Handle nested position:sticky elements

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

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
index 9fbdbbdc0334a6846b9c92221a2d739b6697cc32..f29810a3c90ae406eb4c6d4ab6d22dd2cbfe4616 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObjectTest.cpp
@@ -249,4 +249,296 @@ TEST_F(LayoutBoxModelObjectTest, StickyPositionAnonymousContainer) {
       IntRect(15, 165, 100, 100),
       enclosingIntRect(getScrollContainerRelativeStickyBoxRect(constraints)));
 }
+
+// Verifies that the sticky constraints are correct when we have a simple case
+// of nested position:sticky.
+TEST_F(LayoutBoxModelObjectTest, StickyPositionNested) {
+  setBodyInnerHTML(
+      "<style>#scroller { height: 100px; width: 100px; overflow-y: auto; }"
+      "#prePadding { height: 50px }"
+      "#stickyParent { position: sticky; top: 0; height: 50px; }"
+      "#stickyChild { position: sticky; top: 0; height: 25px; }"
+      "#postPadding { height: 200px }</style>"
+      "<div id='scroller'><div id='prePadding'></div><div id='stickyParent'>"
+      "<div id='stickyChild'></div></div><div id='postPadding'></div></div>");
+
+  // Make sure that the constraints are cached before scrolling, or they will
+  // simply be calculated post-scroll and thus not require offset correction.
+
+  LayoutBoxModelObject* stickyParent =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyParent"));
+  stickyParent->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyChild =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyChild"));
+  stickyChild->updateStickyPositionConstraints();
+
+  // Scroll the page down.
+  LayoutBoxModelObject* scroller =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("scroller"));
+  PaintLayerScrollableArea* scrollableArea = scroller->getScrollableArea();
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 100));
+  ASSERT_EQ(100.0, scrollableArea->scrollPosition().y());
+
+  // Both the parent and child sticky divs are attempting to place themselves at
+  // the top of the scrollable area. To achieve this the parent must offset on
+  // the y-axis against its starting position. The child is offset relative to
+  // its parent so the child should not move at all.
+
+  EXPECT_EQ(LayoutSize(0, 50), stickyParent->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyChild->stickyPositionOffset());
+}
+
+// Verifies that the sticky constraints are correct when the child has a
+// larger edge constraint value than the parent.
+TEST_F(LayoutBoxModelObjectTest, StickyPositionNestedChildLargerTop) {
+  setBodyInnerHTML(
+      "<style>#scroller { height: 100px; width: 100px; overflow-y: auto; }"
+      "#prePadding { height: 50px }"
+      "#stickyParent { position: sticky; top: 0; height: 50px; }"
+      "#stickyChild { position: sticky; top: 25px; height: 25px; }"
+      "#postPadding { height: 200px }</style>"
+      "<div id='scroller'><div id='prePadding'></div><div id='stickyParent'>"
+      "<div id='stickyChild'></div></div><div id='postPadding'></div></div>");
+
+  // Make sure that the constraints are cached before scrolling, or they will
+  // simply be calculated post-scroll and thus not require offset correction.
+
+  LayoutBoxModelObject* stickyParent =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyParent"));
+  stickyParent->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyChild =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyChild"));
+  stickyChild->updateStickyPositionConstraints();
+
+  // Scroll the page down.
+  LayoutBoxModelObject* scroller =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("scroller"));
+  PaintLayerScrollableArea* scrollableArea = scroller->getScrollableArea();
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 100));
+  ASSERT_EQ(100.0, scrollableArea->scrollPosition().y());
+
+  // The parent is attempting to place itself at the top of the scrollable area,
+  // whilst the child is attempting to be 25 pixels from the top. To achieve
+  // this both must offset on the y-axis against their starting positions, but
+  // note the child is offset relative to the parent.
+  EXPECT_EQ(LayoutSize(0, 50), stickyParent->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 25), stickyChild->stickyPositionOffset());
+}
+
+// Verifies that the sticky constraints are correct when the child has a
+// smaller edge constraint value than the parent.
+TEST_F(LayoutBoxModelObjectTest, StickyPositionNestedParentLargerTop) {
+  setBodyInnerHTML(
+      "<style>#scroller { height: 100px; width: 100px; overflow-y: auto; }"
+      "#prePadding { height: 50px }"
+      "#stickyParent { position: sticky; top: 25px; height: 50px; }"
+      "#stickyChild { position: sticky; top: 0; height: 25px; }"
+      "#postPadding { height: 200px }</style>"
+      "<div id='scroller'><div id='prePadding'></div><div id='stickyParent'>"
+      "<div id='stickyChild'></div></div><div id='postPadding'></div></div>");
+
+  // Make sure that the constraints are cached before scrolling, or they will
+  // simply be calculated post-scroll and thus not require offset correction.
+
+  LayoutBoxModelObject* stickyParent =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyParent"));
+  stickyParent->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyChild =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyChild"));
+  stickyChild->updateStickyPositionConstraints();
+
+  // Scroll the page down.
+  LayoutBoxModelObject* scroller =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("scroller"));
+  PaintLayerScrollableArea* scrollableArea = scroller->getScrollableArea();
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 100));
+  ASSERT_EQ(100.0, scrollableArea->scrollPosition().y());
+
+  // The parent is attempting to place itself 25 pixels from the top of the
+  // scrollable area, whilst the child is attempting to be at the top. However,
+  // the child must stay contained within the parent, so it should be pushed
+  // down to the same height. As always, the child offset is relative.
+  EXPECT_EQ(LayoutSize(0, 75), stickyParent->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyChild->stickyPositionOffset());
+}
+
+// Verifies that the sticky constraints are correct when the child has a large
+// enough edge constraint value to try and push outside of its parent.
+TEST_F(LayoutBoxModelObjectTest,
+       StickyPositionNestedChildPushingOutsideParent) {
+  setBodyInnerHTML(
+      "<style> #scroller { height: 100px; width: 100px; overflow-y: auto; }"
+      "#prePadding { height: 50px; }"
+      "#stickyParent { position: sticky; top: 0; height: 50px; }"
+      "#stickyChild { position: sticky; top: 50px; height: 25px; }"
+      "#postPadding { height: 200px }</style>"
+      "<div id='scroller'><div id='prePadding'></div><div id='stickyParent'>"
+      "<div id='stickyChild'></div></div><div id='postPadding'></div></div>");
+
+  // Make sure that the constraints are cached before scrolling, or they will
+  // simply be calculated post-scroll and thus not require offset correction.
+
+  LayoutBoxModelObject* stickyParent =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyParent"));
+  stickyParent->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyChild =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyChild"));
+  stickyChild->updateStickyPositionConstraints();
+
+  // Scroll the page down.
+  LayoutBoxModelObject* scroller =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("scroller"));
+  PaintLayerScrollableArea* scrollableArea = scroller->getScrollableArea();
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 100));
+  ASSERT_EQ(100.0, scrollableArea->scrollPosition().y());
+
+  // The parent is attempting to place itself at the top of the scrollable area,
+  // whilst the child is attempting to be 50 pixels from the top. However, there
+  // is only 25 pixels of space for the child to move into, so it should be
+  // capped by that offset. As always, the child offset is relative.
+  EXPECT_EQ(LayoutSize(0, 50), stickyParent->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 25), stickyChild->stickyPositionOffset());
+}
+
+// Verifies that the sticky constraints are correct in the case of triple
+// nesting. Triple (or more) nesting must be tested as the grandchild sticky
+// offset must be corrected for both the containing block and the viewport.
+TEST_F(LayoutBoxModelObjectTest, StickyPositionNestedTripleNestedDiv) {
+  setBodyInnerHTML(
+      "<style>#scroller { height: 200px; width: 100px; overflow-y: auto; }"
+      "#prePadding { height: 50px; }"
+      "#sticky1 { position: sticky; top: 0; height: 100px; }"
+      "#sticky2 { position: sticky; top: 0; height: 75px; }"
+      "#sticky3 { position: sticky; top: 25px; height: 25px; }"
+      "#postPadding { height: 400px }</style>"
+      "<div id='scroller'><div id='prePadding'></div><div id='sticky1'>"
+      "<div id='sticky2'><div id='sticky3'></div></div></div>"
+      "<div id='postPadding'></div></div>");
+
+  // Make sure that the constraints are cached before scrolling, or they will
+  // simply be calculated post-scroll and thus not require offset correction.
+
+  LayoutBoxModelObject* stickyOne =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("sticky1"));
+  stickyOne->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyTwo =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("sticky2"));
+  stickyTwo->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyThree =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("sticky3"));
+  stickyThree->updateStickyPositionConstraints();
+
+  // Scroll the page down.
+  LayoutBoxModelObject* scroller =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("scroller"));
+  PaintLayerScrollableArea* scrollableArea = scroller->getScrollableArea();
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 100));
+  ASSERT_EQ(100.0, scrollableArea->scrollPosition().y());
+
+  // The grandparent and parent divs are attempting to place themselves at the
+  // top of the scrollable area. The child div is attempting to place itself at
+  // an offset of 25 pixels to the top of the scrollable area. The result of
+  // this sticky offset calculation is quite simple, but internally the child
+  // offset has to offset both against its containing block and against its
+  // viewport ancestor (the grandparent).
+  EXPECT_EQ(LayoutSize(0, 50), stickyOne->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyTwo->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 25), stickyThree->stickyPositionOffset());
+}
+
+// Verifies that the sticky constraints are correct in the case of tables.
+// Tables are special as the containing block for all child elements is always
+// the root level <table>.
+TEST_F(LayoutBoxModelObjectTest, StickyPositionNestedTableExample) {
+  setBodyInnerHTML(
+      "<style>#scroller { height: 100px; width: 100px; overflow-y: auto; }"
+      "#prePadding { height: 50px; }"
+      "#stickyDiv { position: sticky; top: 0; height: 200px; }"
+      "#table { border-collapse: collapse; }"
+      "#stickyThead { position: sticky; top: 0px; }"
+      "#stickyTr { position: sticky; top: 0px; }"
+      "#stickyTh { position: sticky; top: 0px; }"
+      "#postPadding { height: 200px; }</style>"
+      "<div id='scroller'><div id='prePadding'></div><div id='stickyDiv'>"
+      "<table id='table'><thead id='stickyThead'><tr id='stickyTr'>"
+      "<th id='stickyTh'>Header</th></tr></thread><tbody><tr><td>0</td></tr>"
+      "<tr><td>1</td></tr><tr><td>2</td></tr><tr><td>3</td></tr></tbody>"
+      "</table></div><div id='postPadding'></div></div>");
+
+  LOG(INFO) << document().body()->innerHTML();
+
+  // Make sure that the constraints are cached before scrolling, or they will
+  // simply be calculated post-scroll and thus not require offset correction.
+
+  LayoutBoxModelObject* stickyDiv =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyDiv"));
+  stickyDiv->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyThead =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyThead"));
+  stickyThead->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyTr =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyTr"));
+  stickyTr->updateStickyPositionConstraints();
+
+  LayoutBoxModelObject* stickyTh =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("stickyTh"));
+  stickyTh->updateStickyPositionConstraints();
+
+  // Scroll the page down.
+  LayoutBoxModelObject* scroller =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("scroller"));
+  PaintLayerScrollableArea* scrollableArea = scroller->getScrollableArea();
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 150));
+  ASSERT_EQ(150.0, scrollableArea->scrollPosition().y());
+
+  // All sticky elements are attempting to stick to the top of the scrollable
+  // area. For the root sticky div, this requires an offset. All the other
+  // descendant sticky elements are positioned relatively so don't need offset.
+  EXPECT_EQ(LayoutSize(0, 100), stickyDiv->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyThead->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyTr->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyTh->stickyPositionOffset());
+
+  // If we now scroll to the point where the overall sticky div starts to move,
+  // the table headers should continue to stick to the top of the scrollable
+  // area until they run out of <table> space to move in.
+
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 275));
+  ASSERT_EQ(275.0, scrollableArea->scrollPosition().y());
+
+  // NOTE(smcgruer): Currently fails - the <th> also moves 12
+  // NOTE(smcgruer): I'm not sure that 12 is correct. My hankerchief math gets
+  // me something like (275 - 50 - 200) = 25? But it renders correct aisde from
+  // the <th>...
+  EXPECT_EQ(LayoutSize(0, 200), stickyDiv->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 12), stickyThead->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyTr->stickyPositionOffset());
+  EXPECT_EQ(LayoutSize(0, 0), stickyTh->stickyPositionOffset());
+
+  // Finally, if we scroll so that the table is off the top of the page, the
+  // sticky header should go off the top with it.
+
+  scrollableArea->scrollToAbsolutePosition(
+      FloatPoint(scrollableArea->scrollPosition().x(), 350));
+  ASSERT_EQ(350.0, scrollableArea->scrollPosition().y());
+
+  // TODO(smcgruer): Do EXPECT_EQ for this scenario. It's currently broken
+  // anyway.
+}
+
 }  // namespace blink