Bug 1559077 - Implement Element.part. r=bzbarsky

Differential Revision: https://phabricator.services.mozilla.com/D48707

--HG--
extra : moz-landing-system : lando

dom/base/Element.cpp

@@ -539,6 +539,16 @@ nsDOMTokenList* Element::ClassList() {
   return slots->mClassList;
 }
 
+nsDOMTokenList* Element::Part() {
+  Element::nsDOMSlots* slots = DOMSlots();
+
+  if (!slots->mPart) {
+    slots->mPart = new nsDOMTokenList(this, nsGkAtoms::part);
+  }
+
+  return slots->mPart;
+}
+
 void Element::GetAttributeNames(nsTArray<nsString>& aResult) {
   uint32_t count = mAttrs.AttrCount();
   for (uint32_t i = 0; i < count; ++i) {

dom/base/Element.h

@@ -1030,6 +1030,8 @@ class Element : public FragmentOrElement {
   }
 
   nsDOMTokenList* ClassList();
+  nsDOMTokenList* Part();
+
   nsDOMAttributeMap* Attributes() {
     nsDOMSlots* slots = DOMSlots();
     if (!slots->mAttributeMap) {

dom/base/FragmentOrElement.cpp

@@ -597,6 +597,9 @@ void FragmentOrElement::nsDOMSlots::Traverse(
 
   NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mClassList");
   aCb.NoteXPCOMChild(mClassList.get());
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mPart");
+  aCb.NoteXPCOMChild(mPart.get());
 }
 
 void FragmentOrElement::nsDOMSlots::Unlink() {
@@ -608,6 +611,7 @@ void FragmentOrElement::nsDOMSlots::Unlink() {
   }
   mChildrenList = nullptr;
   mClassList = nullptr;
+  mPart = nullptr;
 }
 
 size_t FragmentOrElement::nsDOMSlots::SizeOfIncludingThis(

dom/base/FragmentOrElement.h

@@ -247,6 +247,11 @@ class FragmentOrElement : public nsIContent {
      * An object implementing the .classList property for this element.
      */
     RefPtr<nsDOMTokenList> mClassList;
+
+    /**
+     * An object implementing the .part property for this element.
+     */
+    RefPtr<nsDOMTokenList> mPart;
   };
 
   /**

dom/webidl/Element.webidl

@@ -33,6 +33,10 @@ interface Element : Node {
   [Constant, PutForwards=value]
   readonly attribute DOMTokenList classList;
 
+  // https://drafts.csswg.org/css-shadow-parts/#idl
+  [SameObject, PutForwards=value, Pref="layout.css.shadow-parts.enabled"]
+  readonly attribute DOMTokenList part;
+
   [SameObject]
   readonly attribute NamedNodeMap attributes;
   [Pure]

testing/web-platform/meta/css/css-shadow-parts/invalidation-change-part-name-idl-domtokenlist.html.ini

@@ -1,4 +0,0 @@
-[invalidation-change-part-name-idl-domtokenlist.html]
-  [Part in selected host changed color via part IDL DOMTokenList attribute.]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/invalidation-change-part-name-idl-setter.html.ini

@@ -1,4 +0,0 @@
-[invalidation-change-part-name-idl-setter.html]
-  [Part in selected host changed color via part IDL attribute setter.]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/part-name-idl.html.ini

@@ -1,13 +0,0 @@
-[part-name-idl.html]
-  [Access to .part returns an empty DOMTokenList.]
-    expected: FAIL
-
-  [Changes in DOMTokenList are refected in attribute.]
-    expected: FAIL
-
-  [DOMTokenList created by access is persisted.]
-    expected: FAIL
-
-  [Multiple names give a DOMTokenList with multiple entries.]
-    expected: FAIL
-