Bug 476384 - Use the TLD as a CJK font hint for UTF-8 pages. r=jfkthame

Differential Revision: https://phabricator.services.mozilla.com/D103188

dom/base/Document.cpp

@@ -16633,11 +16633,85 @@ void Document::DoCacheAllKnownLangPrefs() {
   mMayNeedFontPrefsUpdate = false;
 }
 
+nsAtom* Document::CJKFromTLD() {
+  // Using mOriginalURI instead of mBaseDomain, because the former
+  // does not change over time.
+  if (!mOriginalURI) {
+    return nsGkAtoms::Unicode;
+  }
+  nsCOMPtr<nsIURI> innermost = NS_GetInnermostURI(mOriginalURI);
+  nsAutoCString tld;
+  nsAutoCString host;
+  innermost->GetAsciiHost(host);
+  if (host.IsEmpty()) {
+    return nsGkAtoms::Unicode;
+  }
+  // First let's see if the host is DNS-absolute and ends with a
+  // dot and get rid of that one.
+  if (host.Last() == '.') {
+    host.SetLength(host.Length() - 1);
+  }
+  int32_t index = host.RFindChar('.');
+  if (index == kNotFound) {
+    return nsGkAtoms::Unicode;
+  }
+  // We tolerate an IPv4 component as generic "TLD", so don't
+  // bother checking.
+  ToLowerCase(Substring(host, index + 1, host.Length() - (index + 1)), tld);
+
+  if (tld.Length() == 2) {
+    if (tld.EqualsLiteral("cn") || tld.EqualsLiteral("sg")) {
+      return nsGkAtoms::Chinese;
+    }
+
+    if (tld.EqualsLiteral("tw")) {
+      return nsGkAtoms::Taiwanese;
+    }
+
+    if (tld.EqualsLiteral("hk") || tld.EqualsLiteral("mo")) {
+      return nsGkAtoms::HongKongChinese;
+    }
+
+    if (tld.EqualsLiteral("jp")) {
+      return nsGkAtoms::Japanese;
+    }
+
+    if (tld.EqualsLiteral("kr") || tld.EqualsLiteral("kp")) {
+      return nsGkAtoms::ko;
+    }
+  } else if (StringBeginsWith(tld, "xn--"_ns)) {
+    if (tld.EqualsLiteral("xn--clchc0ea0b2g2a9gcd") ||
+        tld.EqualsLiteral("xn--fiqs8S") || tld.EqualsLiteral("xn--fiqz9S") ||
+        tld.EqualsLiteral("xn--yfro4i67o") ||
+        tld.EqualsLiteral("xn--clchc0ea0b2g2a9gcd") ||
+        tld.EqualsLiteral("xn--yfro4i67o")) {
+      return nsGkAtoms::Chinese;
+    }
+
+    if (tld.EqualsLiteral("xn--kprw13d") || tld.EqualsLiteral("xn--kpry57d")) {
+      return nsGkAtoms::Taiwanese;
+    }
+
+    if (tld.EqualsLiteral("xn--j6w193g") || tld.EqualsLiteral("xn--mix891f")) {
+      return nsGkAtoms::HongKongChinese;
+    }
+
+    if (tld.EqualsLiteral("xn--3e0b707e")) {
+      return nsGkAtoms::ko;
+    }
+  }
+
+  return nsGkAtoms::Unicode;
+}
+
 void Document::RecomputeLanguageFromCharset() {
   nsLanguageAtomService* service = nsLanguageAtomService::GetService();
   RefPtr<nsAtom> language = service->LookupCharSet(mCharacterSet);
   if (language == nsGkAtoms::Unicode) {
-    language = service->GetLocaleLanguage();
+    language = CJKFromTLD();
+    if (language == nsGkAtoms::Unicode) {
+      language = service->GetLocaleLanguage();
+    }
   }
 
   if (language == mLanguageFromCharset) {

dom/base/Document.h

@@ -3868,6 +3868,7 @@ class Document : public nsINode,
 
  private:
   void DoCacheAllKnownLangPrefs();
+  nsAtom* CJKFromTLD();
   void RecomputeLanguageFromCharset();
   bool GetSHEntryHasUserInteraction();