any binding that mutates nodes in place (the JS and Java bindings both go through YGNodeStyleSetDisplay). Setting the display before inserting the child works, which is what the existing tests do.

The fix recomputes the owner's count in YGNodeStyleSetDisplay when a node that has an owner switches to or from display: contents.

Changelog: [General][Fixed] - Fix stale layout when a child switches to display: contents after being inserted

X-link: react/yoga#2028

Reviewed By: javache

Differential Revision: D122122520

Pulled By: cipolleschi

[meta-codesync]

@cipolleschi has exported this pull request. If you are a Meta employee, you can view the originating Diff in D122122520.

[meta-codesync]

@cipolleschi merged this pull request in 19a6722.