Issue #2862 - Split the css lowering functionality out to a separate file for easier maintenance

layout/style/CSSNestingLowerer.cpp

@@ -0,0 +1,961 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "CSSNestingLowerer.h"
+
+#include "mozilla/Assertions.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace css {
+
+namespace {
+
+class CSSNestingLowerer final
+{
+  using SelectorList = nsTArray<nsString>;
+
+public:
+  explicit CSSNestingLowerer(const nsAString& aInput)
+    : mInput(aInput)
+    , mPos(0)
+    , mSawNesting(false)
+  {
+  }
+
+  bool Lower(nsAString& aOutput)
+  {
+    nsAutoString lowered;
+    if (!ProcessStylesheet(lowered, false)) {
+      return false;
+    }
+
+    SkipWhitespaceAndComments();
+    if (mPos != mInput.Length() || !mSawNesting) {
+      return false;
+    }
+
+    aOutput.Assign(lowered);
+    return true;
+  }
+
+private:
+  static constexpr auto kCSSWhitespace = " \t\r\n\f";
+
+  static bool
+  IsCSSWhitespace(char16_t aChar)
+  {
+    return aChar == ' ' || aChar == '\t' || aChar == '\r' ||
+           aChar == '\n' || aChar == '\f';
+  }
+
+  bool
+  AtEnd() const
+  {
+    return mPos >= mInput.Length();
+  }
+
+  char16_t
+  Peek() const
+  {
+    MOZ_ASSERT(!AtEnd(), "cannot peek past end");
+    return mInput.CharAt(mPos);
+  }
+
+  bool
+  StartsWithComment() const
+  {
+    return mPos + 1 < mInput.Length() &&
+           mInput.CharAt(mPos) == '/' &&
+           mInput.CharAt(mPos + 1) == '*';
+  }
+
+  bool
+  SkipComment()
+  {
+    MOZ_ASSERT(StartsWithComment(), "expected comment");
+
+    mPos += 2;
+    while (mPos + 1 < mInput.Length()) {
+      if (mInput.CharAt(mPos) == '*' && mInput.CharAt(mPos + 1) == '/') {
+        mPos += 2;
+        return true;
+      }
+      ++mPos;
+    }
+
+    return false;
+  }
+
+  void
+  SkipWhitespaceAndComments()
+  {
+    while (!AtEnd()) {
+      if (IsCSSWhitespace(Peek())) {
+        ++mPos;
+        continue;
+      }
+      if (StartsWithComment()) {
+        if (!SkipComment()) {
+          mPos = mInput.Length();
+          return;
+        }
+        continue;
+      }
+      break;
+    }
+  }
+
+  bool
+  SkipString(char16_t aQuote)
+  {
+    MOZ_ASSERT(!AtEnd() && Peek() == aQuote, "expected string start");
+
+    ++mPos;
+    while (!AtEnd()) {
+      char16_t c = Peek();
+      ++mPos;
+      if (c == aQuote) {
+        return true;
+      }
+      if (c == '\\' && !AtEnd()) {
+        ++mPos;
+        continue;
+      }
+      if (c == '\n' || c == '\r' || c == '\f') {
+        return false;
+      }
+    }
+
+    return false;
+  }
+
+  static void
+  TrimWhitespace(nsAString& aText)
+  {
+    uint32_t start = 0;
+    uint32_t end = aText.Length();
+
+    while (start < end && IsCSSWhitespace(aText.CharAt(start))) {
+      ++start;
+    }
+    while (end > start && IsCSSWhitespace(aText.CharAt(end - 1))) {
+      --end;
+    }
+
+    if (start == 0 && end == aText.Length()) {
+      return;
+    }
+
+    aText.Assign(Substring(aText, start, end - start));
+  }
+
+  bool
+  SplitSelectorList(const nsAString& aSelectorText, SelectorList& aSelectors)
+  {
+    uint32_t itemStart = 0;
+    int32_t parenDepth = 0;
+    int32_t bracketDepth = 0;
+    bool inComment = false;
+    char16_t stringQuote = 0;
+
+    for (uint32_t i = 0; i < aSelectorText.Length(); ++i) {
+      char16_t c = aSelectorText.CharAt(i);
+
+      if (inComment) {
+        if (c == '*' && i + 1 < aSelectorText.Length() &&
+            aSelectorText.CharAt(i + 1) == '/') {
+          inComment = false;
+          ++i;
+        }
+        continue;
+      }
+
+      if (stringQuote) {
+        if (c == '\\') {
+          ++i;
+          continue;
+        }
+        if (c == stringQuote) {
+          stringQuote = 0;
+        }
+        continue;
+      }
+
+      if (c == '/' && i + 1 < aSelectorText.Length() &&
+          aSelectorText.CharAt(i + 1) == '*') {
+        inComment = true;
+        ++i;
+        continue;
+      }
+
+      if (c == '"' || c == '\'') {
+        stringQuote = c;
+        continue;
+      }
+
+      if (c == '(') {
+        ++parenDepth;
+        continue;
+      }
+      if (c == ')' && parenDepth > 0) {
+        --parenDepth;
+        continue;
+      }
+      if (c == '[') {
+        ++bracketDepth;
+        continue;
+      }
+      if (c == ']' && bracketDepth > 0) {
+        --bracketDepth;
+        continue;
+      }
+
+      if (c == ',' && parenDepth == 0 && bracketDepth == 0) {
+        nsAutoString selector;
+        selector.Assign(Substring(aSelectorText, itemStart, i - itemStart));
+        TrimWhitespace(selector);
+        if (!selector.IsEmpty()) {
+          aSelectors.AppendElement(selector);
+        }
+        itemStart = i + 1;
+      }
+    }
+
+    nsAutoString selector;
+    selector.Assign(Substring(aSelectorText, itemStart));
+    TrimWhitespace(selector);
+    if (!selector.IsEmpty()) {
+      aSelectors.AppendElement(selector);
+    }
+
+    return !aSelectors.IsEmpty();
+  }
+
+  bool
+  SelectorHasAmpersand(const nsAString& aSelector) const
+  {
+    bool inComment = false;
+    char16_t stringQuote = 0;
+
+    for (uint32_t i = 0; i < aSelector.Length(); ++i) {
+      char16_t c = aSelector.CharAt(i);
+
+      if (inComment) {
+        if (c == '*' && i + 1 < aSelector.Length() &&
+            aSelector.CharAt(i + 1) == '/') {
+          inComment = false;
+          ++i;
+        }
+        continue;
+      }
+
+      if (stringQuote) {
+        if (c == '\\') {
+          ++i;
+          continue;
+        }
+        if (c == stringQuote) {
+          stringQuote = 0;
+        }
+        continue;
+      }
+
+      if (c == '/' && i + 1 < aSelector.Length() &&
+          aSelector.CharAt(i + 1) == '*') {
+        inComment = true;
+        ++i;
+        continue;
+      }
+
+      if (c == '"' || c == '\'') {
+        stringQuote = c;
+        continue;
+      }
+
+      if (c == '&') {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  void
+  ReplaceAmpersands(const nsAString& aSelector,
+                    const nsAString& aParent,
+                    nsAString& aOutput) const
+  {
+    bool inComment = false;
+    char16_t stringQuote = 0;
+
+    for (uint32_t i = 0; i < aSelector.Length(); ++i) {
+      char16_t c = aSelector.CharAt(i);
+
+      if (inComment) {
+        aOutput.Append(c);
+        if (c == '*' && i + 1 < aSelector.Length() &&
+            aSelector.CharAt(i + 1) == '/') {
+          aOutput.Append('/');
+          inComment = false;
+          ++i;
+        }
+        continue;
+      }
+
+      if (stringQuote) {
+        aOutput.Append(c);
+        if (c == '\\' && i + 1 < aSelector.Length()) {
+          aOutput.Append(aSelector.CharAt(i + 1));
+          ++i;
+          continue;
+        }
+        if (c == stringQuote) {
+          stringQuote = 0;
+        }
+        continue;
+      }
+
+      if (c == '/' && i + 1 < aSelector.Length() &&
+          aSelector.CharAt(i + 1) == '*') {
+        aOutput.AppendLiteral("/*");
+        inComment = true;
+        ++i;
+        continue;
+      }
+
+      if (c == '"' || c == '\'') {
+        aOutput.Append(c);
+        stringQuote = c;
+        continue;
+      }
+
+      if (c == '&') {
+        aOutput.Append(aParent);
+        continue;
+      }
+
+      aOutput.Append(c);
+    }
+  }
+
+  bool
+  ExpandNestedSelectors(const SelectorList& aParents,
+                        const nsAString& aNestedSelectorText,
+                        SelectorList& aSelectors)
+  {
+    SelectorList nestedSelectors;
+    if (!SplitSelectorList(aNestedSelectorText, nestedSelectors)) {
+      return false;
+    }
+
+    for (const nsString& nestedSelector : nestedSelectors) {
+      bool hasAmpersand = SelectorHasAmpersand(nestedSelector);
+      for (const nsString& parentSelector : aParents) {
+        nsAutoString combined;
+        if (hasAmpersand) {
+          ReplaceAmpersands(nestedSelector, parentSelector, combined);
+        } else {
+          combined.Assign(parentSelector);
+          if (!combined.IsEmpty()) {
+            combined.Append(' ');
+          }
+          combined.Append(nestedSelector);
+        }
+        TrimWhitespace(combined);
+        if (!combined.IsEmpty()) {
+          aSelectors.AppendElement(combined);
+        }
+      }
+    }
+
+    return !aSelectors.IsEmpty();
+  }
+
+  static void
+  AppendSelectors(const SelectorList& aSelectors, nsAString& aOutput)
+  {
+    for (uint32_t i = 0; i < aSelectors.Length(); ++i) {
+      if (i) {
+        aOutput.AppendLiteral(", ");
+      }
+      aOutput.Append(aSelectors[i]);
+    }
+  }
+
+  static bool
+  StartsNestedSelector(char16_t aChar)
+  {
+    switch (aChar) {
+      case '.':
+      case '#':
+      case '[':
+      case ':':
+      case '&':
+      case '>':
+      case '+':
+      case '~':
+      case '*':
+        return true;
+      default:
+        return false;
+    }
+  }
+
+  static bool
+  StartsPotentialTypeSelector(char16_t aChar)
+  {
+    return (aChar >= 'a' && aChar <= 'z') ||
+           (aChar >= 'A' && aChar <= 'Z') ||
+           aChar == '_' ||
+           aChar == '\\' ||
+           aChar >= 0x80;
+  }
+
+  bool
+  LooksLikeTypeSelectorRule() const
+  {
+    if (AtEnd() || !StartsPotentialTypeSelector(Peek())) {
+      return false;
+    }
+
+    uint32_t pos = mPos;
+    int32_t parenDepth = 0;
+    int32_t bracketDepth = 0;
+    bool inComment = false;
+    char16_t stringQuote = 0;
+
+    while (pos < mInput.Length()) {
+      char16_t c = mInput.CharAt(pos);
+
+      if (inComment) {
+        if (c == '*' && pos + 1 < mInput.Length() &&
+            mInput.CharAt(pos + 1) == '/') {
+          inComment = false;
+          ++pos;
+        }
+        ++pos;
+        continue;
+      }
+
+      if (stringQuote) {
+        if (c == '\\' && pos + 1 < mInput.Length()) {
+          pos += 2;
+          continue;
+        }
+        if (c == stringQuote) {
+          stringQuote = 0;
+        }
+        ++pos;
+        continue;
+      }
+
+      if (c == '/' && pos + 1 < mInput.Length() &&
+          mInput.CharAt(pos + 1) == '*') {
+        inComment = true;
+        pos += 2;
+        continue;
+      }
+
+      if (c == '"' || c == '\'') {
+        stringQuote = c;
+        ++pos;
+        continue;
+      }
+
+      if (c == '(') {
+        ++parenDepth;
+        ++pos;
+        continue;
+      }
+      if (c == ')' && parenDepth > 0) {
+        --parenDepth;
+        ++pos;
+        continue;
+      }
+      if (c == '[') {
+        ++bracketDepth;
+        ++pos;
+        continue;
+      }
+      if (c == ']' && bracketDepth > 0) {
+        --bracketDepth;
+        ++pos;
+        continue;
+      }
+
+      if (parenDepth == 0 && bracketDepth == 0) {
+        if (c == '{') {
+          return true;
+        }
+        if (c == ';' || c == '}') {
+          return false;
+        }
+      }
+
+      ++pos;
+    }
+
+    return false;
+  }
+
+  static bool
+  IsAtRuleNameChar(char16_t aChar)
+  {
+    return (aChar >= 'a' && aChar <= 'z') ||
+           (aChar >= 'A' && aChar <= 'Z') ||
+           (aChar >= '0' && aChar <= '9') ||
+           aChar == '-';
+  }
+
+  static void
+  LowercaseASCII(nsACString& aText)
+  {
+    for (uint32_t i = 0; i < aText.Length(); ++i) {
+      char c = aText.CharAt(i);
+      if (c >= 'A' && c <= 'Z') {
+        aText.BeginWriting()[i] = c - 'A' + 'a';
+      }
+    }
+  }
+
+  static bool
+  ShouldProcessGroupRule(const nsACString& aName)
+  {
+    return aName.EqualsLiteral("media") ||
+           aName.EqualsLiteral("supports") ||
+           aName.EqualsLiteral("document") ||
+           aName.EqualsLiteral("layer");
+  }
+
+  void
+  FlushDeclarations(const SelectorList& aSelectors,
+                    nsAString& aDeclarations,
+                    nsAString& aOutput)
+  {
+    nsAutoString declarations;
+    declarations.Assign(aDeclarations);
+    TrimWhitespace(declarations);
+    aDeclarations.Truncate();
+
+    if (declarations.IsEmpty()) {
+      return;
+    }
+
+    AppendSelectors(aSelectors, aOutput);
+    aOutput.AppendLiteral(" { ");
+    aOutput.Append(declarations);
+    aOutput.AppendLiteral(" }\n");
+  }
+
+  bool
+  ReadRawBlockBody(nsAString& aBody)
+  {
+    uint32_t start = mPos;
+    int32_t depth = 0;
+
+    while (!AtEnd()) {
+      char16_t c = Peek();
+      if (c == '"' || c == '\'') {
+        if (!SkipString(c)) {
+          return false;
+        }
+        continue;
+      }
+      if (StartsWithComment()) {
+        if (!SkipComment()) {
+          return false;
+        }
+        continue;
+      }
+      if (c == '{') {
+        ++depth;
+        ++mPos;
+        continue;
+      }
+      if (c == '}') {
+        if (depth == 0) {
+          aBody.Assign(Substring(mInput, start, mPos - start));
+          ++mPos;
+          return true;
+        }
+        --depth;
+        ++mPos;
+        continue;
+      }
+      ++mPos;
+    }
+
+    return false;
+  }
+
+  bool
+  ReadQualifiedRulePrelude(nsAString& aPrelude)
+  {
+    uint32_t start = mPos;
+    int32_t parenDepth = 0;
+    int32_t bracketDepth = 0;
+
+    while (!AtEnd()) {
+      char16_t c = Peek();
+      if (c == '"' || c == '\'') {
+        if (!SkipString(c)) {
+          return false;
+        }
+        continue;
+      }
+      if (StartsWithComment()) {
+        if (!SkipComment()) {
+          return false;
+        }
+        continue;
+      }
+      if (c == '(') {
+        ++parenDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == ')' && parenDepth > 0) {
+        --parenDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == '[') {
+        ++bracketDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == ']' && bracketDepth > 0) {
+        --bracketDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == '{' && parenDepth == 0 && bracketDepth == 0) {
+        aPrelude.Assign(Substring(mInput, start, mPos - start));
+        TrimWhitespace(aPrelude);
+        ++mPos;
+        return !aPrelude.IsEmpty();
+      }
+      if ((c == ';' || c == '}') && parenDepth == 0 && bracketDepth == 0) {
+        return false;
+      }
+      ++mPos;
+    }
+
+    return false;
+  }
+
+  bool
+  ReadAtRulePrelude(nsAString& aPrelude, nsACString& aName, bool& aHasBlock)
+  {
+    MOZ_ASSERT(!AtEnd() && Peek() == '@', "expected at-rule");
+
+    uint32_t start = mPos;
+    ++mPos;
+    aName.Truncate();
+    while (!AtEnd() && IsAtRuleNameChar(Peek())) {
+      char16_t c = Peek();
+      aName.Append(char(c <= 0x7f ? c : '?'));
+      ++mPos;
+    }
+    LowercaseASCII(aName);
+
+    int32_t parenDepth = 0;
+    int32_t bracketDepth = 0;
+    while (!AtEnd()) {
+      char16_t c = Peek();
+      if (c == '"' || c == '\'') {
+        if (!SkipString(c)) {
+          return false;
+        }
+        continue;
+      }
+      if (StartsWithComment()) {
+        if (!SkipComment()) {
+          return false;
+        }
+        continue;
+      }
+      if (c == '(') {
+        ++parenDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == ')' && parenDepth > 0) {
+        --parenDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == '[') {
+        ++bracketDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == ']' && bracketDepth > 0) {
+        --bracketDepth;
+        ++mPos;
+        continue;
+      }
+      if (parenDepth == 0 && bracketDepth == 0) {
+        if (c == ';') {
+          aPrelude.Assign(Substring(mInput, start, mPos - start));
+          TrimWhitespace(aPrelude);
+          ++mPos;
+          aHasBlock = false;
+          return true;
+        }
+        if (c == '{') {
+          aPrelude.Assign(Substring(mInput, start, mPos - start));
+          TrimWhitespace(aPrelude);
+          ++mPos;
+          aHasBlock = true;
+          return true;
+        }
+      }
+      ++mPos;
+    }
+
+    return false;
+  }
+
+  bool
+  ConsumeDeclaration(nsAString& aDeclaration)
+  {
+    uint32_t start = mPos;
+    int32_t parenDepth = 0;
+    int32_t bracketDepth = 0;
+    int32_t braceDepth = 0;
+
+    while (!AtEnd()) {
+      char16_t c = Peek();
+      if (c == '"' || c == '\'') {
+        if (!SkipString(c)) {
+          return false;
+        }
+        continue;
+      }
+      if (StartsWithComment()) {
+        if (!SkipComment()) {
+          return false;
+        }
+        continue;
+      }
+      if (c == '(') {
+        ++parenDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == ')' && parenDepth > 0) {
+        --parenDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == '[') {
+        ++bracketDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == ']' && bracketDepth > 0) {
+        --bracketDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == '{') {
+        ++braceDepth;
+        ++mPos;
+        continue;
+      }
+      if (c == '}') {
+        if (braceDepth == 0 && parenDepth == 0 && bracketDepth == 0) {
+          break;
+        }
+        if (braceDepth > 0) {
+          --braceDepth;
+        }
+        ++mPos;
+        continue;
+      }
+      if (c == ';' && parenDepth == 0 && bracketDepth == 0 &&
+          braceDepth == 0) {
+        ++mPos;
+        break;
+      }
+      ++mPos;
+    }
+
+    aDeclaration.Assign(Substring(mInput, start, mPos - start));
+    TrimWhitespace(aDeclaration);
+    if (aDeclaration.IsEmpty()) {
+      return false;
+    }
+    if (aDeclaration.Last() != ';') {
+      aDeclaration.Append(';');
+    }
+    return true;
+  }
+
+  bool
+  ParseAtRule(nsAString& aOutput, const SelectorList* aParents)
+  {
+    nsAutoString prelude;
+    nsAutoCString name;
+    bool hasBlock = false;
+    if (!ReadAtRulePrelude(prelude, name, hasBlock)) {
+      return false;
+    }
+
+    if (!hasBlock) {
+      aOutput.Append(prelude);
+      aOutput.AppendLiteral(";\n");
+      return true;
+    }
+
+    if (!ShouldProcessGroupRule(name)) {
+      nsAutoString body;
+      if (!ReadRawBlockBody(body)) {
+        return false;
+      }
+      aOutput.Append(prelude);
+      aOutput.AppendLiteral(" {");
+      aOutput.Append(body);
+      aOutput.AppendLiteral("}\n");
+      return true;
+    }
+
+    nsAutoString inner;
+    if (aParents) {
+      mSawNesting = true;
+      if (!ProcessStyleContext(*aParents, inner)) {
+        return false;
+      }
+    } else {
+      if (!ProcessStylesheet(inner, true)) {
+        return false;
+      }
+    }
+
+    aOutput.Append(prelude);
+    aOutput.AppendLiteral(" {\n");
+    aOutput.Append(inner);
+    aOutput.AppendLiteral("}\n");
+    return true;
+  }
+
+  bool
+  ParseQualifiedRule(nsAString& aOutput, const SelectorList* aParents)
+  {
+    nsAutoString prelude;
+    if (!ReadQualifiedRulePrelude(prelude)) {
+      return false;
+    }
+
+    SelectorList selectors;
+    if (aParents) {
+      mSawNesting = true;
+      if (!ExpandNestedSelectors(*aParents, prelude, selectors)) {
+        return false;
+      }
+    } else if (!SplitSelectorList(prelude, selectors)) {
+      return false;
+    }
+
+    return ProcessStyleContext(selectors, aOutput);
+  }
+
+  bool
+  ProcessStyleContext(const SelectorList& aSelectors, nsAString& aOutput)
+  {
+    nsAutoString declarations;
+
+    while (!AtEnd()) {
+      SkipWhitespaceAndComments();
+      if (AtEnd()) {
+        return false;
+      }
+
+      char16_t c = Peek();
+      if (c == '}') {
+        ++mPos;
+        FlushDeclarations(aSelectors, declarations, aOutput);
+        return true;
+      }
+
+      if (c == '@') {
+        FlushDeclarations(aSelectors, declarations, aOutput);
+        if (!ParseAtRule(aOutput, &aSelectors)) {
+          return false;
+        }
+        continue;
+      }
+
+      if (StartsNestedSelector(c) || LooksLikeTypeSelectorRule()) {
+        FlushDeclarations(aSelectors, declarations, aOutput);
+        if (!ParseQualifiedRule(aOutput, &aSelectors)) {
+          return false;
+        }
+        continue;
+      }
+
+      nsAutoString declaration;
+      if (!ConsumeDeclaration(declaration)) {
+        return false;
+      }
+      if (!declarations.IsEmpty()) {
+        declarations.Append(' ');
+      }
+      declarations.Append(declaration);
+    }
+
+    return false;
+  }
+
+  bool
+  ProcessStylesheet(nsAString& aOutput, bool aStopAtBlockEnd)
+  {
+    while (!AtEnd()) {
+      SkipWhitespaceAndComments();
+      if (AtEnd()) {
+        return !aStopAtBlockEnd;
+      }
+
+      if (Peek() == '}') {
+        if (!aStopAtBlockEnd) {
+          return false;
+        }
+        ++mPos;
+        return true;
+      }
+
+      if (Peek() == '@') {
+        if (!ParseAtRule(aOutput, nullptr)) {
+          return false;
+        }
+      } else {
+        if (!ParseQualifiedRule(aOutput, nullptr)) {
+          return false;
+        }
+      }
+    }
+
+    return !aStopAtBlockEnd;
+  }
+
+  const nsAString& mInput;
+  uint32_t mPos;
+  bool mSawNesting;
+};
+
+} // namespace
+
+bool
+LowerBasicCSSNesting(const nsAString& aInput, nsAString& aOutput)
+{
+  CSSNestingLowerer lowerer(aInput);
+  return lowerer.Lower(aOutput);
+}
+
+} // namespace css
+} // namespace mozilla

layout/style/CSSNestingLowerer.h

@@ -0,0 +1,19 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef CSSNestingLowerer_h
+#define CSSNestingLowerer_h
+
+class nsAString;
+
+namespace mozilla {
+namespace css {
+
+bool LowerBasicCSSNesting(const nsAString& aInput, nsAString& aOutput);
+
+} // namespace css
+} // namespace mozilla
+
+#endif // CSSNestingLowerer_h

layout/style/moz.build

@@ -127,6 +127,7 @@ UNIFIED_SOURCES += [
     'CounterStyleManager.cpp',
     'CSS.cpp',
     'CSSLexer.cpp',
+    'CSSNestingLowerer.cpp',
     'CSSRuleList.cpp',
     'CSSStyleSheet.cpp',
     'CSSVariableDeclarations.cpp',

layout/style/nsCSSParser.cpp

@@ -18,6 +18,7 @@
 #include <regex>     // for std::regex and std::regex_match
 
 #include "nsCSSParser.h"
+#include "CSSNestingLowerer.h"
 #include "nsAlgorithm.h"
 #include "nsCSSProps.h"
 #include "nsCSSKeywords.h"
@@ -206,940 +207,6 @@ OKLabToSRGBColor(float aL, float aA, float aB, float aAlpha)
     nsStyleUtil::FloatToColorComponent(mozilla::clamped(aAlpha, 0.0f, 1.0f)));
 }
 
-class CSSNestingLowerer final
-{
-  using SelectorList = nsTArray<nsString>;
-
-public:
-  explicit CSSNestingLowerer(const nsAString& aInput)
-    : mInput(aInput)
-    , mPos(0)
-    , mSawNesting(false)
-  {
-  }
-
-  bool Lower(nsAString& aOutput)
-  {
-    nsAutoString lowered;
-    if (!ProcessStylesheet(lowered, false)) {
-      return false;
-    }
-
-    SkipWhitespaceAndComments();
-    if (mPos != mInput.Length() || !mSawNesting) {
-      return false;
-    }
-
-    aOutput.Assign(lowered);
-    return true;
-  }
-
-private:
-  static constexpr auto kCSSWhitespace = " \t\r\n\f";
-
-  static bool
-  IsCSSWhitespace(char16_t aChar)
-  {
-    return aChar == ' ' || aChar == '\t' || aChar == '\r' ||
-           aChar == '\n' || aChar == '\f';
-  }
-
-  bool
-  AtEnd() const
-  {
-    return mPos >= mInput.Length();
-  }
-
-  char16_t
-  Peek() const
-  {
-    MOZ_ASSERT(!AtEnd(), "cannot peek past end");
-    return mInput.CharAt(mPos);
-  }
-
-  bool
-  StartsWithComment() const
-  {
-    return mPos + 1 < mInput.Length() &&
-           mInput.CharAt(mPos) == '/' &&
-           mInput.CharAt(mPos + 1) == '*';
-  }
-
-  bool
-  SkipComment()
-  {
-    MOZ_ASSERT(StartsWithComment(), "expected comment");
-
-    mPos += 2;
-    while (mPos + 1 < mInput.Length()) {
-      if (mInput.CharAt(mPos) == '*' && mInput.CharAt(mPos + 1) == '/') {
-        mPos += 2;
-        return true;
-      }
-      ++mPos;
-    }
-
-    return false;
-  }
-
-  void
-  SkipWhitespaceAndComments()
-  {
-    while (!AtEnd()) {
-      if (IsCSSWhitespace(Peek())) {
-        ++mPos;
-        continue;
-      }
-      if (StartsWithComment()) {
-        if (!SkipComment()) {
-          mPos = mInput.Length();
-          return;
-        }
-        continue;
-      }
-      break;
-    }
-  }
-
-  bool
-  SkipString(char16_t aQuote)
-  {
-    MOZ_ASSERT(!AtEnd() && Peek() == aQuote, "expected string start");
-
-    ++mPos;
-    while (!AtEnd()) {
-      char16_t c = Peek();
-      ++mPos;
-      if (c == aQuote) {
-        return true;
-      }
-      if (c == '\\' && !AtEnd()) {
-        ++mPos;
-        continue;
-      }
-      if (c == '\n' || c == '\r' || c == '\f') {
-        return false;
-      }
-    }
-
-    return false;
-  }
-
-  static void
-  TrimWhitespace(nsAString& aText)
-  {
-    uint32_t start = 0;
-    uint32_t end = aText.Length();
-
-    while (start < end && IsCSSWhitespace(aText.CharAt(start))) {
-      ++start;
-    }
-    while (end > start && IsCSSWhitespace(aText.CharAt(end - 1))) {
-      --end;
-    }
-
-    if (start == 0 && end == aText.Length()) {
-      return;
-    }
-
-    aText.Assign(Substring(aText, start, end - start));
-  }
-
-  bool
-  SplitSelectorList(const nsAString& aSelectorText, SelectorList& aSelectors)
-  {
-    uint32_t itemStart = 0;
-    int32_t parenDepth = 0;
-    int32_t bracketDepth = 0;
-    bool inComment = false;
-    char16_t stringQuote = 0;
-
-    for (uint32_t i = 0; i < aSelectorText.Length(); ++i) {
-      char16_t c = aSelectorText.CharAt(i);
-
-      if (inComment) {
-        if (c == '*' && i + 1 < aSelectorText.Length() &&
-            aSelectorText.CharAt(i + 1) == '/') {
-          inComment = false;
-          ++i;
-        }
-        continue;
-      }
-
-      if (stringQuote) {
-        if (c == '\\') {
-          ++i;
-          continue;
-        }
-        if (c == stringQuote) {
-          stringQuote = 0;
-        }
-        continue;
-      }
-
-      if (c == '/' && i + 1 < aSelectorText.Length() &&
-          aSelectorText.CharAt(i + 1) == '*') {
-        inComment = true;
-        ++i;
-        continue;
-      }
-
-      if (c == '"' || c == '\'') {
-        stringQuote = c;
-        continue;
-      }
-
-      if (c == '(') {
-        ++parenDepth;
-        continue;
-      }
-      if (c == ')' && parenDepth > 0) {
-        --parenDepth;
-        continue;
-      }
-      if (c == '[') {
-        ++bracketDepth;
-        continue;
-      }
-      if (c == ']' && bracketDepth > 0) {
-        --bracketDepth;
-        continue;
-      }
-
-      if (c == ',' && parenDepth == 0 && bracketDepth == 0) {
-        nsAutoString selector;
-        selector.Assign(Substring(aSelectorText, itemStart, i - itemStart));
-        TrimWhitespace(selector);
-        if (!selector.IsEmpty()) {
-          aSelectors.AppendElement(selector);
-        }
-        itemStart = i + 1;
-      }
-    }
-
-    nsAutoString selector;
-    selector.Assign(Substring(aSelectorText, itemStart));
-    TrimWhitespace(selector);
-    if (!selector.IsEmpty()) {
-      aSelectors.AppendElement(selector);
-    }
-
-    return !aSelectors.IsEmpty();
-  }
-
-  bool
-  SelectorHasAmpersand(const nsAString& aSelector) const
-  {
-    bool inComment = false;
-    char16_t stringQuote = 0;
-
-    for (uint32_t i = 0; i < aSelector.Length(); ++i) {
-      char16_t c = aSelector.CharAt(i);
-
-      if (inComment) {
-        if (c == '*' && i + 1 < aSelector.Length() &&
-            aSelector.CharAt(i + 1) == '/') {
-          inComment = false;
-          ++i;
-        }
-        continue;
-      }
-
-      if (stringQuote) {
-        if (c == '\\') {
-          ++i;
-          continue;
-        }
-        if (c == stringQuote) {
-          stringQuote = 0;
-        }
-        continue;
-      }
-
-      if (c == '/' && i + 1 < aSelector.Length() &&
-          aSelector.CharAt(i + 1) == '*') {
-        inComment = true;
-        ++i;
-        continue;
-      }
-
-      if (c == '"' || c == '\'') {
-        stringQuote = c;
-        continue;
-      }
-
-      if (c == '&') {
-        return true;
-      }
-    }
-
-    return false;
-  }
-
-  void
-  ReplaceAmpersands(const nsAString& aSelector,
-                    const nsAString& aParent,
-                    nsAString& aOutput) const
-  {
-    bool inComment = false;
-    char16_t stringQuote = 0;
-
-    for (uint32_t i = 0; i < aSelector.Length(); ++i) {
-      char16_t c = aSelector.CharAt(i);
-
-      if (inComment) {
-        aOutput.Append(c);
-        if (c == '*' && i + 1 < aSelector.Length() &&
-            aSelector.CharAt(i + 1) == '/') {
-          aOutput.Append('/');
-          inComment = false;
-          ++i;
-        }
-        continue;
-      }
-
-      if (stringQuote) {
-        aOutput.Append(c);
-        if (c == '\\' && i + 1 < aSelector.Length()) {
-          aOutput.Append(aSelector.CharAt(i + 1));
-          ++i;
-          continue;
-        }
-        if (c == stringQuote) {
-          stringQuote = 0;
-        }
-        continue;
-      }
-
-      if (c == '/' && i + 1 < aSelector.Length() &&
-          aSelector.CharAt(i + 1) == '*') {
-        aOutput.AppendLiteral("/*");
-        inComment = true;
-        ++i;
-        continue;
-      }
-
-      if (c == '"' || c == '\'') {
-        aOutput.Append(c);
-        stringQuote = c;
-        continue;
-      }
-
-      if (c == '&') {
-        aOutput.Append(aParent);
-        continue;
-      }
-
-      aOutput.Append(c);
-    }
-  }
-
-  bool
-  ExpandNestedSelectors(const SelectorList& aParents,
-                        const nsAString& aNestedSelectorText,
-                        SelectorList& aSelectors)
-  {
-    SelectorList nestedSelectors;
-    if (!SplitSelectorList(aNestedSelectorText, nestedSelectors)) {
-      return false;
-    }
-
-    for (const nsString& nestedSelector : nestedSelectors) {
-      bool hasAmpersand = SelectorHasAmpersand(nestedSelector);
-      for (const nsString& parentSelector : aParents) {
-        nsAutoString combined;
-        if (hasAmpersand) {
-          ReplaceAmpersands(nestedSelector, parentSelector, combined);
-        } else {
-          combined.Assign(parentSelector);
-          if (!combined.IsEmpty()) {
-            combined.Append(' ');
-          }
-          combined.Append(nestedSelector);
-        }
-        TrimWhitespace(combined);
-        if (!combined.IsEmpty()) {
-          aSelectors.AppendElement(combined);
-        }
-      }
-    }
-
-    return !aSelectors.IsEmpty();
-  }
-
-  static void
-  AppendSelectors(const SelectorList& aSelectors, nsAString& aOutput)
-  {
-    for (uint32_t i = 0; i < aSelectors.Length(); ++i) {
-      if (i) {
-        aOutput.AppendLiteral(", ");
-      }
-      aOutput.Append(aSelectors[i]);
-    }
-  }
-
-  static bool
-  StartsNestedSelector(char16_t aChar)
-  {
-    switch (aChar) {
-      case '.':
-      case '#':
-      case '[':
-      case ':':
-      case '&':
-      case '>':
-      case '+':
-      case '~':
-      case '*':
-        return true;
-      default:
-        return false;
-    }
-  }
-
-  static bool
-  StartsPotentialTypeSelector(char16_t aChar)
-  {
-    return (aChar >= 'a' && aChar <= 'z') ||
-           (aChar >= 'A' && aChar <= 'Z') ||
-           aChar == '_' ||
-           aChar == '\\' ||
-           aChar >= 0x80;
-  }
-
-  bool
-  LooksLikeTypeSelectorRule() const
-  {
-    if (AtEnd() || !StartsPotentialTypeSelector(Peek())) {
-      return false;
-    }
-
-    uint32_t pos = mPos;
-    int32_t parenDepth = 0;
-    int32_t bracketDepth = 0;
-    bool inComment = false;
-    char16_t stringQuote = 0;
-
-    while (pos < mInput.Length()) {
-      char16_t c = mInput.CharAt(pos);
-
-      if (inComment) {
-        if (c == '*' && pos + 1 < mInput.Length() &&
-            mInput.CharAt(pos + 1) == '/') {
-          inComment = false;
-          ++pos;
-        }
-        ++pos;
-        continue;
-      }
-
-      if (stringQuote) {
-        if (c == '\\' && pos + 1 < mInput.Length()) {
-          pos += 2;
-          continue;
-        }
-        if (c == stringQuote) {
-          stringQuote = 0;
-        }
-        ++pos;
-        continue;
-      }
-
-      if (c == '/' && pos + 1 < mInput.Length() &&
-          mInput.CharAt(pos + 1) == '*') {
-        inComment = true;
-        pos += 2;
-        continue;
-      }
-
-      if (c == '"' || c == '\'') {
-        stringQuote = c;
-        ++pos;
-        continue;
-      }
-
-      if (c == '(') {
-        ++parenDepth;
-        ++pos;
-        continue;
-      }
-      if (c == ')' && parenDepth > 0) {
-        --parenDepth;
-        ++pos;
-        continue;
-      }
-      if (c == '[') {
-        ++bracketDepth;
-        ++pos;
-        continue;
-      }
-      if (c == ']' && bracketDepth > 0) {
-        --bracketDepth;
-        ++pos;
-        continue;
-      }
-
-      if (parenDepth == 0 && bracketDepth == 0) {
-        if (c == '{') {
-          return true;
-        }
-        if (c == ';' || c == '}') {
-          return false;
-        }
-      }
-
-      ++pos;
-    }
-
-    return false;
-  }
-
-  static bool
-  IsAtRuleNameChar(char16_t aChar)
-  {
-    return (aChar >= 'a' && aChar <= 'z') ||
-           (aChar >= 'A' && aChar <= 'Z') ||
-           (aChar >= '0' && aChar <= '9') ||
-           aChar == '-';
-  }
-
-  static void
-  LowercaseASCII(nsACString& aText)
-  {
-    for (uint32_t i = 0; i < aText.Length(); ++i) {
-      char c = aText.CharAt(i);
-      if (c >= 'A' && c <= 'Z') {
-        aText.BeginWriting()[i] = c - 'A' + 'a';
-      }
-    }
-  }
-
-  static bool
-  ShouldProcessGroupRule(const nsACString& aName)
-  {
-    return aName.EqualsLiteral("media") ||
-           aName.EqualsLiteral("supports") ||
-           aName.EqualsLiteral("document") ||
-           aName.EqualsLiteral("layer");
-  }
-
-  void
-  FlushDeclarations(const SelectorList& aSelectors,
-                    nsAString& aDeclarations,
-                    nsAString& aOutput)
-  {
-    nsAutoString declarations;
-    declarations.Assign(aDeclarations);
-    TrimWhitespace(declarations);
-    aDeclarations.Truncate();
-
-    if (declarations.IsEmpty()) {
-      return;
-    }
-
-    AppendSelectors(aSelectors, aOutput);
-    aOutput.AppendLiteral(" { ");
-    aOutput.Append(declarations);
-    aOutput.AppendLiteral(" }\n");
-  }
-
-  bool
-  ReadRawBlockBody(nsAString& aBody)
-  {
-    uint32_t start = mPos;
-    int32_t depth = 0;
-
-    while (!AtEnd()) {
-      char16_t c = Peek();
-      if (c == '"' || c == '\'') {
-        if (!SkipString(c)) {
-          return false;
-        }
-        continue;
-      }
-      if (StartsWithComment()) {
-        if (!SkipComment()) {
-          return false;
-        }
-        continue;
-      }
-      if (c == '{') {
-        ++depth;
-        ++mPos;
-        continue;
-      }
-      if (c == '}') {
-        if (depth == 0) {
-          aBody.Assign(Substring(mInput, start, mPos - start));
-          ++mPos;
-          return true;
-        }
-        --depth;
-        ++mPos;
-        continue;
-      }
-      ++mPos;
-    }
-
-    return false;
-  }
-
-  bool
-  ReadQualifiedRulePrelude(nsAString& aPrelude)
-  {
-    uint32_t start = mPos;
-    int32_t parenDepth = 0;
-    int32_t bracketDepth = 0;
-
-    while (!AtEnd()) {
-      char16_t c = Peek();
-      if (c == '"' || c == '\'') {
-        if (!SkipString(c)) {
-          return false;
-        }
-        continue;
-      }
-      if (StartsWithComment()) {
-        if (!SkipComment()) {
-          return false;
-        }
-        continue;
-      }
-      if (c == '(') {
-        ++parenDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == ')' && parenDepth > 0) {
-        --parenDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == '[') {
-        ++bracketDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == ']' && bracketDepth > 0) {
-        --bracketDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == '{' && parenDepth == 0 && bracketDepth == 0) {
-        aPrelude.Assign(Substring(mInput, start, mPos - start));
-        TrimWhitespace(aPrelude);
-        ++mPos;
-        return !aPrelude.IsEmpty();
-      }
-      if ((c == ';' || c == '}') && parenDepth == 0 && bracketDepth == 0) {
-        return false;
-      }
-      ++mPos;
-    }
-
-    return false;
-  }
-
-  bool
-  ReadAtRulePrelude(nsAString& aPrelude, nsACString& aName, bool& aHasBlock)
-  {
-    MOZ_ASSERT(!AtEnd() && Peek() == '@', "expected at-rule");
-
-    uint32_t start = mPos;
-    ++mPos;
-    aName.Truncate();
-    while (!AtEnd() && IsAtRuleNameChar(Peek())) {
-      char16_t c = Peek();
-      aName.Append(char(c <= 0x7f ? c : '?'));
-      ++mPos;
-    }
-    LowercaseASCII(aName);
-
-    int32_t parenDepth = 0;
-    int32_t bracketDepth = 0;
-    while (!AtEnd()) {
-      char16_t c = Peek();
-      if (c == '"' || c == '\'') {
-        if (!SkipString(c)) {
-          return false;
-        }
-        continue;
-      }
-      if (StartsWithComment()) {
-        if (!SkipComment()) {
-          return false;
-        }
-        continue;
-      }
-      if (c == '(') {
-        ++parenDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == ')' && parenDepth > 0) {
-        --parenDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == '[') {
-        ++bracketDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == ']' && bracketDepth > 0) {
-        --bracketDepth;
-        ++mPos;
-        continue;
-      }
-      if (parenDepth == 0 && bracketDepth == 0) {
-        if (c == ';') {
-          aPrelude.Assign(Substring(mInput, start, mPos - start));
-          TrimWhitespace(aPrelude);
-          ++mPos;
-          aHasBlock = false;
-          return true;
-        }
-        if (c == '{') {
-          aPrelude.Assign(Substring(mInput, start, mPos - start));
-          TrimWhitespace(aPrelude);
-          ++mPos;
-          aHasBlock = true;
-          return true;
-        }
-      }
-      ++mPos;
-    }
-
-    return false;
-  }
-
-  bool
-  ConsumeDeclaration(nsAString& aDeclaration)
-  {
-    uint32_t start = mPos;
-    int32_t parenDepth = 0;
-    int32_t bracketDepth = 0;
-    int32_t braceDepth = 0;
-
-    while (!AtEnd()) {
-      char16_t c = Peek();
-      if (c == '"' || c == '\'') {
-        if (!SkipString(c)) {
-          return false;
-        }
-        continue;
-      }
-      if (StartsWithComment()) {
-        if (!SkipComment()) {
-          return false;
-        }
-        continue;
-      }
-      if (c == '(') {
-        ++parenDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == ')' && parenDepth > 0) {
-        --parenDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == '[') {
-        ++bracketDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == ']' && bracketDepth > 0) {
-        --bracketDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == '{') {
-        ++braceDepth;
-        ++mPos;
-        continue;
-      }
-      if (c == '}') {
-        if (braceDepth == 0 && parenDepth == 0 && bracketDepth == 0) {
-          break;
-        }
-        if (braceDepth > 0) {
-          --braceDepth;
-        }
-        ++mPos;
-        continue;
-      }
-      if (c == ';' && parenDepth == 0 && bracketDepth == 0 &&
-          braceDepth == 0) {
-        ++mPos;
-        break;
-      }
-      ++mPos;
-    }
-
-    aDeclaration.Assign(Substring(mInput, start, mPos - start));
-    TrimWhitespace(aDeclaration);
-    if (aDeclaration.IsEmpty()) {
-      return false;
-    }
-    if (aDeclaration.Last() != ';') {
-      aDeclaration.Append(';');
-    }
-    return true;
-  }
-
-  bool
-  ParseAtRule(nsAString& aOutput, const SelectorList* aParents)
-  {
-    nsAutoString prelude;
-    nsAutoCString name;
-    bool hasBlock = false;
-    if (!ReadAtRulePrelude(prelude, name, hasBlock)) {
-      return false;
-    }
-
-    if (!hasBlock) {
-      aOutput.Append(prelude);
-      aOutput.AppendLiteral(";\n");
-      return true;
-    }
-
-    if (!ShouldProcessGroupRule(name)) {
-      nsAutoString body;
-      if (!ReadRawBlockBody(body)) {
-        return false;
-      }
-      aOutput.Append(prelude);
-      aOutput.AppendLiteral(" {");
-      aOutput.Append(body);
-      aOutput.AppendLiteral("}\n");
-      return true;
-    }
-
-    nsAutoString inner;
-    if (aParents) {
-      mSawNesting = true;
-      if (!ProcessStyleContext(*aParents, inner)) {
-        return false;
-      }
-    } else {
-      if (!ProcessStylesheet(inner, true)) {
-        return false;
-      }
-    }
-
-    aOutput.Append(prelude);
-    aOutput.AppendLiteral(" {\n");
-    aOutput.Append(inner);
-    aOutput.AppendLiteral("}\n");
-    return true;
-  }
-
-  bool
-  ParseQualifiedRule(nsAString& aOutput, const SelectorList* aParents)
-  {
-    nsAutoString prelude;
-    if (!ReadQualifiedRulePrelude(prelude)) {
-      return false;
-    }
-
-    SelectorList selectors;
-    if (aParents) {
-      mSawNesting = true;
-      if (!ExpandNestedSelectors(*aParents, prelude, selectors)) {
-        return false;
-      }
-    } else if (!SplitSelectorList(prelude, selectors)) {
-      return false;
-    }
-
-    return ProcessStyleContext(selectors, aOutput);
-  }
-
-  bool
-  ProcessStyleContext(const SelectorList& aSelectors, nsAString& aOutput)
-  {
-    nsAutoString declarations;
-
-    while (!AtEnd()) {
-      SkipWhitespaceAndComments();
-      if (AtEnd()) {
-        return false;
-      }
-
-      char16_t c = Peek();
-      if (c == '}') {
-        ++mPos;
-        FlushDeclarations(aSelectors, declarations, aOutput);
-        return true;
-      }
-
-      if (c == '@') {
-        FlushDeclarations(aSelectors, declarations, aOutput);
-        if (!ParseAtRule(aOutput, &aSelectors)) {
-          return false;
-        }
-        continue;
-      }
-
-      if (StartsNestedSelector(c) || LooksLikeTypeSelectorRule()) {
-        FlushDeclarations(aSelectors, declarations, aOutput);
-        if (!ParseQualifiedRule(aOutput, &aSelectors)) {
-          return false;
-        }
-        continue;
-      }
-
-      nsAutoString declaration;
-      if (!ConsumeDeclaration(declaration)) {
-        return false;
-      }
-      if (!declarations.IsEmpty()) {
-        declarations.Append(' ');
-      }
-      declarations.Append(declaration);
-    }
-
-    return false;
-  }
-
-  bool
-  ProcessStylesheet(nsAString& aOutput, bool aStopAtBlockEnd)
-  {
-    while (!AtEnd()) {
-      SkipWhitespaceAndComments();
-      if (AtEnd()) {
-        return !aStopAtBlockEnd;
-      }
-
-      if (Peek() == '}') {
-        if (!aStopAtBlockEnd) {
-          return false;
-        }
-        ++mPos;
-        return true;
-      }
-
-      if (Peek() == '@') {
-        if (!ParseAtRule(aOutput, nullptr)) {
-          return false;
-        }
-      } else {
-        if (!ParseQualifiedRule(aOutput, nullptr)) {
-          return false;
-        }
-      }
-    }
-
-    return !aStopAtBlockEnd;
-  }
-
-  const nsAString& mInput;
-  uint32_t mPos;
-  bool mSawNesting;
-};
-
 static_assert(css::eAuthorSheetFeatures == 0 &&
               css::eUserSheetFeatures == 1 &&
               css::eAgentSheetFeatures == 2,
@@ -2761,12 +1828,10 @@ CSSParserImpl::ParseSheet(const nsAString& aInput,
 
   nsAutoString loweredInput;
   const nsAString* input = &aInput;
-  if (sNestingEnabled) {
+  if (sNestingEnabled &&
-    CSSNestingLowerer lowerer(aInput);
+      mozilla::css::LowerBasicCSSNesting(aInput, loweredInput)) {
-    if (lowerer.Lower(loweredInput)) {
     input = &loweredInput;
   }
-  }
 
   nsCSSScanner scanner(*input, aLineNumber);
   css::ErrorReporter reporter(scanner, mSheet, mChildLoader, aSheetURI);