Initial implementation of Collapsing Margins computational logic for LayoutNG

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm_test.cc

Index: third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm_test.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm_test.cc b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm_test.cc
index 04be0f9cc33523c4eeca5a35c2fa36545d2f9dac..fa0801ea3241e90b4ac47f55ad7cdc1b6f88e1b0 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm_test.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm_test.cc
@@ -65,8 +65,7 @@ TEST_F(NGBlockLayoutAlgorithmTest, LayoutBlockChildren) {
   while (!algorithm.Layout(space, &frag))
     ;
   EXPECT_EQ(frag->Width(), LayoutUnit(kWidth));
-  EXPECT_EQ(frag->Height(),
-            LayoutUnit(kHeight1 + kHeight2 + kMarginTop + kMarginBottom));
+  EXPECT_EQ(frag->Height(), LayoutUnit(kHeight1 + kHeight2 + kMarginTop));
   EXPECT_EQ(frag->Type(), NGPhysicalFragmentBase::FragmentBox);
   ASSERT_EQ(frag->Children().size(), 2UL);
 
@@ -79,5 +78,112 @@ TEST_F(NGBlockLayoutAlgorithmTest, LayoutBlockChildren) {
   EXPECT_EQ(child->TopOffset(), kHeight1 + kMarginTop);
 }
 
+// Verifies the collapsing margins case for the next pair:
+// - top margin of a box and top margin of its first in-flow child.
+//
+// Test case's HTML representation:
+// <div style="margin-top: 20px; height: 50px;">  <!-- DIV1 -->
+//    <div style="margin-top: 10px"></div>        <!-- DIV2 -->
+// </div>
+//
+// Expected:
+//   Margins are collapsed resulting a single margin 20px = max(20px, 10px)
+TEST_F(NGBlockLayoutAlgorithmTest, CollapsingMarginsCase1) {
+  const int kHeight = 50;
+  const int kDiv1MarginTop = 20;
+  const int kDiv2MarginTop = 10;
+
+  // DIV1
+  RefPtr<ComputedStyle> div1_style = ComputedStyle::create();
+  div1_style->setHeight(Length(kHeight, Fixed));
+  div1_style->setMarginTop(Length(kDiv1MarginTop, Fixed));
+  NGBox* div1 = new NGBox(div1_style.get());
+
+  // DIV2
+  RefPtr<ComputedStyle> div2_style = ComputedStyle::create();
+  div2_style->setMarginTop(Length(kDiv2MarginTop, Fixed));
+  NGBox* div2 = new NGBox(div2_style.get());
+
+  div1->SetFirstChild(div2);
+
+  NGConstraintSpace* space = new NGConstraintSpace(
+      HorizontalTopBottom, NGLogicalSize(LayoutUnit(100), NGSizeIndefinite));
+  NGBlockLayoutAlgorithm algorithm(style_, div1);
+  NGPhysicalFragment* frag;
+  while (!algorithm.Layout(space, &frag))
+    ;
+
+  EXPECT_EQ(frag->MarginStrut().margin_block_start, kDiv1MarginTop);
+  ASSERT_EQ(frag->Children().size(), 1UL);
+  const NGPhysicalFragmentBase* div2_fragment = frag->Children()[0];
+  EXPECT_EQ(div2_fragment->MarginStrut().margin_block_start, kDiv2MarginTop);
+}
+
+// Verifies the collapsing margins case for the next pair:
+// - bottom margin of box and top margin of its next in-flow following sibling.
+//
+// Test case's HTML representation:
+// <div style="margin-bottom: 20px; height: 50px;">  <!-- DIV1 -->
+//    <div style="margin-bottom: -15px"></div>       <!-- DIV2 -->
+// </div>
+// <div style="margin-top: 10px; height: 50px;">     <!-- DIV3 -->
+//    <div style="margin-top: -30px"></div>          <!-- DIV4 -->
+// </div>
+//
+// Expected:
+//   Margins are collapsed resulting an overlap
+//   -10px = max(20px, 10px) - max(abs(-15px), abs(-30px))
+//   between DIV2 and DIV3.
+TEST_F(NGBlockLayoutAlgorithmTest, CollapsingMarginsCase2) {
+  const int kHeight = 50;
+  const int kDiv1MarginBottom = 20;
+  const int kDiv2MarginBottom = -15;
+  const int kDiv3MarginTop = 10;
+  const int kDiv4MarginTop = -30;
+  const int kExpectedCollapsedMargin = -10;
+
+  // DIV1
+  RefPtr<ComputedStyle> div1_style = ComputedStyle::create();
+  div1_style->setHeight(Length(kHeight, Fixed));
+  div1_style->setMarginBottom(Length(kDiv1MarginBottom, Fixed));
+  NGBox* div1 = new NGBox(div1_style.get());
+
+  // DIV2
+  RefPtr<ComputedStyle> div2_style = ComputedStyle::create();
+  div2_style->setMarginBottom(Length(kDiv2MarginBottom, Fixed));
+  NGBox* div2 = new NGBox(div2_style.get());
+
+  // DIV3
+  RefPtr<ComputedStyle> div3_style = ComputedStyle::create();
+  div3_style->setHeight(Length(kHeight, Fixed));
+  div3_style->setMarginTop(Length(kDiv3MarginTop, Fixed));
+  NGBox* div3 = new NGBox(div3_style.get());
+
+  // DIV4
+  RefPtr<ComputedStyle> div4_style = ComputedStyle::create();
+  div4_style->setMarginTop(Length(kDiv4MarginTop, Fixed));
+  NGBox* div4 = new NGBox(div4_style.get());
+
+  div1->SetFirstChild(div2);
+  div3->SetFirstChild(div4);
+  div1->SetNextSibling(div3);
+
+  NGConstraintSpace* space = new NGConstraintSpace(
+      HorizontalTopBottom, NGLogicalSize(LayoutUnit(100), NGSizeIndefinite));
+  NGBlockLayoutAlgorithm algorithm(style_, div1);
+  NGPhysicalFragment* frag;
+  while (!algorithm.Layout(space, &frag))
+    ;
+
+  ASSERT_EQ(frag->Children().size(), 2UL);
+
+  const NGPhysicalFragmentBase* child = frag->Children()[0];
+  EXPECT_EQ(child->Height(), kHeight);
+  EXPECT_EQ(child->TopOffset(), 0);
+
+  child = frag->Children()[1];
+  EXPECT_EQ(child->Height(), kHeight);
+  EXPECT_EQ(child->TopOffset(), kHeight + kExpectedCollapsedMargin);
+}
 }  // namespace
 }  // namespace blink