AXSelection: Ensure that line break elements are not treated as text objects

Line break elements are not defined as text nodes in Blink.
However, traditionally we have been able to set a selection before or after a line break and
our accessibility code on the browser side treats objects with the line break role as text objects.
These tests ensure that line break elements are not treated as text objects for selection purposes.
Also, adds more selection tests for text fields.
R=dmazzoni@chromium.org, dtseng@chromium.org, aleventhal@chromium.org

Change-Id: I4cf968225322a9bbc4eb2ace4b80c07dffc5a801
Bug: 639340
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1498611Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637574}

third_party/blink/renderer/modules/accessibility/ax_selection_test.cc

@@ -17,7 +17,9 @@
 #include "third_party/blink/renderer/core/editing/selection_template.h"
 #include "third_party/blink/renderer/core/frame/settings.h"
 #include "third_party/blink/renderer/core/html/forms/text_control_element.h"
+#include "third_party/blink/renderer/core/html/html_br_element.h"
 #include "third_party/blink/renderer/core/html/html_div_element.h"
+#include "third_party/blink/renderer/core/html/html_paragraph_element.h"
 #include "third_party/blink/renderer/core/page/page.h"
 #include "third_party/blink/renderer/modules/accessibility/ax_object.h"
 #include "third_party/blink/renderer/modules/accessibility/ax_position.h"
@@ -254,6 +256,96 @@ TEST_F(AccessibilitySelectionTest, SetSelectionInTextWithWhiteSpace) {
       GetSelectionText(ax_selection));
 }
 
+TEST_F(AccessibilitySelectionTest, SetSelectionAcrossLineBreak) {
+  SetBodyInnerHTML(R"HTML(
+      <p id="paragraph">Hello<br id="br">How are you.</p>
+      )HTML");
+
+  const Node* paragraph = GetDocument().QuerySelector("p");
+  ASSERT_NE(nullptr, paragraph);
+  ASSERT_TRUE(IsHTMLParagraphElement(paragraph));
+  const Node* br = GetDocument().QuerySelector("br");
+  ASSERT_NE(nullptr, br);
+  ASSERT_TRUE(IsHTMLBRElement(br));
+  const Node* line2 = GetDocument().QuerySelector("p")->lastChild();
+  ASSERT_NE(nullptr, line2);
+  ASSERT_TRUE(line2->IsTextNode());
+
+  const AXObject* ax_br = GetAXObjectByElementId("br");
+  ASSERT_NE(nullptr, ax_br);
+  ASSERT_EQ(ax::mojom::Role::kLineBreak, ax_br->RoleValue());
+  const AXObject* ax_line2 = GetAXObjectByElementId("paragraph")->LastChild();
+  ASSERT_NE(nullptr, ax_line2);
+  ASSERT_EQ(ax::mojom::Role::kStaticText, ax_line2->RoleValue());
+
+  const auto ax_base = AXPosition::CreatePositionBeforeObject(*ax_br);
+  const auto ax_extent = AXPosition::CreatePositionInTextObject(*ax_line2, 0);
+
+  AXSelection::Builder builder;
+  const AXSelection ax_selection =
+      builder.SetBase(ax_base).SetExtent(ax_extent).Build();
+  const SelectionInDOMTree dom_selection = ax_selection.AsSelection();
+  EXPECT_EQ(paragraph, dom_selection.Base().AnchorNode());
+  EXPECT_EQ(1, dom_selection.Base().OffsetInContainerNode());
+  EXPECT_EQ(line2, dom_selection.Extent().AnchorNode());
+  EXPECT_EQ(0, dom_selection.Extent().OffsetInContainerNode());
+
+  // The selection anchor marker '^' should be before the line break and the
+  // selection focus marker '|' should be after it.
+  EXPECT_EQ(
+      "++<Paragraph>\n"
+      "++++<StaticText: Hello>\n"
+      "^++++<LineBreak: \n>\n"
+      "|++++<StaticText: |How are you.>\n",
+      GetSelectionText(ax_selection));
+}
+
+TEST_F(AccessibilitySelectionTest, SetSelectionAcrossLineBreakInEditableText) {
+  SetBodyInnerHTML(R"HTML(
+      <p contenteditable id="paragraph">Hello<br id="br">How are you.</p>
+      )HTML");
+
+  const Node* paragraph = GetDocument().QuerySelector("p");
+  ASSERT_NE(nullptr, paragraph);
+  ASSERT_TRUE(IsHTMLParagraphElement(paragraph));
+  const Node* br = GetDocument().QuerySelector("br");
+  ASSERT_NE(nullptr, br);
+  ASSERT_TRUE(IsHTMLBRElement(br));
+  const Node* line2 = GetDocument().QuerySelector("p")->lastChild();
+  ASSERT_NE(nullptr, line2);
+  ASSERT_TRUE(line2->IsTextNode());
+
+  const AXObject* ax_br = GetAXObjectByElementId("br");
+  ASSERT_NE(nullptr, ax_br);
+  ASSERT_EQ(ax::mojom::Role::kLineBreak, ax_br->RoleValue());
+  const AXObject* ax_line2 = GetAXObjectByElementId("paragraph")->LastChild();
+  ASSERT_NE(nullptr, ax_line2);
+  ASSERT_EQ(ax::mojom::Role::kStaticText, ax_line2->RoleValue());
+
+  const auto ax_base = AXPosition::CreatePositionBeforeObject(*ax_br);
+  // In the case of text objects, CreateFirstPositionInObject(*...) should
+  // behave identically to CreatePositionInTextObject(*..., 0).
+  const auto ax_extent = AXPosition::CreateFirstPositionInObject(*ax_line2);
+
+  AXSelection::Builder builder;
+  const AXSelection ax_selection =
+      builder.SetBase(ax_base).SetExtent(ax_extent).Build();
+  const SelectionInDOMTree dom_selection = ax_selection.AsSelection();
+  EXPECT_EQ(paragraph, dom_selection.Base().AnchorNode());
+  EXPECT_EQ(1, dom_selection.Base().OffsetInContainerNode());
+  EXPECT_EQ(line2, dom_selection.Extent().AnchorNode());
+  EXPECT_EQ(0, dom_selection.Extent().OffsetInContainerNode());
+
+  // The selection anchor marker '^' should be before the line break and the
+  // selection focus marker '|' should be after it.
+  EXPECT_EQ(
+      "++<Paragraph>\n"
+      "++++<StaticText: Hello>\n"
+      "^++++<LineBreak: \n>\n"
+      "|++++<StaticText: |How are you.>\n",
+      GetSelectionText(ax_selection));
+}
+
 //
 // Get selection tests.
 // Retrieving a selection with endpoints which have no corresponding objects in
@@ -427,7 +519,7 @@ TEST_F(AccessibilitySelectionTest, SetSelectionAroundListBullet) {
       "++++<List>\n"
       "++++++<ListItem>\n"
       "++++++++<ListMarker: \xE2\x80\xA2 >\n"
-      "++++++++<StaticText: Item 1.>\n"
+      "^++++++++<StaticText: Item 1.>\n"
       "++++++<ListItem>\n"
       "++++++++<ListMarker: \xE2\x80\xA2 >\n"
       "++++++++<StaticText: Item 2.|>\n",
@@ -694,6 +786,60 @@ TEST_F(AccessibilitySelectionTest, SelectingTheWholeOfTheTextField) {
   EXPECT_EQ("backward", ToTextControl(*input).selectionDirection());
 }
 
+TEST_F(AccessibilitySelectionTest, SelectEachConsecutiveCharacterInTextField) {
+  SetBodyInnerHTML(R"HTML(
+      <input id="input" value="Inside text field.">
+      )HTML");
+
+  Element* const input = GetDocument().QuerySelector("input");
+  ASSERT_NE(nullptr, input);
+  ASSERT_TRUE(IsTextControl(input));
+  TextControlElement& text_control = ToTextControl(*input);
+  ASSERT_LE(1u, text_control.value().length());
+
+  const AXObject* ax_input = GetAXObjectByElementId("input");
+  ASSERT_NE(nullptr, ax_input);
+  ASSERT_EQ(ax::mojom::Role::kTextField, ax_input->RoleValue());
+
+  for (unsigned int i = 0; i < text_control.value().length() - 1; ++i) {
+    AXSelection::Builder builder;
+    AXSelection ax_selection =
+        builder.SetBase(AXPosition::CreatePositionInTextObject(*ax_input, i))
+            .SetExtent(AXPosition::CreatePositionInTextObject(*ax_input, i + 1))
+            .Build();
+
+    testing::Message message;
+    message << "While selecting forward character "
+            << char{text_control.value()[i]} << " at position " << i
+            << " in text field.";
+    SCOPED_TRACE(message);
+    EXPECT_TRUE(ax_selection.Select());
+
+    EXPECT_EQ(i, text_control.selectionStart());
+    EXPECT_EQ(i + 1, text_control.selectionEnd());
+    EXPECT_EQ("forward", text_control.selectionDirection());
+  }
+
+  for (unsigned int i = text_control.value().length(); i > 0; --i) {
+    AXSelection::Builder builder;
+    AXSelection ax_selection =
+        builder.SetBase(AXPosition::CreatePositionInTextObject(*ax_input, i))
+            .SetExtent(AXPosition::CreatePositionInTextObject(*ax_input, i - 1))
+            .Build();
+
+    testing::Message message;
+    message << "While selecting backward character "
+            << char{text_control.value()[i]} << " at position " << i
+            << " in text field.";
+    SCOPED_TRACE(message);
+    EXPECT_TRUE(ax_selection.Select());
+
+    EXPECT_EQ(i - 1, text_control.selectionStart());
+    EXPECT_EQ(i, text_control.selectionEnd());
+    EXPECT_EQ("backward", text_control.selectionDirection());
+  }
+}
+
 TEST_F(AccessibilitySelectionTest, InvalidSelectionInTextField) {
   SetBodyInnerHTML(R"HTML(
       <p id="before">Before text field.</p>
@@ -870,6 +1016,66 @@ TEST_F(AccessibilitySelectionTest, SelectTheWholeOfTheTextarea) {
   EXPECT_EQ("backward", ToTextControl(*textarea).selectionDirection());
 }
 
+TEST_F(AccessibilitySelectionTest, SelectEachConsecutiveCharacterInTextarea) {
+  SetBodyInnerHTML(R"HTML(
+      <textarea id="textarea">
+        Inside
+        textarea
+        field.
+      </textarea>
+      )HTML");
+
+  Element* const textarea = GetDocument().QuerySelector("textarea");
+  ASSERT_NE(nullptr, textarea);
+  ASSERT_TRUE(IsTextControl(textarea));
+  TextControlElement& text_control = ToTextControl(*textarea);
+  ASSERT_LE(1u, text_control.value().length());
+
+  const AXObject* ax_textarea = GetAXObjectByElementId("textarea");
+  ASSERT_NE(nullptr, ax_textarea);
+  ASSERT_EQ(ax::mojom::Role::kTextField, ax_textarea->RoleValue());
+
+  for (unsigned int i = 0; i < text_control.value().length() - 1; ++i) {
+    AXSelection::Builder builder;
+    AXSelection ax_selection =
+        builder.SetBase(AXPosition::CreatePositionInTextObject(*ax_textarea, i))
+            .SetExtent(
+                AXPosition::CreatePositionInTextObject(*ax_textarea, i + 1))
+            .Build();
+
+    testing::Message message;
+    message << "While selecting forward character "
+            << char{text_control.value()[i]} << " at position " << i
+            << " in textarea.";
+    SCOPED_TRACE(message);
+    EXPECT_TRUE(ax_selection.Select());
+
+    EXPECT_EQ(i, text_control.selectionStart());
+    EXPECT_EQ(i + 1, text_control.selectionEnd());
+    EXPECT_EQ("forward", text_control.selectionDirection());
+  }
+
+  for (unsigned int i = text_control.value().length(); i > 0; --i) {
+    AXSelection::Builder builder;
+    AXSelection ax_selection =
+        builder.SetBase(AXPosition::CreatePositionInTextObject(*ax_textarea, i))
+            .SetExtent(
+                AXPosition::CreatePositionInTextObject(*ax_textarea, i - 1))
+            .Build();
+
+    testing::Message message;
+    message << "While selecting backward character "
+            << char{text_control.value()[i]} << " at position " << i
+            << " in textarea.";
+    SCOPED_TRACE(message);
+    EXPECT_TRUE(ax_selection.Select());
+
+    EXPECT_EQ(i - 1, text_control.selectionStart());
+    EXPECT_EQ(i, text_control.selectionEnd());
+    EXPECT_EQ("backward", text_control.selectionDirection());
+  }
+}
+
 TEST_F(AccessibilitySelectionTest, InvalidSelectionInTextarea) {
   SetBodyInnerHTML(R"HTML(
       <p id="before">Before textarea field.</p>

third_party/blink/renderer/modules/accessibility/testing/accessibility_selection_test.cc

@@ -149,8 +149,15 @@ class AXSelectionSerializer final {
   }
 
   void SerializeSubtree(const AXObject& subtree) {
-    if (subtree.ChildCount() == 0)
+    if (subtree.ChildCount() == 0) {
+      // Though they are in this particular case both equivalent to an "after
+      // object" position, "Before children" and "after children" positions are
+      // still valid within empty subtrees.
+      const auto position = AXPosition::CreateFirstPositionInObject(subtree);
+      HandleSelection(position);
       return;
+    }
+
     for (const AXObject* child : subtree.Children()) {
       DCHECK(child);
       const auto position = AXPosition::CreatePositionBeforeObject(*child);
@@ -165,6 +172,8 @@ class AXSelectionSerializer final {
       }
       --tree_level_;
     }
+
+    // Handle any "after children" positions.
     HandleSelection(AXPosition::CreateLastPositionInObject(subtree));
   }