Exclude position:absolute elements when picking an anchor for ScrollAnchoring

third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp

 // Copyright 2015 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/ScrollAnchor.h"
 
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "platform/testing/HistogramTester.h"
@@ skipping 207 matching lines @@
         "<div id=f>fixed</div>"
         "<div id=c>content</div>");
 
     scrollLayoutViewport(DoubleSize(0, 50));
 
     setHeight(document().body(), 1100);
     EXPECT_EQ(document().getElementById("c")->layoutObject(),
         scrollAnchor(layoutViewport()).anchorObject());
 }
 
-TEST_F(ScrollAnchorTest, ExcludeAbsolutePosition)
+// This test verifies that position:absolute elements that stick to the viewport
+// are not selected as anchors.
+TEST_F(ScrollAnchorTest, ExcludeAbsolutePositionThatSticksToViewport)
 {
     setBodyInnerHTML(
         "<style>"
         "    body { margin: 0; }"
         "    #scroller { overflow: scroll; width: 500px; height: 400px; }"
         "    #space { height: 1000px; }"
         "    #abs {"
         "        position: absolute; background-color: red;"
-        "        left: 200px; top: 100px; width: 100px; height: 100px;"
+        "        width: 100px; height: 100px;"
         "    }"
         "    #rel {"
         "        position: relative; background-color: green;"
         "        left: 50px; top: 100px; width: 100px; height: 75px;"
         "    }"
         "</style>"
         "<div id='scroller'><div id='space'>"
         "    <div id='abs'></div>"
         "    <div id='rel'></div>"
         "</div></div>");
@@ skipping 10 matching lines @@
     EXPECT_EQ(relPos->layoutObject(), scrollAnchor(scroller).anchorObject());
 
     scrollerElement->setAttribute(HTMLNames::styleAttr, "position: relative");
     scroller->scrollBy(DoubleSize(0, 25), UserScroll);
     setHeight(relPos, 125);
 
     // When the scroller is position:relative, the anchor may be position:absolute.
     EXPECT_EQ(absPos->layoutObject(), scrollAnchor(scroller).anchorObject());
 }
 
+// This test verifies that position:absolute elements with top/right/bottom/left
+// set are not selected as anchors.
+TEST_F(ScrollAnchorTest, ExcludeOffsettedAbsolutePosition)
+{
+    setBodyInnerHTML(
+        "<style>"
+        "    body { margin: 0; }"
+        "    #scroller { overflow: scroll; width: 500px; height: 400px; position:relative; }"
+        "    #space { height: 1000px; }"
+        "    #abs {"
+        "        position: absolute; background-color: red;"
+        "        width: 100px; height: 100px;"
+        "    }"
+        "    #rel {"
+        "        position: relative; background-color: green;"
+        "        left: 50px; top: 100px; width: 100px; height: 75px;"
+        "    }"
+        "    .top { top: 10px }"
+        "    .left { left: 10px }"
+        "    .right { right: 10px }"
+        "    .bottom { bottom: 10px }"
+        "</style>"
+        "<div id='scroller'><div id='space'>"
+        "    <div id='abs'></div>"
+        "    <div id='rel'></div>"
+        "</div></div>");
+
+    Element* scrollerElement = document().getElementById("scroller");
+    ScrollableArea* scroller = scrollerForElement(scrollerElement);
+    Element* relPos = document().getElementById("rel");
+    Element* absPos = document().getElementById("abs");
+
+    scroller->scrollBy(DoubleSize(0, 25), UserScroll);
+    setHeight(relPos, 100);
+    // Pick absolute anchor.
+    EXPECT_EQ(absPos->layoutObject(), scrollAnchor(scroller).anchorObject());
+
+    absPos->setAttribute(HTMLNames::classAttr, "top");
+    scroller->scrollBy(DoubleSize(0, 25), UserScroll);
+    setHeight(relPos, 125);
+    // Don't pick absolute anchor since top is set.
+    EXPECT_EQ(relPos->layoutObject(), scrollAnchor(scroller).anchorObject());
+
+    absPos->removeAttribute(HTMLNames::classAttr);
+    absPos->setAttribute(HTMLNames::classAttr, "right");
+    scroller->scrollBy(DoubleSize(0, 25), UserScroll);
+    setHeight(relPos, 150);
+    // Don't pick absolute anchor since right is set.
+    EXPECT_EQ(relPos->layoutObject(), scrollAnchor(scroller).anchorObject());
+
+    absPos->removeAttribute(HTMLNames::classAttr);
+    absPos->setAttribute(HTMLNames::classAttr, "bottom");
+    scroller->scrollBy(DoubleSize(0, 25), UserScroll);
+    setHeight(relPos, 175);
+    // Don't pick absolute anchor since bottom is set.
+    EXPECT_EQ(relPos->layoutObject(), scrollAnchor(scroller).anchorObject());
+
+    absPos->removeAttribute(HTMLNames::classAttr);
+    absPos->setAttribute(HTMLNames::classAttr, "left");
+    scroller->scrollBy(DoubleSize(0, 25), UserScroll);
+    setHeight(relPos, 200);
+    // Don't pick absolute anchor since left is set.
+    EXPECT_EQ(relPos->layoutObject(), scrollAnchor(scroller).anchorObject());
+}
+
 // Test that we descend into zero-height containers that have overflowing content.
 TEST_F(ScrollAnchorTest, DescendsIntoContainerWithOverflow)
 {
     setBodyInnerHTML(
         "<style>"
         "    body { height: 1000; }"
         "    #outer { width: 300px; }"
         "    #zeroheight { height: 0px; }"
         "    #changer { height: 100px; background-color: red; }"
         "    #bottom { margin-top: 600px; }"
@@ skipping 191 matching lines @@
         "<div id=c></div>"
         "<div id=d></div>");
 
     checkCorner("b", Corner::TopRight, DoublePoint(-20,  20),  DoubleSize(0, 0));
     checkCorner("a", Corner::TopRight, DoublePoint(-420, 20),  DoubleSize(400, 0));
     checkCorner("d", Corner::TopRight, DoublePoint(-20,  320), DoubleSize(0, -300));
     checkCorner("c", Corner::TopRight, DoublePoint(-420, 320), DoubleSize(400, -300));
 }
 
 }