THUAI6/CAPI/cpp/grpc/include/re2/re2.h

// Copyright 2003-2009 The RE2 Authors.  All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#ifndef RE2_RE2_H_
#define RE2_RE2_H_

// C++ interface to the re2 regular-expression library.
// RE2 supports Perl-style regular expressions (with extensions like
// \d, \w, \s, ...).
//
// -----------------------------------------------------------------------
// REGEXP SYNTAX:
//
// This module uses the re2 library and hence supports
// its syntax for regular expressions, which is similar to Perl's with
// some of the more complicated things thrown away.  In particular,
// backreferences and generalized assertions are not available, nor is \Z.
//
// See https://github.com/google/re2/wiki/Syntax for the syntax
// supported by RE2, and a comparison with PCRE and PERL regexps.
//
// For those not familiar with Perl's regular expressions,
// here are some examples of the most commonly used extensions:
//
//   "hello (\\w+) world"  -- \w matches a "word" character
//   "version (\\d+)"      -- \d matches a digit
//   "hello\\s+world"      -- \s matches any whitespace character
//   "\\b(\\w+)\\b"        -- \b matches non-empty string at word boundary
//   "(?i)hello"           -- (?i) turns on case-insensitive matching
//   "/\\*(.*?)\\*/"       -- .*? matches . minimum no. of times possible
//
// The double backslashes are needed when writing C++ string literals.
// However, they should NOT be used when writing C++11 raw string literals:
//
//   R"(hello (\w+) world)"  -- \w matches a "word" character
//   R"(version (\d+))"      -- \d matches a digit
//   R"(hello\s+world)"      -- \s matches any whitespace character
//   R"(\b(\w+)\b)"          -- \b matches non-empty string at word boundary
//   R"((?i)hello)"          -- (?i) turns on case-insensitive matching
//   R"(/\*(.*?)\*/)"        -- .*? matches . minimum no. of times possible
//
// When using UTF-8 encoding, case-insensitive matching will perform
// simple case folding, not full case folding.
//
// -----------------------------------------------------------------------
// MATCHING INTERFACE:
//
// The "FullMatch" operation checks that supplied text matches a
// supplied pattern exactly.
//
// Example: successful match
//    CHECK(RE2::FullMatch("hello", "h.*o"));
//
// Example: unsuccessful match (requires full match):
//    CHECK(!RE2::FullMatch("hello", "e"));
//
// -----------------------------------------------------------------------
// UTF-8 AND THE MATCHING INTERFACE:
//
// By default, the pattern and input text are interpreted as UTF-8.
// The RE2::Latin1 option causes them to be interpreted as Latin-1.
//
// Example:
//    CHECK(RE2::FullMatch(utf8_string, RE2(utf8_pattern)));
//    CHECK(RE2::FullMatch(latin1_string, RE2(latin1_pattern, RE2::Latin1)));
//
// -----------------------------------------------------------------------
// MATCHING WITH SUBSTRING EXTRACTION:
//
// You can supply extra pointer arguments to extract matched substrings.
// On match failure, none of the pointees will have been modified.
// On match success, the substrings will be converted (as necessary) and
// their values will be assigned to their pointees until all conversions
// have succeeded or one conversion has failed.
// On conversion failure, the pointees will be in an indeterminate state
// because the caller has no way of knowing which conversion failed.
// However, conversion cannot fail for types like string and StringPiece
// that do not inspect the substring contents. Hence, in the common case
// where all of the pointees are of such types, failure is always due to
// match failure and thus none of the pointees will have been modified.
//
// Example: extracts "ruby" into "s" and 1234 into "i"
//    int i;
//    std::string s;
//    CHECK(RE2::FullMatch("ruby:1234", "(\\w+):(\\d+)", &s, &i));
//
// Example: fails because string cannot be stored in integer
//    CHECK(!RE2::FullMatch("ruby", "(.*)", &i));
//
// Example: fails because there aren't enough sub-patterns
//    CHECK(!RE2::FullMatch("ruby:1234", "\\w+:\\d+", &s));
//
// Example: does not try to extract any extra sub-patterns
//    CHECK(RE2::FullMatch("ruby:1234", "(\\w+):(\\d+)", &s));
//
// Example: does not try to extract into NULL
//    CHECK(RE2::FullMatch("ruby:1234", "(\\w+):(\\d+)", NULL, &i));
//
// Example: integer overflow causes failure
//    CHECK(!RE2::FullMatch("ruby:1234567891234", "\\w+:(\\d+)", &i));
//
// NOTE(rsc): Asking for substrings slows successful matches quite a bit.
// This may get a little faster in the future, but right now is slower
// than PCRE.  On the other hand, failed matches run *very* fast (faster
// than PCRE), as do matches without substring extraction.
//
// -----------------------------------------------------------------------
// PARTIAL MATCHES
//
// You can use the "PartialMatch" operation when you want the pattern
// to match any substring of the text.
//
// Example: simple search for a string:
//      CHECK(RE2::PartialMatch("hello", "ell"));
//
// Example: find first number in a string
//      int number;
//      CHECK(RE2::PartialMatch("x*100 + 20", "(\\d+)", &number));
//      CHECK_EQ(number, 100);
//
// -----------------------------------------------------------------------
// PRE-COMPILED REGULAR EXPRESSIONS
//
// RE2 makes it easy to use any string as a regular expression, without
// requiring a separate compilation step.
//
// If speed is of the essence, you can create a pre-compiled "RE2"
// object from the pattern and use it multiple times.  If you do so,
// you can typically parse text faster than with sscanf.
//
// Example: precompile pattern for faster matching:
//    RE2 pattern("h.*o");
//    while (ReadLine(&str)) {
//      if (RE2::FullMatch(str, pattern)) ...;
//    }
//
// -----------------------------------------------------------------------
// SCANNING TEXT INCREMENTALLY
//
// The "Consume" operation may be useful if you want to repeatedly
// match regular expressions at the front of a string and skip over
// them as they match.  This requires use of the "StringPiece" type,
// which represents a sub-range of a real string.
//
// Example: read lines of the form "var = value" from a string.
//      std::string contents = ...;     // Fill string somehow
//      StringPiece input(contents);    // Wrap a StringPiece around it
//
//      std::string var;
//      int value;
//      while (RE2::Consume(&input, "(\\w+) = (\\d+)\n", &var, &value)) {
//        ...;
//      }
//
// Each successful call to "Consume" will set "var/value", and also
// advance "input" so it points past the matched text.  Note that if the
// regular expression matches an empty string, input will advance
// by 0 bytes.  If the regular expression being used might match
// an empty string, the loop body must check for this case and either
// advance the string or break out of the loop.
//
// The "FindAndConsume" operation is similar to "Consume" but does not
// anchor your match at the beginning of the string.  For example, you
// could extract all words from a string by repeatedly calling
//     RE2::FindAndConsume(&input, "(\\w+)", &word)
//
// -----------------------------------------------------------------------
// USING VARIABLE NUMBER OF ARGUMENTS
//
// The above operations require you to know the number of arguments
// when you write the code.  This is not always possible or easy (for
// example, the regular expression may be calculated at run time).
// You can use the "N" version of the operations when the number of
// match arguments are determined at run time.
//
// Example:
//   const RE2::Arg* args[10];
//   int n;
//   // ... populate args with pointers to RE2::Arg values ...
//   // ... set n to the number of RE2::Arg objects ...
//   bool match = RE2::FullMatchN(input, pattern, args, n);
//
// The last statement is equivalent to
//
//   bool match = RE2::FullMatch(input, pattern,
//                               *args[0], *args[1], ..., *args[n - 1]);
//
// -----------------------------------------------------------------------
// PARSING HEX/OCTAL/C-RADIX NUMBERS
//
// By default, if you pass a pointer to a numeric value, the
// corresponding text is interpreted as a base-10 number.  You can
// instead wrap the pointer with a call to one of the operators Hex(),
// Octal(), or CRadix() to interpret the text in another base.  The
// CRadix operator interprets C-style "0" (base-8) and "0x" (base-16)
// prefixes, but defaults to base-10.
//
// Example:
//   int a, b, c, d;
//   CHECK(RE2::FullMatch("100 40 0100 0x40", "(.*) (.*) (.*) (.*)",
//         RE2::Octal(&a), RE2::Hex(&b), RE2::CRadix(&c), RE2::CRadix(&d));
// will leave 64 in a, b, c, and d.

#include <stddef.h>
#include <stdint.h>
#include <algorithm>
#include <map>
#include <mutex>
#include <string>
#include <type_traits>
#include <vector>

#if defined(__APPLE__)
#include <TargetConditionals.h>
#endif

#include "re2/stringpiece.h"

namespace re2
{
    class Prog;
    class Regexp;
}  // namespace re2

namespace re2
{

    // Interface for regular expression matching.  Also corresponds to a
    // pre-compiled regular expression.  An "RE2" object is safe for
    // concurrent use by multiple threads.
    class RE2
    {
    public:
        // We convert user-passed pointers into special Arg objects
        class Arg;
        class Options;

        // Defined in set.h.
        class Set;

        enum ErrorCode
        {
            NoError = 0,

            // Unexpected error
            ErrorInternal,

            // Parse errors
            ErrorBadEscape,          // bad escape sequence
            ErrorBadCharClass,       // bad character class
            ErrorBadCharRange,       // bad character class range
            ErrorMissingBracket,     // missing closing ]
            ErrorMissingParen,       // missing closing )
            ErrorUnexpectedParen,    // unexpected closing )
            ErrorTrailingBackslash,  // trailing \ at end of regexp
            ErrorRepeatArgument,     // repeat argument missing, e.g. "*"
            ErrorRepeatSize,         // bad repetition argument
            ErrorRepeatOp,           // bad repetition operator
            ErrorBadPerlOp,          // bad perl operator
            ErrorBadUTF8,            // invalid UTF-8 in regexp
            ErrorBadNamedCapture,    // bad named capture group
            ErrorPatternTooLarge     // pattern too large (compile failed)
        };

        // Predefined common options.
        // If you need more complicated things, instantiate
        // an Option class, possibly passing one of these to
        // the Option constructor, change the settings, and pass that
        // Option class to the RE2 constructor.
        enum CannedOptions
        {
            DefaultOptions = 0,
            Latin1,  // treat input as Latin-1 (default UTF-8)
            POSIX,   // POSIX syntax, leftmost-longest match
            Quiet    // do not log about regexp parse errors
        };

        // Need to have the const char* and const std::string& forms for implicit
        // conversions when passing string literals to FullMatch and PartialMatch.
        // Otherwise the StringPiece form would be sufficient.
#ifndef SWIG
        RE2(const char* pattern);
        RE2(const std::string& pattern);
#endif
        RE2(const StringPiece& pattern);
        RE2(const StringPiece& pattern, const Options& options);
        ~RE2();

        // Returns whether RE2 was created properly.
        bool ok() const
        {
            return error_code() == NoError;
        }

        // The string specification for this RE2.  E.g.
        //   RE2 re("ab*c?d+");
        //   re.pattern();    // "ab*c?d+"
        const std::string& pattern() const
        {
            return pattern_;
        }

        // If RE2 could not be created properly, returns an error string.
        // Else returns the empty string.
        const std::string& error() const
        {
            return *error_;
        }

        // If RE2 could not be created properly, returns an error code.
        // Else returns RE2::NoError (== 0).
        ErrorCode error_code() const
        {
            return error_code_;
        }

        // If RE2 could not be created properly, returns the offending
        // portion of the regexp.
        const std::string& error_arg() const
        {
            return error_arg_;
        }

        // Returns the program size, a very approximate measure of a regexp's "cost".
        // Larger numbers are more expensive than smaller numbers.
        int ProgramSize() const;
        int ReverseProgramSize() const;

        // If histogram is not null, outputs the program fanout
        // as a histogram bucketed by powers of 2.
        // Returns the number of the largest non-empty bucket.
        int ProgramFanout(std::vector<int>* histogram) const;
        int ReverseProgramFanout(std::vector<int>* histogram) const;

        // Returns the underlying Regexp; not for general use.
        // Returns entire_regexp_ so that callers don't need
        // to know about prefix_ and prefix_foldcase_.
        re2::Regexp* Regexp() const
        {
            return entire_regexp_;
        }

        /***** The array-based matching interface ******/

        // The functions here have names ending in 'N' and are used to implement
        // the functions whose names are the prefix before the 'N'. It is sometimes
        // useful to invoke them directly, but the syntax is awkward, so the 'N'-less
        // versions should be preferred.
        static bool FullMatchN(const StringPiece& text, const RE2& re, const Arg* const args[], int n);
        static bool PartialMatchN(const StringPiece& text, const RE2& re, const Arg* const args[], int n);
        static bool ConsumeN(StringPiece* input, const RE2& re, const Arg* const args[], int n);
        static bool FindAndConsumeN(StringPiece* input, const RE2& re, const Arg* const args[], int n);

#ifndef SWIG

    private:
        template<typename F, typename SP>
        static inline bool Apply(F f, SP sp, const RE2& re)
        {
            return f(sp, re, NULL, 0);
        }

        template<typename F, typename SP, typename... A>
        static inline bool Apply(F f, SP sp, const RE2& re, const A&... a)
        {
            const Arg* const args[] = {&a...};
            const int n = sizeof...(a);
            return f(sp, re, args, n);
        }

    public:
        // In order to allow FullMatch() et al. to be called with a varying number
        // of arguments of varying types, we use two layers of variadic templates.
        // The first layer constructs the temporary Arg objects. The second layer
        // (above) constructs the array of pointers to the temporary Arg objects.

        /***** The useful part: the matching interface *****/

        // Matches "text" against "re".  If pointer arguments are
        // supplied, copies matched sub-patterns into them.
        //
        // You can pass in a "const char*" or a "std::string" for "text".
        // You can pass in a "const char*" or a "std::string" or a "RE2" for "re".
        //
        // The provided pointer arguments can be pointers to any scalar numeric
        // type, or one of:
        //    std::string     (matched piece is copied to string)
        //    StringPiece     (StringPiece is mutated to point to matched piece)
        //    T               (where "bool T::ParseFrom(const char*, size_t)" exists)
        //    (void*)NULL     (the corresponding matched sub-pattern is not copied)
        //
        // Returns true iff all of the following conditions are satisfied:
        //   a. "text" matches "re" fully - from the beginning to the end of "text".
        //   b. The number of matched sub-patterns is >= number of supplied pointers.
        //   c. The "i"th argument has a suitable type for holding the
        //      string captured as the "i"th sub-pattern.  If you pass in
        //      NULL for the "i"th argument, or pass fewer arguments than
        //      number of sub-patterns, the "i"th captured sub-pattern is
        //      ignored.
        //
        // CAVEAT: An optional sub-pattern that does not exist in the
        // matched string is assigned the empty string.  Therefore, the
        // following will return false (because the empty string is not a
        // valid number):
        //    int number;
        //    RE2::FullMatch("abc", "[a-z]+(\\d+)?", &number);
        template<typename... A>
        static bool FullMatch(const StringPiece& text, const RE2& re, A&&... a)
        {
            return Apply(FullMatchN, text, re, Arg(std::forward<A>(a))...);
        }

        // Like FullMatch(), except that "re" is allowed to match a substring
        // of "text".
        //
        // Returns true iff all of the following conditions are satisfied:
        //   a. "text" matches "re" partially - for some substring of "text".
        //   b. The number of matched sub-patterns is >= number of supplied pointers.
        //   c. The "i"th argument has a suitable type for holding the
        //      string captured as the "i"th sub-pattern.  If you pass in
        //      NULL for the "i"th argument, or pass fewer arguments than
        //      number of sub-patterns, the "i"th captured sub-pattern is
        //      ignored.
        template<typename... A>
        static bool PartialMatch(const StringPiece& text, const RE2& re, A&&... a)
        {
            return Apply(PartialMatchN, text, re, Arg(std::forward<A>(a))...);
        }

        // Like FullMatch() and PartialMatch(), except that "re" has to match
        // a prefix of the text, and "input" is advanced past the matched
        // text.  Note: "input" is modified iff this routine returns true
        // and "re" matched a non-empty substring of "input".
        //
        // Returns true iff all of the following conditions are satisfied:
        //   a. "input" matches "re" partially - for some prefix of "input".
        //   b. The number of matched sub-patterns is >= number of supplied pointers.
        //   c. The "i"th argument has a suitable type for holding the
        //      string captured as the "i"th sub-pattern.  If you pass in
        //      NULL for the "i"th argument, or pass fewer arguments than
        //      number of sub-patterns, the "i"th captured sub-pattern is
        //      ignored.
        template<typename... A>
        static bool Consume(StringPiece* input, const RE2& re, A&&... a)
        {
            return Apply(ConsumeN, input, re, Arg(std::forward<A>(a))...);
        }

        // Like Consume(), but does not anchor the match at the beginning of
        // the text.  That is, "re" need not start its match at the beginning
        // of "input".  For example, "FindAndConsume(s, "(\\w+)", &word)" finds
        // the next word in "s" and stores it in "word".
        //
        // Returns true iff all of the following conditions are satisfied:
        //   a. "input" matches "re" partially - for some substring of "input".
        //   b. The number of matched sub-patterns is >= number of supplied pointers.
        //   c. The "i"th argument has a suitable type for holding the
        //      string captured as the "i"th sub-pattern.  If you pass in
        //      NULL for the "i"th argument, or pass fewer arguments than
        //      number of sub-patterns, the "i"th captured sub-pattern is
        //      ignored.
        template<typename... A>
        static bool FindAndConsume(StringPiece* input, const RE2& re, A&&... a)
        {
            return Apply(FindAndConsumeN, input, re, Arg(std::forward<A>(a))...);
        }
#endif

        // Replace the first match of "re" in "str" with "rewrite".
        // Within "rewrite", backslash-escaped digits (\1 to \9) can be
        // used to insert text matching corresponding parenthesized group
        // from the pattern.  \0 in "rewrite" refers to the entire matching
        // text.  E.g.,
        //
        //   std::string s = "yabba dabba doo";
        //   CHECK(RE2::Replace(&s, "b+", "d"));
        //
        // will leave "s" containing "yada dabba doo"
        //
        // Returns true if the pattern matches and a replacement occurs,
        // false otherwise.
        static bool Replace(std::string* str, const RE2& re, const StringPiece& rewrite);

        // Like Replace(), except replaces successive non-overlapping occurrences
        // of the pattern in the string with the rewrite. E.g.
        //
        //   std::string s = "yabba dabba doo";
        //   CHECK(RE2::GlobalReplace(&s, "b+", "d"));
        //
        // will leave "s" containing "yada dada doo"
        // Replacements are not subject to re-matching.
        //
        // Because GlobalReplace only replaces non-overlapping matches,
        // replacing "ana" within "banana" makes only one replacement, not two.
        //
        // Returns the number of replacements made.
        static int GlobalReplace(std::string* str, const RE2& re, const StringPiece& rewrite);

        // Like Replace, except that if the pattern matches, "rewrite"
        // is copied into "out" with substitutions.  The non-matching
        // portions of "text" are ignored.
        //
        // Returns true iff a match occurred and the extraction happened
        // successfully;  if no match occurs, the string is left unaffected.
        //
        // REQUIRES: "text" must not alias any part of "*out".
        static bool Extract(const StringPiece& text, const RE2& re, const StringPiece& rewrite, std::string* out);

        // Escapes all potentially meaningful regexp characters in
        // 'unquoted'.  The returned string, used as a regular expression,
        // will match exactly the original string.  For example,
        //           1.5-2.0?
        // may become:
        //           1\.5\-2\.0\?
        static std::string QuoteMeta(const StringPiece& unquoted);

        // Computes range for any strings matching regexp. The min and max can in
        // some cases be arbitrarily precise, so the caller gets to specify the
        // maximum desired length of string returned.
        //
        // Assuming PossibleMatchRange(&min, &max, N) returns successfully, any
        // string s that is an anchored match for this regexp satisfies
        //   min <= s && s <= max.
        //
        // Note that PossibleMatchRange() will only consider the first copy of an
        // infinitely repeated element (i.e., any regexp element followed by a '*' or
        // '+' operator). Regexps with "{N}" constructions are not affected, as those
        // do not compile down to infinite repetitions.
        //
        // Returns true on success, false on error.
        bool PossibleMatchRange(std::string* min, std::string* max, int maxlen) const;

        // Generic matching interface

        // Type of match.
        enum Anchor
        {
            UNANCHORED,    // No anchoring
            ANCHOR_START,  // Anchor at start only
            ANCHOR_BOTH    // Anchor at start and end
        };

        // Return the number of capturing subpatterns, or -1 if the
        // regexp wasn't valid on construction.  The overall match ($0)
        // does not count: if the regexp is "(a)(b)", returns 2.
        int NumberOfCapturingGroups() const
        {
            return num_captures_;
        }

        // Return a map from names to capturing indices.
        // The map records the index of the leftmost group
        // with the given name.
        // Only valid until the re is deleted.
        const std::map<std::string, int>& NamedCapturingGroups() const;

        // Return a map from capturing indices to names.
        // The map has no entries for unnamed groups.
        // Only valid until the re is deleted.
        const std::map<int, std::string>& CapturingGroupNames() const;

        // General matching routine.
        // Match against text starting at offset startpos
        // and stopping the search at offset endpos.
        // Returns true if match found, false if not.
        // On a successful match, fills in submatch[] (up to nsubmatch entries)
        // with information about submatches.
        // I.e. matching RE2("(foo)|(bar)baz") on "barbazbla" will return true, with
        // submatch[0] = "barbaz", submatch[1].data() = NULL, submatch[2] = "bar",
        // submatch[3].data() = NULL, ..., up to submatch[nsubmatch-1].data() = NULL.
        // Caveat: submatch[] may be clobbered even on match failure.
        //
        // Don't ask for more match information than you will use:
        // runs much faster with nsubmatch == 1 than nsubmatch > 1, and
        // runs even faster if nsubmatch == 0.
        // Doesn't make sense to use nsubmatch > 1 + NumberOfCapturingGroups(),
        // but will be handled correctly.
        //
        // Passing text == StringPiece(NULL, 0) will be handled like any other
        // empty string, but note that on return, it will not be possible to tell
        // whether submatch i matched the empty string or did not match:
        // either way, submatch[i].data() == NULL.
        bool Match(const StringPiece& text, size_t startpos, size_t endpos, Anchor re_anchor, StringPiece* submatch, int nsubmatch) const;

        // Check that the given rewrite string is suitable for use with this
        // regular expression.  It checks that:
        //   * The regular expression has enough parenthesized subexpressions
        //     to satisfy all of the \N tokens in rewrite
        //   * The rewrite string doesn't have any syntax errors.  E.g.,
        //     '\' followed by anything other than a digit or '\'.
        // A true return value guarantees that Replace() and Extract() won't
        // fail because of a bad rewrite string.
        bool CheckRewriteString(const StringPiece& rewrite, std::string* error) const;

        // Returns the maximum submatch needed for the rewrite to be done by
        // Replace(). E.g. if rewrite == "foo \\2,\\1", returns 2.
        static int MaxSubmatch(const StringPiece& rewrite);

        // Append the "rewrite" string, with backslash subsitutions from "vec",
        // to string "out".
        // Returns true on success.  This method can fail because of a malformed
        // rewrite string.  CheckRewriteString guarantees that the rewrite will
        // be sucessful.
        bool Rewrite(std::string* out, const StringPiece& rewrite, const StringPiece* vec, int veclen) const;

        // Constructor options
        class Options
        {
        public:
            // The options are (defaults in parentheses):
            //
            //   utf8             (true)  text and pattern are UTF-8; otherwise Latin-1
            //   posix_syntax     (false) restrict regexps to POSIX egrep syntax
            //   longest_match    (false) search for longest match, not first match
            //   log_errors       (true)  log syntax and execution errors to ERROR
            //   max_mem          (see below)  approx. max memory footprint of RE2
            //   literal          (false) interpret string as literal, not regexp
            //   never_nl         (false) never match \n, even if it is in regexp
            //   dot_nl           (false) dot matches everything including new line
            //   never_capture    (false) parse all parens as non-capturing
            //   case_sensitive   (true)  match is case-sensitive (regexp can override
            //                              with (?i) unless in posix_syntax mode)
            //
            // The following options are only consulted when posix_syntax == true.
            // When posix_syntax == false, these features are always enabled and
            // cannot be turned off; to perform multi-line matching in that case,
            // begin the regexp with (?m).
            //   perl_classes     (false) allow Perl's \d \s \w \D \S \W
            //   word_boundary    (false) allow Perl's \b \B (word boundary and not)
            //   one_line         (false) ^ and $ only match beginning and end of text
            //
            // The max_mem option controls how much memory can be used
            // to hold the compiled form of the regexp (the Prog) and
            // its cached DFA graphs.  Code Search placed limits on the number
            // of Prog instructions and DFA states: 10,000 for both.
            // In RE2, those limits would translate to about 240 KB per Prog
            // and perhaps 2.5 MB per DFA (DFA state sizes vary by regexp; RE2 does a
            // better job of keeping them small than Code Search did).
            // Each RE2 has two Progs (one forward, one reverse), and each Prog
            // can have two DFAs (one first match, one longest match).
            // That makes 4 DFAs:
            //
            //   forward, first-match    - used for UNANCHORED or ANCHOR_START searches
            //                               if opt.longest_match() == false
            //   forward, longest-match  - used for all ANCHOR_BOTH searches,
            //                               and the other two kinds if
            //                               opt.longest_match() == true
            //   reverse, first-match    - never used
            //   reverse, longest-match  - used as second phase for unanchored searches
            //
            // The RE2 memory budget is statically divided between the two
            // Progs and then the DFAs: two thirds to the forward Prog
            // and one third to the reverse Prog.  The forward Prog gives half
            // of what it has left over to each of its DFAs.  The reverse Prog
            // gives it all to its longest-match DFA.
            //
            // Once a DFA fills its budget, it flushes its cache and starts over.
            // If this happens too often, RE2 falls back on the NFA implementation.

            // For now, make the default budget something close to Code Search.
            static const int kDefaultMaxMem = 8 << 20;

            enum Encoding
            {
                EncodingUTF8 = 1,
                EncodingLatin1
            };

            Options() :
                encoding_(EncodingUTF8),
                posix_syntax_(false),
                longest_match_(false),
                log_errors_(true),
                max_mem_(kDefaultMaxMem),
                literal_(false),
                never_nl_(false),
                dot_nl_(false),
                never_capture_(false),
                case_sensitive_(true),
                perl_classes_(false),
                word_boundary_(false),
                one_line_(false)
            {
            }

            /*implicit*/ Options(CannedOptions);

            Encoding encoding() const
            {
                return encoding_;
            }
            void set_encoding(Encoding encoding)
            {
                encoding_ = encoding;
            }

            bool posix_syntax() const
            {
                return posix_syntax_;
            }
            void set_posix_syntax(bool b)
            {
                posix_syntax_ = b;
            }

            bool longest_match() const
            {
                return longest_match_;
            }
            void set_longest_match(bool b)
            {
                longest_match_ = b;
            }

            bool log_errors() const
            {
                return log_errors_;
            }
            void set_log_errors(bool b)
            {
                log_errors_ = b;
            }

            int64_t max_mem() const
            {
                return max_mem_;
            }
            void set_max_mem(int64_t m)
            {
                max_mem_ = m;
            }

            bool literal() const
            {
                return literal_;
            }
            void set_literal(bool b)
            {
                literal_ = b;
            }

            bool never_nl() const
            {
                return never_nl_;
            }
            void set_never_nl(bool b)
            {
                never_nl_ = b;
            }

            bool dot_nl() const
            {
                return dot_nl_;
            }
            void set_dot_nl(bool b)
            {
                dot_nl_ = b;
            }

            bool never_capture() const
            {
                return never_capture_;
            }
            void set_never_capture(bool b)
            {
                never_capture_ = b;
            }

            bool case_sensitive() const
            {
                return case_sensitive_;
            }
            void set_case_sensitive(bool b)
            {
                case_sensitive_ = b;
            }

            bool perl_classes() const
            {
                return perl_classes_;
            }
            void set_perl_classes(bool b)
            {
                perl_classes_ = b;
            }

            bool word_boundary() const
            {
                return word_boundary_;
            }
            void set_word_boundary(bool b)
            {
                word_boundary_ = b;
            }

            bool one_line() const
            {
                return one_line_;
            }
            void set_one_line(bool b)
            {
                one_line_ = b;
            }

            void Copy(const Options& src)
            {
                *this = src;
            }

            int ParseFlags() const;

        private:
            Encoding encoding_;
            bool posix_syntax_;
            bool longest_match_;
            bool log_errors_;
            int64_t max_mem_;
            bool literal_;
            bool never_nl_;
            bool dot_nl_;
            bool never_capture_;
            bool case_sensitive_;
            bool perl_classes_;
            bool word_boundary_;
            bool one_line_;
        };

        // Returns the options set in the constructor.
        const Options& options() const
        {
            return options_;
        }

        // Argument converters; see below.
        template<typename T>
        static Arg CRadix(T* ptr);
        template<typename T>
        static Arg Hex(T* ptr);
        template<typename T>
        static Arg Octal(T* ptr);

    private:
        void Init(const StringPiece& pattern, const Options& options);

        bool DoMatch(const StringPiece& text, Anchor re_anchor, size_t* consumed, const Arg* const args[], int n) const;

        re2::Prog* ReverseProg() const;

        std::string pattern_;         // string regular expression
        Options options_;             // option flags
        re2::Regexp* entire_regexp_;  // parsed regular expression
        const std::string* error_;    // error indicator (or points to empty string)
        ErrorCode error_code_;        // error code
        std::string error_arg_;       // fragment of regexp showing error
        std::string prefix_;          // required prefix (before suffix_regexp_)
        bool prefix_foldcase_;        // prefix_ is ASCII case-insensitive
        re2::Regexp* suffix_regexp_;  // parsed regular expression, prefix_ removed
        re2::Prog* prog_;             // compiled program for regexp
        int num_captures_;            // number of capturing groups
        bool is_one_pass_;            // can use prog_->SearchOnePass?

        // Reverse Prog for DFA execution only
        mutable re2::Prog* rprog_;
        // Map from capture names to indices
        mutable const std::map<std::string, int>* named_groups_;
        // Map from capture indices to names
        mutable const std::map<int, std::string>* group_names_;

        mutable std::once_flag rprog_once_;
        mutable std::once_flag named_groups_once_;
        mutable std::once_flag group_names_once_;

        RE2(const RE2&) = delete;
        RE2& operator=(const RE2&) = delete;
    };

    /***** Implementation details *****/

    namespace re2_internal
    {

        // Types for which the 3-ary Parse() function template has specializations.
        template<typename T>
        struct Parse3ary : public std::false_type
        {
        };
        template<>
        struct Parse3ary<void> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<std::string> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<StringPiece> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<char> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<signed char> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<unsigned char> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<float> : public std::true_type
        {
        };
        template<>
        struct Parse3ary<double> : public std::true_type
        {
        };

        template<typename T>
        bool Parse(const char* str, size_t n, T* dest);

        // Types for which the 4-ary Parse() function template has specializations.
        template<typename T>
        struct Parse4ary : public std::false_type
        {
        };
        template<>
        struct Parse4ary<long> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<unsigned long> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<short> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<unsigned short> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<int> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<unsigned int> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<long long> : public std::true_type
        {
        };
        template<>
        struct Parse4ary<unsigned long long> : public std::true_type
        {
        };

        template<typename T>
        bool Parse(const char* str, size_t n, T* dest, int radix);

    }  // namespace re2_internal

    class RE2::Arg
    {
    private:
        template<typename T>
        using CanParse3ary = typename std::enable_if<
            re2_internal::Parse3ary<T>::value,
            int>::type;

        template<typename T>
        using CanParse4ary = typename std::enable_if<
            re2_internal::Parse4ary<T>::value,
            int>::type;

#if !defined(_MSC_VER)
        template<typename T>
        using CanParseFrom = typename std::enable_if<
            std::is_member_function_pointer<
                decltype(static_cast<bool (T::*)(const char*, size_t)>(
                    &T::ParseFrom
                ))>::value,
            int>::type;
#endif

    public:
        Arg() :
            Arg(nullptr)
        {
        }
        Arg(std::nullptr_t ptr) :
            arg_(ptr),
            parser_(DoNothing)
        {
        }

        template<typename T, CanParse3ary<T> = 0>
        Arg(T* ptr) :
            arg_(ptr),
            parser_(DoParse3ary<T>)
        {
        }

        template<typename T, CanParse4ary<T> = 0>
        Arg(T* ptr) :
            arg_(ptr),
            parser_(DoParse4ary<T>)
        {
        }

#if !defined(_MSC_VER)
        template<typename T, CanParseFrom<T> = 0>
        Arg(T* ptr) :
            arg_(ptr),
            parser_(DoParseFrom<T>)
        {
        }
#endif

        typedef bool (*Parser)(const char* str, size_t n, void* dest);

        template<typename T>
        Arg(T* ptr, Parser parser) :
            arg_(ptr),
            parser_(parser)
        {
        }

        bool Parse(const char* str, size_t n) const
        {
            return (*parser_)(str, n, arg_);
        }

    private:
        static bool DoNothing(const char* /*str*/, size_t /*n*/, void* /*dest*/)
        {
            return true;
        }

        template<typename T>
        static bool DoParse3ary(const char* str, size_t n, void* dest)
        {
            return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest));
        }

        template<typename T>
        static bool DoParse4ary(const char* str, size_t n, void* dest)
        {
            return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest), 10);
        }

#if !defined(_MSC_VER)
        template<typename T>
        static bool DoParseFrom(const char* str, size_t n, void* dest)
        {
            if (dest == NULL)
                return true;
            return reinterpret_cast<T*>(dest)->ParseFrom(str, n);
        }
#endif

        void* arg_;
        Parser parser_;
    };

    template<typename T>
    inline RE2::Arg RE2::CRadix(T* ptr)
    {
        return RE2::Arg(ptr, [](const char* str, size_t n, void* dest) -> bool
                        { return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest), 0); });
    }

    template<typename T>
    inline RE2::Arg RE2::Hex(T* ptr)
    {
        return RE2::Arg(ptr, [](const char* str, size_t n, void* dest) -> bool
                        { return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest), 16); });
    }

    template<typename T>
    inline RE2::Arg RE2::Octal(T* ptr)
    {
        return RE2::Arg(ptr, [](const char* str, size_t n, void* dest) -> bool
                        { return re2_internal::Parse(str, n, reinterpret_cast<T*>(dest), 8); });
    }

#ifndef SWIG
// Silence warnings about missing initializers for members of LazyRE2.
#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ >= 6
#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
#endif

    // Helper for writing global or static RE2s safely.
    // Write
    //     static LazyRE2 re = {".*"};
    // and then use *re instead of writing
    //     static RE2 re(".*");
    // The former is more careful about multithreaded
    // situations than the latter.
    //
    // N.B. This class never deletes the RE2 object that
    // it constructs: that's a feature, so that it can be used
    // for global and function static variables.
    class LazyRE2
    {
    private:
        struct NoArg
        {
        };

    public:
        typedef RE2 element_type;  // support std::pointer_traits

        // Constructor omitted to preserve braced initialization in C++98.

        // Pretend to be a pointer to Type (never NULL due to on-demand creation):
        RE2& operator*() const
        {
            return *get();
        }
        RE2* operator->() const
        {
            return get();
        }

        // Named accessor/initializer:
        RE2* get() const
        {
            std::call_once(once_, &LazyRE2::Init, this);
            return ptr_;
        }

        // All data fields must be public to support {"foo"} initialization.
        const char* pattern_;
        RE2::CannedOptions options_;
        NoArg barrier_against_excess_initializers_;

        mutable RE2* ptr_;
        mutable std::once_flag once_;

    private:
        static void Init(const LazyRE2* lazy_re2)
        {
            lazy_re2->ptr_ = new RE2(lazy_re2->pattern_, lazy_re2->options_);
        }

        void operator=(const LazyRE2&);  // disallowed
    };
#endif

    namespace hooks
    {

// Most platforms support thread_local. Older versions of iOS don't support
// thread_local, but for the sake of brevity, we lump together all versions
// of Apple platforms that aren't macOS. If an iOS application really needs
// the context pointee someday, we can get more specific then...
//
// As per https://github.com/google/re2/issues/325, thread_local support in
// MinGW seems to be buggy. (FWIW, Abseil folks also avoid it.)
#define RE2_HAVE_THREAD_LOCAL
#if (defined(__APPLE__) && !TARGET_OS_OSX) || defined(__MINGW32__)
#undef RE2_HAVE_THREAD_LOCAL
#endif

// A hook must not make any assumptions regarding the lifetime of the context
// pointee beyond the current invocation of the hook. Pointers and references
// obtained via the context pointee should be considered invalidated when the
// hook returns. Hence, any data about the context pointee (e.g. its pattern)
// would have to be copied in order for it to be kept for an indefinite time.
//
// A hook must not use RE2 for matching. Control flow reentering RE2::Match()
// could result in infinite mutual recursion. To discourage that possibility,
// RE2 will not maintain the context pointer correctly when used in that way.
#ifdef RE2_HAVE_THREAD_LOCAL
        extern thread_local const RE2* context;
#endif

        struct DFAStateCacheReset
        {
            int64_t state_budget;
            size_t state_cache_size;
        };

        struct DFASearchFailure
        {
            // Nothing yet...
        };

#define DECLARE_HOOK(type)                    \
    using type##Callback = void(const type&); \
    void Set##type##Hook(type##Callback* cb); \
    type##Callback* Get##type##Hook();

        DECLARE_HOOK(DFAStateCacheReset)
        DECLARE_HOOK(DFASearchFailure)

#undef DECLARE_HOOK

    }  // namespace hooks

}  // namespace re2

using re2::LazyRE2;
using re2::RE2;

#endif  // RE2_RE2_H_