Bug 1795221: Implement LINKS_TO relation as a tree traversal r=Jamie

Differential Revision: https://phabricator.services.mozilla.com/D159451

accessible/base/CacheConstants.h

@@ -81,7 +81,6 @@ static constexpr RelationData kRelationTypeAtoms[] = {
      Some(RelationType::DESCRIPTION_FOR)},
     {nsGkAtoms::aria_flowto, nullptr, RelationType::FLOWS_TO,
      Some(RelationType::FLOWS_FROM)},
-    {nsGkAtoms::link, nullptr, RelationType::LINKS_TO, Nothing()},
 };
 
 }  // namespace a11y

accessible/base/Pivot.cpp

@@ -652,7 +652,7 @@ uint16_t PivotRadioNameRule::Match(Accessible* aAcc) {
   }
 
   if (remote->IsHTMLRadioButton()) {
-    nsString currName = remote->GetCachedHTMLRadioNameAttribute();
+    nsString currName = remote->GetCachedHTMLNameAttribute();
     if (!currName.IsEmpty() && mName.Equals(currName)) {
       result |= nsIAccessibleTraversalRule::FILTER_MATCH;
     }
@@ -660,3 +660,18 @@ uint16_t PivotRadioNameRule::Match(Accessible* aAcc) {
 
   return result;
 }
+
+// MustPruneSameDocRule
+
+uint16_t MustPruneSameDocRule::Match(Accessible* aAcc) {
+  if (!aAcc) {
+    return nsIAccessibleTraversalRule::FILTER_IGNORE_SUBTREE;
+  }
+
+  if (nsAccUtils::MustPrune(aAcc) || aAcc->IsOuterDoc()) {
+    return nsIAccessibleTraversalRule::FILTER_MATCH |
+           nsIAccessibleTraversalRule::FILTER_IGNORE_SUBTREE;
+  }
+
+  return nsIAccessibleTraversalRule::FILTER_MATCH;
+}

accessible/base/Pivot.h

@@ -136,6 +136,16 @@ class PivotRadioNameRule : public PivotRule {
   const nsString& mName;
 };
 
+/**
+ * This rule doesn't search iframes. Subtrees that should be
+ * pruned by way of nsAccUtils::MustPrune are also not searched.
+ */
+
+class MustPruneSameDocRule : public PivotRule {
+ public:
+  virtual uint16_t Match(Accessible* aAcc) override;
+};
+
 }  // namespace a11y
 }  // namespace mozilla
 

accessible/generic/LocalAccessible.cpp

@@ -1369,7 +1369,6 @@ void LocalAccessible::DOMAttributeChanged(int32_t aNameSpaceID,
 
   if (aAttribute == nsGkAtoms::href) {
     mDoc->QueueCacheUpdate(this, CacheDomain::Value);
-    mDoc->QueueCacheUpdate(this, CacheDomain::Relations);
   }
 
   if (aAttribute == nsGkAtoms::aria_controls ||
@@ -1432,6 +1431,13 @@ void LocalAccessible::DOMAttributeChanged(int32_t aNameSpaceID,
   if (aAttribute == nsGkAtoms::accesskey) {
     mDoc->QueueCacheUpdate(this, CacheDomain::Actions);
   }
+
+  if (aAttribute == nsGkAtoms::name &&
+      (mContent && mContent->IsHTMLElement(nsGkAtoms::a))) {
+    // If an anchor's name changed, it's possible a LINKS_TO relation
+    // also changed. Push a cache update for Relations.
+    mDoc->QueueCacheUpdate(this, CacheDomain::Relations);
+  }
 }
 
 void LocalAccessible::ARIAGroupPosition(int32_t* aLevel, int32_t* aSetSize,
@@ -3618,18 +3624,21 @@ already_AddRefed<AccAttributes> LocalAccessible::BundleFieldsForCache(
   }
 
   if (aCacheDomain & CacheDomain::Relations && mContent) {
-    if (IsHTMLRadioButton()) {
+    if (IsHTMLRadioButton() ||
+        (mContent->IsElement() &&
+         mContent->AsElement()->IsHTMLElement(nsGkAtoms::a))) {
       // HTML radio buttons with the same name should be grouped
       // and returned together when their MEMBER_OF relation is
-      // requested. We cache the name attribute, if it exists, here.
+      // requested. Computing LINKS_TO also requires we cache `name` on
+      // anchor elements.
       nsString name;
       mContent->AsElement()->GetAttr(kNameSpaceID_None, nsGkAtoms::name, name);
       if (!name.IsEmpty()) {
-        fields->SetAttribute(nsGkAtoms::radioLabel, std::move(name));
+        fields->SetAttribute(nsGkAtoms::attributeName, std::move(name));
       } else if (aUpdateType != CacheUpdateType::Initial) {
         // It's possible we used to have a name and it's since been
         // removed. Send a delete entry.
-        fields->SetAttribute(nsGkAtoms::radioLabel, DeleteEntry());
+        fields->SetAttribute(nsGkAtoms::attributeName, DeleteEntry());
       }
     }
 
@@ -3646,10 +3655,6 @@ already_AddRefed<AccAttributes> LocalAccessible::BundleFieldsForCache(
                 dom::HTMLLabelElement::FromNode(mContent)) {
           rel.AppendTarget(mDoc, labelEl->GetControl());
         }
-      } else if (data.mType == RelationType::LINKS_TO) {
-        // This has no implicit relation, so it's safe to call RelationByType
-        // directly.
-        rel = RelationByType(RelationType::LINKS_TO);
       } else {
         // We use an IDRefsIterator here instead of calling RelationByType
         // directly because we only want to cache explicit relations. Implicit

accessible/ipc/RemoteAccessibleBase.cpp

@@ -693,6 +693,43 @@ Relation RemoteAccessibleBase<Derived>::RelationByType(
     return Relation();
   }
 
+  if (aType == RelationType::LINKS_TO && Role() == roles::LINK) {
+    Pivot p = Pivot(mDoc);
+    nsString href;
+    Value(href);
+    if (!href.IsEmpty()) {
+      // `Value` will give us the entire URL, we're only interested in the ID
+      // after the hash. Split that part out.
+      for (auto s : href.Split('#')) {
+        href = s;
+      }
+      MustPruneSameDocRule rule;
+      Accessible* nameMatch = nullptr;
+      for (Accessible* match = p.Next(mDoc, rule); match;
+           match = p.Next(match, rule)) {
+        nsString currID;
+        match->DOMNodeID(currID);
+        MOZ_ASSERT(match->IsRemote());
+        if (href.Equals(currID)) {
+          return Relation(match->AsRemote());
+        }
+        if (!nameMatch) {
+          nsString currName = match->AsRemote()->GetCachedHTMLNameAttribute();
+          if (match->TagName() == nsGkAtoms::a && href.Equals(currName)) {
+            // If we find an element with a matching ID, we should return
+            // that, but if we don't we should return the first anchor with
+            // a matching name. To avoid doing two traversals, store the first
+            // name match here.
+            nameMatch = match;
+          }
+        }
+      }
+      return nameMatch ? Relation(nameMatch->AsRemote()) : Relation();
+    }
+
+    return Relation();
+  }
+
   // Handle ARIA tree, treegrid parent/child relations. Each of these cases
   // relies on cached group info. To find the parent of an accessible, use the
   // unified conceptual parent.
@@ -1007,15 +1044,13 @@ RemoteAccessibleBase<Derived>::GetCachedARIAAttributes() const {
 }
 
 template <class Derived>
-nsString RemoteAccessibleBase<Derived>::GetCachedHTMLRadioNameAttribute()
-    const {
+nsString RemoteAccessibleBase<Derived>::GetCachedHTMLNameAttribute() const {
   if (mCachedFields) {
     if (auto maybeName =
-            mCachedFields->GetAttribute<nsString>(nsGkAtoms::radioLabel)) {
+            mCachedFields->GetAttribute<nsString>(nsGkAtoms::attributeName)) {
       return *maybeName;
     }
   }
-
   return nsString();
 }
 

accessible/ipc/RemoteAccessibleBase.h

@@ -348,7 +348,7 @@ class RemoteAccessibleBase : public Accessible, public HyperTextAccessibleBase {
   RefPtr<const AccAttributes> GetCachedTextAttributes();
   RefPtr<const AccAttributes> GetCachedARIAAttributes() const;
 
-  nsString GetCachedHTMLRadioNameAttribute() const;
+  nsString GetCachedHTMLNameAttribute() const;
 
   virtual HyperTextAccessibleBase* AsHyperTextBase() override {
     return IsHyperText() ? static_cast<HyperTextAccessibleBase*>(this)

accessible/tests/browser/e10s/browser_caching_relations.js

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
+requestLongerTimeout(2);
 
 /* import-globals-from ../../mochitest/relations.js */
 loadScripts({ name: "relations.js", dir: MOCHITESTS_DIR });
@@ -358,21 +359,28 @@ addAccessibleTask(
  */
 addAccessibleTask(
   `
-  <a id="link" href="#item">
+  <a id="link" href="#item">a</a>
   <div id="item">hello</div>
-  <div id="item2">world</div>`,
+  <div id="item2">world</div>
+  <a id="link2" href="#anchor">b</a>
+  <a id="namedLink" name="anchor">c</a>`,
   async function(browser, accDoc) {
     const link = findAccessibleChildByID(accDoc, "link");
+    const link2 = findAccessibleChildByID(accDoc, "link2");
+    const namedLink = findAccessibleChildByID(accDoc, "namedLink");
     const item = findAccessibleChildByID(accDoc, "item");
     const item2 = findAccessibleChildByID(accDoc, "item2");
 
     await testCachedRelation(link, RELATION_LINKS_TO, item);
+    await testCachedRelation(link2, RELATION_LINKS_TO, namedLink);
 
     await invokeContentTask(browser, [], () => {
       content.document.getElementById("link").href = "";
+      content.document.getElementById("namedLink").name = "newName";
     });
 
     await testCachedRelation(link, RELATION_LINKS_TO, null);
+    await testCachedRelation(link2, RELATION_LINKS_TO, null);
 
     await invokeContentTask(browser, [], () => {
       content.document.getElementById("link").href = "#item2";