DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042
/* -*- 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/ArrayUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/PodOperations.h"

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

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

#include "frontend/TokenKind.h"
#include "js/UniquePtr.h"
#include "js/Vector.h"
#include "vm/RegExpObject.h"

struct KeywordInfo;

namespace js {
namespace frontend {

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) {
        MOZ_ASSERT(left.begin <= left.end);
        MOZ_ASSERT(left.end <= right.begin);
        MOZ_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 };

class TokenStream;

struct Token
{
  private:
    // Sometimes the parser needs to inform the tokenizer to interpret
    // subsequent text in a particular manner: for example, to tokenize a
    // keyword as an identifier, not as the actual keyword, on the right-hand
    // side of a dotted property access.  Such information is communicated to
    // the tokenizer as a Modifier when getting the next token.
    //
    // Ideally this definition would reside in TokenStream as that's the real
    // user, but the debugging-use of it here causes a cyclic dependency (and
    // C++ provides no way to forward-declare an enum inside a class).  So
    // define it here, then typedef it into TokenStream with static consts to
    // bring the initializers into scope.
    enum Modifier
    {
        // Normal operation.
        None,

        // 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.
        Operand,

        // Treat keywords as names by returning TOK_NAME.
        KeywordIsName,

        // Treat subsequent characters as the tail of a template literal, after
        // a template substitution, beginning with a "}", continuing with zero
        // or more template literal characters, and ending with either "${" or
        // the end of the template literal.  For example:
        //
        //   var entity = "world";
        //   var s = `Hello ${entity}!`;
        //                          ^ TemplateTail context
        TemplateTail,
    };
    enum ModifierException
    {
        NoException,

        // Used in following 2 cases:
        // a) After |yield| we look for a token on the same line that starts an
        // expression (Operand): |yield <expr>|.  If no token is found, the
        // |yield| stands alone, and the next token on a subsequent line must
        // be: a comma continuing a comma expression, a semicolon terminating
        // the statement that ended with |yield|, or the start of another
        // statement (possibly an expression statement).  The comma/semicolon
        // cases are gotten as operators (None), contrasting with Operand
        // earlier.
        // b) After an arrow function with a block body in an expression
        // statement, the next token must be: a colon in a conditional
        // expression, a comma continuing a comma expression, a semicolon
        // terminating the statement, or the token on a subsequent line that is
        // the start of another statement (possibly an expression statement).
        // Colon is gotten as operator (None), and it should only be gotten in
        // conditional expression and missing it results in SyntaxError.
        // Comma/semicolon cases are also gotten as operators (None), and 4th
        // case is gotten after them.  If no comma/semicolon found but EOL,
        // the next token should be gotten as operand in 4th case (especially if
        // '/' is the first character).  So we should peek the token as
        // operand before try getting colon/comma/semicolon.
        // See also the comment in Parser::assignExpr().
        NoneIsOperand,

        // If a semicolon is inserted automatically, the next token is already
        // gotten with None, but we expect Operand.
        OperandIsNone,

        // If name of method definition is `get` or `set`, the next token is
        // already gotten with KeywordIsName, but we expect None.
        NoneIsKeywordIsName,
    };
    friend class TokenStream;

  public:
    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;
#ifdef DEBUG
    Modifier modifier;                  // Modifier used to get this token
    ModifierException modifierException; // Exception for this modifier
#endif

    // Mutators

    void setName(PropertyName* name) {
        MOZ_ASSERT(type == TOK_NAME);
        u.name = name;
    }

    void setAtom(JSAtom* atom) {
        MOZ_ASSERT(type == TOK_STRING ||
                   type == TOK_TEMPLATE_HEAD ||
                   type == TOK_NO_SUBS_TEMPLATE);
        u.atom = atom;
    }

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

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

    // Type-safe accessors

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

    bool nameContainsEscape() const {
        PropertyName* n = name();
        return pos.begin + n->length() != pos.end;
    }

    JSAtom* atom() const {
        MOZ_ASSERT(type == TOK_STRING ||
                   type == TOK_TEMPLATE_HEAD ||
                   type == TOK_NO_SUBS_TEMPLATE);
        return u.atom;
    }

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

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

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

struct CompileError {
    JSErrorReport report;
    char* message;
    CompileError() : message(nullptr) {}
    ~CompileError();
    void throwError(JSContext* cx);

  private:
    // CompileError owns raw allocated memory, so disable assignment and copying
    // for safety.
    void operator=(const CompileError&) = delete;
    CompileError(const CompileError&) = 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 char16_t characters 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<char16_t, 32> CharBuffer;

    TokenStream(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
                const char16_t* base, size_t length, StrictModeGetter* smg);

    ~TokenStream();

    MOZ_MUST_USE bool checkOptions();

    // 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; }
    bool getMutedErrors() const { return mutedErrors; }
    JSVersion versionNumber() const { return VersionNumber(options().version); }
    JSVersion versionWithFlags() const { return options().version; }

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

    PropertyName* nextName() const {
        if (nextToken().type == TOK_YIELD)
            return cx->names().yield;
        MOZ_ASSERT(nextToken().type == TOK_NAME);
        return nextToken().name();
    }

    bool nextNameContainsEscape() const {
        if (nextToken().type == TOK_YIELD)
            return false;
        MOZ_ASSERT(nextToken().type == TOK_NAME);
        return nextToken().nameContainsEscape();
    }

    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 reportErrorNoOffset(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, ...);

    JSAtom* getRawTemplateStringAtom() {
        MOZ_ASSERT(currentToken().type == TOK_TEMPLATE_HEAD ||
                   currentToken().type == TOK_NO_SUBS_TEMPLATE);
        const char16_t* cur = userbuf.rawCharPtrAt(currentToken().pos.begin + 1);
        const char16_t* end;
        if (currentToken().type == TOK_TEMPLATE_HEAD) {
            // Of the form    |`...${|   or   |}...${|
            end = userbuf.rawCharPtrAt(currentToken().pos.end - 2);
        } else {
            // NO_SUBS_TEMPLATE is of the form   |`...`|   or   |}...`|
            end = userbuf.rawCharPtrAt(currentToken().pos.end - 1);
        }

        CharBuffer charbuf(cx);
        while (cur < end) {
            int32_t ch = *cur;
            if (ch == '\r') {
                ch = '\n';
                if ((cur + 1 < end) && (*(cur + 1) == '\n'))
                    cur++;
            }
            if (!charbuf.append(ch))
                return nullptr;
            cur++;
        }
        return AtomizeChars(cx, charbuf.begin(), charbuf.length());
    }

  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(); }

    static JSAtom* atomize(ExclusiveContext* cx, CharBuffer& cb);
    MOZ_MUST_USE bool putIdentInTokenbuf(const char16_t* 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;        // Hit a syntax error, at start or during a
                                // token.
        bool hitOOM:1;          // Hit OOM.

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

  public:
    typedef Token::Modifier Modifier;
    static constexpr Modifier None = Token::None;
    static constexpr Modifier Operand = Token::Operand;
    static constexpr Modifier KeywordIsName = Token::KeywordIsName;
    static constexpr Modifier TemplateTail = Token::TemplateTail;

    typedef Token::ModifierException ModifierException;
    static constexpr ModifierException NoException = Token::NoException;
    static constexpr ModifierException NoneIsOperand = Token::NoneIsOperand;
    static constexpr ModifierException OperandIsNone = Token::OperandIsNone;
    static constexpr ModifierException NoneIsKeywordIsName = Token::NoneIsKeywordIsName;

    void addModifierException(ModifierException modifierException) {
#ifdef DEBUG
        const Token& next = nextToken();
        if (next.modifierException == NoneIsOperand)
        {
            // Token after yield expression without operand already has
            // NoneIsOperand exception.
            MOZ_ASSERT(modifierException == OperandIsNone);
            MOZ_ASSERT(next.type != TOK_DIV,
                       "next token requires contextual specifier to be parsed unambiguously");

            // Do not update modifierException.
            return;
        }

        MOZ_ASSERT(next.modifierException == NoException);
        switch (modifierException) {
          case NoneIsOperand:
            MOZ_ASSERT(next.modifier == Operand);
            MOZ_ASSERT(next.type != TOK_DIV,
                       "next token requires contextual specifier to be parsed unambiguously");
            break;
          case OperandIsNone:
            MOZ_ASSERT(next.modifier == None);
            MOZ_ASSERT(next.type != TOK_DIV && next.type != TOK_REGEXP,
                       "next token requires contextual specifier to be parsed unambiguously");
            break;
          case NoneIsKeywordIsName:
            MOZ_ASSERT(next.modifier == KeywordIsName);
            MOZ_ASSERT(next.type != TOK_NAME);
            break;
          default:
            MOZ_CRASH("unexpected modifier exception");
        }
        tokens[(cursor + 1) & ntokensMask].modifierException = modifierException;
#endif
    }

    void
    verifyConsistentModifier(Modifier modifier, Token lookaheadToken) {
#ifdef DEBUG
        // Easy case: modifiers match.
        if (modifier == lookaheadToken.modifier)
            return;

        if (lookaheadToken.modifierException == OperandIsNone) {
            // getToken(Operand) permissibly following getToken().
            if (modifier == Operand && lookaheadToken.modifier == None)
                return;
        }

        if (lookaheadToken.modifierException == NoneIsOperand) {
            // getToken() permissibly following getToken(Operand).
            if (modifier == None && lookaheadToken.modifier == Operand)
                return;
        }

        if (lookaheadToken.modifierException == NoneIsKeywordIsName) {
            // getToken() permissibly following getToken(KeywordIsName).
            if (modifier == None && lookaheadToken.modifier == KeywordIsName)
                return;
        }

        MOZ_ASSERT_UNREACHABLE("this token was previously looked up with a "
                               "different modifier, potentially making "
                               "tokenization non-deterministic");
#endif
    }

    // Advance to the next token.  If the token stream encountered an error,
    // return false.  Otherwise return true and store the token kind in |*ttp|.
    MOZ_MUST_USE bool getToken(TokenKind* ttp, Modifier modifier = None) {
        // Check for a pushed-back token resulting from mismatching lookahead.
        if (lookahead != 0) {
            MOZ_ASSERT(!flags.hadError);
            lookahead--;
            cursor = (cursor + 1) & ntokensMask;
            TokenKind tt = currentToken().type;
            MOZ_ASSERT(tt != TOK_EOL);
            verifyConsistentModifier(modifier, currentToken());
            *ttp = tt;
            return true;
        }

        return getTokenInternal(ttp, modifier);
    }

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

    MOZ_MUST_USE bool peekToken(TokenKind* ttp, Modifier modifier = None) {
        if (lookahead > 0) {
            MOZ_ASSERT(!flags.hadError);
            verifyConsistentModifier(modifier, nextToken());
            *ttp = nextToken().type;
            return true;
        }
        if (!getTokenInternal(ttp, modifier))
            return false;
        ungetToken();
        return true;
    }

    MOZ_MUST_USE bool peekTokenPos(TokenPos* posp, Modifier modifier = None) {
        if (lookahead == 0) {
            TokenKind tt;
            if (!getTokenInternal(&tt, modifier))
                return false;
            ungetToken();
            MOZ_ASSERT(hasLookahead());
        } else {
            MOZ_ASSERT(!flags.hadError);
            verifyConsistentModifier(modifier, nextToken());
        }
        *posp = nextToken().pos;
        return true;
    }

    // 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
    // return true and store TOK_EOL in |*ttp|.  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.)
    MOZ_ALWAYS_INLINE MOZ_MUST_USE bool
    peekTokenSameLine(TokenKind* ttp, 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) {
            bool onThisLine;
            if (!srcCoords.isOnThisLine(curr.pos.end, lineno, &onThisLine))
                return reportError(JSMSG_OUT_OF_MEMORY);
            if (onThisLine) {
                MOZ_ASSERT(!flags.hadError);
                verifyConsistentModifier(modifier, nextToken());
                *ttp = nextToken().type;
                return true;
            }
        }

        // 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.
        TokenKind tmp;
        if (!getToken(&tmp, modifier))
            return false;
        const Token& next = currentToken();
        ungetToken();

        *ttp = srcCoords.lineNum(curr.pos.end) == srcCoords.lineNum(next.pos.begin)
             ? next.type
             : TOK_EOL;
        return true;
    }

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

    void consumeKnownToken(TokenKind tt, Modifier modifier = None) {
        bool matched;
        MOZ_ASSERT(hasLookahead());
        MOZ_ALWAYS_TRUE(matchToken(&matched, tt, modifier));
        MOZ_ALWAYS_TRUE(matched);
    }

    // Like matchToken(..., TOK_NAME) but further matching the name token only
    // if it has the given characters, without containing escape sequences.
    // If the name token has the given characters yet *does* contain an escape,
    // a syntax error will be reported.
    //
    // This latter behavior makes this method unsuitable for use in any context
    // where ASI might occur.  In such places, an escaped "contextual keyword"
    // on a new line is the start of an ExpressionStatement, not a continuation
    // of a StatementListItem (or ImportDeclaration or ExportDeclaration, in
    // modules).
    MOZ_MUST_USE bool matchContextualKeyword(bool* matchedp, Handle<PropertyName*> keyword,
                                             Modifier modifier = None)
    {
        TokenKind token;
        if (!getToken(&token, modifier))
            return false;
        if (token == TOK_NAME && currentToken().name() == keyword) {
            if (currentToken().nameContainsEscape()) {
                reportError(JSMSG_ESCAPED_KEYWORD);
                return false;
            }

            *matchedp = true;
        } else {
            *matchedp = false;
            ungetToken();
        }
        return true;
    }

    MOZ_MUST_USE bool nextTokenEndsExpr(bool* endsExpr) {
        TokenKind tt;
        if (!peekToken(&tt))
            return false;
        *endsExpr = isExprEnding[tt];
        return true;
    }

    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!
        explicit Position(AutoKeepAtoms&) { }
      private:
        Position(const Position&) = delete;
        friend class TokenStream;
        const char16_t* buf;
        Flags flags;
        unsigned lineno;
        size_t linebase;
        size_t prevLinebase;
        Token currentToken;
        unsigned lookahead;
        Token lookaheadTokens[maxLookahead];
    };

    MOZ_MUST_USE bool advance(size_t position);
    void tell(Position*);
    void seek(const Position& pos);
    MOZ_MUST_USE bool seek(const Position& pos, const TokenStream& other);
#ifdef DEBUG
    inline bool debugHasNoLookahead() const {
        return lookahead == 0;
    }
#endif

    const char16_t* rawCharPtrAt(size_t offset) const {
        return userbuf.rawCharPtrAt(offset);
    }

    const char16_t* rawLimit() const {
        return userbuf.limit();
    }

    bool hasDisplayURL() const {
        return displayURL_ != nullptr;
    }

    char16_t* displayURL() {
        return displayURL_.get();
    }

    bool hasSourceMapURL() const {
        return sourceMapURL_ != nullptr;
    }

    char16_t* sourceMapURL() {
        return sourceMapURL_.get();
    }

    // If |atom| 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.
    MOZ_MUST_USE bool checkForKeyword(JSAtom* atom, TokenKind* ttp);

    // Same semantics as above, but for the provided keyword.
    MOZ_MUST_USE bool checkForKeyword(const KeywordInfo* kw, 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);

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

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

        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 ReadOnlyCompileOptions& 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.)
    //
    // buf[0..length-1] often represents a substring of some larger source,
    // where we have only the substring in memory. The |startOffset| argument
    // indicates the offset within this larger string at which our string
    // begins, the offset of |buf[0]|.
    class TokenBuf {
      public:
        TokenBuf(ExclusiveContext* cx, const char16_t* buf, size_t length, size_t startOffset)
          : base_(buf),
            startOffset_(startOffset),
            limit_(buf + length),
            ptr(buf)
        { }

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

        bool atStart() const {
            return offset() == 0;
        }

        size_t startOffset() const {
            return startOffset_;
        }

        size_t offset() const {
            return startOffset_ + mozilla::PointerRangeSize(base_, ptr);
        }

        const char16_t* rawCharPtrAt(size_t offset) const {
            MOZ_ASSERT(startOffset_ <= offset);
            MOZ_ASSERT(offset - startOffset_ <= mozilla::PointerRangeSize(base_, limit_));
            return base_ + (offset - startOffset_);
        }

        const char16_t* limit() const {
            return limit_;
        }

        char16_t getRawChar() {
            return *ptr++;      // this will nullptr-crash if poisoned
        }

        char16_t peekRawChar() const {
            return *ptr;        // this will nullptr-crash if poisoned
        }

        bool matchRawChar(char16_t c) {
            if (*ptr == c) {    // this will nullptr-crash if poisoned
                ptr++;
                return true;
            }
            return false;
        }

        bool matchRawCharBackwards(char16_t c) {
            MOZ_ASSERT(ptr);     // make sure it hasn't been poisoned
            if (*(ptr - 1) == c) {
                ptr--;
                return true;
            }
            return false;
        }

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

        const char16_t* addressOfNextRawChar(bool allowPoisoned = false) const {
            MOZ_ASSERT_IF(!allowPoisoned, ptr);     // make sure it hasn't been poisoned
            return ptr;
        }

        // Use this with caution!
        void setAddressOfNextRawChar(const char16_t* a, bool allowPoisoned = false) {
            MOZ_ASSERT_IF(!allowPoisoned, a);
            ptr = a;
        }

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

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

        // Returns the offset of the next EOL, but stops once 'max' characters
        // have been scanned (*including* the char at startOffset_).
        size_t findEOLMax(size_t start, size_t max);

      private:
        const char16_t* base_;          // base of buffer
        uint32_t startOffset_;          // offset of base_[0]
        const char16_t* limit_;         // limit for quick bounds check
        const char16_t* ptr;            // next char to get
    };

    MOZ_MUST_USE bool getTokenInternal(TokenKind* ttp, Modifier modifier);

    MOZ_MUST_USE bool getBracedUnicode(uint32_t* code);
    MOZ_MUST_USE bool getStringOrTemplateToken(int untilChar, Token** tp);

    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, char16_t* cp);

    MOZ_MUST_USE bool getDirectives(bool isMultiline, bool shouldWarnDeprecated);
    MOZ_MUST_USE bool getDirective(bool isMultiline, bool shouldWarnDeprecated,
                                   const char* directive, int directiveLength,
                                   const char* errorMsgPragma,
                                   UniquePtr<char16_t[], JS::FreePolicy>* destination);
    MOZ_MUST_USE bool getDisplayURL(bool isMultiline, bool shouldWarnDeprecated);
    MOZ_MUST_USE bool getSourceMappingURL(bool isMultiline, bool shouldWarnDeprecated);

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

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

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

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

    void skipCharsIgnoreEOL(int n) {
        while (--n >= 0)
            getCharIgnoreEOL();
    }

    void updateLineInfoForEOL();
    void updateFlagsForEOL();

    const Token& nextToken() const {
        MOZ_ASSERT(hasLookahead());
        return tokens[(cursor + 1) & ntokensMask];
    }

    bool hasLookahead() const { return lookahead > 0; }

    // Options used for parsing/tokenizing.
    const ReadOnlyCompileOptions& 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
    size_t              linebase;           // start of current line
    size_t              prevLinebase;       // start of previous line;  size_t(-1) if on the first line
    TokenBuf            userbuf;            // user input buffer
    const char*         filename;           // input filename or null
    UniqueTwoByteChars  displayURL_;        // the user's requested source URL or null
    UniqueTwoByteChars  sourceMapURL_;      // source map's filename or null
    CharBuffer          tokenbuf;           // current token string buffer
    uint8_t             isExprEnding[TOK_LIMIT];// which tokens definitely terminate exprs?
    ExclusiveContext*   const cx;
    bool                mutedErrors;
    StrictModeGetter*   strictModeGetter;  // used to test for strict mode
};

extern const char*
TokenKindToDesc(TokenKind tt);

} // 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 */