gecko-dev/layout/style/nsStyleSet.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: NPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Netscape Public License
 * Version 1.1 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 * http://www.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is 
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Daniel Glazman <glazman@netscape.com>
 *   Brian Ryner    <bryner@brianryner.com>
 *
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the NPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the NPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */
#include "nsStyleSet.h"
#include "nsNetUtil.h"
#include "nsICSSStyleSheet.h"
#include "nsIDocument.h"
#include "nsRuleWalker.h"
#include "nsStyleContext.h"
#include "nsICSSStyleRule.h"
#include "nsCSSAnonBoxes.h"
#include "nsCSSPseudoElements.h"
#include "nsIContent.h"
#include "nsIFrame.h"

nsIURI *nsStyleSet::gQuirkURI = 0;

nsStyleSet::nsStyleSet()
  : mRuleTree(nsnull),
    mRuleWalker(nsnull),
    mDestroyedCount(0),
    mBatching(0),
    mInShutdown(PR_FALSE),
    mDirty(0)
{
}

nsresult
nsStyleSet::Init(nsIPresContext *aPresContext)
{
  if (!gQuirkURI) {
    static const char kQuirk_href[] = "resource://gre/res/quirk.css";
    NS_NewURI(&gQuirkURI, kQuirk_href);
    NS_ENSURE_TRUE(gQuirkURI, NS_ERROR_OUT_OF_MEMORY);
  }

  if (!BuildDefaultStyleData(aPresContext)) {
    mDefaultStyleData.Destroy(0, aPresContext);
    return NS_ERROR_OUT_OF_MEMORY;
  }

  mRuleTree = nsRuleNode::CreateRootNode(aPresContext);
  if (!mRuleTree) {
    mDefaultStyleData.Destroy(0, aPresContext);
    return NS_ERROR_OUT_OF_MEMORY;
  }

  mRuleWalker = new nsRuleWalker(mRuleTree);
  if (!mRuleWalker) {
    mRuleTree->Destroy();
    mDefaultStyleData.Destroy(0, aPresContext);
    return NS_ERROR_OUT_OF_MEMORY;
  }

  return NS_OK;
}

struct RuleProcessorEnumData {
  RuleProcessorEnumData(nsCOMArray<nsIStyleRuleProcessor> *aRuleProcessors) 
    : mRuleProcessors(aRuleProcessors),
      mPrevProcessor(nsnull)
  {}

  nsCOMArray<nsIStyleRuleProcessor>* mRuleProcessors;
  nsIStyleRuleProcessor*  mPrevProcessor;
};

static PRBool
EnumRuleProcessor(nsIStyleSheet *aSheet, void* aData)
{
  RuleProcessorEnumData* data = (RuleProcessorEnumData*)aData;

  nsCOMPtr<nsIStyleRuleProcessor> processor;
  nsresult result = aSheet->GetStyleRuleProcessor(*getter_AddRefs(processor),
                                                  data->mPrevProcessor);
  if (NS_SUCCEEDED(result) && processor) {
    if (processor != data->mPrevProcessor) {
      if (!data->mRuleProcessors->AppendObject(processor))
        return PR_FALSE;
      data->mPrevProcessor = processor; // ref is held by array
    }
  }
  return PR_TRUE;
}

nsresult
nsStyleSet::GatherRuleProcessors(PRInt32 aType)
{
  mRuleProcessors[aType].Clear();
  if (mSheets[aType].Count()) {
    RuleProcessorEnumData data(&mRuleProcessors[aType]);
    if (!mSheets[aType].EnumerateBackwards(EnumRuleProcessor, &data))
      return NS_ERROR_OUT_OF_MEMORY;
  }

  return NS_OK;
}

#ifdef DEBUG
#define CHECK_APPLICABLE \
PR_BEGIN_MACRO \
  PRBool applicable = PR_TRUE; \
  aSheet->GetApplicable(applicable); \
  NS_ASSERTION(applicable, "Inapplicable sheet being placed in style set"); \
PR_END_MACRO
#else
#define CHECK_APPLICABLE
#endif

nsresult
nsStyleSet::AppendStyleSheet(sheetType aType, nsIStyleSheet *aSheet)
{
  NS_PRECONDITION(aSheet, "null arg");
  CHECK_APPLICABLE;
  mSheets[aType].RemoveObject(aSheet);
  if (!mSheets[aType].AppendObject(aSheet))
    return NS_ERROR_OUT_OF_MEMORY;

  if (!mBatching)
    return GatherRuleProcessors(aType);

  mDirty |= 1 << aType;
  return NS_OK;
}

nsresult
nsStyleSet::PrependStyleSheet(sheetType aType, nsIStyleSheet *aSheet)
{
  NS_PRECONDITION(aSheet, "null arg");
  CHECK_APPLICABLE;
  mSheets[aType].RemoveObject(aSheet);
  if (!mSheets[aType].InsertObjectAt(aSheet, 0))
    return NS_ERROR_OUT_OF_MEMORY;

  if (!mBatching)
    return GatherRuleProcessors(aType);

  mDirty |= 1 << aType;
  return NS_OK;
}

nsresult
nsStyleSet::RemoveStyleSheet(sheetType aType, nsIStyleSheet *aSheet)
{
  NS_PRECONDITION(aSheet, "null arg");
#ifdef DEBUG
  PRBool complete = PR_TRUE;
  aSheet->GetComplete(complete);
  NS_ASSERTION(complete, "Incomplete sheet being removed from style set");
#endif
  mSheets[aType].RemoveObject(aSheet);
  if (!mBatching)
    return GatherRuleProcessors(aType);

  mDirty |= 1 << aType;
  return NS_OK;
}

nsresult
nsStyleSet::ReplaceSheets(sheetType aType,
                          const nsCOMArray<nsIStyleSheet> &aNewSheets)
{
  mSheets[aType].Clear();
  if (!mSheets[aType].AppendObjects(aNewSheets))
    return NS_ERROR_OUT_OF_MEMORY;

  if (!mBatching)
    return GatherRuleProcessors(aType);

  mDirty |= 1 << aType;
  return NS_OK;
}

// -------- Doc Sheets

nsresult
nsStyleSet::AddDocStyleSheet(nsIStyleSheet* aSheet, nsIDocument* aDocument)
{
  NS_PRECONDITION(aSheet && aDocument, "null arg");
  CHECK_APPLICABLE;

  nsCOMArray<nsIStyleSheet>& docSheets = mSheets[eDocSheet];

  docSheets.RemoveObject(aSheet);
  // lowest index last
  PRInt32 newDocIndex = aDocument->GetIndexOfStyleSheet(aSheet);
  PRInt32 count = docSheets.Count();
  for (PRInt32 index = 0; index < count; index++) {
    nsIStyleSheet* sheet = docSheets.ObjectAt(index);
    PRInt32 sheetDocIndex = aDocument->GetIndexOfStyleSheet(sheet);
    if (sheetDocIndex < newDocIndex) {
      if (!docSheets.InsertObjectAt(aSheet, index))
        return NS_ERROR_OUT_OF_MEMORY;

      index = count; // break loop
    }
  }
  if (docSheets.Count() == count) { // didn't insert it
    if (!docSheets.AppendObject(aSheet))
      return NS_ERROR_OUT_OF_MEMORY;
  }
  if (!mBatching)
    return GatherRuleProcessors(eDocSheet);

  mDirty |= 1 << eDocSheet;
  return NS_OK;
}

#undef CHECK_APPLICABLE

// Batching
void
nsStyleSet::BeginUpdate()
{
  ++mBatching;
}

nsresult
nsStyleSet::EndUpdate()
{
  NS_ASSERTION(mBatching > 0, "Unbalanced EndUpdate");
  if (--mBatching) {
    // We're not completely done yet.
    return NS_OK;
  }

  for (int i = 0; i < eSheetTypeCount; ++i) {
    if (mDirty & (1 << i)) {
      nsresult rv = GatherRuleProcessors(i);
      NS_ENSURE_SUCCESS(rv, rv);
    }
  }

  mDirty = 0;
  return NS_OK;
}

void
nsStyleSet::EnableQuirkStyleSheet(PRBool aEnable)
{
  if (!mQuirkStyleSheet) {
    // first find the quirk sheet:
    // - run through all of the agent sheets and check for a CSSStyleSheet that
    //   has the URL we want
    PRInt32 nSheets = mSheets[eAgentSheet].Count();
    for (PRInt32 i = 0; i < nSheets; ++i) {
      nsIStyleSheet *sheet = mSheets[eAgentSheet].ObjectAt(i);
      NS_ASSERTION(sheet, "mAgentSheets should not contain null sheets");

      nsICSSStyleSheet *cssSheet = NS_STATIC_CAST(nsICSSStyleSheet*, sheet);
      NS_ASSERTION(nsCOMPtr<nsICSSStyleSheet>(do_QueryInterface(sheet)) == cssSheet,
                   "Agent sheet must be a CSSStyleSheet");

      nsCOMPtr<nsIStyleSheet> quirkSheet;
      PRBool bHasSheet = PR_FALSE;
      if (NS_SUCCEEDED(cssSheet->ContainsStyleSheet(gQuirkURI, bHasSheet, 
                                                    getter_AddRefs(quirkSheet))) 
          && bHasSheet) {
        NS_ASSERTION(quirkSheet, "QuirkSheet must be set: ContainsStyleSheet is hosed");
        // cache the sheet for faster lookup next time
        mQuirkStyleSheet = quirkSheet;
        // only one quirk style sheet can exist, so stop looking
        break;
      }
    }
  }
  NS_ASSERTION(mQuirkStyleSheet, "no quirk stylesheet");
  if (mQuirkStyleSheet) {
#ifdef DEBUG_dbaron_off // XXX Make this |DEBUG| once it stops firing.
    PRInt32 count = mRuleProcessors[eAgentSheet].Count()
    PRBool applicableNow;
    mQuirkStyleSheet->GetApplicable(applicableNow);
    NS_ASSERTION(count == 0 || aEnable == applicableNow,
                 "enabling/disabling quirk stylesheet too late or incomplete quirk stylesheet");
    if (count != 0 && aEnable == applicableNow)
      printf("WARNING: We set the quirks mode too many times.\n"); // we do!
#endif
    mQuirkStyleSheet->SetEnabled(aEnable);
  }
}

struct RulesMatchingData : public ElementRuleProcessorData {
  RulesMatchingData(nsIPresContext* aPresContext,
                    nsIAtom* aMedium,
                    nsIContent* aContent,
                    nsRuleWalker* aRuleWalker)
    : ElementRuleProcessorData(aPresContext, aContent, aRuleWalker),
      mMedium(aMedium)
  {
  }
  nsIAtom*          mMedium;
};

static PRBool
EnumRulesMatching(nsIStyleRuleProcessor* aProcessor, void* aData)
{
  RulesMatchingData* data = (RulesMatchingData*)aData;

  aProcessor->RulesMatching(data, data->mMedium);
  return PR_TRUE;
}

/**
 * |GetContext| implements sharing of style contexts (not just the data
 * on the rule nodes) between siblings and cousins of the same
 * generation.  (It works for cousins of the same generation since
 * |aParentContext| could itself be a shared context.)
 */
already_AddRefed<nsStyleContext>
nsStyleSet::GetContext(nsIPresContext* aPresContext, 
                       nsStyleContext* aParentContext, 
                       nsIAtom* aPseudoTag)
{
  nsStyleContext* result = nsnull;
  nsRuleNode* ruleNode = mRuleWalker->GetCurrentNode();
      
  if (aParentContext)
    result = aParentContext->FindChildWithRules(aPseudoTag, ruleNode).get();

#ifdef NOISY_DEBUG
  if (result)
    fprintf(stdout, "--- SharedSC %d ---\n", ++gSharedCount);
  else
    fprintf(stdout, "+++ NewSC %d +++\n", ++gNewCount);
#endif

  if (!result) {
    result = NS_NewStyleContext(aParentContext, aPseudoTag, ruleNode,
                                aPresContext).get();
    if (!aParentContext && result)
      mRoots.AppendElement(result);
  }

  return result;
}

void
nsStyleSet::AddImportantRules(nsRuleNode* aCurrLevelNode,
                              nsRuleNode* aLastPrevLevelNode)
{
  if (!aCurrLevelNode || aCurrLevelNode == aLastPrevLevelNode)
    return;

  AddImportantRules(aCurrLevelNode->GetParent(), aLastPrevLevelNode);

  nsIStyleRule *rule = aCurrLevelNode->GetRule();
  nsCOMPtr<nsICSSStyleRule> cssRule(do_QueryInterface(rule));
  if (cssRule) {
    nsCOMPtr<nsIStyleRule> impRule = cssRule->GetImportantRule();
    if (impRule)
      mRuleWalker->Forward(impRule);
  }
}

// Enumerate the rules in a way that cares about the order of the rules.
void
nsStyleSet::FileRules(nsIStyleRuleProcessor::EnumFunc aCollectorFunc, 
                      RuleProcessorData* aData)
{

  // Cascading order:
  // [least important]
  //  1. UA normal rules                    = Agent     normal
  //  2. User normal rules                  = User      normal
  //  3. Author normal rules                = Document  normal
  //  4. Override normal rules              = Override  normal
  //  5. Author !important rules            = Document !important
  //  6. Override !important rules          = Override !important
  //  7. User !important rules              = User     !important
  //  8. UA !important rules                = Agent    !important
  // [most important]

  nsRuleNode* lastAgentRN = nsnull;
  if (mRuleProcessors[eAgentSheet].Count()) {
    mRuleProcessors[eAgentSheet].EnumerateForwards(aCollectorFunc, aData);
    lastAgentRN = mRuleWalker->GetCurrentNode();
  }

  nsRuleNode* lastUserRN = lastAgentRN;
  if (mRuleProcessors[eUserSheet].Count()) {
    mRuleProcessors[eUserSheet].EnumerateForwards(aCollectorFunc, aData);
    lastUserRN = mRuleWalker->GetCurrentNode();
  }

  nsRuleNode* lastDocRN = lastUserRN;
  PRBool useRuleProcessors = PR_TRUE;
  if (mStyleRuleSupplier) {
    // We can supply additional document-level sheets that should be walked.
    mStyleRuleSupplier->WalkRules(this, aCollectorFunc, aData);
    mStyleRuleSupplier->UseDocumentRules(aData->mContent, &useRuleProcessors);
  }
  if (useRuleProcessors && mRuleProcessors[eDocSheet].Count()) {
    mRuleProcessors[eDocSheet].EnumerateForwards(aCollectorFunc, aData);
  }
  lastDocRN = mRuleWalker->GetCurrentNode();

  nsRuleNode* lastOvrRN = lastDocRN;
  if (mRuleProcessors[eOverrideSheet].Count()) {
    mRuleProcessors[eOverrideSheet].EnumerateForwards(aCollectorFunc, aData);
    lastOvrRN = mRuleWalker->GetCurrentNode();
  }

  AddImportantRules(lastDocRN, lastUserRN);   //doc
  AddImportantRules(lastOvrRN, lastDocRN);    //ovr
  AddImportantRules(lastUserRN, lastAgentRN); //user
  AddImportantRules(lastAgentRN, nsnull);     //agent

}

// Enumerate all the rules in a way that doesn't care about the order
// of the rules and break out if the enumeration is halted.
void
nsStyleSet::WalkRuleProcessors(nsIStyleRuleProcessor::EnumFunc aFunc,
                               RuleProcessorData* aData)
{
  // Walk the agent rules first.
  if (mRuleProcessors[eAgentSheet].Count() &&
      !mRuleProcessors[eAgentSheet].EnumerateForwards(aFunc, aData))
    return;

  // Walk the user rules next.
  if (mRuleProcessors[eUserSheet].Count() &&
      !mRuleProcessors[eUserSheet].EnumerateForwards(aFunc, aData))
    return;

  PRBool useRuleProcessors = PR_TRUE;
  if (mStyleRuleSupplier) {
    // We can supply additional document-level sheets that should be walked.
    // XXX We ignore whether the enumerator wants to halt here!
    mStyleRuleSupplier->WalkRules(this, aFunc, aData);
    mStyleRuleSupplier->UseDocumentRules(aData->mContent, &useRuleProcessors);
  }

  // Now walk the doc rules.
  if (mRuleProcessors[eDocSheet].Count() && useRuleProcessors &&
      !mRuleProcessors[eDocSheet].EnumerateForwards(aFunc, aData))
    return;
  
  // Walk the override rules last.
  if (mRuleProcessors[eOverrideSheet].Count())
    mRuleProcessors[eOverrideSheet].EnumerateForwards(aFunc, aData);
}

PRBool nsStyleSet::BuildDefaultStyleData(nsIPresContext* aPresContext)
{
  NS_ASSERTION(!mDefaultStyleData.mResetData &&
               !mDefaultStyleData.mInheritedData,
               "leaking default style data");
  mDefaultStyleData.mResetData = new (aPresContext) nsResetStyleData;
  if (!mDefaultStyleData.mResetData)
    return PR_FALSE;
  mDefaultStyleData.mInheritedData = new (aPresContext) nsInheritedStyleData;
  if (!mDefaultStyleData.mInheritedData)
    return PR_FALSE;

#define SSARG_PRESCONTEXT aPresContext

#define CREATE_DATA(name, type, args) \
  if (!(mDefaultStyleData.m##type##Data->m##name##Data = \
          new (aPresContext) nsStyle##name args)) \
    return PR_FALSE;

#define STYLE_STRUCT_INHERITED(name, checkdata_cb, ctor_args) \
  CREATE_DATA(name, Inherited, ctor_args)
#define STYLE_STRUCT_RESET(name, checkdata_cb, ctor_args) \
  CREATE_DATA(name, Reset, ctor_args)

#include "nsStyleStructList.h"

#undef STYLE_STRUCT_INHERITED
#undef STYLE_STRUCT_RESET
#undef SSARG_PRESCONTEXT

  return PR_TRUE;
}

already_AddRefed<nsStyleContext>
nsStyleSet::ResolveStyleFor(nsIPresContext* aPresContext,
                            nsIContent* aContent,
                            nsStyleContext* aParentContext)
{
  nsStyleContext*  result = nsnull;

  NS_ASSERTION(aContent, "must have content");
  NS_ASSERTION(aPresContext, "must have pres context");
  NS_ASSERTION(aContent->IsContentOfType(nsIContent::eELEMENT),
               "content must be element");

  if (aContent && aPresContext) {
    if (mRuleProcessors[eAgentSheet].Count() ||
        mRuleProcessors[eUserSheet].Count()  ||
        mRuleProcessors[eDocSheet].Count()   ||
        mRuleProcessors[eOverrideSheet].Count()) {
      nsCOMPtr<nsIAtom> medium;
      aPresContext->GetMedium(getter_AddRefs(medium));
      RulesMatchingData data(aPresContext, medium, aContent, mRuleWalker);
      FileRules(EnumRulesMatching, &data);
      result = GetContext(aPresContext, aParentContext, nsnull).get();

      // Now reset the walker back to the root of the tree.
      mRuleWalker->Reset();
    }
  }

  return result;
}

already_AddRefed<nsStyleContext>
nsStyleSet::ResolveStyleForNonElement(nsIPresContext* aPresContext,
                                      nsStyleContext* aParentContext)
{
  nsStyleContext* result = nsnull;

  NS_ASSERTION(aPresContext, "must have pres context");

  if (aPresContext) {
    if (mRuleProcessors[eAgentSheet].Count() ||
        mRuleProcessors[eUserSheet].Count()  ||
        mRuleProcessors[eDocSheet].Count()   ||
        mRuleProcessors[eOverrideSheet].Count()) {
      result = GetContext(aPresContext, aParentContext,
                          nsCSSAnonBoxes::mozNonElement).get();
      NS_ASSERTION(mRuleWalker->AtRoot(), "rule walker must be at root");
    }
  }

  return result;
}


struct PseudoRulesMatchingData : public PseudoRuleProcessorData {
  PseudoRulesMatchingData(nsIPresContext* aPresContext,
                          nsIAtom* aMedium,
                          nsIContent* aParentContent,
                          nsIAtom* aPseudoTag,
                          nsICSSPseudoComparator* aComparator,
                          nsRuleWalker* aRuleWalker)
    : PseudoRuleProcessorData(aPresContext, aParentContent, aPseudoTag,
                              aComparator, aRuleWalker),
      mMedium(aMedium)
  {
  }
  nsIAtom*                mMedium;
};

static PRBool
EnumPseudoRulesMatching(nsIStyleRuleProcessor* aProcessor, void* aData)
{
  PseudoRulesMatchingData* data = (PseudoRulesMatchingData*)aData;

  aProcessor->RulesMatching(data, data->mMedium);
  return PR_TRUE;
}

already_AddRefed<nsStyleContext>
nsStyleSet::ResolvePseudoStyleFor(nsIPresContext* aPresContext,
                                  nsIContent* aParentContent,
                                  nsIAtom* aPseudoTag,
                                  nsStyleContext* aParentContext,
                                  nsICSSPseudoComparator* aComparator)
{
  nsStyleContext*  result = nsnull;

  NS_ASSERTION(aPseudoTag, "must have pseudo tag");
  NS_ASSERTION(aPresContext, "must have pres context");
  NS_ASSERTION(!aParentContent ||
               aParentContent->IsContentOfType(nsIContent::eELEMENT),
               "content (if non-null) must be element");

  if (aPseudoTag && aPresContext) {
    if (mRuleProcessors[eAgentSheet].Count() ||
        mRuleProcessors[eUserSheet].Count()  ||
        mRuleProcessors[eDocSheet].Count()   ||
        mRuleProcessors[eOverrideSheet].Count()) {
      nsCOMPtr<nsIAtom> medium;
      aPresContext->GetMedium(getter_AddRefs(medium));
      PseudoRulesMatchingData data(aPresContext, medium, aParentContent, 
                                   aPseudoTag, aComparator, mRuleWalker);
      FileRules(EnumPseudoRulesMatching, &data);

      result = GetContext(aPresContext, aParentContext, aPseudoTag).get();

      // Now reset the walker back to the root of the tree.
      mRuleWalker->Reset();
    }
  }

  return result;
}

already_AddRefed<nsStyleContext>
nsStyleSet::ProbePseudoStyleFor(nsIPresContext* aPresContext,
                                  nsIContent* aParentContent,
                                  nsIAtom* aPseudoTag,
                                  nsStyleContext* aParentContext)
{
  nsStyleContext*  result = nsnull;

  NS_ASSERTION(aPseudoTag, "must have pseudo tag");
  NS_ASSERTION(aPresContext, "must have pres context");
  NS_ASSERTION(!aParentContent ||
               aParentContent->IsContentOfType(nsIContent::eELEMENT),
               "content (if non-null) must be element");

  if (aPseudoTag && aPresContext) {
    if (mRuleProcessors[eAgentSheet].Count() ||
        mRuleProcessors[eUserSheet].Count()  ||
        mRuleProcessors[eDocSheet].Count()   ||
        mRuleProcessors[eOverrideSheet].Count()) {
      nsCOMPtr<nsIAtom> medium;
      aPresContext->GetMedium(getter_AddRefs(medium));
      PseudoRulesMatchingData data(aPresContext, medium, aParentContent, 
                                   aPseudoTag, nsnull, mRuleWalker);
      FileRules(EnumPseudoRulesMatching, &data);

      if (!mRuleWalker->AtRoot())
        result = GetContext(aPresContext, aParentContext, aPseudoTag).get();

      // Now reset the walker back to the root of the tree.
      mRuleWalker->Reset();
    }
  }

  // For :before and :after pseudo-elements, having display: none or no
  // 'content' property is equivalent to not having the pseudo-element
  // at all.
  if (result &&
      (aPseudoTag == nsCSSPseudoElements::before ||
       aPseudoTag == nsCSSPseudoElements::after)) {
    const nsStyleDisplay *display = result->GetStyleDisplay();
    const nsStyleContent *content = result->GetStyleContent();
    // XXXldb What is contentCount for |content: ""|?
    if (display->mDisplay == NS_STYLE_DISPLAY_NONE ||
        content->ContentCount() == 0) {
      result->Release();
      result = nsnull;
    }
  }
  
  return result;
}

void
nsStyleSet::BeginShutdown(nsIPresContext* aPresContext)
{
  mInShutdown = 1;
  mRoots.Clear(); // no longer valid, since we won't keep it up to date
}

void
nsStyleSet::Shutdown(nsIPresContext* aPresContext)
{
  delete mRuleWalker;
  mRuleWalker = nsnull;

  mRuleTree->Destroy();
  mRuleTree = nsnull;

  mDefaultStyleData.Destroy(0, aPresContext);
}

static const PRInt32 kGCInterval = 1000;

void
nsStyleSet::NotifyStyleContextDestroyed(nsIPresContext* aPresContext,
                                        nsStyleContext* aStyleContext)
{
  if (mInShutdown)
    return;

  if (!aStyleContext->GetParent()) {
    mRoots.RemoveElement(aStyleContext);
  }

  if (++mDestroyedCount == kGCInterval) {
    mDestroyedCount = 0;

    // Mark the style context tree by marking all roots, which will mark
    // all descendants.  This will reach style contexts in the
    // undisplayed map and "additional style contexts" since they are
    // descendants of the root.
    for (PRInt32 i = mRoots.Count() - 1; i >= 0; --i) {
      NS_STATIC_CAST(nsStyleContext*,mRoots[i])->Mark();
    }

    // Sweep the rule tree.
    NS_ASSERTION(mRuleWalker->AtRoot(), "Rule walker should be at root");
#ifdef DEBUG
    PRBool deleted =
#endif
      mRuleTree->Sweep();

    NS_ASSERTION(!deleted, "Root node must not be gc'd");
  }
}

void
nsStyleSet::ClearStyleData(nsIPresContext* aPresContext)
{
  mRuleTree->ClearStyleData();

  for (PRInt32 i = mRoots.Count() - 1; i >= 0; --i) {
    NS_STATIC_CAST(nsStyleContext*,mRoots[i])->ClearStyleData(aPresContext);
  }
}

already_AddRefed<nsStyleContext>
nsStyleSet::ReParentStyleContext(nsIPresContext* aPresContext,
                                 nsStyleContext* aStyleContext, 
                                 nsStyleContext* aNewParentContext)
{
  NS_ASSERTION(aPresContext, "must have pres context");
  NS_ASSERTION(aStyleContext, "must have style context");

  if (aPresContext && aStyleContext) {
    if (aStyleContext->GetParent() == aNewParentContext) {
      aStyleContext->AddRef();
      return aStyleContext;
    }
    else {  // really a new parent
      nsIAtom* pseudoTag = aStyleContext->GetPseudoType();

      nsRuleNode* ruleNode = aStyleContext->GetRuleNode();
      mRuleWalker->SetCurrentNode(ruleNode);

      already_AddRefed<nsStyleContext> result =
          GetContext(aPresContext, aNewParentContext, pseudoTag);
      mRuleWalker->Reset();
      return result;
    }
  }
  return nsnull;
}

struct StatefulData : public StateRuleProcessorData {
  StatefulData(nsIPresContext* aPresContext, nsIAtom* aMedium,
               nsIContent* aContent, PRInt32 aStateMask)
    : StateRuleProcessorData(aPresContext, aContent, aStateMask),
      mMedium(aMedium),
      mHasStyle(PR_FALSE)
  {}
  nsIAtom*        mMedium;
  PRBool          mHasStyle;
}; 

static PRBool SheetHasStatefulStyle(nsIStyleRuleProcessor* aProcessor,
                                    void *aData)
{
  StatefulData* data = (StatefulData*)aData;
  PRBool hasStyle;
  aProcessor->HasStateDependentStyle(data, data->mMedium, &hasStyle);
  if (hasStyle) {
    data->mHasStyle = PR_TRUE;
    // Stop iteration.  Note that nsStyleSet::WalkRuleProcessors uses
    // this to stop its own iteration in some cases, but not all (the
    // style rule supplier case).  Since this optimization is only for
    // the case where we have a lot more work to do, it's not worth the
    // code needed to make the stopping perfect.
    return PR_FALSE;
  }
  return PR_TRUE; // continue
}

// Test if style is dependent on content state
PRBool
nsStyleSet::HasStateDependentStyle(nsIPresContext* aPresContext,
                                   nsIContent*     aContent,
                                   PRInt32         aStateMask)
{
  PRBool result = PR_FALSE;

  if (aContent->IsContentOfType(nsIContent::eELEMENT) &&
      (mRuleProcessors[eAgentSheet].Count() ||
       mRuleProcessors[eUserSheet].Count()  ||
       mRuleProcessors[eDocSheet].Count()   ||
       mRuleProcessors[eOverrideSheet].Count())) {  
    nsCOMPtr<nsIAtom> medium;
    aPresContext->GetMedium(getter_AddRefs(medium));
    StatefulData data(aPresContext, medium, aContent, aStateMask);
    WalkRuleProcessors(SheetHasStatefulStyle, &data);
    result = data.mHasStyle;
  }

  return result;
}

struct AttributeData : public AttributeRuleProcessorData {
  AttributeData(nsIPresContext* aPresContext, nsIAtom* aMedium,
               nsIContent* aContent, nsIAtom* aAttribute, PRInt32 aModType)
    : AttributeRuleProcessorData(aPresContext, aContent, aAttribute, aModType),
      mMedium(aMedium),
      mHasStyle(PR_FALSE)
  {}
  nsIAtom*        mMedium;
  PRBool          mHasStyle;
}; 

static PRBool
SheetHasAttributeStyle(nsIStyleRuleProcessor* aProcessor, void *aData)
{
  AttributeData* data = (AttributeData*)aData;
  PRBool hasStyle;
  aProcessor->HasAttributeDependentStyle(data, data->mMedium, &hasStyle);
  if (hasStyle) {
    data->mHasStyle = PR_TRUE;
    // Stop iteration.  Note that nsStyleSet::WalkRuleProcessors uses
    // this to stop its own iteration in some cases, but not all (the
    // style rule supplier case).  Since this optimization is only for
    // the case where we have a lot more work to do, it's not worth the
    // code needed to make the stopping perfect.
    return PR_FALSE;
  }
  return PR_TRUE; // continue
}

// Test if style is dependent on content state
PRBool
nsStyleSet::HasAttributeDependentStyle(nsIPresContext* aPresContext,
                                       nsIContent*     aContent,
                                       nsIAtom*        aAttribute,
                                       PRInt32         aModType)
{
  PRBool result = PR_FALSE;

  if (aContent->IsContentOfType(nsIContent::eELEMENT) &&
      (mRuleProcessors[eAgentSheet].Count() ||
       mRuleProcessors[eUserSheet].Count()  ||
       mRuleProcessors[eDocSheet].Count()   ||
       mRuleProcessors[eOverrideSheet].Count())) {  
    nsCOMPtr<nsIAtom> medium;
    aPresContext->GetMedium(getter_AddRefs(medium));
    AttributeData data(aPresContext, medium, aContent, aAttribute, aModType);
    WalkRuleProcessors(SheetHasAttributeStyle, &data);
    result = data.mHasStyle;
  }

  return result;
}