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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef frontend_TokenStream_h
#define frontend_TokenStream_h

// JS lexical scanner interface.

#include "mozilla/DebugOnly.h"
#include "mozilla/PodOperations.h"

#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>

#include "jscntxt.h"
#include "jspubtd.h"

#include "js/Vector.h"
#include "vm/RegExpObject.h"

namespace js {
namespace frontend {

// Values of this type are used to index into arrays such as isExprEnding[],
// so the first value must be zero.
enum TokenKind {
    TOK_ERROR = 0,                 // well-known as the only code < EOF
    TOK_EOF,                       // end of file
    TOK_EOL,                       // end of line; only returned by peekTokenSameLine()
    TOK_SEMI,                      // semicolon
    TOK_COMMA,                     // comma operator
    TOK_HOOK, TOK_COLON,           // conditional (?:)
    TOK_INC, TOK_DEC,              // increment/decrement (++ --)
    TOK_DOT,                       // member operator (.)
    TOK_TRIPLEDOT,                 // for rest arguments (...)
    TOK_LB, TOK_RB,                // left and right brackets
    TOK_LC, TOK_RC,                // left and right curlies (braces)
    TOK_LP, TOK_RP,                // left and right parentheses
    TOK_NAME,                      // identifier
    TOK_NUMBER,                    // numeric constant
    TOK_STRING,                    // string constant
    TOK_REGEXP,                    // RegExp constant
    TOK_TRUE,                      // true
    TOK_FALSE,                     // false
    TOK_NULL,                      // null
    TOK_THIS,                      // this
    TOK_FUNCTION,                  // function keyword
    TOK_IF,                        // if keyword
    TOK_ELSE,                      // else keyword
    TOK_SWITCH,                    // switch keyword
    TOK_CASE,                      // case keyword
    TOK_DEFAULT,                   // default keyword
    TOK_WHILE,                     // while keyword
    TOK_DO,                        // do keyword
    TOK_FOR,                       // for keyword
    TOK_BREAK,                     // break keyword
    TOK_CONTINUE,                  // continue keyword
    TOK_VAR,                       // var keyword
    TOK_CONST,                     // const keyword
    TOK_WITH,                      // with keyword
    TOK_RETURN,                    // return keyword
    TOK_NEW,                       // new keyword
    TOK_DELETE,                    // delete keyword
    TOK_TRY,                       // try keyword
    TOK_CATCH,                     // catch keyword
    TOK_FINALLY,                   // finally keyword
    TOK_THROW,                     // throw keyword
    TOK_DEBUGGER,                  // debugger keyword
    TOK_YIELD,                     // yield from generator function
    TOK_LET,                       // let keyword
    TOK_EXPORT,                    // export keyword
    TOK_IMPORT,                    // import keyword
    TOK_RESERVED,                  // reserved keywords
    TOK_STRICT_RESERVED,           // reserved keywords in strict mode

    // The following token types occupy contiguous ranges to enable easy
    // range-testing.

    // Binary operators tokens, TOK_OR thru TOK_MOD. These must be in the same
    // order as F(OR) and friends in FOR_EACH_PARSE_NODE_KIND in ParseNode.h.
    TOK_OR,                        // logical or (||)
    TOK_BINOP_FIRST = TOK_OR,
    TOK_AND,                       // logical and (&&)
    TOK_BITOR,                     // bitwise-or (|)
    TOK_BITXOR,                    // bitwise-xor (^)
    TOK_BITAND,                    // bitwise-and (&)

    // Equality operation tokens, per TokenKindIsEquality.
    TOK_STRICTEQ,
    TOK_EQUALITY_START = TOK_STRICTEQ,
    TOK_EQ,
    TOK_STRICTNE,
    TOK_NE,
    TOK_EQUALITY_LAST = TOK_NE,

    // Relational ops (< <= > >=), per TokenKindIsRelational.
    TOK_LT,
    TOK_RELOP_START = TOK_LT,
    TOK_LE,
    TOK_GT,
    TOK_GE,
    TOK_RELOP_LAST = TOK_GE,

    TOK_INSTANCEOF,                // |instanceof| keyword
    TOK_IN,                        // |in| keyword

    // Shift ops (<< >> >>>), per TokenKindIsShift.
    TOK_LSH,
    TOK_SHIFTOP_START = TOK_LSH,
    TOK_RSH,
    TOK_URSH,
    TOK_SHIFTOP_LAST = TOK_URSH,

    TOK_ADD,
    TOK_SUB,
    TOK_MUL,
    TOK_DIV,
    TOK_MOD,
    TOK_BINOP_LAST = TOK_MOD,

    // Unary operation tokens.
    TOK_TYPEOF,
    TOK_VOID,
    TOK_NOT,
    TOK_BITNOT,

    TOK_ARROW,                     // function arrow (=>)

    // Assignment ops (= += -= etc.), per TokenKindIsAssignment
    TOK_ASSIGN,
    TOK_ASSIGNMENT_START = TOK_ASSIGN,
    TOK_ADDASSIGN,
    TOK_SUBASSIGN,
    TOK_BITORASSIGN,
    TOK_BITXORASSIGN,
    TOK_BITANDASSIGN,
    TOK_LSHASSIGN,
    TOK_RSHASSIGN,
    TOK_URSHASSIGN,
    TOK_MULASSIGN,
    TOK_DIVASSIGN,
    TOK_MODASSIGN,
    TOK_ASSIGNMENT_LAST = TOK_MODASSIGN,

    TOK_LIMIT                      // domain size
};

inline bool
TokenKindIsBinaryOp(TokenKind tt)
{
    return TOK_BINOP_FIRST <= tt && tt <= TOK_BINOP_LAST;
}

inline bool
TokenKindIsEquality(TokenKind tt)
{
    return TOK_EQUALITY_START <= tt && tt <= TOK_EQUALITY_LAST;
}

inline bool
TokenKindIsRelational(TokenKind tt)
{
    return TOK_RELOP_START <= tt && tt <= TOK_RELOP_LAST;
}

inline bool
TokenKindIsShift(TokenKind tt)
{
    return TOK_SHIFTOP_START <= tt && tt <= TOK_SHIFTOP_LAST;
}

inline bool
TokenKindIsAssignment(TokenKind tt)
{
    return TOK_ASSIGNMENT_START <= tt && tt <= TOK_ASSIGNMENT_LAST;
}

inline bool
TokenKindIsDecl(TokenKind tt)
{
#if JS_HAS_BLOCK_SCOPE
    return tt == TOK_VAR || tt == TOK_LET;
#else
    return tt == TOK_VAR;
#endif
}

struct TokenPos {
    uint32_t    begin;  // Offset of the token's first char.
    uint32_t    end;    // Offset of 1 past the token's last char.

    TokenPos() {}
    TokenPos(uint32_t begin, uint32_t end) : begin(begin), end(end) {}

    // Return a TokenPos that covers left, right, and anything in between.
    static TokenPos box(const TokenPos &left, const TokenPos &right) {
        JS_ASSERT(left.begin <= left.end);
        JS_ASSERT(left.end <= right.begin);
        JS_ASSERT(right.begin <= right.end);
        return TokenPos(left.begin, right.end);
    }

    bool operator==(const TokenPos& bpos) const {
        return begin == bpos.begin && end == bpos.end;
    }

    bool operator!=(const TokenPos& bpos) const {
        return begin != bpos.begin || end != bpos.end;
    }

    bool operator <(const TokenPos& bpos) const {
        return begin < bpos.begin;
    }

    bool operator <=(const TokenPos& bpos) const {
        return begin <= bpos.begin;
    }

    bool operator >(const TokenPos& bpos) const {
        return !(*this <= bpos);
    }

    bool operator >=(const TokenPos& bpos) const {
        return !(*this < bpos);
    }

    bool encloses(const TokenPos& pos) const {
        return begin <= pos.begin && pos.end <= end;
    }
};

enum DecimalPoint { NoDecimal = false, HasDecimal = true };

struct Token {
    TokenKind           type;           // char value or above enumerator
    TokenPos            pos;            // token position in file
    union {
      private:
        friend struct Token;
        PropertyName    *name;          // non-numeric atom
        JSAtom          *atom;          // potentially-numeric atom
        struct {
            double      value;          // floating point number
            DecimalPoint decimalPoint;  // literal contains '.'
        } number;
        RegExpFlag      reflags;        // regexp flags; use tokenbuf to access
                                        //   regexp chars
    } u;

    // Mutators

    void setName(PropertyName *name) {
        JS_ASSERT(type == TOK_NAME);
        JS_ASSERT(!IsPoisonedPtr(name));
        u.name = name;
    }

    void setAtom(JSAtom *atom) {
        JS_ASSERT(type == TOK_STRING);
        JS_ASSERT(!IsPoisonedPtr(atom));
        u.atom = atom;
    }

    void setRegExpFlags(js::RegExpFlag flags) {
        JS_ASSERT(type == TOK_REGEXP);
        JS_ASSERT((flags & AllFlags) == flags);
        u.reflags = flags;
    }

    void setNumber(double n, DecimalPoint decimalPoint) {
        JS_ASSERT(type == TOK_NUMBER);
        u.number.value = n;
        u.number.decimalPoint = decimalPoint;
    }

    // Type-safe accessors

    PropertyName *name() const {
        JS_ASSERT(type == TOK_NAME);
        return u.name->asPropertyName(); // poor-man's type verification
    }

    JSAtom *atom() const {
        JS_ASSERT(type == TOK_STRING);
        return u.atom;
    }

    js::RegExpFlag regExpFlags() const {
        JS_ASSERT(type == TOK_REGEXP);
        JS_ASSERT((u.reflags & AllFlags) == u.reflags);
        return u.reflags;
    }

    double number() const {
        JS_ASSERT(type == TOK_NUMBER);
        return u.number.value;
    }

    DecimalPoint decimalPoint() const {
        JS_ASSERT(type == TOK_NUMBER);
        return u.number.decimalPoint;
    }
};

struct CompileError {
    JSErrorReport report;
    char *message;
    ErrorArgumentsType argumentsType;
    CompileError()
      : message(NULL), argumentsType(ArgumentsAreUnicode)
    {
        mozilla::PodZero(&report);
    }
    ~CompileError();
    void throwError(JSContext *cx);

  private:
    // CompileError owns raw allocated memory, so disable assignment and copying
    // for safety.
    void operator=(const CompileError &) MOZ_DELETE;
    CompileError(const CompileError &) MOZ_DELETE;
};

// Ideally, tokenizing would be entirely independent of context.  But the
// strict mode flag, which is in SharedContext, affects tokenizing, and
// TokenStream needs to see it.
//
// This class is a tiny back-channel from TokenStream to the strict mode flag
// that avoids exposing the rest of SharedContext to TokenStream.
//
class StrictModeGetter {
  public:
    virtual bool strictMode() = 0;
};

// TokenStream is the lexical scanner for Javascript source text.
//
// It takes a buffer of jschars and linearly scans it into |Token|s.
// Internally the class uses a four element circular buffer |tokens| of
// |Token|s. As an index for |tokens|, the member |cursor| points to the
// current token.
// Calls to getToken() increase |cursor| by one and return the new current
// token. If a TokenStream was just created, the current token is initialized
// with random data (i.e. not initialized). It is therefore important that
// one of the first four member functions listed below is called first.
// The circular buffer lets us go back up to two tokens from the last
// scanned token. Internally, the relative number of backward steps that were
// taken (via ungetToken()) after the last token was scanned is stored in
// |lookahead|.
//
// The following table lists in which situations it is safe to call each listed
// function. No checks are made by the functions in non-debug builds.
//
// Function Name     | Precondition; changes to |lookahead|
// ------------------+---------------------------------------------------------
// getToken          | none; if |lookahead > 0| then |lookahead--|
// peekToken         | none; if |lookahead == 0| then |lookahead == 1|
// peekTokenSameLine | none; if |lookahead == 0| then |lookahead == 1|
// matchToken        | none; if |lookahead > 0| and the match succeeds then
//                   |       |lookahead--|
// consumeKnownToken | none; if |lookahead > 0| then |lookahead--|
// ungetToken        | 0 <= |lookahead| <= |maxLookahead - 1|; |lookahead++|
//
// The behavior of the token scanning process (see getTokenInternal()) can be
// modified by calling one of the first four above listed member functions with
// an optional argument of type Modifier.  However, the modifier will be
// ignored unless |lookahead == 0| holds.  Due to constraints of the grammar,
// this turns out not to be a problem in practice. See the
// mozilla.dev.tech.js-engine.internals thread entitled 'Bug in the scanner?'
// for more details:
// https://groups.google.com/forum/?fromgroups=#!topic/mozilla.dev.tech.js-engine.internals/2JLH5jRcr7E).
//
// The methods seek() and tell() allow to rescan from a previous visited
// location of the buffer.
//
class MOZ_STACK_CLASS TokenStream
{
    // Unicode separators that are treated as line terminators, in addition to \n, \r.
    enum {
        LINE_SEPARATOR = 0x2028,
        PARA_SEPARATOR = 0x2029
    };

    static const size_t ntokens = 4;                // 1 current + 2 lookahead, rounded
                                                    // to power of 2 to avoid divmod by 3
    static const unsigned maxLookahead = 2;
    static const unsigned ntokensMask = ntokens - 1;

  public:
    typedef Vector<jschar, 32> CharBuffer;

    TokenStream(ExclusiveContext *cx, const CompileOptions &options,
                const jschar *base, size_t length, StrictModeGetter *smg);

    ~TokenStream();

    // Accessors.
    const Token &currentToken() const { return tokens[cursor]; }
    bool isCurrentTokenType(TokenKind type) const {
        return currentToken().type == type;
    }
    const CharBuffer &getTokenbuf() const { return tokenbuf; }
    const char *getFilename() const { return filename; }
    unsigned getLineno() const { return lineno; }
    unsigned getColumn() const { return userbuf.addressOfNextRawChar() - linebase - 1; }
    JSPrincipals *getOriginPrincipals() const { return originPrincipals; }
    JSVersion versionNumber() const { return VersionNumber(options().version); }
    JSVersion versionWithFlags() const { return options().version; }

    PropertyName *currentName() const {
        if (isCurrentTokenType(TOK_YIELD))
            return cx->names().yield;
        JS_ASSERT(isCurrentTokenType(TOK_NAME));
        return currentToken().name();
    }

    bool isCurrentTokenAssignment() const {
        return TokenKindIsAssignment(currentToken().type);
    }

    // Flag methods.
    bool isEOF() const { return flags.isEOF; }
    bool sawOctalEscape() const { return flags.sawOctalEscape; }
    bool hadError() const { return flags.hadError; }

    // TokenStream-specific error reporters.
    bool reportError(unsigned errorNumber, ...);
    bool reportWarning(unsigned errorNumber, ...);

    static const uint32_t NoOffset = UINT32_MAX;

    // General-purpose error reporters.  You should avoid calling these
    // directly, and instead use the more succinct alternatives (e.g.
    // reportError()) in TokenStream, Parser, and BytecodeEmitter.
    bool reportCompileErrorNumberVA(uint32_t offset, unsigned flags, unsigned errorNumber,
                                    va_list args);
    bool reportStrictModeErrorNumberVA(uint32_t offset, bool strictMode, unsigned errorNumber,
                                       va_list args);
    bool reportStrictWarningErrorNumberVA(uint32_t offset, unsigned errorNumber,
                                          va_list args);

    // asm.js reporter
    void reportAsmJSError(uint32_t offset, unsigned errorNumber, ...);

  private:
    // These are private because they should only be called by the tokenizer
    // while tokenizing not by, for example, BytecodeEmitter.
    bool reportStrictModeError(unsigned errorNumber, ...);
    bool strictMode() const { return strictModeGetter && strictModeGetter->strictMode(); }

    void onError();
    static JSAtom *atomize(ExclusiveContext *cx, CharBuffer &cb);
    bool putIdentInTokenbuf(const jschar *identStart);

    struct Flags
    {
        bool isEOF:1;           // Hit end of file.
        bool isDirtyLine:1;     // Non-whitespace since start of line.
        bool sawOctalEscape:1;  // Saw an octal character escape.
        bool hadError:1;        // Returned TOK_ERROR from getToken.

        Flags()
          : isEOF(), isDirtyLine(), sawOctalEscape(), hadError()
        {}
    };

  public:
    // Sometimes the parser needs to modify how tokens are created.
    enum Modifier
    {
        None,           // Normal operation.
        Operand,        // Looking for an operand, not an operator.  In
                        //   practice, this means that when '/' is seen,
                        //   we look for a regexp instead of just returning
                        //   TOK_DIV.
        KeywordIsName,  // Treat keywords as names by returning TOK_NAME.
    };

    // Get the next token from the stream, make it the current token, and
    // return its kind.
    TokenKind getToken(Modifier modifier = None) {
        // Check for a pushed-back token resulting from mismatching lookahead.
        if (lookahead != 0) {
            lookahead--;
            cursor = (cursor + 1) & ntokensMask;
            TokenKind tt = currentToken().type;
            JS_ASSERT(tt != TOK_EOL);
            return tt;
        }

        return getTokenInternal(modifier);
    }

    // Push the last scanned token back into the stream.
    void ungetToken() {
        JS_ASSERT(lookahead < maxLookahead);
        lookahead++;
        cursor = (cursor - 1) & ntokensMask;
    }

    TokenKind peekToken(Modifier modifier = None) {
        if (lookahead != 0)
            return tokens[(cursor + 1) & ntokensMask].type;
        TokenKind tt = getTokenInternal(modifier);
        ungetToken();
        return tt;
    }

    // This is like peekToken(), with one exception:  if there is an EOL
    // between the end of the current token and the start of the next token, it
    // returns TOK_EOL.  In that case, no token with TOK_EOL is actually
    // created, just a TOK_EOL TokenKind is returned, and currentToken()
    // shouldn't be consulted.  (This is the only place TOK_EOL is produced.)
    JS_ALWAYS_INLINE TokenKind peekTokenSameLine(Modifier modifier = None) {
       const Token &curr = currentToken();

        // If lookahead != 0, we have scanned ahead at least one token, and
        // |lineno| is the line that the furthest-scanned token ends on.  If
        // it's the same as the line that the current token ends on, that's a
        // stronger condition than what we are looking for, and we don't need
        // to return TOK_EOL.
        if (lookahead != 0 && srcCoords.isOnThisLine(curr.pos.end, lineno))
            return tokens[(cursor + 1) & ntokensMask].type;

        // The above check misses two cases where we don't have to return
        // TOK_EOL.
        // - The next token starts on the same line, but is a multi-line token.
        // - The next token starts on the same line, but lookahead==2 and there
        //   is a newline between the next token and the one after that.
        // The following test is somewhat expensive but gets these cases (and
        // all others) right.
        (void)getToken(modifier);
        const Token &next = currentToken();
        ungetToken();
        return srcCoords.lineNum(curr.pos.end) == srcCoords.lineNum(next.pos.begin)
               ? next.type
               : TOK_EOL;
    }

    // Get the next token from the stream if its kind is |tt|.
    bool matchToken(TokenKind tt, Modifier modifier = None) {
        if (getToken(modifier) == tt)
            return true;
        ungetToken();
        return false;
    }

    void consumeKnownToken(TokenKind tt) {
        JS_ALWAYS_TRUE(matchToken(tt));
    }

    bool matchContextualKeyword(Handle<PropertyName*> keyword) {
        if (getToken() == TOK_NAME && currentToken().name() == keyword)
            return true;
        ungetToken();
        return false;
    }

    bool nextTokenEndsExpr() {
        return isExprEnding[peekToken()];
    }

    class MOZ_STACK_CLASS Position {
      public:
        // The Token fields may contain pointers to atoms, so for correct
        // rooting we must ensure collection of atoms is disabled while objects
        // of this class are live.  Do this by requiring a dummy AutoKeepAtoms
        // reference in the constructor.
        //
        // This class is explicity ignored by the analysis, so don't add any
        // more pointers to GC things here!
        Position(AutoKeepAtoms&) { }
      private:
        Position(const Position&) MOZ_DELETE;
        friend class TokenStream;
        const jschar *buf;
        Flags flags;
        unsigned lineno;
        const jschar *linebase;
        const jschar *prevLinebase;
        Token currentToken;
        unsigned lookahead;
        Token lookaheadTokens[maxLookahead];
    };

    void advance(size_t position);
    void tell(Position *);
    void seek(const Position &pos);
    bool seek(const Position &pos, const TokenStream &other);

    size_t positionToOffset(const Position &pos) const {
        return pos.buf - userbuf.base();
    }

    bool hasSourceMap() const {
        return sourceMap != NULL;
    }

    // Give up responsibility for managing the sourceMap filename's memory.
    jschar *releaseSourceMap() {
        JS_ASSERT(hasSourceMap());
        jschar *sm = sourceMap;
        sourceMap = NULL;
        return sm;
    }

    // If the name at s[0:length] is not a keyword in this version, return
    // true with *ttp unchanged.
    //
    // If it is a reserved word in this version and strictness mode, and thus
    // can't be present in correct code, report a SyntaxError and return false.
    //
    // If it is a keyword, like "if", the behavior depends on ttp. If ttp is
    // null, report a SyntaxError ("if is a reserved identifier") and return
    // false. If ttp is non-null, return true with the keyword's TokenKind in
    // *ttp.
    bool checkForKeyword(const jschar *s, size_t length, TokenKind *ttp);

    // This class maps a userbuf offset (which is 0-indexed) to a line number
    // (which is 1-indexed) and a column index (which is 0-indexed).
    class SourceCoords
    {
        // For a given buffer holding source code, |lineStartOffsets_| has one
        // element per line of source code, plus one sentinel element.  Each
        // non-sentinel element holds the buffer offset for the start of the
        // corresponding line of source code.  For this example script:
        //
        // 1  // xyz            [line starts at offset 0]
        // 2  var x;            [line starts at offset 7]
        // 3                    [line starts at offset 14]
        // 4  var y;            [line starts at offset 15]
        //
        // |lineStartOffsets_| is:
        //
        //   [0, 7, 14, 15, MAX_PTR]
        //
        // To convert a "line number" to a "line index" (i.e. an index into
        // |lineStartOffsets_|), subtract |initialLineNum_|.  E.g. line 3's
        // line index is (3 - initialLineNum_), which is 2.  Therefore
        // lineStartOffsets_[2] holds the buffer offset for the start of line 3,
        // which is 14.  (Note that |initialLineNum_| is often 1, but not
        // always.)
        //
        // The first element is always 0, and the last element is always the
        // MAX_PTR sentinel.
        //
        // offset-to-line/column lookups are O(log n) in the worst case (binary
        // search), but in practice they're heavily clustered and we do better
        // than that by using the previous lookup's result (lastLineIndex_) as
        // a starting point.
        //
        // Checking if an offset lies within a particular line number
        // (isOnThisLine()) is O(1).
        //
        Vector<uint32_t, 128> lineStartOffsets_;
        uint32_t            initialLineNum_;

        // This is mutable because it's modified on every search, but that fact
        // isn't visible outside this class.
        mutable uint32_t    lastLineIndex_;

        uint32_t lineIndexOf(uint32_t offset) const;

        static const uint32_t MAX_PTR = UINT32_MAX;

        uint32_t lineIndexToNum(uint32_t lineIndex) const { return lineIndex + initialLineNum_; }
        uint32_t lineNumToIndex(uint32_t lineNum)   const { return lineNum   - initialLineNum_; }

      public:
        SourceCoords(ExclusiveContext *cx, uint32_t ln);

        void add(uint32_t lineNum, uint32_t lineStartOffset);
        bool fill(const SourceCoords &other);

        bool isOnThisLine(uint32_t offset, uint32_t lineNum) const {
            uint32_t lineIndex = lineNumToIndex(lineNum);
            JS_ASSERT(lineIndex + 1 < lineStartOffsets_.length());  // +1 due to sentinel
            return lineStartOffsets_[lineIndex] <= offset &&
                   offset < lineStartOffsets_[lineIndex + 1];
        }

        uint32_t lineNum(uint32_t offset) const;
        uint32_t columnIndex(uint32_t offset) const;
        void lineNumAndColumnIndex(uint32_t offset, uint32_t *lineNum, uint32_t *columnIndex) const;
    };

    SourceCoords srcCoords;

    JSAtomState &names() const {
        return cx->names();
    }

    ExclusiveContext *context() const {
        return cx;
    }

    const CompileOptions &options() const {
        return options_;
    }

  private:
    // This is the low-level interface to the JS source code buffer.  It just
    // gets raw chars, basically.  TokenStreams functions are layered on top
    // and do some extra stuff like converting all EOL sequences to '\n',
    // tracking the line number, and setting |flags.isEOF|.  (The "raw" in "raw
    // chars" refers to the lack of EOL sequence normalization.)
    class TokenBuf {
      public:
        TokenBuf(ExclusiveContext *cx, const jschar *buf, size_t length)
          : base_(buf), limit_(buf + length), ptr(buf),
            skipBase(cx, &base_), skipLimit(cx, &limit_), skipPtr(cx, &ptr)
        { }

        bool hasRawChars() const {
            return ptr < limit_;
        }

        bool atStart() const {
            return ptr == base_;
        }

        const jschar *base() const {
            return base_;
        }

        const jschar *limit() const {
            return limit_;
        }

        jschar getRawChar() {
            return *ptr++;      // this will NULL-crash if poisoned
        }

        jschar peekRawChar() const {
            return *ptr;        // this will NULL-crash if poisoned
        }

        bool matchRawChar(jschar c) {
            if (*ptr == c) {    // this will NULL-crash if poisoned
                ptr++;
                return true;
            }
            return false;
        }

        bool matchRawCharBackwards(jschar c) {
            JS_ASSERT(ptr);     // make sure it hasn't been poisoned
            if (*(ptr - 1) == c) {
                ptr--;
                return true;
            }
            return false;
        }

        void ungetRawChar() {
            JS_ASSERT(ptr);     // make sure it hasn't been poisoned
            ptr--;
        }

        const jschar *addressOfNextRawChar(bool allowPoisoned = false) const {
            JS_ASSERT_IF(!allowPoisoned, ptr);     // make sure it hasn't been poisoned
            return ptr;
        }

        // Use this with caution!
        void setAddressOfNextRawChar(const jschar *a, bool allowPoisoned = false) {
            JS_ASSERT_IF(!allowPoisoned, a);
            ptr = a;
        }

#ifdef DEBUG
        // Poison the TokenBuf so it cannot be accessed again.
        void poison() {
            ptr = NULL;
        }
#endif

        static bool isRawEOLChar(int32_t c) {
            return (c == '\n' || c == '\r' || c == LINE_SEPARATOR || c == PARA_SEPARATOR);
        }

        // Finds the next EOL, but stops once 'max' jschars have been scanned
        // (*including* the starting jschar).
        const jschar *findEOLMax(const jschar *p, size_t max);

      private:
        const jschar *base_;            // base of buffer
        const jschar *limit_;           // limit for quick bounds check
        const jschar *ptr;              // next char to get

        // We are not yet moving strings
        SkipRoot skipBase, skipLimit, skipPtr;
    };

    TokenKind getTokenInternal(Modifier modifier);

    int32_t getChar();
    int32_t getCharIgnoreEOL();
    void ungetChar(int32_t c);
    void ungetCharIgnoreEOL(int32_t c);
    Token *newToken(ptrdiff_t adjust);
    bool peekUnicodeEscape(int32_t *c);
    bool matchUnicodeEscapeIdStart(int32_t *c);
    bool matchUnicodeEscapeIdent(int32_t *c);
    bool peekChars(int n, jschar *cp);
    bool getSourceMappingURL(bool isMultiline, bool shouldWarnDeprecated);

    // |expect| cannot be an EOL char.
    bool matchChar(int32_t expect) {
        MOZ_ASSERT(!TokenBuf::isRawEOLChar(expect));
        return JS_LIKELY(userbuf.hasRawChars()) &&
               userbuf.matchRawChar(expect);
    }

    void consumeKnownChar(int32_t expect) {
        mozilla::DebugOnly<int32_t> c = getChar();
        JS_ASSERT(c == expect);
    }

    int32_t peekChar() {
        int32_t c = getChar();
        ungetChar(c);
        return c;
    }

    void skipChars(int n) {
        while (--n >= 0)
            getChar();
    }

    void updateLineInfoForEOL();
    void updateFlagsForEOL();

    // Options used for parsing/tokenizing.
    const CompileOptions &options_;

    Token               tokens[ntokens];    // circular token buffer
    unsigned            cursor;             // index of last parsed token
    unsigned            lookahead;          // count of lookahead tokens
    unsigned            lineno;             // current line number
    Flags               flags;              // flags -- see above
    const jschar        *linebase;          // start of current line;  points into userbuf
    const jschar        *prevLinebase;      // start of previous line;  NULL if on the first line
    TokenBuf            userbuf;            // user input buffer
    const char          *filename;          // input filename or null
    jschar              *sourceMap;         // source map's filename or null
    CharBuffer          tokenbuf;           // current token string buffer
    bool                maybeEOL[256];      // probabilistic EOL lookup table
    bool                maybeStrSpecial[256];   // speeds up string scanning
    uint8_t             isExprEnding[TOK_LIMIT];// which tokens definitely terminate exprs?
    ExclusiveContext    *const cx;
    JSPrincipals        *const originPrincipals;
    StrictModeGetter    *strictModeGetter;  // used to test for strict mode

    // The tokens array stores pointers to JSAtoms. These are rooted by the
    // atoms table using AutoKeepAtoms in the Parser. This SkipRoot tells the
    // exact rooting analysis to ignore the atoms in the tokens array.
    SkipRoot            tokenSkip;

    // Bug 846011
    SkipRoot            linebaseSkip;
    SkipRoot            prevLinebaseSkip;
};

// Steal one JSREPORT_* bit (see jsapi.h) to tell that arguments to the error
// message have const jschar* type, not const char*.
#define JSREPORT_UC 0x100

} // namespace frontend
} // namespace js

extern JS_FRIEND_API(int)
js_fgets(char *buf, int size, FILE *file);

#ifdef DEBUG
extern const char *
TokenKindToString(js::frontend::TokenKind tt);
#endif

#endif /* frontend_TokenStream_h */