layout/generic/nsTextRunTransformations.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 "nsTextRunTransformations.h"

#include "mozilla/MemoryReporting.h"
#include "mozilla/Move.h"

#include "nsGkAtoms.h"
#include "nsStyleConsts.h"
#include "nsStyleContextInlines.h"
#include "nsUnicharUtils.h"
#include "nsUnicodeProperties.h"
#include "nsSpecialCasingData.h"
#include "mozilla/gfx/2D.h"
#include "nsTextFrameUtils.h"
#include "nsIPersistentProperties2.h"
#include "GreekCasing.h"
#include "IrishCasing.h"

using namespace mozilla;
using namespace mozilla::gfx;

// Unicode characters needing special casing treatment in tr/az languages
#define LATIN_CAPITAL_LETTER_I_WITH_DOT_ABOVE 0x0130
#define LATIN_SMALL_LETTER_DOTLESS_I 0x0131

// Greek sigma needs custom handling for the lowercase transform; for details
// see comments under "case NS_STYLE_TEXT_TRANSFORM_LOWERCASE" within
// nsCaseTransformTextRunFactory::RebuildTextRun(), and bug 740120.
#define GREEK_CAPITAL_LETTER_SIGMA 0x03A3
#define GREEK_SMALL_LETTER_FINAL_SIGMA 0x03C2
#define GREEK_SMALL_LETTER_SIGMA 0x03C3

already_AddRefed<nsTransformedTextRun> nsTransformedTextRun::Create(
    const gfxTextRunFactory::Parameters* aParams,
    nsTransformingTextRunFactory* aFactory, gfxFontGroup* aFontGroup,
    const char16_t* aString, uint32_t aLength,
    const gfx::ShapedTextFlags aFlags, const nsTextFrameUtils::Flags aFlags2,
    nsTArray<RefPtr<nsTransformedCharStyle>>&& aStyles, bool aOwnsFactory) {
  NS_ASSERTION(!(aFlags & gfx::ShapedTextFlags::TEXT_IS_8BIT),
               "didn't expect text to be marked as 8-bit here");

  void* storage =
      AllocateStorageForTextRun(sizeof(nsTransformedTextRun), aLength);
  if (!storage) {
    return nullptr;
  }

  RefPtr<nsTransformedTextRun> result = new (storage)
      nsTransformedTextRun(aParams, aFactory, aFontGroup, aString, aLength,
                           aFlags, aFlags2, Move(aStyles), aOwnsFactory);
  return result.forget();
}

void nsTransformedTextRun::SetCapitalization(uint32_t aStart, uint32_t aLength,
                                             bool* aCapitalization) {
  if (mCapitalize.IsEmpty()) {
    if (!mCapitalize.AppendElements(GetLength())) return;
    memset(mCapitalize.Elements(), 0, GetLength() * sizeof(bool));
  }
  memcpy(mCapitalize.Elements() + aStart, aCapitalization,
         aLength * sizeof(bool));
  mNeedsRebuild = true;
}

bool nsTransformedTextRun::SetPotentialLineBreaks(Range aRange,
                                                  const uint8_t* aBreakBefore) {
  bool changed = gfxTextRun::SetPotentialLineBreaks(aRange, aBreakBefore);
  if (changed) {
    mNeedsRebuild = true;
  }
  return changed;
}

size_t nsTransformedTextRun::SizeOfExcludingThis(
    mozilla::MallocSizeOf aMallocSizeOf) {
  size_t total = gfxTextRun::SizeOfExcludingThis(aMallocSizeOf);
  total += mStyles.ShallowSizeOfExcludingThis(aMallocSizeOf);
  total += mCapitalize.ShallowSizeOfExcludingThis(aMallocSizeOf);
  if (mOwnsFactory) {
    total += aMallocSizeOf(mFactory);
  }
  return total;
}

size_t nsTransformedTextRun::SizeOfIncludingThis(
    mozilla::MallocSizeOf aMallocSizeOf) {
  return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
}

already_AddRefed<nsTransformedTextRun>
nsTransformingTextRunFactory::MakeTextRun(
    const char16_t* aString, uint32_t aLength,
    const gfxTextRunFactory::Parameters* aParams, gfxFontGroup* aFontGroup,
    gfx::ShapedTextFlags aFlags, nsTextFrameUtils::Flags aFlags2,
    nsTArray<RefPtr<nsTransformedCharStyle>>&& aStyles, bool aOwnsFactory) {
  return nsTransformedTextRun::Create(aParams, this, aFontGroup, aString,
                                      aLength, aFlags, aFlags2, Move(aStyles),
                                      aOwnsFactory);
}

already_AddRefed<nsTransformedTextRun>
nsTransformingTextRunFactory::MakeTextRun(
    const uint8_t* aString, uint32_t aLength,
    const gfxTextRunFactory::Parameters* aParams, gfxFontGroup* aFontGroup,
    gfx::ShapedTextFlags aFlags, nsTextFrameUtils::Flags aFlags2,
    nsTArray<RefPtr<nsTransformedCharStyle>>&& aStyles, bool aOwnsFactory) {
  // We'll only have a Unicode code path to minimize the amount of code needed
  // for these rarely used features
  NS_ConvertASCIItoUTF16 unicodeString(reinterpret_cast<const char*>(aString),
                                       aLength);
  return MakeTextRun(unicodeString.get(), aLength, aParams, aFontGroup,
                     aFlags & ~gfx::ShapedTextFlags::TEXT_IS_8BIT, aFlags2,
                     Move(aStyles), aOwnsFactory);
}

void MergeCharactersInTextRun(gfxTextRun* aDest, gfxTextRun* aSrc,
                              const bool* aCharsToMerge,
                              const bool* aDeletedChars) {
  aDest->ResetGlyphRuns();

  gfxTextRun::GlyphRunIterator iter(aSrc, gfxTextRun::Range(aSrc));
  uint32_t offset = 0;
  AutoTArray<gfxTextRun::DetailedGlyph, 2> glyphs;
  while (iter.NextRun()) {
    const gfxTextRun::GlyphRun* run = iter.GetGlyphRun();
    nsresult rv = aDest->AddGlyphRun(run->mFont, run->mMatchType, offset, false,
                                     run->mOrientation);
    if (NS_FAILED(rv)) return;

    bool anyMissing = false;
    uint32_t mergeRunStart = iter.GetStringStart();
    const gfxTextRun::CompressedGlyph* srcGlyphs = aSrc->GetCharacterGlyphs();
    gfxTextRun::CompressedGlyph mergedGlyph = srcGlyphs[mergeRunStart];
    uint32_t stringEnd = iter.GetStringEnd();
    for (uint32_t k = iter.GetStringStart(); k < stringEnd; ++k) {
      const gfxTextRun::CompressedGlyph g = srcGlyphs[k];
      if (g.IsSimpleGlyph()) {
        if (!anyMissing) {
          gfxTextRun::DetailedGlyph details;
          details.mGlyphID = g.GetSimpleGlyph();
          details.mAdvance = g.GetSimpleAdvance();
          glyphs.AppendElement(details);
        }
      } else {
        if (g.IsMissing()) {
          anyMissing = true;
          glyphs.Clear();
        }
        if (g.GetGlyphCount() > 0) {
          glyphs.AppendElements(aSrc->GetDetailedGlyphs(k), g.GetGlyphCount());
        }
      }

      if (k + 1 < iter.GetStringEnd() && aCharsToMerge[k + 1]) {
        // next char is supposed to merge with current, so loop without
        // writing current merged glyph to the destination
        continue;
      }

      // If the start of the merge run is actually a character that should
      // have been merged with the previous character (this can happen
      // if there's a font change in the middle of a case-mapped character,
      // that decomposed into a sequence of base+diacritics, for example),
      // just discard the entire merge run. See comment at start of this
      // function.
      NS_WARNING_ASSERTION(
          !aCharsToMerge[mergeRunStart],
          "unable to merge across a glyph run boundary, glyph(s) discarded");
      if (!aCharsToMerge[mergeRunStart]) {
        if (anyMissing) {
          mergedGlyph.SetMissing(glyphs.Length());
        } else {
          mergedGlyph.SetComplex(mergedGlyph.IsClusterStart(),
                                 mergedGlyph.IsLigatureGroupStart(),
                                 glyphs.Length());
        }
        aDest->SetGlyphs(offset, mergedGlyph, glyphs.Elements());
        ++offset;

        while (offset < aDest->GetLength() && aDeletedChars[offset]) {
          aDest->SetGlyphs(offset++, gfxTextRun::CompressedGlyph(), nullptr);
        }
      }

      glyphs.Clear();
      anyMissing = false;
      mergeRunStart = k + 1;
      if (mergeRunStart < stringEnd) {
        mergedGlyph = srcGlyphs[mergeRunStart];
      }
    }
    NS_ASSERTION(glyphs.Length() == 0,
                 "Leftover glyphs, don't request merging of the last character "
                 "with its next!");
  }
  NS_ASSERTION(offset == aDest->GetLength(), "Bad offset calculations");
}

gfxTextRunFactory::Parameters GetParametersForInner(
    nsTransformedTextRun* aTextRun, gfx::ShapedTextFlags* aFlags,
    DrawTarget* aRefDrawTarget) {
  gfxTextRunFactory::Parameters params = {
      aRefDrawTarget, nullptr, nullptr,
      nullptr,        0,       aTextRun->GetAppUnitsPerDevUnit()};
  *aFlags = aTextRun->GetFlags();
  return params;
}

// Some languages have special casing conventions that differ from the
// default Unicode mappings.
// The enum values here are named for well-known exemplar languages that
// exhibit the behavior in question; multiple lang tags may map to the
// same setting here, if the behavior is shared by other languages.
enum LanguageSpecificCasingBehavior {
  eLSCB_None,    // default non-lang-specific behavior
  eLSCB_Dutch,   // treat "ij" digraph as a unit for capitalization
  eLSCB_Greek,   // strip accent when uppercasing Greek vowels
  eLSCB_Irish,   // keep prefix letters as lowercase when uppercasing Irish
  eLSCB_Turkish  // preserve dotted/dotless-i distinction in uppercase
};

static LanguageSpecificCasingBehavior GetCasingFor(const nsAtom* aLang) {
  if (!aLang) {
    return eLSCB_None;
  }
  if (aLang == nsGkAtoms::tr || aLang == nsGkAtoms::az ||
      aLang == nsGkAtoms::ba || aLang == nsGkAtoms::crh ||
      aLang == nsGkAtoms::tt) {
    return eLSCB_Turkish;
  }
  if (aLang == nsGkAtoms::nl) {
    return eLSCB_Dutch;
  }
  if (aLang == nsGkAtoms::el) {
    return eLSCB_Greek;
  }
  if (aLang == nsGkAtoms::ga) {
    return eLSCB_Irish;
  }

  // Is there a region subtag we should ignore?
  nsAtomString langStr(const_cast<nsAtom*>(aLang));
  int index = langStr.FindChar('-');
  if (index > 0) {
    langStr.Truncate(index);
    RefPtr<nsAtom> truncatedLang = NS_Atomize(langStr);
    return GetCasingFor(truncatedLang);
  }

  return eLSCB_None;
}

bool nsCaseTransformTextRunFactory::TransformString(
    const nsAString& aString, nsString& aConvertedString, bool aAllUppercase,
    const nsAtom* aLanguage, nsTArray<bool>& aCharsToMergeArray,
    nsTArray<bool>& aDeletedCharsArray, const nsTransformedTextRun* aTextRun,
    uint32_t aOffsetInTextRun, nsTArray<uint8_t>* aCanBreakBeforeArray,
    nsTArray<RefPtr<nsTransformedCharStyle>>* aStyleArray) {
  bool auxiliaryOutputArrays = aCanBreakBeforeArray && aStyleArray;
  MOZ_ASSERT(!auxiliaryOutputArrays || aTextRun,
             "text run must be provided to use aux output arrays");

  uint32_t length = aString.Length();
  const char16_t* str = aString.BeginReading();

  bool mergeNeeded = false;

  bool capitalizeDutchIJ = false;
  bool prevIsLetter = false;
  bool ntPrefix = false;  // true immediately after a word-initial 'n' or 't'
                          // when doing Irish lowercasing
  uint32_t sigmaIndex = uint32_t(-1);
  nsUGenCategory cat;

  uint8_t style = aAllUppercase ? NS_STYLE_TEXT_TRANSFORM_UPPERCASE : 0;
  bool forceNonFullWidth = false;
  const nsAtom* lang = aLanguage;

  LanguageSpecificCasingBehavior languageSpecificCasing = GetCasingFor(lang);
  mozilla::GreekCasing::State greekState;
  mozilla::IrishCasing::State irishState;
  uint32_t irishMark = uint32_t(-1);  // location of possible prefix letter(s)
                                      // in the output string
  uint32_t irishMarkSrc =
      uint32_t(-1);                   // corresponding location in source
                                      // string (may differ from output due to
                                      // expansions like eszet -> 'SS')
  uint32_t greekMark = uint32_t(-1);  // location of uppercase ETA that may need
                                      // tonos added (if it is disjunctive eta)
  const char16_t kGreekUpperEta = 0x0397;

  for (uint32_t i = 0; i < length; ++i, ++aOffsetInTextRun) {
    uint32_t ch = str[i];

    RefPtr<nsTransformedCharStyle> charStyle;
    if (aTextRun) {
      charStyle = aTextRun->mStyles[aOffsetInTextRun];
      style = aAllUppercase ? NS_STYLE_TEXT_TRANSFORM_UPPERCASE
                            : charStyle->mTextTransform;
      forceNonFullWidth = charStyle->mForceNonFullWidth;

      nsAtom* newLang =
          charStyle->mExplicitLanguage ? charStyle->mLanguage.get() : nullptr;
      if (lang != newLang) {
        lang = newLang;
        languageSpecificCasing = GetCasingFor(lang);
        greekState.Reset();
        irishState.Reset();
        irishMark = uint32_t(-1);
        irishMarkSrc = uint32_t(-1);
        greekMark = uint32_t(-1);
      }
    }

    int extraChars = 0;
    const mozilla::unicode::MultiCharMapping* mcm;
    bool inhibitBreakBefore = false;  // have we just deleted preceding hyphen?

    if (NS_IS_HIGH_SURROGATE(ch) && i < length - 1 &&
        NS_IS_LOW_SURROGATE(str[i + 1])) {
      ch = SURROGATE_TO_UCS4(ch, str[i + 1]);
    }

    switch (style) {
      case NS_STYLE_TEXT_TRANSFORM_LOWERCASE:
        if (languageSpecificCasing == eLSCB_Turkish) {
          if (ch == 'I') {
            ch = LATIN_SMALL_LETTER_DOTLESS_I;
            prevIsLetter = true;
            sigmaIndex = uint32_t(-1);
            break;
          }
          if (ch == LATIN_CAPITAL_LETTER_I_WITH_DOT_ABOVE) {
            ch = 'i';
            prevIsLetter = true;
            sigmaIndex = uint32_t(-1);
            break;
          }
        }

        cat = mozilla::unicode::GetGenCategory(ch);

        if (languageSpecificCasing == eLSCB_Irish &&
            cat == nsUGenCategory::kLetter) {
          // See bug 1018805 for Irish lowercasing requirements
          if (!prevIsLetter && (ch == 'n' || ch == 't')) {
            ntPrefix = true;
          } else {
            if (ntPrefix && mozilla::IrishCasing::IsUpperVowel(ch)) {
              aConvertedString.Append('-');
              ++extraChars;
            }
            ntPrefix = false;
          }
        } else {
          ntPrefix = false;
        }

        // Special lowercasing behavior for Greek Sigma: note that this is
        // listed as context-sensitive in Unicode's SpecialCasing.txt, but is
        // *not* a language-specific mapping; it applies regardless of the
        // language of the element.
        //
        // The lowercase mapping for CAPITAL SIGMA should be to SMALL SIGMA
        // (i.e. the non-final form) whenever there is a following letter, or
        // when the CAPITAL SIGMA occurs in isolation (neither preceded nor
        // followed by a LETTER); and to FINAL SIGMA when it is preceded by
        // another letter but not followed by one.
        //
        // To implement the context-sensitive nature of this mapping, we keep
        // track of whether the previous character was a letter. If not, CAPITAL
        // SIGMA will map directly to SMALL SIGMA. If the previous character
        // was a letter, CAPITAL SIGMA maps to FINAL SIGMA and we record the
        // position in the converted string; if we then encounter another
        // letter, that FINAL SIGMA is replaced with a standard SMALL SIGMA.

        // If sigmaIndex is not -1, it marks where we have provisionally mapped
        // a CAPITAL SIGMA to FINAL SIGMA; if we now find another letter, we
        // need to change it to SMALL SIGMA.
        if (sigmaIndex != uint32_t(-1)) {
          if (cat == nsUGenCategory::kLetter) {
            aConvertedString.SetCharAt(GREEK_SMALL_LETTER_SIGMA, sigmaIndex);
          }
        }

        if (ch == GREEK_CAPITAL_LETTER_SIGMA) {
          // If preceding char was a letter, map to FINAL instead of SMALL,
          // and note where it occurred by setting sigmaIndex; we'll change it
          // to standard SMALL SIGMA later if another letter follows
          if (prevIsLetter) {
            ch = GREEK_SMALL_LETTER_FINAL_SIGMA;
            sigmaIndex = aConvertedString.Length();
          } else {
            // CAPITAL SIGMA not preceded by a letter is unconditionally mapped
            // to SMALL SIGMA
            ch = GREEK_SMALL_LETTER_SIGMA;
            sigmaIndex = uint32_t(-1);
          }
          prevIsLetter = true;
          break;
        }

        // ignore diacritics for the purpose of contextual sigma mapping;
        // otherwise, reset prevIsLetter appropriately and clear the
        // sigmaIndex marker
        if (cat != nsUGenCategory::kMark) {
          prevIsLetter = (cat == nsUGenCategory::kLetter);
          sigmaIndex = uint32_t(-1);
        }

        mcm = mozilla::unicode::SpecialLower(ch);
        if (mcm) {
          int j = 0;
          while (j < 2 && mcm->mMappedChars[j + 1]) {
            aConvertedString.Append(mcm->mMappedChars[j]);
            ++extraChars;
            ++j;
          }
          ch = mcm->mMappedChars[j];
          break;
        }

        ch = ToLowerCase(ch);
        break;

      case NS_STYLE_TEXT_TRANSFORM_UPPERCASE:
        if (languageSpecificCasing == eLSCB_Turkish && ch == 'i') {
          ch = LATIN_CAPITAL_LETTER_I_WITH_DOT_ABOVE;
          break;
        }

        if (languageSpecificCasing == eLSCB_Greek) {
          bool markEta;
          bool updateEta;
          ch = mozilla::GreekCasing::UpperCase(ch, greekState, markEta,
                                               updateEta);
          if (markEta) {
            greekMark = aConvertedString.Length();
          } else if (updateEta) {
            // Remove the TONOS from an uppercase ETA-TONOS that turned out
            // not to be disjunctive-eta.
            MOZ_ASSERT(aConvertedString.Length() > 0 &&
                           greekMark < aConvertedString.Length(),
                       "bad greekMark!");
            aConvertedString.SetCharAt(kGreekUpperEta, greekMark);
            greekMark = uint32_t(-1);
          }
          break;
        }

        if (languageSpecificCasing == eLSCB_Irish) {
          bool mark;
          uint8_t action;
          ch = mozilla::IrishCasing::UpperCase(ch, irishState, mark, action);
          if (mark) {
            irishMark = aConvertedString.Length();
            irishMarkSrc = i;
            break;
          } else if (action) {
            nsString& str = aConvertedString;  // shorthand
            switch (action) {
              case 1:
                // lowercase a single prefix letter
                NS_ASSERTION(str.Length() > 0 && irishMark < str.Length(),
                             "bad irishMark!");
                str.SetCharAt(ToLowerCase(str[irishMark]), irishMark);
                irishMark = uint32_t(-1);
                irishMarkSrc = uint32_t(-1);
                break;
              case 2:
                // lowercase two prefix letters (immediately before current pos)
                NS_ASSERTION(str.Length() >= 2 && irishMark == str.Length() - 2,
                             "bad irishMark!");
                str.SetCharAt(ToLowerCase(str[irishMark]), irishMark);
                str.SetCharAt(ToLowerCase(str[irishMark + 1]), irishMark + 1);
                irishMark = uint32_t(-1);
                irishMarkSrc = uint32_t(-1);
                break;
              case 3:
                // lowercase one prefix letter, and delete following hyphen
                // (which must be the immediately-preceding char)
                NS_ASSERTION(str.Length() >= 2 && irishMark == str.Length() - 2,
                             "bad irishMark!");
                MOZ_ASSERT(
                    irishMark != uint32_t(-1) && irishMarkSrc != uint32_t(-1),
                    "failed to set irishMarks");
                str.Replace(irishMark, 2, ToLowerCase(str[irishMark]));
                aDeletedCharsArray[irishMarkSrc + 1] = true;
                // Remove the trailing entries (corresponding to the deleted
                // hyphen) from the auxiliary arrays.
                aCharsToMergeArray.SetLength(aCharsToMergeArray.Length() - 1);
                if (auxiliaryOutputArrays) {
                  aStyleArray->SetLength(aStyleArray->Length() - 1);
                  aCanBreakBeforeArray->SetLength(
                      aCanBreakBeforeArray->Length() - 1);
                  inhibitBreakBefore = true;
                }
                mergeNeeded = true;
                irishMark = uint32_t(-1);
                irishMarkSrc = uint32_t(-1);
                break;
            }
            // ch has been set to the uppercase for current char;
            // No need to check for SpecialUpper here as none of the characters
            // that could trigger an Irish casing action have special mappings.
            break;
          }
          // If we didn't have any special action to perform, fall through
          // to check for special uppercase (ß)
        }

        mcm = mozilla::unicode::SpecialUpper(ch);
        if (mcm) {
          int j = 0;
          while (j < 2 && mcm->mMappedChars[j + 1]) {
            aConvertedString.Append(mcm->mMappedChars[j]);
            ++extraChars;
            ++j;
          }
          ch = mcm->mMappedChars[j];
          break;
        }

        ch = ToUpperCase(ch);
        break;

      case NS_STYLE_TEXT_TRANSFORM_CAPITALIZE:
        if (aTextRun) {
          if (capitalizeDutchIJ && ch == 'j') {
            ch = 'J';
            capitalizeDutchIJ = false;
            break;
          }
          capitalizeDutchIJ = false;
          if (aOffsetInTextRun < aTextRun->mCapitalize.Length() &&
              aTextRun->mCapitalize[aOffsetInTextRun]) {
            if (languageSpecificCasing == eLSCB_Turkish && ch == 'i') {
              ch = LATIN_CAPITAL_LETTER_I_WITH_DOT_ABOVE;
              break;
            }
            if (languageSpecificCasing == eLSCB_Dutch && ch == 'i') {
              ch = 'I';
              capitalizeDutchIJ = true;
              break;
            }

            mcm = mozilla::unicode::SpecialTitle(ch);
            if (mcm) {
              int j = 0;
              while (j < 2 && mcm->mMappedChars[j + 1]) {
                aConvertedString.Append(mcm->mMappedChars[j]);
                ++extraChars;
                ++j;
              }
              ch = mcm->mMappedChars[j];
              break;
            }

            ch = ToTitleCase(ch);
          }
        }
        break;

      case NS_STYLE_TEXT_TRANSFORM_FULL_WIDTH:
        ch = mozilla::unicode::GetFullWidth(ch);
        break;

      default:
        break;
    }

    if (forceNonFullWidth) {
      ch = mozilla::unicode::GetFullWidthInverse(ch);
    }

    if (ch == uint32_t(-1)) {
      aDeletedCharsArray.AppendElement(true);
      mergeNeeded = true;
    } else {
      aDeletedCharsArray.AppendElement(false);
      aCharsToMergeArray.AppendElement(false);
      if (auxiliaryOutputArrays) {
        aStyleArray->AppendElement(charStyle);
        aCanBreakBeforeArray->AppendElement(
            inhibitBreakBefore
                ? gfxShapedText::CompressedGlyph::FLAG_BREAK_TYPE_NONE
                : aTextRun->CanBreakBefore(aOffsetInTextRun));
      }

      if (IS_IN_BMP(ch)) {
        aConvertedString.Append(ch);
      } else {
        aConvertedString.Append(H_SURROGATE(ch));
        aConvertedString.Append(L_SURROGATE(ch));
        i++;
        aOffsetInTextRun++;
        aDeletedCharsArray.AppendElement(
            true);  // not exactly deleted, but the
                    // trailing surrogate is skipped
        ++extraChars;
      }

      while (extraChars-- > 0) {
        mergeNeeded = true;
        aCharsToMergeArray.AppendElement(true);
        if (auxiliaryOutputArrays) {
          aStyleArray->AppendElement(charStyle);
          aCanBreakBeforeArray->AppendElement(
              gfxShapedText::CompressedGlyph::FLAG_BREAK_TYPE_NONE);
        }
      }
    }
  }

  return mergeNeeded;
}

void nsCaseTransformTextRunFactory::RebuildTextRun(
    nsTransformedTextRun* aTextRun, DrawTarget* aRefDrawTarget,
    gfxMissingFontRecorder* aMFR) {
  nsAutoString convertedString;
  AutoTArray<bool, 50> charsToMergeArray;
  AutoTArray<bool, 50> deletedCharsArray;
  AutoTArray<uint8_t, 50> canBreakBeforeArray;
  AutoTArray<RefPtr<nsTransformedCharStyle>, 50> styleArray;

  bool mergeNeeded =
      TransformString(aTextRun->mString, convertedString, mAllUppercase,
                      nullptr, charsToMergeArray, deletedCharsArray, aTextRun,
                      0, &canBreakBeforeArray, &styleArray);

  gfx::ShapedTextFlags flags;
  gfxTextRunFactory::Parameters innerParams =
      GetParametersForInner(aTextRun, &flags, aRefDrawTarget);
  gfxFontGroup* fontGroup = aTextRun->GetFontGroup();

  RefPtr<nsTransformedTextRun> transformedChild;
  RefPtr<gfxTextRun> cachedChild;
  gfxTextRun* child;

  if (mInnerTransformingTextRunFactory) {
    transformedChild = mInnerTransformingTextRunFactory->MakeTextRun(
        convertedString.BeginReading(), convertedString.Length(), &innerParams,
        fontGroup, flags, nsTextFrameUtils::Flags(), Move(styleArray), false);
    child = transformedChild.get();
  } else {
    cachedChild = fontGroup->MakeTextRun(
        convertedString.BeginReading(), convertedString.Length(), &innerParams,
        flags, nsTextFrameUtils::Flags(), aMFR);
    child = cachedChild.get();
  }
  if (!child) return;
  // Copy potential linebreaks into child so they're preserved
  // (and also child will be shaped appropriately)
  NS_ASSERTION(convertedString.Length() == canBreakBeforeArray.Length(),
               "Dropped characters or break-before values somewhere!");
  gfxTextRun::Range range(0, uint32_t(canBreakBeforeArray.Length()));
  child->SetPotentialLineBreaks(range, canBreakBeforeArray.Elements());
  if (transformedChild) {
    transformedChild->FinishSettingProperties(aRefDrawTarget, aMFR);
  }

  if (mergeNeeded) {
    // Now merge multiple characters into one multi-glyph character as required
    // and deal with skipping deleted accent chars
    NS_ASSERTION(charsToMergeArray.Length() == child->GetLength(),
                 "source length mismatch");
    NS_ASSERTION(deletedCharsArray.Length() == aTextRun->GetLength(),
                 "destination length mismatch");
    MergeCharactersInTextRun(aTextRun, child, charsToMergeArray.Elements(),
                             deletedCharsArray.Elements());
  } else {
    // No merging to do, so just copy; this produces a more optimized textrun.
    // We can't steal the data because the child may be cached and stealing
    // the data would break the cache.
    aTextRun->ResetGlyphRuns();
    aTextRun->CopyGlyphDataFrom(child, gfxTextRun::Range(child), 0);
  }
}