Bug 234485: Map xml:lang attribute into style so that it's used for font selection and hyphenation. r=bzbarsky

The code in nsHTMLStyleSheet implements LangRule to map xml:lang into style and the code to manage its uniqueness. The change to nsGenericHTMLElement fixes the mapping of the HTML lang attribute to do cascading the way all other rule mapping does so that the cascading works correctly. The tests test that the correct style language is used for hyphenation by copying over a set of hyphenation reftests that check its basic response to languages. There are no specific tests for font selection, but font selection is known to use the same language data from style. I verified manually (see other attachments to bug) that the rule uniqueness is being managed correctly. --HG-- rename : layout/reftests/text/auto-hyphenation-1.html => layout/reftests/text/auto-hyphenation-xmllang-1.xhtml rename : layout/reftests/text/auto-hyphenation-10.html => layout/reftests/text/auto-hyphenation-xmllang-10.xhtml rename : layout/reftests/text/auto-hyphenation-1.html => layout/reftests/text/auto-hyphenation-xmllang-11a.xhtml rename : layout/reftests/text/auto-hyphenation-1.html => layout/reftests/text/auto-hyphenation-xmllang-11b.xhtml rename : layout/reftests/text/auto-hyphenation-4.html => layout/reftests/text/auto-hyphenation-xmllang-12a.xhtml rename : layout/reftests/text/auto-hyphenation-4.html => layout/reftests/text/auto-hyphenation-xmllang-12b.xhtml rename : layout/reftests/text/auto-hyphenation-1.html => layout/reftests/text/auto-hyphenation-xmllang-13a.xhtml rename : layout/reftests/text/auto-hyphenation-1.html => layout/reftests/text/auto-hyphenation-xmllang-13b.xhtml rename : layout/reftests/text/auto-hyphenation-4.html => layout/reftests/text/auto-hyphenation-xmllang-14a.xhtml rename : layout/reftests/text/auto-hyphenation-4.html => layout/reftests/text/auto-hyphenation-xmllang-14b.xhtml rename : layout/reftests/text/auto-hyphenation-1a.html => layout/reftests/text/auto-hyphenation-xmllang-1a.xhtml rename : layout/reftests/text/auto-hyphenation-2.html => layout/reftests/text/auto-hyphenation-xmllang-2.xhtml rename : layout/reftests/text/auto-hyphenation-3.html => layout/reftests/text/auto-hyphenation-xmllang-3.xhtml rename : layout/reftests/text/auto-hyphenation-4.html => layout/reftests/text/auto-hyphenation-xmllang-4.xhtml rename : layout/reftests/text/auto-hyphenation-5.html => layout/reftests/text/auto-hyphenation-xmllang-5.xhtml rename : layout/reftests/text/auto-hyphenation-6.html => layout/reftests/text/auto-hyphenation-xmllang-6.xhtml rename : layout/reftests/text/auto-hyphenation-7.html => layout/reftests/text/auto-hyphenation-xmllang-7.xhtml rename : layout/reftests/text/auto-hyphenation-8.html => layout/reftests/text/auto-hyphenation-xmllang-8.xhtml rename : layout/reftests/text/auto-hyphenation-9.html => layout/reftests/text/auto-hyphenation-xmllang-9.xhtml
2024-09-13 09:24:08 -07:00 · 2013-05-30 16:00:20 +08:00 · 2013-05-30 16:00:20 +08:00 · b31121a2a1
commit b31121a2a1
parent c18b9f7a1a
23 changed files with 414 additions and 5 deletions
--- a/content/html/content/src/nsGenericHTMLElement.cpp
+++ b/content/html/content/src/nsGenericHTMLElement.cpp
@ -1461,10 +1461,12 @@ nsGenericHTMLElement::MapCommonAttributesInto(const nsMappedAttributes* aAttribu
  }

  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Font)) {
-    const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::lang);
-    if (value && value->Type() == nsAttrValue::eString) {
-      aData->ValueForLang()->SetStringValue(value->GetStringValue(),
-                                            eCSSUnit_Ident);
+    nsCSSValue* lang = aData->ValueForLang();
+    if (lang->GetUnit() == eCSSUnit_Null) {
+      const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::lang);
+      if (value && value->Type() == nsAttrValue::eString) {
+        lang->SetStringValue(value->GetStringValue(), eCSSUnit_Ident);
+      }
    }
  }

--- a/layout/reftests/text/auto-hyphenation-xmllang-1.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-1.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- simple test for automatic hyphenation -->
+<body xml:lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-10.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-10.xhtml
@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that hyphenation is not applied when language is not specified -->
+<body>
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-11a.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-11a.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that xml:lang beats lang -->
+<body xml:lang="en-us" lang="x-unknown-language">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-11b.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-11b.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that xml:lang beats lang -->
+<body lang="x-unknown-language" xml:lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-12a.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-12a.xhtml
@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that xml:lang beats lang -->
+<!-- check that hyphenation is not applied to unknown language -->
+<body xml:lang="x-unknown-language" lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-12b.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-12b.xhtml
@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that xml:lang beats lang -->
+<!-- check that hyphenation is not applied to unknown language -->
+<body lang="en-us" xml:lang="x-unknown-language">
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-13a.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-13a.xhtml
@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that innermost beats xml:lang vs. lang difference -->
+<body lang="x-unknown-language">
+<div xml:lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+supercalifragilisticexpialidocious
+</div>
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-13b.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-13b.xhtml
@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that innermost beats xml:lang vs. lang difference -->
+<body xml:lang="x-unknown-language">
+<div lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+supercalifragilisticexpialidocious
+</div>
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-14a.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-14a.xhtml
@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that innermost beats xml:lang vs. lang difference -->
+<!-- check that hyphenation is not applied to unknown language -->
+<body lang="en-us">
+<div xml:lang="x-unknown-language">
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-14b.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-14b.xhtml
@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that innermost beats xml:lang vs. lang difference -->
+<!-- check that hyphenation is not applied to unknown language -->
+<body xml:lang="en-us">
+<div lang="x-unknown-language">
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-1a.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-1a.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- adding random <span>s should not affect hyphenation -->
+<body xml:lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+super<span>cali</span>frag<span>ili</span>sti<span>cex</span>pialidoc<span>i</span>ous
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-2.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-2.xhtml
@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- mixed languages in a word should inhibit automatic hyphenation -->
+<body xml:lang="en-us">
+<div style="width: 5em; -moz-hyphens: auto; font-family:sans-serif;">
+supercalifragilisticexpialidocious
+super<span xml:lang="foo">cali</span>fragilisticexpialidocious
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-3.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-3.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that -moz-hyphens:none prevents break at &shy; -->
+<body xml:lang="en-us">
+<div style="width: 5em; -moz-hyphens: none;">
+su&#173;per&#173;cal&#173;ifrag&#173;ilis&#173;tic&#173;ex&#173;pi&#173;ali&#173;do&#173;cious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-4.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-4.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that hyphenation is not applied to unknown language -->
+<body xml:lang="x-unknown-language">
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-5.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-5.xhtml
@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+<style type="text/css">
+div {
+  margin:       10px;
+  width:        10px;
+  font-family:  monospace;
+  -moz-hyphens: auto;
+}
+</style>
+</head>
+<!-- test some hyphenations that involve overlapping patterns -->
+<body xml:lang="en-us">
+<div>
+photo
+</div>
+<div>
+photograph
+</div>
+<div>
+photographer
+</div>
+<div>
+photographical
+</div>
+</body>
+</html>
--- a/layout/reftests/text/auto-hyphenation-xmllang-6.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-6.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- style changes don't break hyphenation -->
+<body xml:lang="en-us">
+<div style="width: 0; -moz-hyphens: auto;">
+hy<span style="color:red">phen</span>ation
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-7.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-7.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- style changes don't break hyphenation -->
+<body xml:lang="en-us">
+<div style="width: 0; -moz-hyphens: auto;">
+h<span style="color:red">yphena</span>tion
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-8.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-8.xhtml
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that hyphenation is not applied when language is not specified -->
+<body>
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/auto-hyphenation-xmllang-9.xhtml
+++ b/layout/reftests/text/auto-hyphenation-xmllang-9.xhtml
@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="iso-8859-1" ?>
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hyphenation test</title></head>
+<!-- check that hyphenation is not applied when language is not specified -->
+<body>
+<div style="width: 5em; -moz-hyphens: auto;">
+supercalifragilisticexpialidocious
+</div>
+</body>
+</html>
+
--- a/layout/reftests/text/reftest.list
+++ b/layout/reftests/text/reftest.list
@ -219,6 +219,26 @@ pref(gfx.font_rendering.graphite.enabled,true) HTTP(..) == glyph-decomposition-g
 == auto-hyphenation-8.html auto-hyphenation-8-ref.html
 == auto-hyphenation-9.html auto-hyphenation-9-ref.html
 == auto-hyphenation-10.html auto-hyphenation-10-ref.html
+== auto-hyphenation-xmllang-1.xhtml auto-hyphenation-1-ref.html
+!= auto-hyphenation-xmllang-1.xhtml auto-hyphenation-1-notref.html
+== auto-hyphenation-xmllang-1a.xhtml auto-hyphenation-1-ref.html
+== auto-hyphenation-xmllang-2.xhtml auto-hyphenation-2-ref.html
+== auto-hyphenation-xmllang-3.xhtml auto-hyphenation-3-ref.html
+== auto-hyphenation-xmllang-4.xhtml auto-hyphenation-4-ref.html
+== auto-hyphenation-xmllang-5.xhtml auto-hyphenation-5-ref.html
+== auto-hyphenation-xmllang-6.xhtml auto-hyphenation-6-ref.html
+== auto-hyphenation-xmllang-7.xhtml auto-hyphenation-7-ref.html
+== auto-hyphenation-xmllang-8.xhtml auto-hyphenation-8-ref.html
+== auto-hyphenation-xmllang-9.xhtml auto-hyphenation-9-ref.html
+== auto-hyphenation-xmllang-10.xhtml auto-hyphenation-10-ref.html
+== auto-hyphenation-xmllang-11a.xhtml auto-hyphenation-1-ref.html
+== auto-hyphenation-xmllang-11b.xhtml auto-hyphenation-1-ref.html
+== auto-hyphenation-xmllang-12a.xhtml auto-hyphenation-4-ref.html
+== auto-hyphenation-xmllang-12b.xhtml auto-hyphenation-4-ref.html
+== auto-hyphenation-xmllang-13a.xhtml auto-hyphenation-1-ref.html
+== auto-hyphenation-xmllang-13b.xhtml auto-hyphenation-1-ref.html
+== auto-hyphenation-xmllang-14a.xhtml auto-hyphenation-4-ref.html
+== auto-hyphenation-xmllang-14b.xhtml auto-hyphenation-4-ref.html
 == auto-hyphenation-af-1.html auto-hyphenation-af-1-ref.html
 == auto-hyphenation-bg-1.html auto-hyphenation-bg-1-ref.html
 == auto-hyphenation-ca-1.html auto-hyphenation-ca-1-ref.html
--- a/layout/style/nsHTMLStyleSheet.cpp
+++ b/layout/style/nsHTMLStyleSheet.cpp
@ -32,7 +32,9 @@
 #include "nsCSSRuleProcessor.h"
 #include "mozilla/dom/Element.h"
 #include "nsCSSFrameConstructor.h"
+#include "nsHashKeys.h"

+using namespace mozilla;
 using namespace mozilla::dom;

 NS_IMPL_ISUPPORTS1(nsHTMLStyleSheet::HTMLColorRule, nsIStyleRule)
@ -94,6 +96,31 @@ nsHTMLStyleSheet::TableQuirkColorRule::MapRuleInfoInto(nsRuleData* aRuleData)
  }
 }

+
+NS_IMPL_ISUPPORTS1(nsHTMLStyleSheet::LangRule, nsIStyleRule)
+
+/* virtual */ void
+nsHTMLStyleSheet::LangRule::MapRuleInfoInto(nsRuleData* aRuleData)
+{
+  if (aRuleData->mSIDs & NS_STYLE_INHERIT_BIT(Font)) {
+    nsCSSValue* lang = aRuleData->ValueForLang();
+    if (lang->GetUnit() == eCSSUnit_Null) {
+      lang->SetStringValue(mLang, eCSSUnit_Ident);
+    }
+  }
+}
+
+#ifdef DEBUG
+/* virtual */ void
+nsHTMLStyleSheet::LangRule::List(FILE* out, int32_t aIndent) const
+{
+  for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
+  fputs("[lang rule] { language: \"", out);
+  fputs(NS_ConvertUTF16toUTF8(mLang).get(), out);
+  fputs("\" }\n", out);
+}
+#endif
+
 // -----------------------------------------------------------

 struct MappedAttrTableEntry : public PLDHashEntryHdr {
@ -138,7 +165,64 @@ static PLDHashTableOps MappedAttrTable_Ops = {
  PL_DHashMoveEntryStub,
  MappedAttrTable_ClearEntry,
  PL_DHashFinalizeStub,
-  NULL
+  nullptr
+};
+
+// -----------------------------------------------------------
+
+struct LangRuleTableEntry : public PLDHashEntryHdr {
+  nsRefPtr<nsHTMLStyleSheet::LangRule> mRule;
+};
+
+static PLDHashNumber
+LangRuleTable_HashKey(PLDHashTable *table, const void *key)
+{
+  const nsString *lang = static_cast<const nsString*>(key);
+  return HashString(*lang);
+}
+
+static void
+LangRuleTable_ClearEntry(PLDHashTable *table, PLDHashEntryHdr *hdr)
+{
+  LangRuleTableEntry *entry = static_cast<LangRuleTableEntry*>(hdr);
+
+  entry->~LangRuleTableEntry();
+  memset(entry, 0, sizeof(LangRuleTableEntry));
+}
+
+static bool
+LangRuleTable_MatchEntry(PLDHashTable *table, const PLDHashEntryHdr *hdr,
+                         const void *key)
+{
+  const nsString *lang = static_cast<const nsString*>(key);
+  const LangRuleTableEntry *entry = static_cast<const LangRuleTableEntry*>(hdr);
+
+  return entry->mRule->mLang == *lang;
+}
+
+static bool
+LangRuleTable_InitEntry(PLDHashTable *table, PLDHashEntryHdr *hdr,
+                        const void *key)
+{
+  const nsString *lang = static_cast<const nsString*>(key);
+
+  LangRuleTableEntry *entry = new (hdr) LangRuleTableEntry();
+
+  // Create the unique rule for this language
+  entry->mRule = new nsHTMLStyleSheet::LangRule(*lang);
+
+  return true;
+}
+
+static PLDHashTableOps LangRuleTable_Ops = {
+  PL_DHashAllocTable,
+  PL_DHashFreeTable,
+  LangRuleTable_HashKey,
+  LangRuleTable_MatchEntry,
+  PL_DHashMoveEntryStub,
+  LangRuleTable_ClearEntry,
+  PL_DHashFinalizeStub,
+  LangRuleTable_InitEntry
 };

 // -----------------------------------------------------------
@ -152,10 +236,13 @@ nsHTMLStyleSheet::nsHTMLStyleSheet(nsIURI* aURL, nsIDocument* aDocument)
  MOZ_ASSERT(aURL);
  MOZ_ASSERT(aDocument);
  mMappedAttrTable.ops = nullptr;
+  mLangRuleTable.ops = nullptr;
 }

 nsHTMLStyleSheet::~nsHTMLStyleSheet()
 {
+  if (mLangRuleTable.ops)
+    PL_DHashTableFinish(&mLangRuleTable);
  if (mMappedAttrTable.ops)
    PL_DHashTableFinish(&mMappedAttrTable);
 }
@ -212,6 +299,14 @@ nsHTMLStyleSheet::RulesMatching(ElementRuleProcessorData* aData)
  if (!ruleWalker->AuthorStyleDisabled() || aData->mElement->IsSVG()) {
    aData->mElement->WalkContentStyleRules(ruleWalker);
  }
+
+  // http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#language
+  // says that the xml:lang attribute overrides HTML's lang attribute,
+  // so we need to do this after WalkContentStyleRules.
+  nsString lang;
+  if (aData->mElement->GetAttr(kNameSpaceID_XML, nsGkAtoms::lang, lang)) {
+    ruleWalker->Forward(LangRuleFor(lang));
+  }
 }

 // Test if style is dependent on content state
@ -387,6 +482,10 @@ nsHTMLStyleSheet::Reset(nsIURI* aURL)
  mVisitedRule       = nullptr;
  mActiveRule        = nullptr;

+  if (mLangRuleTable.ops) {
+    PL_DHashTableFinish(&mLangRuleTable);
+    mLangRuleTable.ops = nullptr;
+  }
  if (mMappedAttrTable.ops) {
    PL_DHashTableFinish(&mMappedAttrTable);
    mMappedAttrTable.ops = nullptr;
@ -474,6 +573,27 @@ nsHTMLStyleSheet::DropMappedAttributes(nsMappedAttributes* aMapped)
  NS_ASSERTION(entryCount == mMappedAttrTable.entryCount, "not removed");
 }

+nsIStyleRule*
+nsHTMLStyleSheet::LangRuleFor(const nsString& aLanguage)
+{
+  if (!mLangRuleTable.ops) {
+    bool res = PL_DHashTableInit(&mLangRuleTable, &LangRuleTable_Ops,
+                                 nullptr, sizeof(LangRuleTableEntry), 16);
+    if (!res) {
+      NS_ASSERTION(false, "out of memory");
+      mLangRuleTable.ops = nullptr;
+      return nullptr;
+    }
+  }
+  LangRuleTableEntry *entry = static_cast<LangRuleTableEntry*>
+    (PL_DHashTableOperate(&mLangRuleTable, &aLanguage, PL_DHASH_ADD));
+  if (!entry) {
+    NS_ASSERTION(false, "out of memory");
+    return nullptr;
+  }
+  return entry->mRule;
+}
+
 #ifdef DEBUG
 /* virtual */ void
 nsHTMLStyleSheet::List(FILE* out, int32_t aIndent) const
@ -522,6 +642,7 @@ nsHTMLStyleSheet::DOMSizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const
  // - mActiveRule
  // - mTableQuirkColorRule
  // - mTableTHRule
+  // - mLangRuleTable
  //
  // The following members are not measured:
  // - mDocument, because it's non-owning
--- a/layout/style/nsHTMLStyleSheet.h
+++ b/layout/style/nsHTMLStyleSheet.h
@ -20,6 +20,7 @@
 #include "nsIStyleSheet.h"
 #include "pldhash.h"
 #include "mozilla/Attributes.h"
+#include "nsString.h"

 class nsMappedAttributes;

@ -76,6 +77,8 @@ public:
    UniqueMappedAttributes(nsMappedAttributes* aMapped);
  void DropMappedAttributes(nsMappedAttributes* aMapped);

+  nsIStyleRule* LangRuleFor(const nsString& aLanguage);
+
 private: 
  nsHTMLStyleSheet(const nsHTMLStyleSheet& aCopy) MOZ_DELETE;
  nsHTMLStyleSheet& operator=(const nsHTMLStyleSheet& aCopy) MOZ_DELETE;
@ -136,6 +139,26 @@ private:
    virtual void MapRuleInfoInto(nsRuleData* aRuleData) MOZ_OVERRIDE;
  };

+public: // for mLangRuleTable structures only
+
+  // Rule to handle xml:lang attributes, of which we have exactly one
+  // per language string, maintained in mLangRuleTable.
+  class LangRule MOZ_FINAL : public nsIStyleRule {
+  public:
+    LangRule(const nsSubstring& aLang) : mLang(aLang) {}
+
+    NS_DECL_ISUPPORTS
+
+    // nsIStyleRule interface
+    virtual void MapRuleInfoInto(nsRuleData* aRuleData) MOZ_OVERRIDE;
+  #ifdef DEBUG
+    virtual void List(FILE* out = stdout, int32_t aIndent = 0) const MOZ_OVERRIDE;
+  #endif
+
+    nsString mLang;
+  };
+
+private:
  nsCOMPtr<nsIURI>        mURL;
  nsIDocument*            mDocument;
  nsRefPtr<HTMLColorRule> mLinkRule;
@ -145,6 +168,7 @@ private:
  nsRefPtr<TableTHRule>   mTableTHRule;

  PLDHashTable            mMappedAttrTable;
+  PLDHashTable            mLangRuleTable;
 };

 #endif /* !defined(nsHTMLStyleSheet_h_) */