[LayoutNG] Introduce NGPhysicalLineBoxFragment::First/LastLogicalLeaf()

This patch introduces the two helper functions as a preparation for
crrev.com/c/882292, where we need to check if an inline fragment is the
logically first/last leaf in its line to resolve caret position around
line wrap.

Bug: 771398
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I905ddc8923417da7178f8962db9c01e6fdf24754
Reviewed-on: https://chromium-review.googlesource.com/884381Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531703}

third_party/WebKit/Source/core/BUILD.gn

@@ -1945,6 +1945,7 @@ jumbo_source_set("unit_tests") {
     "layout/ng/inline/ng_inline_node_test.cc",
     "layout/ng/inline/ng_line_breaker_test.cc",
     "layout/ng/inline/ng_offset_mapping_test.cc",
+    "layout/ng/inline/ng_physical_line_box_fragment_test.cc",
     "layout/ng/inline/ng_physical_text_fragment_test.cc",
     "layout/ng/ng_absolute_utils_test.cc",
     "layout/ng/ng_base_layout_algorithm_test.cc",

third_party/WebKit/Source/core/layout/ng/inline/ng_physical_line_box_fragment.cc

@@ -4,6 +4,8 @@
 
 #include "core/layout/ng/inline/ng_physical_line_box_fragment.h"
 
+#include "core/style/ComputedStyle.h"
+
 namespace blink {
 
 NGPhysicalLineBoxFragment::NGPhysicalLineBoxFragment(
@@ -33,4 +35,44 @@ NGPhysicalOffsetRect NGPhysicalLineBoxFragment::VisualRectWithContents() const {
   return ContentsVisualRect();
 }
 
+const NGPhysicalFragment* NGPhysicalLineBoxFragment::FirstLogicalLeaf() const {
+  if (Children().IsEmpty())
+    return nullptr;
+  // TODO(xiaochengh): This isn't correct for mixed Bidi. Fix it. Besides, we
+  // should compute and store it during layout.
+  const TextDirection direction = Style().Direction();
+  const NGPhysicalFragment* runner = this;
+  while (runner->IsContainer() && !runner->IsBlockLayoutRoot()) {
+    const NGPhysicalContainerFragment* runner_as_container =
+        ToNGPhysicalContainerFragment(runner);
+    if (runner_as_container->Children().IsEmpty())
+      break;
+    runner = direction == TextDirection::kLtr
+                 ? runner_as_container->Children().front().get()
+                 : runner_as_container->Children().back().get();
+  }
+  DCHECK_NE(runner, this);
+  return runner;
+}
+
+const NGPhysicalFragment* NGPhysicalLineBoxFragment::LastLogicalLeaf() const {
+  if (Children().IsEmpty())
+    return nullptr;
+  // TODO(xiaochengh): This isn't correct for mixed Bidi. Fix it. Besides, we
+  // should compute and store it during layout.
+  const TextDirection direction = Style().Direction();
+  const NGPhysicalFragment* runner = this;
+  while (runner->IsContainer() && !runner->IsBlockLayoutRoot()) {
+    const NGPhysicalContainerFragment* runner_as_container =
+        ToNGPhysicalContainerFragment(runner);
+    if (runner_as_container->Children().IsEmpty())
+      break;
+    runner = direction == TextDirection::kLtr
+                 ? runner_as_container->Children().back().get()
+                 : runner_as_container->Children().front().get();
+  }
+  DCHECK_NE(runner, this);
+  return runner;
+}
+
 }  // namespace blink

third_party/WebKit/Source/core/layout/ng/inline/ng_physical_line_box_fragment.h

@@ -31,6 +31,11 @@ class CORE_EXPORT NGPhysicalLineBoxFragment final
   // VisualRect of itself including contents, in the local coordinate.
   NGPhysicalOffsetRect VisualRectWithContents() const;
 
+  // Returns the first/last leaf fragment in the line in logical order. Returns
+  // nullptr if the line box is empty.
+  const NGPhysicalFragment* FirstLogicalLeaf() const;
+  const NGPhysicalFragment* LastLogicalLeaf() const;
+
   scoped_refptr<NGPhysicalFragment> CloneWithoutOffset() const {
     Vector<scoped_refptr<NGPhysicalFragment>> children_copy(children_);
     return base::AdoptRef(new NGPhysicalLineBoxFragment(

third_party/WebKit/Source/core/layout/ng/inline/ng_physical_line_box_fragment_test.cc

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/layout/ng/inline/ng_physical_line_box_fragment.h"
+
+#include "core/layout/ng/inline/ng_inline_fragment_traversal.h"
+#include "core/layout/ng/inline/ng_physical_text_fragment.h"
+#include "core/layout/ng/ng_layout_test.h"
+#include "core/layout/ng/ng_physical_box_fragment.h"
+
+namespace blink {
+
+class NGPhysicalLineBoxFragmentTest
+    : public NGLayoutTest,
+      private ScopedLayoutNGPaintFragmentsForTest {
+ public:
+  NGPhysicalLineBoxFragmentTest()
+      : NGLayoutTest(), ScopedLayoutNGPaintFragmentsForTest(true) {}
+
+ protected:
+  const NGPhysicalLineBoxFragment* GetLineBox() const {
+    const Element* container = GetElementById("root");
+    DCHECK(container);
+    const LayoutObject* layout_object = container->GetLayoutObject();
+    DCHECK(layout_object) << container;
+    DCHECK(layout_object->IsLayoutBlockFlow()) << container;
+    const NGPhysicalBoxFragment* root_fragment =
+        ToLayoutBlockFlow(layout_object)->CurrentFragment();
+    DCHECK(root_fragment) << container;
+
+    for (const auto& child :
+         NGInlineFragmentTraversal::DescendantsOf(*root_fragment)) {
+      if (child.fragment->IsLineBox())
+        return ToNGPhysicalLineBoxFragment(child.fragment.get());
+    }
+    NOTREACHED();
+    return nullptr;
+  }
+};
+
+#define EXPECT_TEXT_FRAGMENT(text, fragment)                                \
+  {                                                                         \
+    EXPECT_TRUE(fragment);                                                  \
+    EXPECT_TRUE(fragment->IsText());                                        \
+    EXPECT_EQ(text, ToNGPhysicalTextFragment(fragment)->Text().ToString()); \
+  }
+
+#define EXPECT_BOX_FRAGMENT(id, fragment)               \
+  {                                                     \
+    EXPECT_TRUE(fragment);                              \
+    EXPECT_TRUE(fragment->IsBox());                     \
+    EXPECT_TRUE(fragment->GetNode());                   \
+    EXPECT_EQ(GetElementById(id), fragment->GetNode()); \
+  }
+
+TEST_F(NGPhysicalLineBoxFragmentTest, FirstLastLogicalLeafInSimpleText) {
+  SetBodyInnerHTML(
+      "<div id=root>"
+      "<span>foo</span>"
+      "<span>bar</span>"
+      "</div>");
+  EXPECT_TEXT_FRAGMENT("foo", GetLineBox()->FirstLogicalLeaf());
+  EXPECT_TEXT_FRAGMENT("bar", GetLineBox()->LastLogicalLeaf());
+}
+
+TEST_F(NGPhysicalLineBoxFragmentTest, FirstLastLogicalLeafInRtlText) {
+  SetBodyInnerHTML(
+      "<bdo id=root dir=rtl style='display: block'>"
+      "<span>foo</span>"
+      "<span>bar</span>"
+      "</bdo>");
+  EXPECT_TEXT_FRAGMENT("foo", GetLineBox()->FirstLogicalLeaf());
+  EXPECT_TEXT_FRAGMENT("bar", GetLineBox()->LastLogicalLeaf());
+}
+
+TEST_F(NGPhysicalLineBoxFragmentTest,
+       FirstLastLogicalLeafInTextAsDeepDescendants) {
+  SetBodyInnerHTML(
+      "<style>span {border: 1px solid black}</style>"
+      "<div id=root>"
+      "<span><span>f</span>oo</span>"
+      "<span>ba<span>r</span></span>"
+      "</div>");
+  EXPECT_TEXT_FRAGMENT("f", GetLineBox()->FirstLogicalLeaf());
+  EXPECT_TEXT_FRAGMENT("r", GetLineBox()->LastLogicalLeaf());
+}
+
+TEST_F(NGPhysicalLineBoxFragmentTest, FirstLastLogicalLeafWithInlineBlock) {
+  SetBodyInnerHTML(
+      "<div id=root>"
+      "<span id=foo style='display: inline-block'>foo</span>"
+      "bar"
+      "<span id=baz style='display: inline-block'>baz</span>"
+      "</div>");
+  EXPECT_BOX_FRAGMENT("foo", GetLineBox()->FirstLogicalLeaf());
+  EXPECT_BOX_FRAGMENT("baz", GetLineBox()->LastLogicalLeaf());
+}
+
+TEST_F(NGPhysicalLineBoxFragmentTest, FirstLastLogicalLeafWithImages) {
+  SetBodyInnerHTML("<div id=root><img id=img1>foo<img id=img2></div>");
+  EXPECT_BOX_FRAGMENT("img1", GetLineBox()->FirstLogicalLeaf());
+  EXPECT_BOX_FRAGMENT("img2", GetLineBox()->LastLogicalLeaf());
+}
+
+}  // namespace blink