Bug 1889503 - Implement new document.caretPositionFromPoint Shadow DO…

…M behavior r=webidl,smaug,emilio

Spec - https://drafts.csswg.org/cssom-view/Overview#dom-document-caretpositionfrompoint
Spec PR - w3c/csswg-drafts#10200
TAG Review - w3ctag/design-reviews#949

Differential Revision: https://phabricator.services.mozilla.com/D215184

dom/base/Document.cpp

@@ -13881,8 +13881,9 @@ already_AddRefed<TouchList> Document::CreateTouchList(
   return retval.forget();
 }
 
+// https://drafts.csswg.org/cssom-view/Overview#dom-document-caretpositionfrompoint
 already_AddRefed<nsDOMCaretPosition> Document::CaretPositionFromPoint(
-    float aX, float aY) {
+    float aX, float aY, const CaretPositionFromPointOptions& aOptions) {
   using FrameForPointOption = nsLayoutUtils::FrameForPointOption;
 
   nscoord x = nsPresContext::CSSPixelsToAppUnits(aX);
@@ -13922,34 +13923,59 @@ already_AddRefed<nsDOMCaretPosition> Document::CaretPositionFromPoint(
   nsIFrame::ContentOffsets offsets =
       ptFrame->GetContentOffsetsFromPoint(adjustedPoint);
 
-  nsCOMPtr<nsIContent> node = offsets.content;
+  nsCOMPtr<nsINode> node = offsets.content;
   uint32_t offset = offsets.offset;
-  nsCOMPtr<nsIContent> anonNode = node;
+  nsCOMPtr<nsINode> anonNode = node;
   bool nodeIsAnonymous = node && node->IsInNativeAnonymousSubtree();
   if (nodeIsAnonymous) {
     node = ptFrame->GetContent();
-    nsIContent* nonanon = node->FindFirstNonChromeOnlyAccessContent();
-    HTMLTextAreaElement* textArea = HTMLTextAreaElement::FromNode(nonanon);
-    nsITextControlFrame* textFrame = do_QueryFrame(nonanon->GetPrimaryFrame());
-    if (textFrame) {
-      // If the anonymous content node has a child, then we need to make sure
-      // that we get the appropriate child, as otherwise the offset may not be
-      // correct when we construct a range for it.
-      nsCOMPtr<nsIContent> firstChild = anonNode->GetFirstChild();
-      if (firstChild) {
-        anonNode = firstChild;
-      }
+    nsINode* nonChrome =
+        node->AsContent()->FindFirstNonChromeOnlyAccessContent();
+    HTMLTextAreaElement* textArea = HTMLTextAreaElement::FromNode(nonChrome);
+    nsITextControlFrame* textFrame =
+        do_QueryFrame(nonChrome->AsContent()->GetPrimaryFrame());
 
-      if (textArea) {
-        offset =
-            nsContentUtils::GetAdjustedOffsetInTextControl(ptFrame, offset);
-      }
+    if (!textFrame) {
+      return nullptr;
+    }
 
-      node = nonanon;
-    } else {
-      node = nullptr;
-      offset = 0;
+    // If the anonymous content node has a child, then we need to make sure
+    // that we get the appropriate child, as otherwise the offset may not be
+    // correct when we construct a range for it.
+    nsCOMPtr<nsINode> firstChild = anonNode->GetFirstChild();
+    if (firstChild) {
+      anonNode = firstChild;
+    }
+
+    if (textArea) {
+      offset = nsContentUtils::GetAdjustedOffsetInTextControl(ptFrame, offset);
+    }
+
+    node = nonChrome;
+  }
+
+  bool offsetAndNodeNeedsAdjustment = false;
+
+  if (StaticPrefs::
+          dom_shadowdom_new_caretPositionFromPoint_behavior_enabled()) {
+    while (node->IsInShadowTree() &&
+           !aOptions.mShadowRoots.Contains(node->GetContainingShadow())) {
+      node = node->GetContainingShadowHost();
+      offsetAndNodeNeedsAdjustment = true;
+    }
+  }
+
+  if (offsetAndNodeNeedsAdjustment) {
+    const Maybe<uint32_t> maybeIndex = node->ComputeIndexInParentContent();
+    if (MOZ_UNLIKELY(maybeIndex.isNothing())) {
+      // Unlikely to happen, but still return nullptr to avoid leaking
+      // information about the shadow tree.
+      return nullptr;
     }
+    // 5.3.1: Set startOffset to index of startNode’s root's host.
+    offset = maybeIndex.value();
+    // 5.3.2: Set startNode to startNode’s root's host's parent.
+    node = node->GetParentNode();
   }
 
   RefPtr<nsDOMCaretPosition> aCaretPos = new nsDOMCaretPosition(node, offset);

dom/base/Document.h

@@ -3451,8 +3451,8 @@ class Document : public nsINode,
    * @param aY Vertical point at which to determine the caret position, in
    *           page coordinates.
    */
-  already_AddRefed<nsDOMCaretPosition> CaretPositionFromPoint(float aX,
-                                                              float aY);
+  already_AddRefed<nsDOMCaretPosition> CaretPositionFromPoint(
+      float aX, float aY, const CaretPositionFromPointOptions& aOptions);
 
   Element* GetScrollingElement();
   // A way to check whether a given element is what would get returned from

dom/webidl/Document.webidl

@@ -379,9 +379,14 @@ partial interface Document {
     undefined enableStyleSheetsForSet (DOMString? name);
 };
 
+dictionary CaretPositionFromPointOptions {
+  [Pref="dom.shadowdom.new_caretPositionFromPoint_behavior.enabled"]
+  sequence<ShadowRoot> shadowRoots = [];
+};
+
 // https://drafts.csswg.org/cssom-view/#extensions-to-the-document-interface
 partial interface Document {
-    CaretPosition? caretPositionFromPoint (float x, float y);
+    CaretPosition? caretPositionFromPoint(float x, float y, optional CaretPositionFromPointOptions options = {});
 
     readonly attribute Element? scrollingElement;
 };

layout/base/tests/mochitest.toml

@@ -237,6 +237,8 @@ support-files = ["bug1448730.html"]
 ["test_caret_browsing_around_form_controls.html"]
 skip-if = ["os == 'android'"]
 
+["test_caretPositionFromPoint_insertAnonymousContent.html"]
+
 ["test_dynamic_toolbar_max_height.html"]
 support-files = ["file_dynamic_toolbar_max_height.html"]
 

layout/base/tests/test_caretPositionFromPoint_insertAnonymousContent.html

@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8" />
+    <title>Test for caretPositionFromPoint with anonymous content</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <script src="/tests/SimpleTest/EventUtils.js"></script>
+    <link rel="stylesheet" href="/tests/SimpleTest/test.css" />
+  </head>
+  <body>
+    <script>
+      info("Inserting anonymous content into the document frame");
+      let chromeDoc = SpecialPowers.wrap(document);
+      let anonymousContent = chromeDoc.insertAnonymousContent();
+      let div = document.createElement("div");
+      div.style.position = "fixed";
+      div.style.top = "0";
+      div.style.left = "0";
+      div.style.width = "100%";
+      div.style.height = "100%";
+      div.style.pointerEvents = "auto";
+      div.style.backgroundColor = "red";
+      anonymousContent.root.appendChild(div);
+      let caretPos = document.caretPositionFromPoint(
+        innerWidth / 2,
+        innerHeight / 2
+      );
+      is(caretPos, null, "caretPos should be null");
+      info("Removing the anonymous content");
+      chromeDoc.removeAnonymousContent(anonymousContent);
+    </script>
+  </body>
+</html>

modules/libpref/init/StaticPrefList.yaml

@@ -4657,6 +4657,17 @@
   value: @IS_NIGHTLY_BUILD@
   mirror: always
 
+# When this pref is enabled:
+#  - Shadow DOM is not pierced by default anymore
+#  - The method accepts optional CaretPositionFromPointOptions to allow piercing
+#    certain ShadowRoots
+#
+# https://drafts.csswg.org/cssom-view/#dom-document-caretpositionfrompoint
+- name: dom.shadowdom.new_caretPositionFromPoint_behavior.enabled
+  type: bool
+  value: @IS_NIGHTLY_BUILD@
+  mirror: always
+
 # NOTE: This preference is used in unit tests. If it is removed or its default
 # value changes, please update test_sharedMap_static_prefs.js accordingly.
 - name: dom.webcomponents.shadowdom.report_usage

testing/web-platform/meta/shadow-dom/Document-caretPositionFromPoint.tentative.html.ini

@@ -1,18 +1,4 @@
+prefs: [dom.shadowdom.new_caretPositionFromPoint_behavior.enabled:true]
 [Document-caretPositionFromPoint.tentative.html]
-  [document.caretPositionFromPoint() throws when called without the correct parameters]
-    expected: FAIL
-
   [document.caretPositionFromPoint() should return a CaretPosition at the specified location pointing to a textarea element which is the offsetNode.]
     expected: FAIL
-
-  [document.caretPositionFromPoint() should return a CaretPosition at the specified location pointing to the input element's shadow host's parent when the shadow tree is not specified as an argument.]
-    expected: FAIL
-
-  [document.caretPositionFromPoint() should return a CaretPosition at the specified location pointing to the shadow host's parent when the shadow tree is not specified as an argument]
-    expected: FAIL
-
-  [document.caretPositionFromPoint() should return a CaretPosition at the specified location pointing to the outer shadow host's parent when the point is in an inner shadow tree and no shadow tree is specified as an argument]
-    expected: FAIL
-
-  [document.caretPositionFromPoint() should return a CaretPosition at the specified location pointing to the outer shadow tree when the point is in an inner shadow tree and the outer shadow tree is specified as an argument]
-    expected: FAIL