clang/Lex/Preprocessor.cpp

//===--- Preprocess.cpp - C Language Family Preprocessor Implementation ---===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Chris Lattner and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file implements the Preprocessor interface.
//
//===----------------------------------------------------------------------===//
//
// TODO: GCC Diagnostics emitted by the lexer:
//
// ERROR  : __VA_ARGS__ can only appear in the expansion of a C99 variadic macro
//
// Options to support:
//   -H       - Print the name of each header file used.
//   -C -CC   - Do not discard comments for cpp.
//   -P       - Do not emit #line directives.
//   -d[MDNI] - Dump various things.
//   -fworking-directory - #line's with preprocessor's working dir.
//   -fpreprocessed
//   -dependency-file,-M,-MM,-MF,-MG,-MP,-MT,-MQ,-MD,-MMD
//   -W*
//   -w
//
// Messages to emit:
//   "Multiple include guards may be useful for:\n"
//
// TODO: Implement the include guard optimization.
//
//===----------------------------------------------------------------------===//

#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/MacroInfo.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/FileManager.h"
#include "clang/Basic/SourceManager.h"
#include <iostream>
using namespace llvm;
using namespace clang;

//===----------------------------------------------------------------------===//

Preprocessor::Preprocessor(Diagnostic &diags, const LangOptions &opts, 
                           FileManager &FM, SourceManager &SM) 
  : Diags(diags), Features(opts), FileMgr(FM), SourceMgr(SM),
    SystemDirIdx(0), NoCurDirSearch(false),
    CurLexer(0), CurNextDirLookup(0), CurMacroExpander(0) {
  // Clear stats.
  NumDirectives = NumIncluded = NumDefined = NumUndefined = NumPragma = 0;
  NumIf = NumElse = NumEndif = 0;
  NumEnteredSourceFiles = NumMacroExpanded = NumFastMacroExpanded = 0;
  MaxIncludeStackDepth = MaxMacroStackDepth = 0;
  NumSkipped = 0;
      
  // Macro expansion is enabled.
  DisableMacroExpansion = false;
  SkippingContents = false;
}

Preprocessor::~Preprocessor() {
  // Free any active lexers.
  delete CurLexer;
  
  while (!IncludeStack.empty()) {
    delete IncludeStack.back().TheLexer;
    IncludeStack.pop_back();
  }
}

/// getFileInfo - Return the PerFileInfo structure for the specified
/// FileEntry.
Preprocessor::PerFileInfo &Preprocessor::getFileInfo(const FileEntry *FE) {
  if (FE->getUID() >= FileInfo.size())
    FileInfo.resize(FE->getUID()+1);
  return FileInfo[FE->getUID()];
}  


/// AddKeywords - Add all keywords to the symbol table.
///
void Preprocessor::AddKeywords() {
  enum {
    C90Shift = 0,
    EXTC90   = 1 << C90Shift,
    NOTC90   = 2 << C90Shift,
    C99Shift = 2,
    EXTC99   = 1 << C99Shift,
    NOTC99   = 2 << C99Shift,
    CPPShift = 4,
    EXTCPP   = 1 << CPPShift,
    NOTCPP   = 2 << CPPShift,
    Mask     = 3
  };

  // Add keywords and tokens for the current language.
#define KEYWORD(NAME, FLAGS) \
  AddKeyword(#NAME+1, tok::kw##NAME,     \
             (FLAGS >> C90Shift) & Mask, \
             (FLAGS >> C99Shift) & Mask, \
             (FLAGS >> CPPShift) & Mask);
#define ALIAS(NAME, TOK) \
  AddKeyword(NAME, tok::kw_ ## TOK, 0, 0, 0);
#include "clang/Basic/TokenKinds.def"
}

/// Diag - Forwarding function for diagnostics.  This emits a diagnostic at
/// the specified LexerToken's location, translating the token's start
/// position in the current buffer into a SourcePosition object for rendering.
bool Preprocessor::Diag(SourceLocation Loc, unsigned DiagID, 
                        const std::string &Msg) {
  // If we are in a '#if 0' block, don't emit any diagnostics for notes,
  // warnings or extensions.
  if (isSkipping() && Diagnostic::isNoteWarningOrExtension(DiagID))
    return false;
  
  return Diags.Report(Loc, DiagID, Msg);
}
bool Preprocessor::Diag(const LexerToken &Tok, unsigned DiagID,
                        const std::string &Msg) {
  // If we are in a '#if 0' block, don't emit any diagnostics for notes,
  // warnings or extensions.
  if (isSkipping() && Diagnostic::isNoteWarningOrExtension(DiagID))
    return false;
  
  return Diag(Tok.getSourceLocation(), DiagID, Msg);
}

void Preprocessor::PrintStats() {
  std::cerr << "\n*** Preprocessor Stats:\n";
  std::cerr << FileInfo.size() << " files tracked.\n";
  unsigned NumOnceOnlyFiles = 0, MaxNumIncludes = 0, NumSingleIncludedFiles = 0;
  for (unsigned i = 0, e = FileInfo.size(); i != e; ++i) {
    NumOnceOnlyFiles += FileInfo[i].isImport;
    if (MaxNumIncludes < FileInfo[i].NumIncludes)
      MaxNumIncludes = FileInfo[i].NumIncludes;
    NumSingleIncludedFiles += FileInfo[i].NumIncludes == 1;
  }
  std::cerr << "  " << NumOnceOnlyFiles << " #import/#pragma once files.\n";
  std::cerr << "  " << NumSingleIncludedFiles << " included exactly once.\n";
  std::cerr << "  " << MaxNumIncludes << " max times a file is included.\n";
  
  std::cerr << NumDirectives << " directives found:\n";
  std::cerr << "  " << NumDefined << " #define.\n";
  std::cerr << "  " << NumUndefined << " #undef.\n";
  std::cerr << "  " << NumIncluded << " #include/#include_next/#import.\n";
  std::cerr << "    " << NumEnteredSourceFiles << " source files entered.\n";
  std::cerr << "    " << MaxIncludeStackDepth << " max include stack depth\n";
  std::cerr << "  " << NumIf << " #if/#ifndef/#ifdef.\n";
  std::cerr << "  " << NumElse << " #else/#elif.\n";
  std::cerr << "  " << NumEndif << " #endif.\n";
  std::cerr << "  " << NumPragma << " #pragma.\n";
  std::cerr << NumSkipped << " #if/#ifndef#ifdef regions skipped\n";

  std::cerr << NumMacroExpanded << " macros expanded, "
            << NumFastMacroExpanded << " on the fast path.\n";
  if (MaxMacroStackDepth > 1)
    std::cerr << "  " << MaxMacroStackDepth << " max macroexpand stack depth\n";
}

//===----------------------------------------------------------------------===//
// Source File Location Methods.
//===----------------------------------------------------------------------===//


/// LookupFile - Given a "foo" or <foo> reference, look up the indicated file,
/// return null on failure.  isAngled indicates whether the file reference is
/// for system #include's or not (i.e. using <> instead of "").
const FileEntry *Preprocessor::LookupFile(const std::string &Filename, 
                                          bool isSystem,
                                          const DirectoryLookup *FromDir,
                                          const DirectoryLookup *&NextDir) {
  assert(CurLexer && "Cannot enter a #include inside a macro expansion!");
  NextDir = 0;
  
  // If 'Filename' is absolute, check to see if it exists and no searching.
  // FIXME: this should be a sys::Path interface, this doesn't handle things
  // like C:\foo.txt right, nor win32 \\network\device\blah.
  if (Filename[0] == '/') {
    // If this was an #include_next "/absolute/file", fail.
    if (FromDir) return 0;

    // Otherwise, just return the file.
    return FileMgr.getFile(Filename);
  }
  
  // Step #0, unless disabled, check to see if the file is in the #includer's
  // directory.  This search is not done for <> headers.
  if (!isSystem && !FromDir && !NoCurDirSearch) {
    const FileEntry *CurFE = 
      SourceMgr.getFileEntryForFileID(CurLexer->getCurFileID());
    if (CurFE) {
      if (const FileEntry *FE = 
            FileMgr.getFile(CurFE->getDir()->getName()+"/"+Filename)) {
        if (CurNextDirLookup)
          NextDir = CurNextDirLookup;
        else
          NextDir = &SearchDirs[0];
        return FE;
      }
    }
  }
  
  // If this is a system #include, ignore the user #include locs.
  unsigned i = isSystem ? SystemDirIdx : 0;

  // If this is a #include_next request, start searching after the directory the
  // file was found in.
  if (FromDir)
    i = FromDir-&SearchDirs[0];
  
  // Check each directory in sequence to see if it contains this file.
  for (; i != SearchDirs.size(); ++i) {
    // Concatenate the requested file onto the directory.
    // FIXME: should be in sys::Path.
    if (const FileEntry *FE = 
          FileMgr.getFile(SearchDirs[i].getDir()->getName()+"/"+Filename)) {
      NextDir = &SearchDirs[i+1];
      return FE;
    }
  }
  
  // Otherwise, didn't find it.
  return 0;
}

/// EnterSourceFile - Add a source file to the top of the include stack and
/// start lexing tokens from it instead of the current buffer.  Return true
/// on failure.
void Preprocessor::EnterSourceFile(unsigned FileID,
                                   const DirectoryLookup *NextDir) {
  ++NumEnteredSourceFiles;
  
  // Add the current lexer to the include stack.
  if (CurLexer) {
    IncludeStack.push_back(IncludeStackInfo(CurLexer, CurNextDirLookup));
  } else {
    assert(CurMacroExpander == 0 && "Cannot #include a file inside a macro!");
  }

  if (MaxIncludeStackDepth < IncludeStack.size())
    MaxIncludeStackDepth = IncludeStack.size();
  
  const SourceBuffer *Buffer = SourceMgr.getBuffer(FileID);
  
  CurLexer         = new Lexer(Buffer, FileID, *this);
  CurNextDirLookup = NextDir;
}

/// EnterMacro - Add a Macro to the top of the include stack and start lexing
/// tokens from it instead of the current buffer.  Return true on failure.
bool Preprocessor::EnterMacro(LexerToken &Tok) {
  IdentifierTokenInfo *Identifier = Tok.getIdentifierInfo();
  MacroInfo &MI = *Identifier->getMacroInfo();
  SourceLocation ExpandLoc = Tok.getSourceLocation();
  unsigned MacroID = SourceMgr.getMacroID(Identifier, ExpandLoc);
  if (CurLexer) {
    IncludeStack.push_back(IncludeStackInfo(CurLexer, CurNextDirLookup));
    CurLexer         = 0;
    CurNextDirLookup = 0;
  } else if (CurMacroExpander) {
    MacroStack.push_back(CurMacroExpander);
  }

  if (MaxMacroStackDepth < MacroStack.size())
    MaxMacroStackDepth = MacroStack.size();
  
  // TODO: Figure out arguments.
  
  // Mark the macro as currently disabled, so that it is not recursively
  // expanded.
  MI.DisableMacro();
  
  CurMacroExpander = new MacroExpander(MI, MacroID, *this,
                                       Tok.isAtStartOfLine(), 
                                       Tok.hasLeadingSpace());
  return false;
}


//===----------------------------------------------------------------------===//
// Lexer Event Handling.
//===----------------------------------------------------------------------===//

/// HandleIdentifier - This callback is invoked when the lexer reads an
/// identifier.  This callback looks up the identifier in the map and/or
/// potentially macro expands it or turns it into a named token (like 'for').
bool Preprocessor::HandleIdentifier(LexerToken &Identifier) {
  if (Identifier.getIdentifierInfo() == 0) {
    // If we are skipping tokens (because we are in a #if 0 block), there will
    // be no identifier info, just return the token.
    assert(isSkipping() && "Token isn't an identifier?");
    return false;
  }
  IdentifierTokenInfo &ITI = *Identifier.getIdentifierInfo();
  
  // FIXME: Check for poisoning in ITI?
  
  if (MacroInfo *MI = ITI.getMacroInfo()) {
    if (MI->isEnabled() && !DisableMacroExpansion) {
      ++NumMacroExpanded;
      // If we started lexing a macro, enter the macro expansion body.
      // FIXME: Read/Validate the argument list here!
      
      // If this macro expands to no tokens, don't bother to push it onto the
      // expansion stack, only to take it right back off.
      if (MI->getNumTokens() == 0) {
        // Ignore this macro use, just return the next token in the current
        // buffer.
        bool HadLeadingSpace = Identifier.hasLeadingSpace();
        bool IsAtStartOfLine = Identifier.isAtStartOfLine();
        
        if (Lex(Identifier)) return true;
        
        // If the identifier isn't on some OTHER line, inherit the leading
        // whitespace/first-on-a-line property of this token.  This handles
        // stuff like "! XX," -> "! ," and "   XX," -> "    ,", when XX is
        // empty.
        if (!Identifier.isAtStartOfLine()) {
          if (IsAtStartOfLine) Identifier.SetFlag(LexerToken::StartOfLine);
          if (HadLeadingSpace) Identifier.SetFlag(LexerToken::LeadingSpace);
        }
        ++NumFastMacroExpanded;
        return false;
        
      } else if (MI->getNumTokens() == 1 &&
                 // Don't handle identifiers, which might need recursive
                 // expansion.
                 MI->getReplacementToken(0).getIdentifierInfo() == 0) {
        // FIXME: Function-style macros only if no arguments?

        // Otherwise, if this macro expands into a single trivially-expanded
        // token: expand it now.  This handles common cases like 
        // "#define VAL 42".
        
        // Propagate the isAtStartOfLine/hasLeadingSpace markers of the macro
        // identifier to the expanded token.
        bool isAtStartOfLine = Identifier.isAtStartOfLine();
        bool hasLeadingSpace = Identifier.hasLeadingSpace();

        // Replace the result token.
        Identifier = MI->getReplacementToken(0);

        // Restore the StartOfLine/LeadingSpace markers.
        Identifier.SetFlagValue(LexerToken::StartOfLine , isAtStartOfLine);
        Identifier.SetFlagValue(LexerToken::LeadingSpace, hasLeadingSpace);
        
        // FIXME: Get correct macro expansion stack location info!
        
        // Since this is not an identifier token, it can't be macro expanded, so
        // we're done.
        ++NumFastMacroExpanded;
        return false;
      }
    
      // Start expanding the macro (FIXME, pass arguments).
      if (EnterMacro(Identifier))
        return true;
    
      // Now that the macro is at the top of the include stack, ask the
      // preprocessor to read the next token from it.
      return Lex(Identifier);
    }
  }

  // Change the kind of this identifier to the appropriate token kind, e.g.
  // turning "for" into a keyword.
  Identifier.SetKind(ITI.getTokenID());
    
  // If this is an extension token, diagnose its use.
  if (ITI.isExtensionToken() && Diag(Identifier, diag::ext_token_used))
    return true;
  return false;  
}

/// HandleEndOfFile - This callback is invoked when the lexer hits the end of
/// the current file.  This either returns the EOF token or pops a level off
/// the include stack and keeps going.
bool Preprocessor::HandleEndOfFile(LexerToken &Result) {
  assert(!CurMacroExpander &&
         "Ending a file when currently in a macro!");
  
  // If we are in a #if 0 block skipping tokens, and we see the end of the file,
  // this is an error condition.  Just return the EOF token up to
  // SkipExcludedConditionalBlock.  The Lexer will have already have issued
  // errors for the unterminated #if's on the conditional stack.
  if (isSkipping()) {
    Result.StartToken(CurLexer);
    Result.SetKind(tok::eof);
    Result.SetStart(CurLexer->BufferEnd);
    Result.SetEnd(CurLexer->BufferEnd);
    return false;
  }
  
  // If this is a #include'd file, pop it off the include stack and continue
  // lexing the #includer file.
  if (!IncludeStack.empty()) {
    // We're done with the #included file.
    delete CurLexer;
    CurLexer         = IncludeStack.back().TheLexer;
    CurNextDirLookup = IncludeStack.back().TheDirLookup;
    IncludeStack.pop_back();
    return Lex(Result);
  }
  
  Result.StartToken(CurLexer);
  Result.SetKind(tok::eof);
  Result.SetStart(CurLexer->BufferEnd);
  Result.SetEnd(CurLexer->BufferEnd);
  
  // We're done with the #included file.
  delete CurLexer;
  CurLexer = 0;
  return false;
}

/// HandleEndOfMacro - This callback is invoked when the lexer hits the end of
/// the current macro.  This either returns the EOF token or pops a level off
/// the include stack and keeps going.
bool Preprocessor::HandleEndOfMacro(LexerToken &Result) {
  assert(CurMacroExpander && !CurLexer &&
         "Ending a macro when currently in a #include file!");

  // Mark macro not ignored now that it is no longer being expanded.
  CurMacroExpander->getMacro().EnableMacro();
  delete CurMacroExpander;

  if (!MacroStack.empty()) {
    // In a nested macro invocation, continue lexing from the macro.
    CurMacroExpander = MacroStack.back();
    MacroStack.pop_back();
    return Lex(Result);
  } else {
    CurMacroExpander = 0;
    // Handle this like a #include file being popped off the stack.
    return HandleEndOfFile(Result);
  }
}


//===----------------------------------------------------------------------===//
// Utility Methods for Preprocessor Directive Handling.
//===----------------------------------------------------------------------===//

/// DiscardUntilEndOfDirective - Read and discard all tokens remaining on the
/// current line until the tok::eom token is found.
bool Preprocessor::DiscardUntilEndOfDirective() {
  LexerToken Tmp;
  do {
    if (LexUnexpandedToken(Tmp)) return true;
  } while (Tmp.getKind() != tok::eom);
  return false;
}

/// ReadMacroName - Lex and validate a macro name, which occurs after a
/// #define or #undef.  This sets the token kind to eom and discards the rest
/// of the macro line if the macro name is invalid.
bool Preprocessor::ReadMacroName(LexerToken &MacroNameTok) {
  // Read the token, don't allow macro expansion on it.
  if (LexUnexpandedToken(MacroNameTok))
    return true;
  
  // Missing macro name?
  if (MacroNameTok.getKind() == tok::eom)
    return Diag(MacroNameTok, diag::err_pp_missing_macro_name);
  
  if (MacroNameTok.getIdentifierInfo() == 0) {
    if (Diag(MacroNameTok, diag::err_pp_macro_not_identifier))
      return true;
    // Fall through on error.
  } else if (0) {
    // FIXME: Error if defining a C++ named operator.
    
  } else if (0) {
    // FIXME: Error if defining "defined", "__DATE__", and other predef macros
    // in C99 6.10.8.4.
  } else {
    // Okay, we got a good identifier node.  Return it.
    return false;
  }
  
  
  // Invalid macro name, read and discard the rest of the line.  Then set the
  // token kind to tok::eom.
  MacroNameTok.SetKind(tok::eom);
  return DiscardUntilEndOfDirective();
}

/// CheckEndOfDirective - Ensure that the next token is a tok::eom token.  If
/// not, emit a diagnostic and consume up until the eom.
bool Preprocessor::CheckEndOfDirective(const char *DirType) {
  LexerToken Tmp;
  if (Lex(Tmp)) return true;
  // There should be no tokens after the directive, but we allow them as an
  // extension.
  if (Tmp.getKind() != tok::eom) {
    if (Diag(Tmp, diag::ext_pp_extra_tokens_at_eol, DirType) ||
        DiscardUntilEndOfDirective())
      return true;
  }
  return false;
}



/// SkipExcludedConditionalBlock - We just read a #if or related directive and
/// decided that the subsequent tokens are in the #if'd out portion of the
/// file.  Lex the rest of the file, until we see an #endif.  If
/// FoundNonSkipPortion is true, then we have already emitted code for part of
/// this #if directive, so #else/#elif blocks should never be entered. If ElseOk
/// is true, then #else directives are ok, if not, then we have already seen one
/// so a #else directive is a duplicate.  When this returns, the caller can lex
/// the first valid token.
bool Preprocessor::SkipExcludedConditionalBlock(const char *IfTokenLoc,
                                                bool FoundNonSkipPortion,
                                                bool FoundElse) {
  ++NumSkipped;
  assert(MacroStack.empty() && CurMacroExpander == 0 && CurLexer &&
         "Lexing a macro, not a file?");

  CurLexer->pushConditionalLevel(IfTokenLoc, /*isSkipping*/false,
                                 FoundNonSkipPortion, FoundElse);
  
  // Know that we are going to be skipping tokens.  Set this flag to indicate
  // this, which has a couple of effects:
  //  1. If EOF of the current lexer is found, the include stack isn't popped.
  //  2. Identifier information is not looked up for identifier tokens.  As an
  //     effect of this, implicit macro expansion is naturally disabled.
  //  3. "#" tokens at the start of a line are treated as normal tokens, not
  //     implicitly transformed by the lexer.
  //  4. All notes, warnings, and extension messages are disabled.
  //
  SkippingContents = true;
  LexerToken Tok;
  while (1) {
    if (CurLexer->Lex(Tok)) return true;
    
    // If this is the end of the buffer, we have an error.  The lexer will have
    // already handled this error condition, so just return and let the caller
    // lex after this #include.
    if (Tok.getKind() == tok::eof) break;
    
    // If this token is not a preprocessor directive, just skip it.
    if (Tok.getKind() != tok::hash || !Tok.isAtStartOfLine())
      continue;
      
    // We just parsed a # character at the start of a line, so we're in
    // directive mode.  Tell the lexer this so any newlines we see will be
    // converted into an EOM token (this terminates the macro).
    CurLexer->ParsingPreprocessorDirective = true;
    
    // Read the next token, the directive flavor.
    if (LexUnexpandedToken(Tok)) return true;
    
    // If this isn't an identifier directive (e.g. is "# 1\n" or "#\n", or
    // something bogus), skip it.
    if (Tok.getKind() != tok::identifier) {
      CurLexer->ParsingPreprocessorDirective = false;
      continue;
    }
    
    // If the first letter isn't i or e, it isn't intesting to us.  We know that
    // this is safe in the face of spelling differences, because there is no way
    // to spell an i/e in a strange way that is another letter.  Skipping this
    // allows us to avoid computing the spelling for #define/#undef and other
    // common directives.
    char FirstChar = Tok.getStart()[0];
    if (FirstChar >= 'a' && FirstChar <= 'z' && 
        FirstChar != 'i' && FirstChar != 'e') {
      CurLexer->ParsingPreprocessorDirective = false;
      continue;
    }
    
    // Strip out trigraphs and embedded newlines.
    std::string Directive = Lexer::getSpelling(Tok, Features);
    FirstChar = Directive[0];
    if (FirstChar == 'i' && Directive[1] == 'f') {
      if (Directive == "if" || Directive == "ifdef" || Directive == "ifndef") {
        // We know the entire #if/#ifdef/#ifndef block will be skipped, don't
        // bother parsing the condition.
        if (DiscardUntilEndOfDirective()) return true;
        CurLexer->pushConditionalLevel(Tok.getStart(), /*wasskipping*/true,
                                       /*foundnonskip*/false,/*fnddelse*/false);
      }
    } else if (FirstChar == 'e') {
      if (Directive == "endif") {
        if (CheckEndOfDirective("#endif")) return true;
        PPConditionalInfo CondInfo;
        CondInfo.WasSkipping = true; // Silence bogus warning.
        bool InCond = CurLexer->popConditionalLevel(CondInfo);
        assert(!InCond && "Can't be skipping if not in a conditional!");
        
        // If we popped the outermost skipping block, we're done skipping!
        if (!CondInfo.WasSkipping)
          break;
      } else if (Directive == "else") {
        // #else directive in a skipping conditional.  If not in some other
        // skipping conditional, and if #else hasn't already been seen, enter it
        // as a non-skipping conditional.
        if (CheckEndOfDirective("#else")) return true;
        PPConditionalInfo &CondInfo = CurLexer->peekConditionalLevel();
        
        // If this is a #else with a #else before it, report the error.
        if (CondInfo.FoundElse && Diag(Tok, diag::pp_err_else_after_else))
          return true;
        
        // Note that we've seen a #else in this conditional.
        CondInfo.FoundElse = true;
        
        // If the conditional is at the top level, and the #if block wasn't
        // entered, enter the #else block now.
        if (!CondInfo.WasSkipping && !CondInfo.FoundNonSkip) {
          CondInfo.FoundNonSkip = true;
          break;
        }
      } else if (Directive == "elif") {
        PPConditionalInfo &CondInfo = CurLexer->peekConditionalLevel();

        bool ShouldEnter;
        // If this is in a skipping block or if we're already handled this #if
        // block, don't bother parsing the condition.
        if (CondInfo.WasSkipping || CondInfo.FoundNonSkip) {
          if (DiscardUntilEndOfDirective()) return true;
          ShouldEnter = false;
        } else {
          // Evaluate the #elif condition!
          const char *Start = CurLexer->BufferPtr;

          // Restore the value of SkippingContents so that identifiers are
          // looked up, etc, inside the #elif expression.
          assert(SkippingContents && "We have to be skipping here!");
          SkippingContents = false;
          if (EvaluateDirectiveExpression(ShouldEnter))
            return true;
          SkippingContents = true;
        }
        
        // If this is a #elif with a #else before it, report the error.
        if (CondInfo.FoundElse && Diag(Tok, diag::pp_err_elif_after_else))
          return true;
        
        // If this condition is true, enter it!
        if (ShouldEnter) {
          CondInfo.FoundNonSkip = true;
          break;
        }
      }
    }
    
    CurLexer->ParsingPreprocessorDirective = false;
  }

  // Finally, if we are out of the conditional (saw an #endif or ran off the end
  // of the file, just stop skipping and return to lexing whatever came after
  // the #if block.
  SkippingContents = false;

  return false;
}

//===----------------------------------------------------------------------===//
// Preprocessor Directive Handling.
//===----------------------------------------------------------------------===//

/// HandleDirective - This callback is invoked when the lexer sees a # token
/// at the start of a line.  This consumes the directive, modifies the 
/// lexer/preprocessor state, and advances the lexer(s) so that the next token
/// read is the correct one.
bool Preprocessor::HandleDirective(LexerToken &Result) {
  // FIXME: TRADITIONAL: # with whitespace before it not recognized by K&R?
  
  // We just parsed a # character at the start of a line, so we're in directive
  // mode.  Tell the lexer this so any newlines we see will be converted into an
  // EOM token (this terminates the macro).
  CurLexer->ParsingPreprocessorDirective = true;
  
  ++NumDirectives;
  
  // Read the next token, the directive flavor.
  if (LexUnexpandedToken(Result))
    return true;   // Bail out.
  
  switch (Result.getKind()) {
  default: break;
  case tok::eom:
    return false;   // null directive.

#if 0
  case tok::numeric_constant:
    // FIXME: implement # 7 line numbers!
    break;
#endif
  case tok::kw_else:
    return HandleElseDirective(Result);
  case tok::kw_if:
    return HandleIfDirective(Result);
  case tok::identifier:
    // Strip out trigraphs and embedded newlines.
    std::string Directive = Lexer::getSpelling(Result, Features);
    bool isExtension = false;
    switch (Directive.size()) {
    case 4:
      if (Directive == "line")
        ;
      if (Directive == "elif")
        return HandleElifDirective(Result);
      if (Directive == "sccs") {
        isExtension = true;
        // SCCS is the same as #ident.
      }
      break;
    case 5:
      if (Directive == "endif")
        return HandleEndifDirective(Result);
      if (Directive == "ifdef")
        return HandleIfdefDirective(Result, false);
      if (Directive == "undef")
        return HandleUndefDirective(Result);
      if (Directive == "error")
        return HandleUserDiagnosticDirective(Result, false);
      if (Directive == "ident")
        isExtension = true;
      break;
    case 6:
      if (Directive == "define")
        return HandleDefineDirective(Result);
      if (Directive == "ifndef")
        return HandleIfdefDirective(Result, true);
      if (Directive == "import")
        return HandleImportDirective(Result);
      if (Directive == "pragma") {
        // FIXME: implement #pragma
        ++NumPragma;
#if 1
        // Read the rest of the PP line.
        do {
          if (Lex(Result)) return true;
        } while (Result.getKind() != tok::eom);
        
        return false;
#endif
      } else if (Directive == "assert") {
        isExtension = true;
      }
      break;
    case 7:
      if (Directive == "include")  // Handle #include.
        return HandleIncludeDirective(Result);
      if (Directive == "warning")
        return Diag(Result, diag::ext_pp_warning_directive) ||
               HandleUserDiagnosticDirective(Result, true);
      break;
    case 8:
      if (Directive == "unassert") {
        isExtension = true;
      }
      break;
    case 12:
      if (Directive == "include_next") // Handle #include_next.
        return HandleIncludeNextDirective(Result);
      break;
    }
    break;
  }
  
  // If we reached here, the preprocessing token is not valid!
  if (Diag(Result, diag::err_pp_invalid_directive))
    return true;
  
  // Read the rest of the PP line.
  do {
    if (Lex(Result)) return true;
  } while (Result.getKind() != tok::eom);
  
  // Okay, we're done parsing the directive.
  return false;
}

bool Preprocessor::HandleUserDiagnosticDirective(LexerToken &Result, 
                                                 bool isWarning) {
  // Read the rest of the line raw.  We do this because we don't want macros
  // to be expanded and we don't require that the tokens be valid preprocessing
  // tokens.  For example, this is allowed: "#warning `   'foo".  GCC does
  // collapse multiple consequtive white space between tokens, but this isn't
  // specified by the standard.
  std::string Message = CurLexer->ReadToEndOfLine();

  unsigned DiagID = isWarning ? diag::pp_hash_warning : diag::err_pp_hash_error;
  return Diag(Result, DiagID, Message);
}

/// HandleIncludeDirective - The "#include" tokens have just been read, read the
/// file to be included from the lexer, then include it!  This is a common
/// routine with functionality shared between #include, #include_next and
/// #import.
bool Preprocessor::HandleIncludeDirective(LexerToken &IncludeTok,
                                          const DirectoryLookup *LookupFrom,
                                          bool isImport) {
  ++NumIncluded;
  LexerToken FilenameTok;
  if (CurLexer->LexIncludeFilename(FilenameTok))
    return true;
  
  // If the token kind is EOM, the error has already been diagnosed.
  if (FilenameTok.getKind() == tok::eom)
    return false;

  // Check that we don't have infinite #include recursion.
  if (IncludeStack.size() == MaxAllowedIncludeStackDepth-1)
    return Diag(FilenameTok, diag::err_pp_include_too_deep);
  
  // Get the text form of the filename.
  std::string Filename = CurLexer->getSpelling(FilenameTok);
  assert(!Filename.empty() && "Can't have tokens with empty spellings!");
  
  // Make sure the filename is <x> or "x".
  bool isAngled;
  if (Filename[0] == '<') {
    isAngled = true;
    if (Filename[Filename.size()-1] != '>')
      return Diag(FilenameTok, diag::err_pp_expects_filename);
  } else if (Filename[0] == '"') {
    isAngled = false;
    if (Filename[Filename.size()-1] != '"')
      return Diag(FilenameTok, diag::err_pp_expects_filename);
  } else {
    return Diag(FilenameTok, diag::err_pp_expects_filename);
  }
  
  // Remove the quotes.
  Filename = std::string(Filename.begin()+1, Filename.end()-1);
  
  // Diagnose #include "" as invalid.
  if (Filename.empty())
    return Diag(FilenameTok, diag::err_pp_empty_filename);
  
  // Search include directories.
  const DirectoryLookup *NextDir;
  const FileEntry *File = LookupFile(Filename, isAngled, LookupFrom, NextDir);
  if (File == 0)
    return Diag(FilenameTok, diag::err_pp_file_not_found);
  
  // Get information about this file.
  PerFileInfo &FileInfo = getFileInfo(File);
  
  // If this is a #import directive, check that we have not already imported
  // this header.
  if (isImport) {
    // If this has already been imported, don't import it again.
    FileInfo.isImport = true;
    
    // Has this already been #import'ed or #include'd?
    if (FileInfo.NumIncludes) return false;
  } else {
    // Otherwise, if this is a #include of a file that was previously #import'd
    // or if this is the second #include of a #pragma once file, ignore it.
    if (FileInfo.isImport)
      return false;
  }

  // Look up the file, create a File ID for it.
  unsigned FileID = 
    SourceMgr.createFileID(File, FilenameTok.getSourceLocation());
  if (FileID == 0)
    return Diag(FilenameTok, diag::err_pp_file_not_found);

  // Finally, if all is good, enter the new file!
  EnterSourceFile(FileID, NextDir);

  // Increment the number of times this file has been included.
  ++FileInfo.NumIncludes;
  
  return false;
}

/// HandleIncludeNextDirective - Implements #include_next.
///
bool Preprocessor::HandleIncludeNextDirective(LexerToken &IncludeNextTok) {
  if (Diag(IncludeNextTok, diag::ext_pp_include_next_directive))
    return true;
  
  // #include_next is like #include, except that we start searching after
  // the current found directory.  If we can't do this, issue a
  // diagnostic.
  const DirectoryLookup *Lookup = CurNextDirLookup;
  if (IncludeStack.empty()) {
    Lookup = 0;
    if (Diag(IncludeNextTok, diag::pp_include_next_in_primary))
      return true;
  } else if (Lookup == 0) {
    if (Diag(IncludeNextTok, diag::pp_include_next_absolute_path))
      return true;
  }
  
  return HandleIncludeDirective(IncludeNextTok, Lookup);
}

/// HandleImportDirective - Implements #import.
///
bool Preprocessor::HandleImportDirective(LexerToken &ImportTok) {
  if (Diag(ImportTok, diag::ext_pp_import_directive)) return true;
  
  return HandleIncludeDirective(ImportTok, 0, true);
}

/// HandleDefineDirective - Implements #define.  This consumes the entire macro
/// line then lets the caller lex the next real token.
///
bool Preprocessor::HandleDefineDirective(LexerToken &DefineTok) {
  ++NumDefined;
  LexerToken MacroNameTok;
  if (ReadMacroName(MacroNameTok))
    return true;
  
  // Error reading macro name?  If so, diagnostic already issued.
  if (MacroNameTok.getKind() == tok::eom)
    return false;
  
  MacroInfo *MI = new MacroInfo(MacroNameTok.getSourceLocation());
  
  LexerToken Tok;
  if (LexUnexpandedToken(Tok)) return true;
  
  if (Tok.getKind() == tok::eom) {
    // If there is no body to this macro, we have no special handling here.
  } else if (Tok.getKind() == tok::l_paren && !Tok.hasLeadingSpace()) {
    // This is a function-like macro definition.
    //assert(0 && "Function-like macros not implemented!");
#warning function like macros
    return DiscardUntilEndOfDirective();

  } else if (!Tok.hasLeadingSpace()) {
    // C99 requires whitespace between the macro definition and the body.  Emit
    // a diagnostic for something like "#define X+".
    if (Features.C99) {
      if (Diag(Tok, diag::ext_c99_whitespace_required_after_macro_name))
        return true;
    } else {
      // FIXME: C90/C++ do not get this diagnostic, but it does get a similar
      // one in some cases!
    }
  } else {
    // This is a normal token with leading space.  Clear the leading space
    // marker on the first token to get proper expansion.
    Tok.ClearFlag(LexerToken::LeadingSpace);
  }
  
  // Read the rest of the macro body.
  while (Tok.getKind() != tok::eom) {
    MI->AddTokenToBody(Tok);
    
    // FIXME: See create_iso_definition.
    
    // Get the next token of the macro.
    if (LexUnexpandedToken(Tok)) return true;
  }
  
  // Finally, if this identifier already had a macro defined for it, verify that
  // the macro bodies are identical and free the old definition.
  if (MacroInfo *OtherMI = MacroNameTok.getIdentifierInfo()->getMacroInfo()) {
    // FIXME: Verify the definition is the same.
    // Macros must be identical.  This means all tokes and whitespace separation
    // must be the same.
    delete OtherMI;
  }
  
  MacroNameTok.getIdentifierInfo()->setMacroInfo(MI);
  return false;
}


/// HandleUndefDirective - Implements #undef.
///
bool Preprocessor::HandleUndefDirective(LexerToken &UndefTok) {
  ++NumUndefined;
  LexerToken MacroNameTok;
  if (ReadMacroName(MacroNameTok))
    return true;
  
  // Error reading macro name?  If so, diagnostic already issued.
  if (MacroNameTok.getKind() == tok::eom)
    return false;
  
  // Check to see if this is the last token on the #undef line.
  if (CheckEndOfDirective("#undef")) return true;
  
  // Okay, we finally have a valid identifier to undef.
  MacroInfo *MI = MacroNameTok.getIdentifierInfo()->getMacroInfo();
  
  // If the macro is not defined, this is a noop undef, just return.
  if (MI == 0) return false;
  
#if 0 // FIXME: implement warn_unused_macros.
  if (CPP_OPTION (pfile, warn_unused_macros))
    _cpp_warn_if_unused_macro (pfile, node, NULL);
#endif
  
  // Free macro definition.
  delete MI;
  MacroNameTok.getIdentifierInfo()->setMacroInfo(0);
  return false;
}


/// HandleIfdefDirective - Implements the #ifdef/#ifndef directive.  isIfndef is
/// true when this is a #ifndef directive.
///
bool Preprocessor::HandleIfdefDirective(LexerToken &Result, bool isIfndef) {
  ++NumIf;
  LexerToken DirectiveTok = Result;
  
  LexerToken MacroNameTok;
  if (ReadMacroName(MacroNameTok))
    return true;
  
  // Error reading macro name?  If so, diagnostic already issued.
  if (MacroNameTok.getKind() == tok::eom)
    return false;
  
  // Check to see if this is the last token on the #if[n]def line.
  if (CheckEndOfDirective("#ifdef")) return true;
  
  // Should we include the stuff contained by this directive?
  if (!MacroNameTok.getIdentifierInfo()->getMacroInfo() == isIfndef) {
    // Yes, remember that we are inside a conditional, then lex the next token.
    CurLexer->pushConditionalLevel(DirectiveTok.getStart(), /*wasskip*/false,
                                   /*foundnonskip*/true, /*foundelse*/false);
    return false;
  } else {
    // No, skip the contents of this block and return the first token after it.
    return SkipExcludedConditionalBlock(DirectiveTok.getStart(),
                                        /*Foundnonskip*/false, 
                                        /*FoundElse*/false);
  }
}

/// HandleIfDirective - Implements the #if directive.
///
bool Preprocessor::HandleIfDirective(LexerToken &IfToken) {
  ++NumIf;
  const char *Start = CurLexer->BufferPtr;

  bool ConditionalTrue = false;
  if (EvaluateDirectiveExpression(ConditionalTrue))
    return true;
  
  // Should we include the stuff contained by this directive?
  if (ConditionalTrue) {
    // Yes, remember that we are inside a conditional, then lex the next token.
    CurLexer->pushConditionalLevel(IfToken.getStart(), /*wasskip*/false,
                                   /*foundnonskip*/true, /*foundelse*/false);
    return false;
  } else {
    // No, skip the contents of this block and return the first token after it.
    return SkipExcludedConditionalBlock(IfToken.getStart(),
                                        /*Foundnonskip*/false, 
                                        /*FoundElse*/false);
  }
}

/// HandleEndifDirective - Implements the #endif directive.
///
bool Preprocessor::HandleEndifDirective(LexerToken &EndifToken) {
  ++NumEndif;
  // Check that this is the whole directive.
  if (CheckEndOfDirective("#endif")) return true;
  
  PPConditionalInfo CondInfo;
  if (CurLexer->popConditionalLevel(CondInfo)) {
    // No conditionals on the stack: this is an #endif without an #if.
    return Diag(EndifToken, diag::err_pp_endif_without_if);
  }
  
  assert(!CondInfo.WasSkipping && !isSkipping() &&
         "This code should only be reachable in the non-skipping case!");
  return false;
}


bool Preprocessor::HandleElseDirective(LexerToken &Result) {
  ++NumElse;
  // #else directive in a non-skipping conditional... start skipping.
  if (CheckEndOfDirective("#else")) return true;
  
  PPConditionalInfo CI;
  if (CurLexer->popConditionalLevel(CI))
    return Diag(Result, diag::pp_err_else_without_if);

  // If this is a #else with a #else before it, report the error.
  if (CI.FoundElse && Diag(Result, diag::pp_err_else_after_else))
    return true;
  
  // Finally, skip the rest of the contents of this block and return the first
  // token after it.
  return SkipExcludedConditionalBlock(CI.IfLoc, /*Foundnonskip*/true,
                                      /*FoundElse*/true);
}

bool Preprocessor::HandleElifDirective(LexerToken &ElifToken) {
  ++NumElse;
  // #elif directive in a non-skipping conditional... start skipping.
  // We don't care what the condition is, because we will always skip it (since
  // the block immediately before it was included).
  if (DiscardUntilEndOfDirective()) return true;

  PPConditionalInfo CI;
  if (CurLexer->popConditionalLevel(CI))
    return Diag(ElifToken, diag::pp_err_elif_without_if);
  
  // If this is a #elif with a #else before it, report the error.
  if (CI.FoundElse && Diag(ElifToken, diag::pp_err_elif_after_else))
    return true;

  // Finally, skip the rest of the contents of this block and return the first
  // token after it.
  return SkipExcludedConditionalBlock(CI.IfLoc, /*Foundnonskip*/true,
                                      /*FoundElse*/CI.FoundElse);
}