lib/Frontend/TextDiagnosticPrinter.cpp

//===--- TextDiagnosticPrinter.cpp - Diagnostic Printer -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This diagnostic client prints out their diagnostic messages.
//
//===----------------------------------------------------------------------===//

#include "clang/Frontend/TextDiagnosticPrinter.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Lex/Lexer.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallString.h"
#include <algorithm>
using namespace clang;

/// \brief Number of spaces to indent when word-wrapping.
const unsigned WordWrapIndentation = 6;

void TextDiagnosticPrinter::
PrintIncludeStack(SourceLocation Loc, const SourceManager &SM) {
  if (Loc.isInvalid()) return;

  PresumedLoc PLoc = SM.getPresumedLoc(Loc);

  // Print out the other include frames first.
  PrintIncludeStack(PLoc.getIncludeLoc(), SM);

  if (ShowLocation)
    OS << "In file included from " << PLoc.getFilename()
       << ':' << PLoc.getLine() << ":\n";
  else
    OS << "In included file:\n";
}

/// HighlightRange - Given a SourceRange and a line number, highlight (with ~'s)
/// any characters in LineNo that intersect the SourceRange.
void TextDiagnosticPrinter::HighlightRange(const SourceRange &R,
                                           const SourceManager &SM,
                                           unsigned LineNo, FileID FID,
                                           std::string &CaretLine,
                                           const std::string &SourceLine) {
  assert(CaretLine.size() == SourceLine.size() &&
         "Expect a correspondence between source and caret line!");
  if (!R.isValid()) return;

  SourceLocation Begin = SM.getInstantiationLoc(R.getBegin());
  SourceLocation End = SM.getInstantiationLoc(R.getEnd());
  
  // If the End location and the start location are the same and are a macro
  // location, then the range was something that came from a macro expansion
  // or _Pragma.  If this is an object-like macro, the best we can do is to
  // highlight the range.  If this is a function-like macro, we'd also like to
  // highlight the arguments.
  if (Begin == End && R.getEnd().isMacroID())
    End = SM.getInstantiationRange(R.getEnd()).second;
  
  unsigned StartLineNo = SM.getInstantiationLineNumber(Begin);
  if (StartLineNo > LineNo || SM.getFileID(Begin) != FID)
    return;  // No intersection.
  
  unsigned EndLineNo = SM.getInstantiationLineNumber(End);
  if (EndLineNo < LineNo || SM.getFileID(End) != FID)
    return;  // No intersection.
  
  // Compute the column number of the start.
  unsigned StartColNo = 0;
  if (StartLineNo == LineNo) {
    StartColNo = SM.getInstantiationColumnNumber(Begin);
    if (StartColNo) --StartColNo;  // Zero base the col #.
  }

  // Pick the first non-whitespace column.
  while (StartColNo < SourceLine.size() &&
         (SourceLine[StartColNo] == ' ' || SourceLine[StartColNo] == '\t'))
    ++StartColNo;
  
  // Compute the column number of the end.
  unsigned EndColNo = CaretLine.size();
  if (EndLineNo == LineNo) {
    EndColNo = SM.getInstantiationColumnNumber(End);
    if (EndColNo) {
      --EndColNo;  // Zero base the col #.
      
      // Add in the length of the token, so that we cover multi-char tokens.
      EndColNo += Lexer::MeasureTokenLength(End, SM, *LangOpts);
    } else {
      EndColNo = CaretLine.size();
    }
  }
  
  // Pick the last non-whitespace column.
  if (EndColNo <= SourceLine.size())
    while (EndColNo-1 &&
           (SourceLine[EndColNo-1] == ' ' || SourceLine[EndColNo-1] == '\t'))
      --EndColNo;
  else
    EndColNo = SourceLine.size();
  
  // Fill the range with ~'s.
  assert(StartColNo <= EndColNo && "Invalid range!");
  for (unsigned i = StartColNo; i < EndColNo; ++i)
    CaretLine[i] = '~';
}

/// \brief When the source code line we want to print is too long for
/// the terminal, select the "interesting" region.
static void SelectInterestingSourceRegion(std::string &SourceLine,
                                          std::string &CaretLine,
                                          std::string &FixItInsertionLine,
                                          unsigned EndOfCaretToken,
                                          unsigned Columns) {
  if (CaretLine.size() > SourceLine.size())
    SourceLine.resize(CaretLine.size(), ' ');

  // Find the slice that we need to display the full caret line
  // correctly.
  unsigned CaretStart = 0, CaretEnd = CaretLine.size();
  for (; CaretStart != CaretEnd; ++CaretStart)
    if (!isspace(CaretLine[CaretStart]))
      break;

  for (; CaretEnd != CaretStart; --CaretEnd)
    if (!isspace(CaretLine[CaretEnd - 1]))
      break;

  // Make sure we don't chop the string shorter than the caret token
  // itself.
  if (CaretEnd < EndOfCaretToken)
    CaretEnd = EndOfCaretToken;

  // If we have a fix-it line, make sure the slice includes all of the
  // fix-it information.
  if (!FixItInsertionLine.empty()) {
    unsigned FixItStart = 0, FixItEnd = FixItInsertionLine.size();
    for (; FixItStart != FixItEnd; ++FixItStart)
      if (!isspace(FixItInsertionLine[FixItStart]))
        break;
    
    for (; FixItEnd != FixItStart; --FixItEnd)
      if (!isspace(FixItInsertionLine[FixItEnd - 1]))
        break;

    if (FixItStart < CaretStart)
      CaretStart = FixItStart;
    if (FixItEnd > CaretEnd)
      CaretEnd = FixItEnd;
  }

  // CaretLine[CaretStart, CaretEnd) contains all of the interesting
  // parts of the caret line. While this slice is smaller than the
  // number of columns we have, try to grow the slice to encompass
  // more context.

  // If the end of the interesting region comes before we run out of
  // space in the terminal, start at the beginning of the line.
  if (Columns > 3 && CaretEnd < Columns - 3)
    CaretStart = 0;

  unsigned TargetColumns = Columns;
  if (TargetColumns > 8)
    TargetColumns -= 8; // Give us extra room for the ellipses.
  unsigned SourceLength = SourceLine.size();
  while ((CaretEnd - CaretStart) < TargetColumns) {
    bool ExpandedRegion = false;
    // Move the start of the interesting region left until we've
    // pulled in something else interesting.
    if (CaretStart == 1)
      CaretStart = 0;
    else if (CaretStart > 1) {
      unsigned NewStart = CaretStart - 1;
        
      // Skip over any whitespace we see here; we're looking for
      // another bit of interesting text.
      while (NewStart && isspace(SourceLine[NewStart]))
        --NewStart;
      
      // Skip over this bit of "interesting" text.
      while (NewStart && !isspace(SourceLine[NewStart]))
        --NewStart;
      
      // Move up to the non-whitespace character we just saw.
      if (NewStart)
        ++NewStart;

      // If we're still within our limit, update the starting
      // position within the source/caret line.
      if (CaretEnd - NewStart <= TargetColumns) {
        CaretStart = NewStart;
        ExpandedRegion = true;
      }
    }

    // Move the end of the interesting region right until we've
    // pulled in something else interesting.
    if (CaretEnd != SourceLength) {
      unsigned NewEnd = CaretEnd;

      // Skip over any whitespace we see here; we're looking for
      // another bit of interesting text.
      while (NewEnd != SourceLength && isspace(SourceLine[NewEnd - 1]))
        ++NewEnd;
        
      // Skip over this bit of "interesting" text.
      while (NewEnd != SourceLength && !isspace(SourceLine[NewEnd - 1]))
        ++NewEnd;

      if (NewEnd - CaretStart <= TargetColumns) {
        CaretEnd = NewEnd;
        ExpandedRegion = true;
      }
    }

    if (!ExpandedRegion)
      break;
  }

  // [CaretStart, CaretEnd) is the slice we want. Update the various
  // output lines to show only this slice, with two-space padding
  // before the lines so that it looks nicer.
  if (CaretEnd < SourceLine.size())
    SourceLine.replace(CaretEnd, std::string::npos, "...");
  if (CaretEnd < CaretLine.size())
    CaretLine.erase(CaretEnd, std::string::npos);
  if (FixItInsertionLine.size() > CaretEnd)
    FixItInsertionLine.erase(CaretEnd, std::string::npos);
  
  if (CaretStart > 2) {
    SourceLine.replace(0, CaretStart, "  ...");
    CaretLine.replace(0, CaretStart, "     ");
    if (FixItInsertionLine.size() >= CaretStart)
      FixItInsertionLine.replace(0, CaretStart, "     ");
  }
}

void TextDiagnosticPrinter::EmitCaretDiagnostic(SourceLocation Loc,
                                                SourceRange *Ranges,
                                                unsigned NumRanges,
                                                SourceManager &SM,
                                          const CodeModificationHint *Hints,
                                                unsigned NumHints,
                                                unsigned Columns) {
  assert(!Loc.isInvalid() && "must have a valid source location here");

  // If this is a macro ID, first emit information about where this was
  // instantiated (recursively) then emit information about where. the token was
  // spelled from.
  if (!Loc.isFileID()) {
    SourceLocation OneLevelUp = SM.getImmediateInstantiationRange(Loc).first;
    // FIXME: Map ranges?
    EmitCaretDiagnostic(OneLevelUp, Ranges, NumRanges, SM, 0, 0, Columns);

    Loc = SM.getImmediateSpellingLoc(Loc);
    
    // Map the ranges.
    for (unsigned i = 0; i != NumRanges; ++i) {
      SourceLocation S = Ranges[i].getBegin(), E = Ranges[i].getEnd();
      if (S.isMacroID()) S = SM.getImmediateSpellingLoc(S);
      if (E.isMacroID()) E = SM.getImmediateSpellingLoc(E);
      Ranges[i] = SourceRange(S, E);
    }
    
    if (ShowLocation) {
      std::pair<FileID, unsigned> IInfo = SM.getDecomposedInstantiationLoc(Loc);
      
      // Emit the file/line/column that this expansion came from.
      OS << SM.getBuffer(IInfo.first)->getBufferIdentifier() << ':'
         << SM.getLineNumber(IInfo.first, IInfo.second) << ':';
      if (ShowColumn)
        OS << SM.getColumnNumber(IInfo.first, IInfo.second) << ':';
      OS << ' ';
    }
    OS << "note: instantiated from:\n";
    
    EmitCaretDiagnostic(Loc, Ranges, NumRanges, SM, Hints, NumHints, Columns);
    return;
  }
  
  // Decompose the location into a FID/Offset pair.
  std::pair<FileID, unsigned> LocInfo = SM.getDecomposedLoc(Loc);
  FileID FID = LocInfo.first;
  unsigned FileOffset = LocInfo.second;
  
  // Get information about the buffer it points into.
  std::pair<const char*, const char*> BufferInfo = SM.getBufferData(FID);
  const char *BufStart = BufferInfo.first;

  unsigned ColNo = SM.getColumnNumber(FID, FileOffset);
  unsigned CaretEndColNo 
    = ColNo + Lexer::MeasureTokenLength(Loc, SM, *LangOpts);

  // Rewind from the current position to the start of the line.
  const char *TokPtr = BufStart+FileOffset;
  const char *LineStart = TokPtr-ColNo+1; // Column # is 1-based.
  
  
  // Compute the line end.  Scan forward from the error position to the end of
  // the line.
  const char *LineEnd = TokPtr;
  while (*LineEnd != '\n' && *LineEnd != '\r' && *LineEnd != '\0')
    ++LineEnd;
  
  // Copy the line of code into an std::string for ease of manipulation.
  std::string SourceLine(LineStart, LineEnd);
  
  // Create a line for the caret that is filled with spaces that is the same
  // length as the line of source code.
  std::string CaretLine(LineEnd-LineStart, ' ');
  
  // Highlight all of the characters covered by Ranges with ~ characters.
  if (NumRanges) {
    unsigned LineNo = SM.getLineNumber(FID, FileOffset);
    
    for (unsigned i = 0, e = NumRanges; i != e; ++i)
      HighlightRange(Ranges[i], SM, LineNo, FID, CaretLine, SourceLine);
  }
  
  // Next, insert the caret itself.
  if (ColNo-1 < CaretLine.size())
    CaretLine[ColNo-1] = '^';
  else
    CaretLine.push_back('^');
  
  // Scan the source line, looking for tabs.  If we find any, manually expand
  // them to 8 characters and update the CaretLine to match.
  for (unsigned i = 0; i != SourceLine.size(); ++i) {
    if (SourceLine[i] != '\t') continue;
    
    // Replace this tab with at least one space.
    SourceLine[i] = ' ';
    
    // Compute the number of spaces we need to insert.
    unsigned NumSpaces = ((i+8)&~7) - (i+1);
    assert(NumSpaces < 8 && "Invalid computation of space amt");
    
    // Insert spaces into the SourceLine.
    SourceLine.insert(i+1, NumSpaces, ' ');
    
    // Insert spaces or ~'s into CaretLine.
    CaretLine.insert(i+1, NumSpaces, CaretLine[i] == '~' ? '~' : ' ');
  }
  
  // If we are in -fdiagnostics-print-source-range-info mode, we are trying to
  // produce easily machine parsable output.  Add a space before the source line
  // and the caret to make it trivial to tell the main diagnostic line from what
  // the user is intended to see.
  if (PrintRangeInfo) {
    SourceLine = ' ' + SourceLine;
    CaretLine = ' ' + CaretLine;
  }
    
  std::string FixItInsertionLine;
  if (NumHints && PrintFixItInfo) {
    for (const CodeModificationHint *Hint = Hints, *LastHint = Hints + NumHints;
         Hint != LastHint; ++Hint) {
      if (Hint->InsertionLoc.isValid()) {
        // We have an insertion hint. Determine whether the inserted
        // code is on the same line as the caret.
        std::pair<FileID, unsigned> HintLocInfo 
          = SM.getDecomposedInstantiationLoc(Hint->InsertionLoc);
        if (SM.getLineNumber(HintLocInfo.first, HintLocInfo.second) ==
              SM.getLineNumber(FID, FileOffset)) {
          // Insert the new code into the line just below the code
          // that the user wrote.
          unsigned HintColNo 
            = SM.getColumnNumber(HintLocInfo.first, HintLocInfo.second);
          unsigned LastColumnModified 
            = HintColNo - 1 + Hint->CodeToInsert.size();
          if (LastColumnModified > FixItInsertionLine.size())
            FixItInsertionLine.resize(LastColumnModified, ' ');
          std::copy(Hint->CodeToInsert.begin(), Hint->CodeToInsert.end(),
                    FixItInsertionLine.begin() + HintColNo - 1);
        } else {
          FixItInsertionLine.clear();
          break;
        }
      }
    }
  }

  // If the source line is too long for our terminal, select only the
  // "interesting" source region within that line.
  if (Columns && SourceLine.size() > Columns)
    SelectInterestingSourceRegion(SourceLine, CaretLine, FixItInsertionLine,
                                  CaretEndColNo, Columns);

  // Finally, remove any blank spaces from the end of CaretLine.
  while (CaretLine[CaretLine.size()-1] == ' ')
    CaretLine.erase(CaretLine.end()-1);
  
  // Emit what we have computed.
  OS << SourceLine << '\n';
  OS << CaretLine << '\n';

  if (!FixItInsertionLine.empty()) {
    if (PrintRangeInfo) 
      OS << ' ';
    OS << FixItInsertionLine << '\n';
  }
}

/// \brief Skip over whitespace in the string, starting at the given
/// index.
///
/// \returns The index of the first non-whitespace character that is
/// greater than or equal to Idx or, if no such character exists,
/// returns the end of the string.
static unsigned skipWhitespace(unsigned Idx, 
			       const llvm::SmallVectorImpl<char> &Str,
                               unsigned Length) {
  while (Idx < Length && isspace(Str[Idx]))
    ++Idx;
  return Idx;
}

/// \brief If the given character is the start of some kind of
/// balanced punctuation (e.g., quotes or parentheses), return the
/// character that will terminate the punctuation.
///
/// \returns The ending punctuation character, if any, or the NULL
/// character if the input character does not start any punctuation.
static inline char findMatchingPunctuation(char c) {
  switch (c) {
  case '\'': return '\'';
  case '`': return '\'';
  case '"':  return '"';
  case '(':  return ')';
  case '[': return ']'; 
  case '{': return '}';
  default: break;
  }

  return 0;
}

/// \brief Find the end of the word starting at the given offset
/// within a string.
///
/// \returns the index pointing one character past the end of the
/// word.
unsigned findEndOfWord(unsigned Start, 
                       const llvm::SmallVectorImpl<char> &Str,
                       unsigned Length, unsigned Column, 
                       unsigned Columns) {
  unsigned End = Start + 1;

  // Determine if the start of the string is actually opening
  // punctuation, e.g., a quote or parentheses.
  char EndPunct = findMatchingPunctuation(Str[Start]);
  if (!EndPunct) {
    // This is a normal word. Just find the first space character.
    while (End < Length && !isspace(Str[End]))
      ++End;
    return End;
  }

  // We have the start of a balanced punctuation sequence (quotes,
  // parentheses, etc.). Determine the full sequence is.
  llvm::SmallVector<char, 16> PunctuationEndStack;
  PunctuationEndStack.push_back(EndPunct);
  while (End < Length && !PunctuationEndStack.empty()) {
    if (Str[End] == PunctuationEndStack.back())
      PunctuationEndStack.pop_back();
    else if (char SubEndPunct = findMatchingPunctuation(Str[End]))
      PunctuationEndStack.push_back(SubEndPunct);

    ++End;
  }

  // Find the first space character after the punctuation ended.
  while (End < Length && !isspace(Str[End]))
    ++End;

  unsigned PunctWordLength = End - Start;
  if (// If the word fits on this line
      Column + PunctWordLength <= Columns ||
      // ... or the word is "short enough" to take up the next line
      // without too much ugly white space
      PunctWordLength < Columns/3)
    return End; // Take the whole thing as a single "word".

  // The whole quoted/parenthesized string is too long to print as a
  // single "word". Instead, find the "word" that starts just after
  // the punctuation and use that end-point instead. This will recurse
  // until it finds something small enough to consider a word.
  return findEndOfWord(Start + 1, Str, Length, Column + 1, Columns);
}

/// \brief Print the given string to a stream, word-wrapping it to
/// some number of columns in the process.
///
/// \brief OS the stream to which the word-wrapping string will be
/// emitted.
///
/// \brief Str the string to word-wrap and output.
///
/// \brief Columns the number of columns to word-wrap to.
///
/// \brief Column the column number at which the first character of \p
/// Str will be printed. This will be non-zero when part of the first
/// line has already been printed.
///
/// \brief Indentation the number of spaces to indent any lines beyond
/// the first line.
///
/// \returns true if word-wrapping was required, or false if the
/// string fit on the first line.
static bool PrintWordWrapped(llvm::raw_ostream &OS, 
			     const llvm::SmallVectorImpl<char> &Str, 
                             unsigned Columns, 
                             unsigned Column = 0,
                             unsigned Indentation = WordWrapIndentation) {
  unsigned Length = Str.size();
  
  // If there is a newline in this message somewhere, find that
  // newline and split the message into the part before the newline
  // (which will be word-wrapped) and the part from the newline one
  // (which will be emitted unchanged).
  for (unsigned I = 0; I != Length; ++I)
    if (Str[I] == '\n') {
      Length = I;
      break;
    }

  // The string used to indent each line.
  llvm::SmallString<16> IndentStr;
  IndentStr.assign(Indentation, ' ');
  bool Wrapped = false;
  for (unsigned WordStart = 0, WordEnd; WordStart < Length; 
       WordStart = WordEnd) {
    // Find the beginning of the next word.
    WordStart = skipWhitespace(WordStart, Str, Length);
    if (WordStart == Length)
      break;

    // Find the end of this word.
    WordEnd = findEndOfWord(WordStart, Str, Length, Column, Columns);
    
    // Does this word fit on the current line?
    unsigned WordLength = WordEnd - WordStart;
    if (Column + WordLength < Columns) {
      // This word fits on the current line; print it there.
      if (WordStart) {
        OS << ' ';
        Column += 1;
      }
      OS.write(&Str[WordStart], WordLength);
      Column += WordLength;
      continue;
    }

    // This word does not fit on the current line, so wrap to the next
    // line.
    OS << '\n';
    OS.write(&IndentStr[0], Indentation);
    OS.write(&Str[WordStart], WordLength);
    Column = Indentation + WordLength;
    Wrapped = true;
  }
  
  if (Length == Str.size())
    return Wrapped; // We're done.

  // There is a newline in the message, followed by something that
  // will not be word-wrapped. Print that.
  OS.write(&Str[Length], Str.size() - Length);
  return true;
}

void TextDiagnosticPrinter::HandleDiagnostic(Diagnostic::Level Level, 
                                             const DiagnosticInfo &Info) {
  // Keeps track of the the starting position of the location
  // information (e.g., "foo.c:10:4:") that precedes the error
  // message. We use this information to determine how long the
  // file+line+column number prefix is.
  uint64_t StartOfLocationInfo = OS.tell();

  // If the location is specified, print out a file/line/col and include trace
  // if enabled.
  if (Info.getLocation().isValid()) {
    const SourceManager &SM = Info.getLocation().getManager();
    PresumedLoc PLoc = SM.getPresumedLoc(Info.getLocation());
    unsigned LineNo = PLoc.getLine();
    
    // First, if this diagnostic is not in the main file, print out the
    // "included from" lines.
    if (LastWarningLoc != PLoc.getIncludeLoc()) {
      LastWarningLoc = PLoc.getIncludeLoc();
      PrintIncludeStack(LastWarningLoc, SM);
      StartOfLocationInfo = OS.tell();
    }
    
    // Compute the column number.
    if (ShowLocation) {
      OS << PLoc.getFilename() << ':' << LineNo << ':';
      if (ShowColumn)
        if (unsigned ColNo = PLoc.getColumn())
          OS << ColNo << ':';
      
      if (PrintRangeInfo && Info.getNumRanges()) {
        FileID CaretFileID =
          SM.getFileID(SM.getInstantiationLoc(Info.getLocation()));
        bool PrintedRange = false;
        
        for (unsigned i = 0, e = Info.getNumRanges(); i != e; ++i) {
          // Ignore invalid ranges.
          if (!Info.getRange(i).isValid()) continue;

          SourceLocation B = Info.getRange(i).getBegin();
          SourceLocation E = Info.getRange(i).getEnd();
          std::pair<FileID, unsigned> BInfo=SM.getDecomposedInstantiationLoc(B);
          
          E = SM.getInstantiationLoc(E);
          std::pair<FileID, unsigned> EInfo = SM.getDecomposedLoc(E);
          
          // If the start or end of the range is in another file, just discard
          // it.
          if (BInfo.first != CaretFileID || EInfo.first != CaretFileID)
            continue;
          
          // Add in the length of the token, so that we cover multi-char tokens.
          unsigned TokSize = Lexer::MeasureTokenLength(E, SM, *LangOpts);
          
          OS << '{' << SM.getLineNumber(BInfo.first, BInfo.second) << ':'
             << SM.getColumnNumber(BInfo.first, BInfo.second) << '-'
             << SM.getLineNumber(EInfo.first, EInfo.second) << ':'
             << (SM.getColumnNumber(EInfo.first, EInfo.second)+TokSize) << '}';
          PrintedRange = true;
        }
        
        if (PrintedRange)
          OS << ':';
      }
      OS << ' ';
    }
  }
  
  switch (Level) {
  case Diagnostic::Ignored: assert(0 && "Invalid diagnostic type");
  case Diagnostic::Note:    OS << "note: "; break;
  case Diagnostic::Warning: OS << "warning: "; break;
  case Diagnostic::Error:   OS << "error: "; break;
  case Diagnostic::Fatal:   OS << "fatal error: "; break;
  }
  
  llvm::SmallString<100> OutStr;
  Info.FormatDiagnostic(OutStr);
  
  if (PrintDiagnosticOption)
    if (const char *Opt = Diagnostic::getWarningOptionForDiag(Info.getID())) {
      OutStr += " [-W";
      OutStr += Opt;
      OutStr += ']';
    }
  
  if (MessageLength) {
    // We will be word-wrapping the error message, so compute the
    // column number where we currently are (after printing the
    // location information).
    unsigned Column = OS.tell() - StartOfLocationInfo;
    PrintWordWrapped(OS, OutStr, MessageLength, Column);
  } else {
    OS.write(OutStr.begin(), OutStr.size());
  }
  OS << '\n';
  
  // If caret diagnostics are enabled and we have location, we want to
  // emit the caret.  However, we only do this if the location moved
  // from the last diagnostic, if the last diagnostic was a note that
  // was part of a different warning or error diagnostic, or if the
  // diagnostic has ranges.  We don't want to emit the same caret
  // multiple times if one loc has multiple diagnostics.
  if (CaretDiagnostics && Info.getLocation().isValid() &&
      ((LastLoc != Info.getLocation()) || Info.getNumRanges() || 
       (LastCaretDiagnosticWasNote && Level != Diagnostic::Note) ||
       Info.getNumCodeModificationHints())) {
    // Cache the LastLoc, it allows us to omit duplicate source/caret spewage.
    LastLoc = Info.getLocation();
    LastCaretDiagnosticWasNote = (Level == Diagnostic::Note);

    // Get the ranges into a local array we can hack on.
    SourceRange Ranges[20];
    unsigned NumRanges = Info.getNumRanges();
    assert(NumRanges < 20 && "Out of space");
    for (unsigned i = 0; i != NumRanges; ++i)
      Ranges[i] = Info.getRange(i);
    
    unsigned NumHints = Info.getNumCodeModificationHints();
    for (unsigned idx = 0; idx < NumHints; ++idx) {
      const CodeModificationHint &Hint = Info.getCodeModificationHint(idx);
      if (Hint.RemoveRange.isValid()) {
        assert(NumRanges < 20 && "Out of space");
        Ranges[NumRanges++] = Hint.RemoveRange;
      }
    }

    EmitCaretDiagnostic(LastLoc, Ranges, NumRanges, LastLoc.getManager(),
                        Info.getCodeModificationHints(),
                        Info.getNumCodeModificationHints(),
                        MessageLength);
  }
  
  OS.flush();
}