Bug 1542807 part 4 - Exclude fonts loaded from User and UserAgent origin sheets from 'document.fonts'. r=jfkthame

Per https://github.com/w3c/csswg-drafts/issues/6126 these were
never intended to be included in the first place so this is just
fixing a bug.  Note that I'm leaving them in the mRuleFaces array
so that the font loading machinery works the same as before.
I'm just excluding them when queried by document.fonts.

Differential Revision: https://phabricator.services.mozilla.com/D111694

layout/style/FontFaceSet.cpp

@@ -518,7 +518,11 @@ FontFace* FontFaceSet::GetFontFaceAt(uint32_t aIndex) {
   FlushUserFontSet();
 
   if (aIndex < mRuleFaces.Length()) {
-    return mRuleFaces[aIndex].mFontFace;
+    auto& entry = mRuleFaces[aIndex];
+    if (entry.mOrigin.value() != StyleOrigin::Author) {
+      return nullptr;
+    }
+    return entry.mFontFace;
   }
 
   aIndex -= mRuleFaces.Length();
@@ -534,6 +538,20 @@ uint32_t FontFaceSet::Size() {
 
   // Web IDL objects can only expose array index properties up to INT32_MAX.
 
+  size_t total = mNonRuleFaces.Length();
+  for (const auto& entry : mRuleFaces) {
+    if (entry.mOrigin.value() == StyleOrigin::Author) {
+      ++total;
+    }
+  }
+  return std::min<size_t>(total, INT32_MAX);
+}
+
+uint32_t FontFaceSet::SizeIncludingNonAuthorOrigins() {
+  FlushUserFontSet();
+
+  // Web IDL objects can only expose array index properties up to INT32_MAX.
+
   size_t total = mRuleFaces.Length() + mNonRuleFaces.Length();
   return std::min<size_t>(total, INT32_MAX);
 }
@@ -551,8 +569,13 @@ already_AddRefed<FontFaceSetIterator> FontFaceSet::Values() {
 void FontFaceSet::ForEach(JSContext* aCx, FontFaceSetForEachCallback& aCallback,
                           JS::Handle<JS::Value> aThisArg, ErrorResult& aRv) {
   JS::Rooted<JS::Value> thisArg(aCx, aThisArg);
-  for (size_t i = 0; i < Size(); i++) {
+  for (size_t i = 0; i < SizeIncludingNonAuthorOrigins(); i++) {
     RefPtr<FontFace> face = GetFontFaceAt(i);
+    if (!face) {
+      // The font at index |i| is a non-Author origin font, which we shouldn't
+      // expose per spec.
+      continue;
+    }
     aCallback.Call(thisArg, *face, *face, *this, aRv);
     if (aRv.Failed()) {
       return;

layout/style/FontFaceSet.h

@@ -158,8 +158,6 @@ class FontFaceSet final : public DOMEventTargetHelper,
   NS_IMETHOD StyleSheetLoaded(StyleSheet* aSheet, bool aWasDeferred,
                               nsresult aStatus) override;
 
-  FontFace* GetFontFaceAt(uint32_t aIndex);
-
   void FlushUserFontSet();
 
   static nsPresContext* GetPresContextFor(gfxUserFontSet* aUserFontSet) {
@@ -188,6 +186,10 @@ class FontFaceSet final : public DOMEventTargetHelper,
   void Clear();
   bool Delete(FontFace& aFontFace);
   bool Has(FontFace& aFontFace);
+  /**
+   * This returns the number of Author origin fonts only.
+   * (see also SizeIncludingNonAuthorOrigins() below)
+   */
   uint32_t Size();
   already_AddRefed<dom::FontFaceSetIterator> Entries();
   already_AddRefed<dom::FontFaceSetIterator> Values();
@@ -200,7 +202,14 @@ class FontFaceSet final : public DOMEventTargetHelper,
 
   void MarkUserFontSetDirty();
 
+  /**
+   * Unlike Size(), this returns the size including non-Author origin fonts.
+   */
+  uint32_t SizeIncludingNonAuthorOrigins();
+
  private:
+  friend mozilla::dom::FontFaceSetIterator;  // needs GetFontFaceAt()
+
   ~FontFaceSet();
 
   /**
@@ -239,6 +248,12 @@ class FontFaceSet final : public DOMEventTargetHelper,
    */
   void CheckLoadingFinishedAfterDelay();
 
+  /**
+   * Returns the font at aIndex if it's an Author origin font, or nullptr
+   * otherwise.
+   */
+  FontFace* GetFontFaceAt(uint32_t aIndex);
+
   /**
    * Dispatches a FontFaceSetLoadEvent to this object.
    */

layout/style/FontFaceSetIterator.cpp

@@ -42,7 +42,14 @@ void FontFaceSetIterator::Next(JSContext* aCx,
     return;
   }
 
-  FontFace* face = mFontFaceSet->GetFontFaceAt(mNextIndex++);
+  // Skip over non-Author origin fonts (GetFontFaceAt returns nullptr
+  // for those).
+  FontFace* face;
+  while (!(face = mFontFaceSet->GetFontFaceAt(mNextIndex++))) {
+    if (mNextIndex >= mFontFaceSet->SizeIncludingNonAuthorOrigins()) {
+      break;  // this iterator is done
+    }
+  }
 
   if (!face) {
     aResult.mValue.setUndefined();