Update Link to underline on hover

For accessibility, color should not be the only indicator of a link.
Thus, indicate the existence of a link by underlining it on hover.

Bug: 1060186
Change-Id: If8a994fa1226e1e30f6238719a6d8f94f25ffbd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441938Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Livvie Lin <livvielin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813336}

ui/views/controls/link.cc

@@ -71,6 +71,14 @@ bool Link::GetCanProcessEventsWithinSubtree() const {
   return View::GetCanProcessEventsWithinSubtree();
 }
 
+void Link::OnMouseEntered(const ui::MouseEvent& event) {
+  RecalculateFont();
+}
+
+void Link::OnMouseExited(const ui::MouseEvent& event) {
+  RecalculateFont();
+}
+
 bool Link::OnMousePressed(const ui::MouseEvent& event) {
   if (!GetEnabled() ||
       (!event.IsLeftMouseButton() && !event.IsMiddleMouseButton()))
@@ -198,9 +206,10 @@ void Link::OnClick(const ui::Event& event) {
 
 void Link::RecalculateFont() {
   const int style = font_list().GetFontStyle();
-  const int intended_style = ((GetEnabled() && HasFocus()) || force_underline_)
-                                 ? (style | gfx::Font::UNDERLINE)
-                                 : (style & ~gfx::Font::UNDERLINE);
+  const int intended_style =
+      ((GetEnabled() && (HasFocus() || IsMouseHovered())) || force_underline_)
+          ? (style | gfx::Font::UNDERLINE)
+          : (style & ~gfx::Font::UNDERLINE);
 
   if (style != intended_style)
     Label::SetFontList(font_list().DeriveWithStyle(intended_style));

ui/views/controls/link.h

@@ -60,6 +60,8 @@ class VIEWS_EXPORT Link : public Label {
   // Label:
   gfx::NativeCursor GetCursor(const ui::MouseEvent& event) override;
   bool GetCanProcessEventsWithinSubtree() const override;
+  void OnMouseEntered(const ui::MouseEvent& event) override;
+  void OnMouseExited(const ui::MouseEvent& event) override;
   bool OnMousePressed(const ui::MouseEvent& event) override;
   bool OnMouseDragged(const ui::MouseEvent& event) override;
   void OnMouseReleased(const ui::MouseEvent& event) override;

ui/views/controls/link_unittest.cc

@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/strings/utf_string_conversions.h"
+#include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/events/base_event_utils.h"
@@ -31,16 +32,29 @@ class LinkTest : public test::BaseControlTestWidget {
   LinkTest& operator=(const LinkTest&) = delete;
   ~LinkTest() override = default;
 
+  void SetUp() override {
+    test::BaseControlTestWidget::SetUp();
+
+    event_generator_ = std::make_unique<ui::test::EventGenerator>(
+        GetContext(), widget()->GetNativeWindow());
+    event_generator_->set_assume_window_at_origin(false);
+  }
+
  protected:
   void CreateWidgetContent(View* container) override {
+    // Create a widget containing a link which does not take the full size.
     link_ = container->AddChildView(
         std::make_unique<Link>(base::ASCIIToUTF16("TestLink")));
+    link_->SetBoundsRect(
+        gfx::ScaleToEnclosedRect(container->GetLocalBounds(), 0.5f));
   }
 
   Link* link() { return link_; }
+  ui::test::EventGenerator* event_generator() { return event_generator_.get(); }
 
  public:
   Link* link_ = nullptr;
+  std::unique_ptr<ui::test::EventGenerator> event_generator_;
 };
 
 }  // namespace
@@ -75,4 +89,30 @@ TEST_F(LinkTest, TestLinkTap) {
   EXPECT_TRUE(link_clicked);
 }
 
+// This test doesn't work on Mac due to crbug.com/1071633.
+#if !defined(OS_MAC)
+// Tests that hovering and unhovering a link adds and removes an underline.
+TEST_F(LinkTest, TestUnderlineOnHover) {
+  // A non-hovered link should not be underlined.
+  const gfx::Rect link_bounds = link()->GetBoundsInScreen();
+  const gfx::Point off_link = link_bounds.bottom_right() + gfx::Vector2d(1, 1);
+  event_generator()->MoveMouseTo(off_link);
+  EXPECT_FALSE(link()->IsMouseHovered());
+  const auto link_underlined = [link = link()]() {
+    return !!(link->font_list().GetFontStyle() & gfx::Font::UNDERLINE);
+  };
+  EXPECT_FALSE(link_underlined());
+
+  // Hovering the link should underline it.
+  event_generator()->MoveMouseTo(link_bounds.CenterPoint());
+  EXPECT_TRUE(link()->IsMouseHovered());
+  EXPECT_TRUE(link_underlined());
+
+  // Un-hovering the link should remove the underline again.
+  event_generator()->MoveMouseTo(off_link);
+  EXPECT_FALSE(link()->IsMouseHovered());
+  EXPECT_FALSE(link_underlined());
+}
+#endif  // !defined(OS_MAC)
+
 }  // namespace views