Add tests for LayoutableChildren iterator (#1731)

Summary:
Adds unit tests that directly cover the order in which `LayoutableChildren` iterator goes over the descendant nodes. The covered cases are as follows (nodes with `display: contents` are marked green):

### Single `display: contents` node

```mermaid
flowchart TD
R((R)) --> A((A))
R --> B((B))
R --> C((C))

B --> D((D))
B --> E((E))

style B fill:https://github.com/facebook/yoga/issues/090
```

Correct order: `A, D, E, C`

### Multiple `display: contents` nodes

```mermaid
flowchart TD
R((R)) --> A((A))
R --> B((B))
R --> C((C))

A --> D((D))
A --> E((E))

B --> F((F))
B --> G((G))

C --> H((H))
C --> I((I))

style A fill:https://github.com/facebook/yoga/issues/090
style B fill:https://github.com/facebook/yoga/issues/090
style C fill:https://github.com/facebook/yoga/issues/090
```

Correct order: `D, E, F, G, H, I`

### Nested `display: contents` nodes

```mermaid
flowchart TD
R((R)) --> A((A))
R --> B((B))
R --> C((C))

B --> D((D))
B --> E((E))

E --> F((F))
E --> G((G))

style B fill:https://github.com/facebook/yoga/issues/090
style E fill:https://github.com/facebook/yoga/issues/090
```

Correct order: `A, D, F, G, C`

### Leaf `display: contents` node

```mermaid
flowchart TD
R((R)) --> A((A))
R --> B((B))
R --> C((C))

style B fill:https://github.com/facebook/yoga/issues/090
```

Correct order: `A, C`

### Root `display: contents` node

```mermaid
flowchart TD
R((R)) --> A((A))
R --> B((B))
R --> C((C))

style R fill:https://github.com/facebook/yoga/issues/090
```

Correct order: `A, B, C` - `LayoutableChildren` goes over the children with `display: contents` property, setting it on the root node should have no effect.

Changelog: [Internal]

Pull Request resolved: https://github.com/facebook/yoga/pull/1731

Reviewed By: joevilches

Differential Revision: D64981779

Pulled By: NickGerleman

fbshipit-source-id: ee39759c663a40f96ad313f1b775d53ab68fb442

tests/YGLayoutableChildrenTest.cpp

@@ -0,0 +1,191 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gtest/gtest.h>
+#include <yoga/Yoga.h>
+#include <yoga/node/Node.h>
+#include <cstdio>
+
+TEST(YogaTest, layoutable_children_single_contents_node) {
+  YGNodeRef root = YGNodeNew();
+
+  YGNodeRef root_child0 = YGNodeNew();
+  YGNodeRef root_child1 = YGNodeNew();
+  YGNodeRef root_child2 = YGNodeNew();
+
+  YGNodeRef root_grandchild0 = YGNodeNew();
+  YGNodeRef root_grandchild1 = YGNodeNew();
+
+  YGNodeInsertChild(root, root_child0, 0);
+  YGNodeInsertChild(root, root_child1, 1);
+  YGNodeInsertChild(root, root_child2, 2);
+
+  YGNodeInsertChild(root_child1, root_grandchild0, 0);
+  YGNodeInsertChild(root_child1, root_grandchild1, 1);
+
+  YGNodeStyleSetDisplay(root_child1, YGDisplayContents);
+
+  std::vector<facebook::yoga::Node*> order = {
+      facebook::yoga::resolveRef(root_child0),
+      facebook::yoga::resolveRef(root_grandchild0),
+      facebook::yoga::resolveRef(root_grandchild1),
+      facebook::yoga::resolveRef(root_child2),
+  };
+  auto correctOrderIt = order.begin();
+
+  for (auto node : facebook::yoga::resolveRef(root)->getLayoutChildren()) {
+    ASSERT_EQ(node, *correctOrderIt);
+    correctOrderIt++;
+  }
+
+  YGNodeFreeRecursive(root);
+}
+
+TEST(YogaTest, layoutable_children_multiple_contents_nodes) {
+  YGNodeRef root = YGNodeNew();
+
+  YGNodeRef root_child0 = YGNodeNew();
+  YGNodeRef root_child1 = YGNodeNew();
+  YGNodeRef root_child2 = YGNodeNew();
+
+  YGNodeRef root_grandchild0 = YGNodeNew();
+  YGNodeRef root_grandchild1 = YGNodeNew();
+  YGNodeRef root_grandchild2 = YGNodeNew();
+  YGNodeRef root_grandchild3 = YGNodeNew();
+  YGNodeRef root_grandchild4 = YGNodeNew();
+  YGNodeRef root_grandchild5 = YGNodeNew();
+
+  YGNodeInsertChild(root, root_child0, 0);
+  YGNodeInsertChild(root, root_child1, 1);
+  YGNodeInsertChild(root, root_child2, 2);
+
+  YGNodeInsertChild(root_child0, root_grandchild0, 0);
+  YGNodeInsertChild(root_child0, root_grandchild1, 1);
+  YGNodeInsertChild(root_child1, root_grandchild2, 0);
+  YGNodeInsertChild(root_child1, root_grandchild3, 1);
+  YGNodeInsertChild(root_child2, root_grandchild4, 0);
+  YGNodeInsertChild(root_child2, root_grandchild5, 1);
+
+  YGNodeStyleSetDisplay(root_child0, YGDisplayContents);
+  YGNodeStyleSetDisplay(root_child1, YGDisplayContents);
+  YGNodeStyleSetDisplay(root_child2, YGDisplayContents);
+
+  std::vector<facebook::yoga::Node*> order = {
+      facebook::yoga::resolveRef(root_grandchild0),
+      facebook::yoga::resolveRef(root_grandchild1),
+      facebook::yoga::resolveRef(root_grandchild2),
+      facebook::yoga::resolveRef(root_grandchild3),
+      facebook::yoga::resolveRef(root_grandchild4),
+      facebook::yoga::resolveRef(root_grandchild5),
+  };
+  auto correctOrderIt = order.begin();
+
+  for (auto node : facebook::yoga::resolveRef(root)->getLayoutChildren()) {
+    ASSERT_EQ(node, *correctOrderIt);
+    correctOrderIt++;
+  }
+
+  YGNodeFreeRecursive(root);
+}
+
+TEST(YogaTest, layoutable_children_nested_contents_nodes) {
+  YGNodeRef root = YGNodeNew();
+
+  YGNodeRef root_child0 = YGNodeNew();
+  YGNodeRef root_child1 = YGNodeNew();
+  YGNodeRef root_child2 = YGNodeNew();
+
+  YGNodeRef root_grandchild0 = YGNodeNew();
+  YGNodeRef root_grandchild1 = YGNodeNew();
+
+  YGNodeRef root_great_grandchild0 = YGNodeNew();
+  YGNodeRef root_great_grandchild1 = YGNodeNew();
+
+  YGNodeInsertChild(root, root_child0, 0);
+  YGNodeInsertChild(root, root_child1, 1);
+  YGNodeInsertChild(root, root_child2, 2);
+
+  YGNodeInsertChild(root_child1, root_grandchild0, 0);
+  YGNodeInsertChild(root_child1, root_grandchild1, 1);
+
+  YGNodeInsertChild(root_grandchild1, root_great_grandchild0, 0);
+  YGNodeInsertChild(root_grandchild1, root_great_grandchild1, 1);
+
+  YGNodeStyleSetDisplay(root_child1, YGDisplayContents);
+  YGNodeStyleSetDisplay(root_grandchild1, YGDisplayContents);
+
+  std::vector<facebook::yoga::Node*> order = {
+      facebook::yoga::resolveRef(root_child0),
+      facebook::yoga::resolveRef(root_grandchild0),
+      facebook::yoga::resolveRef(root_great_grandchild0),
+      facebook::yoga::resolveRef(root_great_grandchild1),
+      facebook::yoga::resolveRef(root_child2),
+  };
+  auto correctOrderIt = order.begin();
+
+  for (auto node : facebook::yoga::resolveRef(root)->getLayoutChildren()) {
+    ASSERT_EQ(node, *correctOrderIt);
+    correctOrderIt++;
+  }
+
+  YGNodeFreeRecursive(root);
+}
+
+TEST(YogaTest, layoutable_children_contents_leaf_node) {
+  YGNodeRef root = YGNodeNew();
+
+  YGNodeRef root_child0 = YGNodeNew();
+  YGNodeRef root_child1 = YGNodeNew();
+  YGNodeRef root_child2 = YGNodeNew();
+
+  YGNodeInsertChild(root, root_child0, 0);
+  YGNodeInsertChild(root, root_child1, 1);
+  YGNodeInsertChild(root, root_child2, 2);
+
+  YGNodeStyleSetDisplay(root_child1, YGDisplayContents);
+
+  std::vector<facebook::yoga::Node*> order = {
+      facebook::yoga::resolveRef(root_child0),
+      facebook::yoga::resolveRef(root_child2),
+  };
+  auto correctOrderIt = order.begin();
+
+  for (auto node : facebook::yoga::resolveRef(root)->getLayoutChildren()) {
+    ASSERT_EQ(node, *correctOrderIt);
+    correctOrderIt++;
+  }
+
+  YGNodeFreeRecursive(root);
+}
+
+TEST(YogaTest, layoutable_children_contents_root_node) {
+  YGNodeRef root = YGNodeNew();
+
+  YGNodeRef root_child0 = YGNodeNew();
+  YGNodeRef root_child1 = YGNodeNew();
+  YGNodeRef root_child2 = YGNodeNew();
+
+  YGNodeInsertChild(root, root_child0, 0);
+  YGNodeInsertChild(root, root_child1, 1);
+  YGNodeInsertChild(root, root_child2, 2);
+
+  YGNodeStyleSetDisplay(root, YGDisplayContents);
+
+  std::vector<facebook::yoga::Node*> order = {
+      facebook::yoga::resolveRef(root_child0),
+      facebook::yoga::resolveRef(root_child1),
+      facebook::yoga::resolveRef(root_child2),
+  };
+  auto correctOrderIt = order.begin();
+
+  for (auto node : facebook::yoga::resolveRef(root)->getLayoutChildren()) {
+    ASSERT_EQ(node, *correctOrderIt);
+    correctOrderIt++;
+  }
+
+  YGNodeFreeRecursive(root);
+}

yoga/node/LayoutableChildren.h

@@ -4,6 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  */
+#pragma once
 
 #include <cstdint>
 #include <vector>