regex/

builders.rs

#![allow(warnings)]

// This module defines an internal builder that encapsulates all interaction
// with meta::Regex construction, and then 4 public API builders that wrap
// around it. The docs are essentially repeated on each of the 4 public
// builders, with tweaks to the examples as needed.
//
// The reason why there are so many builders is partially because of a misstep
// in the initial API design: the builder constructor takes in the pattern
// strings instead of using the `build` method to accept the pattern strings.
// This means `new` has a different signature for each builder. It probably
// would have been nicer to to use one builder with `fn new()`, and then add
// `build(pat)` and `build_many(pats)` constructors.
//
// The other reason is because I think the `bytes` module should probably
// have its own builder type. That way, it is completely isolated from the
// top-level API.
//
// If I could do it again, I'd probably have a `regex::Builder` and a
// `regex::bytes::Builder`. Each would have `build` and `build_set` (or
// `build_many`) methods for constructing a single pattern `Regex` and a
// multi-pattern `RegexSet`, respectively.

use alloc::{
    string::{String, ToString},
    sync::Arc,
    vec,
    vec::Vec,
};

use regex_automata::{
    meta, nfa::thompson::WhichCaptures, util::syntax, MatchKind,
};

use crate::error::Error;

/// A builder for constructing a `Regex`, `bytes::Regex`, `RegexSet` or a
/// `bytes::RegexSet`.
///
/// This is essentially the implementation of the four different builder types
/// in the public API: `RegexBuilder`, `bytes::RegexBuilder`, `RegexSetBuilder`
/// and `bytes::RegexSetBuilder`.
#[derive(Clone, Debug)]
struct Builder {
    pats: Vec<String>,
    metac: meta::Config,
    syntaxc: syntax::Config,
}

impl Default for Builder {
    fn default() -> Builder {
        let metac = meta::Config::new()
            .nfa_size_limit(Some(10 * (1 << 20)))
            .hybrid_cache_capacity(2 * (1 << 20));
        Builder { pats: vec![], metac, syntaxc: syntax::Config::default() }
    }
}

impl Builder {
    fn new<I, S>(patterns: I) -> Builder
    where
        S: AsRef<str>,
        I: IntoIterator<Item = S>,
    {
        let mut b = Builder::default();
        b.pats.extend(patterns.into_iter().map(|p| p.as_ref().to_string()));
        b
    }

    fn build_one_string(&self) -> Result<crate::Regex, Error> {
        assert_eq!(1, self.pats.len());
        let metac = self
            .metac
            .clone()
            .match_kind(MatchKind::LeftmostFirst)
            .utf8_empty(true);
        let syntaxc = self.syntaxc.clone().utf8(true);
        let pattern = Arc::from(self.pats[0].as_str());
        meta::Builder::new()
            .configure(metac)
            .syntax(syntaxc)
            .build(&pattern)
            .map(|meta| crate::Regex { meta, pattern })
            .map_err(Error::from_meta_build_error)
    }

    fn build_one_bytes(&self) -> Result<crate::bytes::Regex, Error> {
        assert_eq!(1, self.pats.len());
        let metac = self
            .metac
            .clone()
            .match_kind(MatchKind::LeftmostFirst)
            .utf8_empty(false);
        let syntaxc = self.syntaxc.clone().utf8(false);
        let pattern = Arc::from(self.pats[0].as_str());
        meta::Builder::new()
            .configure(metac)
            .syntax(syntaxc)
            .build(&pattern)
            .map(|meta| crate::bytes::Regex { meta, pattern })
            .map_err(Error::from_meta_build_error)
    }

    fn build_many_string(&self) -> Result<crate::RegexSet, Error> {
        let metac = self
            .metac
            .clone()
            .match_kind(MatchKind::All)
            .utf8_empty(true)
            .which_captures(WhichCaptures::None);
        let syntaxc = self.syntaxc.clone().utf8(true);
        let patterns = Arc::from(self.pats.as_slice());
        meta::Builder::new()
            .configure(metac)
            .syntax(syntaxc)
            .build_many(&patterns)
            .map(|meta| crate::RegexSet { meta, patterns })
            .map_err(Error::from_meta_build_error)
    }

    fn build_many_bytes(&self) -> Result<crate::bytes::RegexSet, Error> {
        let metac = self
            .metac
            .clone()
            .match_kind(MatchKind::All)
            .utf8_empty(false)
            .which_captures(WhichCaptures::None);
        let syntaxc = self.syntaxc.clone().utf8(false);
        let patterns = Arc::from(self.pats.as_slice());
        meta::Builder::new()
            .configure(metac)
            .syntax(syntaxc)
            .build_many(&patterns)
            .map(|meta| crate::bytes::RegexSet { meta, patterns })
            .map_err(Error::from_meta_build_error)
    }

    fn case_insensitive(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.case_insensitive(yes);
        self
    }

    fn multi_line(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.multi_line(yes);
        self
    }

    fn dot_matches_new_line(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.dot_matches_new_line(yes);
        self
    }

    fn crlf(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.crlf(yes);
        self
    }

    fn line_terminator(&mut self, byte: u8) -> &mut Builder {
        self.metac = self.metac.clone().line_terminator(byte);
        self.syntaxc = self.syntaxc.line_terminator(byte);
        self
    }

    fn swap_greed(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.swap_greed(yes);
        self
    }

    fn ignore_whitespace(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.ignore_whitespace(yes);
        self
    }

    fn unicode(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.unicode(yes);
        self
    }

    fn octal(&mut self, yes: bool) -> &mut Builder {
        self.syntaxc = self.syntaxc.octal(yes);
        self
    }

    fn size_limit(&mut self, limit: usize) -> &mut Builder {
        self.metac = self.metac.clone().nfa_size_limit(Some(limit));
        self
    }

    fn dfa_size_limit(&mut self, limit: usize) -> &mut Builder {
        self.metac = self.metac.clone().hybrid_cache_capacity(limit);
        self
    }

    fn nest_limit(&mut self, limit: u32) -> &mut Builder {
        self.syntaxc = self.syntaxc.nest_limit(limit);
        self
    }
}

pub(crate) mod string {
    use crate::{error::Error, Regex, RegexSet};

    use super::Builder;

    /// A configurable builder for a [`Regex`].
    ///
    /// This builder can be used to programmatically set flags such as `i`
    /// (case insensitive) and `x` (for verbose mode). This builder can also be
    /// used to configure things like the line terminator and a size limit on
    /// the compiled regular expression.
    #[derive(Clone, Debug)]
    pub struct RegexBuilder {
        builder: Builder,
    }

    impl RegexBuilder {
        /// Create a new builder with a default configuration for the given
        /// pattern.
        ///
        /// If the pattern is invalid or exceeds the configured size limits,
        /// then an error will be returned when [`RegexBuilder::build`] is
        /// called.
        pub fn new(pattern: &str) -> RegexBuilder {
            RegexBuilder { builder: Builder::new([pattern]) }
        }

        /// Compiles the pattern given to `RegexBuilder::new` with the
        /// configuration set on this builder.
        ///
        /// If the pattern isn't a valid regex or if a configured size limit
        /// was exceeded, then an error is returned.
        pub fn build(&self) -> Result<Regex, Error> {
            self.builder.build_one_string()
        }

        /// This configures Unicode mode for the entire pattern.
        ///
        /// Enabling Unicode mode does a number of things:
        ///
        /// * Most fundamentally, it causes the fundamental atom of matching
        /// to be a single codepoint. When Unicode mode is disabled, it's a
        /// single byte. For example, when Unicode mode is enabled, `.` will
        /// match `💩` once, where as it will match 4 times when Unicode mode
        /// is disabled. (Since the UTF-8 encoding of `💩` is 4 bytes long.)
        /// * Case insensitive matching uses Unicode simple case folding rules.
        /// * Unicode character classes like `\p{Letter}` and `\p{Greek}` are
        /// available.
        /// * Perl character classes are Unicode aware. That is, `\w`, `\s` and
        /// `\d`.
        /// * The word boundary assertions, `\b` and `\B`, use the Unicode
        /// definition of a word character.
        ///
        /// Note that if Unicode mode is disabled, then the regex will fail to
        /// compile if it could match invalid UTF-8. For example, when Unicode
        /// mode is disabled, then since `.` matches any byte (except for
        /// `\n`), then it can match invalid UTF-8 and thus building a regex
        /// from it will fail. Another example is `\w` and `\W`. Since `\w` can
        /// only match ASCII bytes when Unicode mode is disabled, it's allowed.
        /// But `\W` can match more than ASCII bytes, including invalid UTF-8,
        /// and so it is not allowed. This restriction can be lifted only by
        /// using a [`bytes::Regex`](crate::bytes::Regex).
        ///
        /// For more details on the Unicode support in this crate, see the
        /// [Unicode section](crate#unicode) in this crate's top-level
        /// documentation.
        ///
        /// The default for this is `true`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"\w")
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally greek letters would be included in \w, but since
        /// // Unicode mode is disabled, it only matches ASCII letters.
        /// assert!(!re.is_match("δ"));
        ///
        /// let re = RegexBuilder::new(r"s")
        ///     .case_insensitive(true)
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally 'ſ' is included when searching for 's' case
        /// // insensitively due to Unicode's simple case folding rules. But
        /// // when Unicode mode is disabled, only ASCII case insensitive rules
        /// // are used.
        /// assert!(!re.is_match("ſ"));
        /// ```
        pub fn unicode(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.unicode(yes);
            self
        }

        /// This configures whether to enable case insensitive matching for the
        /// entire pattern.
        ///
        /// This setting can also be configured using the inline flag `i`
        /// in the pattern. For example, `(?i:foo)` matches `foo` case
        /// insensitively while `(?-i:foo)` matches `foo` case sensitively.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"foo(?-i:bar)quux")
        ///     .case_insensitive(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("FoObarQuUx"));
        /// // Even though case insensitive matching is enabled in the builder,
        /// // it can be locally disabled within the pattern. In this case,
        /// // `bar` is matched case sensitively.
        /// assert!(!re.is_match("fooBARquux"));
        /// ```
        pub fn case_insensitive(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.case_insensitive(yes);
            self
        }

        /// This configures multi-line mode for the entire pattern.
        ///
        /// Enabling multi-line mode changes the behavior of the `^` and `$`
        /// anchor assertions. Instead of only matching at the beginning and
        /// end of a haystack, respectively, multi-line mode causes them to
        /// match at the beginning and end of a line *in addition* to the
        /// beginning and end of a haystack. More precisely, `^` will match at
        /// the position immediately following a `\n` and `$` will match at the
        /// position immediately preceding a `\n`.
        ///
        /// The behavior of this option can be impacted by other settings too:
        ///
        /// * The [`RegexBuilder::line_terminator`] option changes `\n` above
        /// to any ASCII byte.
        /// * The [`RegexBuilder::crlf`] option changes the line terminator to
        /// be either `\r` or `\n`, but never at the position between a `\r`
        /// and `\n`.
        ///
        /// This setting can also be configured using the inline flag `m` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^foo$")
        ///     .multi_line(true)
        ///     .build()
        ///     .unwrap();
        /// assert_eq!(Some(1..4), re.find("\nfoo\n").map(|m| m.range()));
        /// ```
        pub fn multi_line(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.multi_line(yes);
            self
        }

        /// This configures dot-matches-new-line mode for the entire pattern.
        ///
        /// Perhaps surprisingly, the default behavior for `.` is not to match
        /// any character, but rather, to match any character except for the
        /// line terminator (which is `\n` by default). When this mode is
        /// enabled, the behavior changes such that `.` truly matches any
        /// character.
        ///
        /// This setting can also be configured using the inline flag `s` in
        /// the pattern. For example, `(?s:.)` and `\p{any}` are equivalent
        /// regexes.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"foo.bar")
        ///     .dot_matches_new_line(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = "foo\nbar";
        /// assert_eq!(Some("foo\nbar"), re.find(hay).map(|m| m.as_str()));
        /// ```
        pub fn dot_matches_new_line(
            &mut self,
            yes: bool,
        ) -> &mut RegexBuilder {
            self.builder.dot_matches_new_line(yes);
            self
        }

        /// This configures CRLF mode for the entire pattern.
        ///
        /// When CRLF mode is enabled, both `\r` ("carriage return" or CR for
        /// short) and `\n` ("line feed" or LF for short) are treated as line
        /// terminators. This results in the following:
        ///
        /// * Unless dot-matches-new-line mode is enabled, `.` will now match
        /// any character except for `\n` and `\r`.
        /// * When multi-line mode is enabled, `^` will match immediately
        /// following a `\n` or a `\r`. Similarly, `$` will match immediately
        /// preceding a `\n` or a `\r`. Neither `^` nor `$` will ever match
        /// between `\r` and `\n`.
        ///
        /// This setting can also be configured using the inline flag `R` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^foo$")
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = "\r\nfoo\r\n";
        /// // If CRLF mode weren't enabled here, then '$' wouldn't match
        /// // immediately after 'foo', and thus no match would be found.
        /// assert_eq!(Some("foo"), re.find(hay).map(|m| m.as_str()));
        /// ```
        ///
        /// This example demonstrates that `^` will never match at a position
        /// between `\r` and `\n`. (`$` will similarly not match between a `\r`
        /// and a `\n`.)
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^")
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = "\r\n\r\n";
        /// let ranges: Vec<_> = re.find_iter(hay).map(|m| m.range()).collect();
        /// assert_eq!(ranges, vec![0..0, 2..2, 4..4]);
        /// ```
        pub fn crlf(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.crlf(yes);
            self
        }

        /// Configures the line terminator to be used by the regex.
        ///
        /// The line terminator is relevant in two ways for a particular regex:
        ///
        /// * When dot-matches-new-line mode is *not* enabled (the default),
        /// then `.` will match any character except for the configured line
        /// terminator.
        /// * When multi-line mode is enabled (not the default), then `^` and
        /// `$` will match immediately after and before, respectively, a line
        /// terminator.
        ///
        /// In both cases, if CRLF mode is enabled in a particular context,
        /// then it takes precedence over any configured line terminator.
        ///
        /// This option cannot be configured from within the pattern.
        ///
        /// The default line terminator is `\n`.
        ///
        /// # Example
        ///
        /// This shows how to treat the NUL byte as a line terminator. This can
        /// be a useful heuristic when searching binary data.
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^foo$")
        ///     .multi_line(true)
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// let hay = "\x00foo\x00";
        /// assert_eq!(Some(1..4), re.find(hay).map(|m| m.range()));
        /// ```
        ///
        /// This example shows that the behavior of `.` is impacted by this
        /// setting as well:
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r".")
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("\n"));
        /// assert!(!re.is_match("\x00"));
        /// ```
        ///
        /// This shows that building a regex will fail if the byte given
        /// is not ASCII and the pattern could result in matching invalid
        /// UTF-8. This is because any singular non-ASCII byte is not valid
        /// UTF-8, and it is not permitted for a [`Regex`] to match invalid
        /// UTF-8. (It is permissible to use a non-ASCII byte when building a
        /// [`bytes::Regex`](crate::bytes::Regex).)
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// assert!(RegexBuilder::new(r".").line_terminator(0x80).build().is_err());
        /// // Note that using a non-ASCII byte isn't enough on its own to
        /// // cause regex compilation to fail. You actually have to make use
        /// // of it in the regex in a way that leads to matching invalid
        /// // UTF-8. If you don't, then regex compilation will succeed!
        /// assert!(RegexBuilder::new(r"a").line_terminator(0x80).build().is_ok());
        /// ```
        pub fn line_terminator(&mut self, byte: u8) -> &mut RegexBuilder {
            self.builder.line_terminator(byte);
            self
        }

        /// This configures swap-greed mode for the entire pattern.
        ///
        /// When swap-greed mode is enabled, patterns like `a+` will become
        /// non-greedy and patterns like `a+?` will become greedy. In other
        /// words, the meanings of `a+` and `a+?` are switched.
        ///
        /// This setting can also be configured using the inline flag `U` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"a+")
        ///     .swap_greed(true)
        ///     .build()
        ///     .unwrap();
        /// assert_eq!(Some("a"), re.find("aaa").map(|m| m.as_str()));
        /// ```
        pub fn swap_greed(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.swap_greed(yes);
            self
        }

        /// This configures verbose mode for the entire pattern.
        ///
        /// When enabled, whitespace will treated as insignifcant in the
        /// pattern and `#` can be used to start a comment until the next new
        /// line.
        ///
        /// Normally, in most places in a pattern, whitespace is treated
        /// literally. For example ` +` will match one or more ASCII whitespace
        /// characters.
        ///
        /// When verbose mode is enabled, `\#` can be used to match a literal
        /// `#` and `\ ` can be used to match a literal ASCII whitespace
        /// character.
        ///
        /// Verbose mode is useful for permitting regexes to be formatted and
        /// broken up more nicely. This may make them more easily readable.
        ///
        /// This setting can also be configured using the inline flag `x` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// let pat = r"
        ///     \b
        ///     (?<first>\p{Uppercase}\w*)  # always start with uppercase letter
        ///     [\s--\n]+                   # whitespace should separate names
        ///     (?: # middle name can be an initial!
        ///         (?:(?<initial>\p{Uppercase})\.|(?<middle>\p{Uppercase}\w*))
        ///         [\s--\n]+
        ///     )?
        ///     (?<last>\p{Uppercase}\w*)
        ///     \b
        /// ";
        /// let re = RegexBuilder::new(pat)
        ///     .ignore_whitespace(true)
        ///     .build()
        ///     .unwrap();
        ///
        /// let caps = re.captures("Harry Potter").unwrap();
        /// assert_eq!("Harry", &caps["first"]);
        /// assert_eq!("Potter", &caps["last"]);
        ///
        /// let caps = re.captures("Harry J. Potter").unwrap();
        /// assert_eq!("Harry", &caps["first"]);
        /// // Since a middle name/initial isn't required for an overall match,
        /// // we can't assume that 'initial' or 'middle' will be populated!
        /// assert_eq!(Some("J"), caps.name("initial").map(|m| m.as_str()));
        /// assert_eq!(None, caps.name("middle").map(|m| m.as_str()));
        /// assert_eq!("Potter", &caps["last"]);
        ///
        /// let caps = re.captures("Harry James Potter").unwrap();
        /// assert_eq!("Harry", &caps["first"]);
        /// // Since a middle name/initial isn't required for an overall match,
        /// // we can't assume that 'initial' or 'middle' will be populated!
        /// assert_eq!(None, caps.name("initial").map(|m| m.as_str()));
        /// assert_eq!(Some("James"), caps.name("middle").map(|m| m.as_str()));
        /// assert_eq!("Potter", &caps["last"]);
        /// ```
        pub fn ignore_whitespace(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.ignore_whitespace(yes);
            self
        }

        /// This configures octal mode for the entire pattern.
        ///
        /// Octal syntax is a little-known way of uttering Unicode codepoints
        /// in a pattern. For example, `a`, `\x61`, `\u0061` and `\141` are all
        /// equivalent patterns, where the last example shows octal syntax.
        ///
        /// While supporting octal syntax isn't in and of itself a problem,
        /// it does make good error messages harder. That is, in PCRE based
        /// regex engines, syntax like `\1` invokes a backreference, which is
        /// explicitly unsupported this library. However, many users expect
        /// backreferences to be supported. Therefore, when octal support
        /// is disabled, the error message will explicitly mention that
        /// backreferences aren't supported.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// // Normally this pattern would not compile, with an error message
        /// // about backreferences not being supported. But with octal mode
        /// // enabled, octal escape sequences work.
        /// let re = RegexBuilder::new(r"\141")
        ///     .octal(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("a"));
        /// ```
        pub fn octal(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.octal(yes);
            self
        }

        /// Sets the approximate size limit, in bytes, of the compiled regex.
        ///
        /// This roughly corresponds to the number of heap memory, in
        /// bytes, occupied by a single regex. If the regex would otherwise
        /// approximately exceed this limit, then compiling that regex will
        /// fail.
        ///
        /// The main utility of a method like this is to avoid compiling
        /// regexes that use an unexpected amount of resources, such as
        /// time and memory. Even if the memory usage of a large regex is
        /// acceptable, its search time may not be. Namely, worst case time
        /// complexity for search is `O(m * n)`, where `m ~ len(pattern)` and
        /// `n ~ len(haystack)`. That is, search time depends, in part, on the
        /// size of the compiled regex. This means that putting a limit on the
        /// size of the regex limits how much a regex can impact search time.
        ///
        /// For more information about regex size limits, see the section on
        /// [untrusted inputs](crate#untrusted-input) in the top-level crate
        /// documentation.
        ///
        /// The default for this is some reasonable number that permits most
        /// patterns to compile successfully.
        ///
        /// # Example
        ///
        /// ```
        /// # if !cfg!(target_pointer_width = "64") { return; } // see #1041
        /// use regex::RegexBuilder;
        ///
        /// // It may surprise you how big some seemingly small patterns can
        /// // be! Since \w is Unicode aware, this generates a regex that can
        /// // match approximately 140,000 distinct codepoints.
        /// assert!(RegexBuilder::new(r"\w").size_limit(45_000).build().is_err());
        /// ```
        pub fn size_limit(&mut self, bytes: usize) -> &mut RegexBuilder {
            self.builder.size_limit(bytes);
            self
        }

        /// Set the approximate capacity, in bytes, of the cache of transitions
        /// used by the lazy DFA.
        ///
        /// While the lazy DFA isn't always used, in tends to be the most
        /// commonly use regex engine in default configurations. It tends to
        /// adopt the performance profile of a fully build DFA, but without the
        /// downside of taking worst case exponential time to build.
        ///
        /// The downside is that it needs to keep a cache of transitions and
        /// states that are built while running a search, and this cache
        /// can fill up. When it fills up, the cache will reset itself. Any
        /// previously generated states and transitions will then need to be
        /// re-generated. If this happens too many times, then this library
        /// will bail out of using the lazy DFA and switch to a different regex
        /// engine.
        ///
        /// If your regex provokes this particular downside of the lazy DFA,
        /// then it may be beneficial to increase its cache capacity. This will
        /// potentially reduce the frequency of cache resetting (ideally to
        /// `0`). While it won't fix all potential performance problems with
        /// the lazy DFA, increasing the cache capacity does fix some.
        ///
        /// There is no easy way to determine, a priori, whether increasing
        /// this cache capacity will help. In general, the larger your regex,
        /// the more cache it's likely to use. But that isn't an ironclad rule.
        /// For example, a regex like `[01]*1[01]{N}` would normally produce a
        /// fully build DFA that is exponential in size with respect to `N`.
        /// The lazy DFA will prevent exponential space blow-up, but it cache
        /// is likely to fill up, even when it's large and even for smallish
        /// values of `N`.
        ///
        /// If you aren't sure whether this helps or not, it is sensible to
        /// set this to some arbitrarily large number in testing, such as
        /// `usize::MAX`. Namely, this represents the amount of capacity that
        /// *may* be used. It's probably not a good idea to use `usize::MAX` in
        /// production though, since it implies there are no controls on heap
        /// memory used by this library during a search. In effect, set it to
        /// whatever you're willing to allocate for a single regex search.
        pub fn dfa_size_limit(&mut self, bytes: usize) -> &mut RegexBuilder {
            self.builder.dfa_size_limit(bytes);
            self
        }

        /// Set the nesting limit for this parser.
        ///
        /// The nesting limit controls how deep the abstract syntax tree is
        /// allowed to be. If the AST exceeds the given limit (e.g., with too
        /// many nested groups), then an error is returned by the parser.
        ///
        /// The purpose of this limit is to act as a heuristic to prevent stack
        /// overflow for consumers that do structural induction on an AST using
        /// explicit recursion. While this crate never does this (instead using
        /// constant stack space and moving the call stack to the heap), other
        /// crates may.
        ///
        /// This limit is not checked until the entire AST is parsed.
        /// Therefore, if callers want to put a limit on the amount of heap
        /// space used, then they should impose a limit on the length, in
        /// bytes, of the concrete pattern string. In particular, this is
        /// viable since this parser implementation will limit itself to heap
        /// space proportional to the length of the pattern string. See also
        /// the [untrusted inputs](crate#untrusted-input) section in the
        /// top-level crate documentation for more information about this.
        ///
        /// Note that a nest limit of `0` will return a nest limit error for
        /// most patterns but not all. For example, a nest limit of `0` permits
        /// `a` but not `ab`, since `ab` requires an explicit concatenation,
        /// which results in a nest depth of `1`. In general, a nest limit is
        /// not something that manifests in an obvious way in the concrete
        /// syntax, therefore, it should not be used in a granular way.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexBuilder;
        ///
        /// assert!(RegexBuilder::new(r"a").nest_limit(0).build().is_ok());
        /// assert!(RegexBuilder::new(r"ab").nest_limit(0).build().is_err());
        /// ```
        pub fn nest_limit(&mut self, limit: u32) -> &mut RegexBuilder {
            self.builder.nest_limit(limit);
            self
        }
    }

    /// A configurable builder for a [`RegexSet`].
    ///
    /// This builder can be used to programmatically set flags such as
    /// `i` (case insensitive) and `x` (for verbose mode). This builder
    /// can also be used to configure things like the line terminator
    /// and a size limit on the compiled regular expression.
    #[derive(Clone, Debug)]
    pub struct RegexSetBuilder {
        builder: Builder,
    }

    impl RegexSetBuilder {
        /// Create a new builder with a default configuration for the given
        /// patterns.
        ///
        /// If the patterns are invalid or exceed the configured size limits,
        /// then an error will be returned when [`RegexSetBuilder::build`] is
        /// called.
        pub fn new<I, S>(patterns: I) -> RegexSetBuilder
        where
            I: IntoIterator<Item = S>,
            S: AsRef<str>,
        {
            RegexSetBuilder { builder: Builder::new(patterns) }
        }

        /// Compiles the patterns given to `RegexSetBuilder::new` with the
        /// configuration set on this builder.
        ///
        /// If the patterns aren't valid regexes or if a configured size limit
        /// was exceeded, then an error is returned.
        pub fn build(&self) -> Result<RegexSet, Error> {
            self.builder.build_many_string()
        }

        /// This configures Unicode mode for the all of the patterns.
        ///
        /// Enabling Unicode mode does a number of things:
        ///
        /// * Most fundamentally, it causes the fundamental atom of matching
        /// to be a single codepoint. When Unicode mode is disabled, it's a
        /// single byte. For example, when Unicode mode is enabled, `.` will
        /// match `💩` once, where as it will match 4 times when Unicode mode
        /// is disabled. (Since the UTF-8 encoding of `💩` is 4 bytes long.)
        /// * Case insensitive matching uses Unicode simple case folding rules.
        /// * Unicode character classes like `\p{Letter}` and `\p{Greek}` are
        /// available.
        /// * Perl character classes are Unicode aware. That is, `\w`, `\s` and
        /// `\d`.
        /// * The word boundary assertions, `\b` and `\B`, use the Unicode
        /// definition of a word character.
        ///
        /// Note that if Unicode mode is disabled, then the regex will fail to
        /// compile if it could match invalid UTF-8. For example, when Unicode
        /// mode is disabled, then since `.` matches any byte (except for
        /// `\n`), then it can match invalid UTF-8 and thus building a regex
        /// from it will fail. Another example is `\w` and `\W`. Since `\w` can
        /// only match ASCII bytes when Unicode mode is disabled, it's allowed.
        /// But `\W` can match more than ASCII bytes, including invalid UTF-8,
        /// and so it is not allowed. This restriction can be lifted only by
        /// using a [`bytes::RegexSet`](crate::bytes::RegexSet).
        ///
        /// For more details on the Unicode support in this crate, see the
        /// [Unicode section](crate#unicode) in this crate's top-level
        /// documentation.
        ///
        /// The default for this is `true`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"\w"])
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally greek letters would be included in \w, but since
        /// // Unicode mode is disabled, it only matches ASCII letters.
        /// assert!(!re.is_match("δ"));
        ///
        /// let re = RegexSetBuilder::new([r"s"])
        ///     .case_insensitive(true)
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally 'ſ' is included when searching for 's' case
        /// // insensitively due to Unicode's simple case folding rules. But
        /// // when Unicode mode is disabled, only ASCII case insensitive rules
        /// // are used.
        /// assert!(!re.is_match("ſ"));
        /// ```
        pub fn unicode(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.unicode(yes);
            self
        }

        /// This configures whether to enable case insensitive matching for all
        /// of the patterns.
        ///
        /// This setting can also be configured using the inline flag `i`
        /// in the pattern. For example, `(?i:foo)` matches `foo` case
        /// insensitively while `(?-i:foo)` matches `foo` case sensitively.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"foo(?-i:bar)quux"])
        ///     .case_insensitive(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("FoObarQuUx"));
        /// // Even though case insensitive matching is enabled in the builder,
        /// // it can be locally disabled within the pattern. In this case,
        /// // `bar` is matched case sensitively.
        /// assert!(!re.is_match("fooBARquux"));
        /// ```
        pub fn case_insensitive(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.case_insensitive(yes);
            self
        }

        /// This configures multi-line mode for all of the patterns.
        ///
        /// Enabling multi-line mode changes the behavior of the `^` and `$`
        /// anchor assertions. Instead of only matching at the beginning and
        /// end of a haystack, respectively, multi-line mode causes them to
        /// match at the beginning and end of a line *in addition* to the
        /// beginning and end of a haystack. More precisely, `^` will match at
        /// the position immediately following a `\n` and `$` will match at the
        /// position immediately preceding a `\n`.
        ///
        /// The behavior of this option can be impacted by other settings too:
        ///
        /// * The [`RegexSetBuilder::line_terminator`] option changes `\n`
        /// above to any ASCII byte.
        /// * The [`RegexSetBuilder::crlf`] option changes the line terminator
        /// to be either `\r` or `\n`, but never at the position between a `\r`
        /// and `\n`.
        ///
        /// This setting can also be configured using the inline flag `m` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^foo$"])
        ///     .multi_line(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("\nfoo\n"));
        /// ```
        pub fn multi_line(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.multi_line(yes);
            self
        }

        /// This configures dot-matches-new-line mode for the entire pattern.
        ///
        /// Perhaps surprisingly, the default behavior for `.` is not to match
        /// any character, but rather, to match any character except for the
        /// line terminator (which is `\n` by default). When this mode is
        /// enabled, the behavior changes such that `.` truly matches any
        /// character.
        ///
        /// This setting can also be configured using the inline flag `s` in
        /// the pattern. For example, `(?s:.)` and `\p{any}` are equivalent
        /// regexes.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"foo.bar"])
        ///     .dot_matches_new_line(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = "foo\nbar";
        /// assert!(re.is_match(hay));
        /// ```
        pub fn dot_matches_new_line(
            &mut self,
            yes: bool,
        ) -> &mut RegexSetBuilder {
            self.builder.dot_matches_new_line(yes);
            self
        }

        /// This configures CRLF mode for all of the patterns.
        ///
        /// When CRLF mode is enabled, both `\r` ("carriage return" or CR for
        /// short) and `\n` ("line feed" or LF for short) are treated as line
        /// terminators. This results in the following:
        ///
        /// * Unless dot-matches-new-line mode is enabled, `.` will now match
        /// any character except for `\n` and `\r`.
        /// * When multi-line mode is enabled, `^` will match immediately
        /// following a `\n` or a `\r`. Similarly, `$` will match immediately
        /// preceding a `\n` or a `\r`. Neither `^` nor `$` will ever match
        /// between `\r` and `\n`.
        ///
        /// This setting can also be configured using the inline flag `R` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^foo$"])
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = "\r\nfoo\r\n";
        /// // If CRLF mode weren't enabled here, then '$' wouldn't match
        /// // immediately after 'foo', and thus no match would be found.
        /// assert!(re.is_match(hay));
        /// ```
        ///
        /// This example demonstrates that `^` will never match at a position
        /// between `\r` and `\n`. (`$` will similarly not match between a `\r`
        /// and a `\n`.)
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^\n"])
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(!re.is_match("\r\n"));
        /// ```
        pub fn crlf(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.crlf(yes);
            self
        }

        /// Configures the line terminator to be used by the regex.
        ///
        /// The line terminator is relevant in two ways for a particular regex:
        ///
        /// * When dot-matches-new-line mode is *not* enabled (the default),
        /// then `.` will match any character except for the configured line
        /// terminator.
        /// * When multi-line mode is enabled (not the default), then `^` and
        /// `$` will match immediately after and before, respectively, a line
        /// terminator.
        ///
        /// In both cases, if CRLF mode is enabled in a particular context,
        /// then it takes precedence over any configured line terminator.
        ///
        /// This option cannot be configured from within the pattern.
        ///
        /// The default line terminator is `\n`.
        ///
        /// # Example
        ///
        /// This shows how to treat the NUL byte as a line terminator. This can
        /// be a useful heuristic when searching binary data.
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^foo$"])
        ///     .multi_line(true)
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// let hay = "\x00foo\x00";
        /// assert!(re.is_match(hay));
        /// ```
        ///
        /// This example shows that the behavior of `.` is impacted by this
        /// setting as well:
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"."])
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("\n"));
        /// assert!(!re.is_match("\x00"));
        /// ```
        ///
        /// This shows that building a regex will fail if the byte given
        /// is not ASCII and the pattern could result in matching invalid
        /// UTF-8. This is because any singular non-ASCII byte is not valid
        /// UTF-8, and it is not permitted for a [`RegexSet`] to match invalid
        /// UTF-8. (It is permissible to use a non-ASCII byte when building a
        /// [`bytes::RegexSet`](crate::bytes::RegexSet).)
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// assert!(
        ///     RegexSetBuilder::new([r"."])
        ///         .line_terminator(0x80)
        ///         .build()
        ///         .is_err()
        /// );
        /// // Note that using a non-ASCII byte isn't enough on its own to
        /// // cause regex compilation to fail. You actually have to make use
        /// // of it in the regex in a way that leads to matching invalid
        /// // UTF-8. If you don't, then regex compilation will succeed!
        /// assert!(
        ///     RegexSetBuilder::new([r"a"])
        ///         .line_terminator(0x80)
        ///         .build()
        ///         .is_ok()
        /// );
        /// ```
        pub fn line_terminator(&mut self, byte: u8) -> &mut RegexSetBuilder {
            self.builder.line_terminator(byte);
            self
        }

        /// This configures swap-greed mode for all of the patterns.
        ///
        /// When swap-greed mode is enabled, patterns like `a+` will become
        /// non-greedy and patterns like `a+?` will become greedy. In other
        /// words, the meanings of `a+` and `a+?` are switched.
        ///
        /// This setting can also be configured using the inline flag `U` in
        /// the pattern.
        ///
        /// Note that this is generally not useful for a `RegexSet` since a
        /// `RegexSet` can only report whether a pattern matches or not. Since
        /// greediness never impacts whether a match is found or not (only the
        /// offsets of the match), it follows that whether parts of a pattern
        /// are greedy or not doesn't matter for a `RegexSet`.
        ///
        /// The default for this is `false`.
        pub fn swap_greed(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.swap_greed(yes);
            self
        }

        /// This configures verbose mode for all of the patterns.
        ///
        /// When enabled, whitespace will treated as insignifcant in the
        /// pattern and `#` can be used to start a comment until the next new
        /// line.
        ///
        /// Normally, in most places in a pattern, whitespace is treated
        /// literally. For example ` +` will match one or more ASCII whitespace
        /// characters.
        ///
        /// When verbose mode is enabled, `\#` can be used to match a literal
        /// `#` and `\ ` can be used to match a literal ASCII whitespace
        /// character.
        ///
        /// Verbose mode is useful for permitting regexes to be formatted and
        /// broken up more nicely. This may make them more easily readable.
        ///
        /// This setting can also be configured using the inline flag `x` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// let pat = r"
        ///     \b
        ///     (?<first>\p{Uppercase}\w*)  # always start with uppercase letter
        ///     [\s--\n]+                   # whitespace should separate names
        ///     (?: # middle name can be an initial!
        ///         (?:(?<initial>\p{Uppercase})\.|(?<middle>\p{Uppercase}\w*))
        ///         [\s--\n]+
        ///     )?
        ///     (?<last>\p{Uppercase}\w*)
        ///     \b
        /// ";
        /// let re = RegexSetBuilder::new([pat])
        ///     .ignore_whitespace(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("Harry Potter"));
        /// assert!(re.is_match("Harry J. Potter"));
        /// assert!(re.is_match("Harry James Potter"));
        /// assert!(!re.is_match("harry J. Potter"));
        /// ```
        pub fn ignore_whitespace(
            &mut self,
            yes: bool,
        ) -> &mut RegexSetBuilder {
            self.builder.ignore_whitespace(yes);
            self
        }

        /// This configures octal mode for all of the patterns.
        ///
        /// Octal syntax is a little-known way of uttering Unicode codepoints
        /// in a pattern. For example, `a`, `\x61`, `\u0061` and `\141` are all
        /// equivalent patterns, where the last example shows octal syntax.
        ///
        /// While supporting octal syntax isn't in and of itself a problem,
        /// it does make good error messages harder. That is, in PCRE based
        /// regex engines, syntax like `\1` invokes a backreference, which is
        /// explicitly unsupported this library. However, many users expect
        /// backreferences to be supported. Therefore, when octal support
        /// is disabled, the error message will explicitly mention that
        /// backreferences aren't supported.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// // Normally this pattern would not compile, with an error message
        /// // about backreferences not being supported. But with octal mode
        /// // enabled, octal escape sequences work.
        /// let re = RegexSetBuilder::new([r"\141"])
        ///     .octal(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match("a"));
        /// ```
        pub fn octal(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.octal(yes);
            self
        }

        /// Sets the approximate size limit, in bytes, of the compiled regex.
        ///
        /// This roughly corresponds to the number of heap memory, in
        /// bytes, occupied by a single regex. If the regex would otherwise
        /// approximately exceed this limit, then compiling that regex will
        /// fail.
        ///
        /// The main utility of a method like this is to avoid compiling
        /// regexes that use an unexpected amount of resources, such as
        /// time and memory. Even if the memory usage of a large regex is
        /// acceptable, its search time may not be. Namely, worst case time
        /// complexity for search is `O(m * n)`, where `m ~ len(pattern)` and
        /// `n ~ len(haystack)`. That is, search time depends, in part, on the
        /// size of the compiled regex. This means that putting a limit on the
        /// size of the regex limits how much a regex can impact search time.
        ///
        /// For more information about regex size limits, see the section on
        /// [untrusted inputs](crate#untrusted-input) in the top-level crate
        /// documentation.
        ///
        /// The default for this is some reasonable number that permits most
        /// patterns to compile successfully.
        ///
        /// # Example
        ///
        /// ```
        /// # if !cfg!(target_pointer_width = "64") { return; } // see #1041
        /// use regex::RegexSetBuilder;
        ///
        /// // It may surprise you how big some seemingly small patterns can
        /// // be! Since \w is Unicode aware, this generates a regex that can
        /// // match approximately 140,000 distinct codepoints.
        /// assert!(
        ///     RegexSetBuilder::new([r"\w"])
        ///         .size_limit(45_000)
        ///         .build()
        ///         .is_err()
        /// );
        /// ```
        pub fn size_limit(&mut self, bytes: usize) -> &mut RegexSetBuilder {
            self.builder.size_limit(bytes);
            self
        }

        /// Set the approximate capacity, in bytes, of the cache of transitions
        /// used by the lazy DFA.
        ///
        /// While the lazy DFA isn't always used, in tends to be the most
        /// commonly use regex engine in default configurations. It tends to
        /// adopt the performance profile of a fully build DFA, but without the
        /// downside of taking worst case exponential time to build.
        ///
        /// The downside is that it needs to keep a cache of transitions and
        /// states that are built while running a search, and this cache
        /// can fill up. When it fills up, the cache will reset itself. Any
        /// previously generated states and transitions will then need to be
        /// re-generated. If this happens too many times, then this library
        /// will bail out of using the lazy DFA and switch to a different regex
        /// engine.
        ///
        /// If your regex provokes this particular downside of the lazy DFA,
        /// then it may be beneficial to increase its cache capacity. This will
        /// potentially reduce the frequency of cache resetting (ideally to
        /// `0`). While it won't fix all potential performance problems with
        /// the lazy DFA, increasing the cache capacity does fix some.
        ///
        /// There is no easy way to determine, a priori, whether increasing
        /// this cache capacity will help. In general, the larger your regex,
        /// the more cache it's likely to use. But that isn't an ironclad rule.
        /// For example, a regex like `[01]*1[01]{N}` would normally produce a
        /// fully build DFA that is exponential in size with respect to `N`.
        /// The lazy DFA will prevent exponential space blow-up, but it cache
        /// is likely to fill up, even when it's large and even for smallish
        /// values of `N`.
        ///
        /// If you aren't sure whether this helps or not, it is sensible to
        /// set this to some arbitrarily large number in testing, such as
        /// `usize::MAX`. Namely, this represents the amount of capacity that
        /// *may* be used. It's probably not a good idea to use `usize::MAX` in
        /// production though, since it implies there are no controls on heap
        /// memory used by this library during a search. In effect, set it to
        /// whatever you're willing to allocate for a single regex search.
        pub fn dfa_size_limit(
            &mut self,
            bytes: usize,
        ) -> &mut RegexSetBuilder {
            self.builder.dfa_size_limit(bytes);
            self
        }

        /// Set the nesting limit for this parser.
        ///
        /// The nesting limit controls how deep the abstract syntax tree is
        /// allowed to be. If the AST exceeds the given limit (e.g., with too
        /// many nested groups), then an error is returned by the parser.
        ///
        /// The purpose of this limit is to act as a heuristic to prevent stack
        /// overflow for consumers that do structural induction on an AST using
        /// explicit recursion. While this crate never does this (instead using
        /// constant stack space and moving the call stack to the heap), other
        /// crates may.
        ///
        /// This limit is not checked until the entire AST is parsed.
        /// Therefore, if callers want to put a limit on the amount of heap
        /// space used, then they should impose a limit on the length, in
        /// bytes, of the concrete pattern string. In particular, this is
        /// viable since this parser implementation will limit itself to heap
        /// space proportional to the length of the pattern string. See also
        /// the [untrusted inputs](crate#untrusted-input) section in the
        /// top-level crate documentation for more information about this.
        ///
        /// Note that a nest limit of `0` will return a nest limit error for
        /// most patterns but not all. For example, a nest limit of `0` permits
        /// `a` but not `ab`, since `ab` requires an explicit concatenation,
        /// which results in a nest depth of `1`. In general, a nest limit is
        /// not something that manifests in an obvious way in the concrete
        /// syntax, therefore, it should not be used in a granular way.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::RegexSetBuilder;
        ///
        /// assert!(RegexSetBuilder::new([r"a"]).nest_limit(0).build().is_ok());
        /// assert!(RegexSetBuilder::new([r"ab"]).nest_limit(0).build().is_err());
        /// ```
        pub fn nest_limit(&mut self, limit: u32) -> &mut RegexSetBuilder {
            self.builder.nest_limit(limit);
            self
        }
    }
}

pub(crate) mod bytes {
    use crate::{
        bytes::{Regex, RegexSet},
        error::Error,
    };

    use super::Builder;

    /// A configurable builder for a [`Regex`].
    ///
    /// This builder can be used to programmatically set flags such as `i`
    /// (case insensitive) and `x` (for verbose mode). This builder can also be
    /// used to configure things like the line terminator and a size limit on
    /// the compiled regular expression.
    #[derive(Clone, Debug)]
    pub struct RegexBuilder {
        builder: Builder,
    }

    impl RegexBuilder {
        /// Create a new builder with a default configuration for the given
        /// pattern.
        ///
        /// If the pattern is invalid or exceeds the configured size limits,
        /// then an error will be returned when [`RegexBuilder::build`] is
        /// called.
        pub fn new(pattern: &str) -> RegexBuilder {
            RegexBuilder { builder: Builder::new([pattern]) }
        }

        /// Compiles the pattern given to `RegexBuilder::new` with the
        /// configuration set on this builder.
        ///
        /// If the pattern isn't a valid regex or if a configured size limit
        /// was exceeded, then an error is returned.
        pub fn build(&self) -> Result<Regex, Error> {
            self.builder.build_one_bytes()
        }

        /// This configures Unicode mode for the entire pattern.
        ///
        /// Enabling Unicode mode does a number of things:
        ///
        /// * Most fundamentally, it causes the fundamental atom of matching
        /// to be a single codepoint. When Unicode mode is disabled, it's a
        /// single byte. For example, when Unicode mode is enabled, `.` will
        /// match `💩` once, where as it will match 4 times when Unicode mode
        /// is disabled. (Since the UTF-8 encoding of `💩` is 4 bytes long.)
        /// * Case insensitive matching uses Unicode simple case folding rules.
        /// * Unicode character classes like `\p{Letter}` and `\p{Greek}` are
        /// available.
        /// * Perl character classes are Unicode aware. That is, `\w`, `\s` and
        /// `\d`.
        /// * The word boundary assertions, `\b` and `\B`, use the Unicode
        /// definition of a word character.
        ///
        /// Note that unlike the top-level `Regex` for searching `&str`, it
        /// is permitted to disable Unicode mode even if the resulting pattern
        /// could match invalid UTF-8. For example, `(?-u:.)` is not a valid
        /// pattern for a top-level `Regex`, but is valid for a `bytes::Regex`.
        ///
        /// For more details on the Unicode support in this crate, see the
        /// [Unicode section](crate#unicode) in this crate's top-level
        /// documentation.
        ///
        /// The default for this is `true`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"\w")
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally greek letters would be included in \w, but since
        /// // Unicode mode is disabled, it only matches ASCII letters.
        /// assert!(!re.is_match("δ".as_bytes()));
        ///
        /// let re = RegexBuilder::new(r"s")
        ///     .case_insensitive(true)
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally 'ſ' is included when searching for 's' case
        /// // insensitively due to Unicode's simple case folding rules. But
        /// // when Unicode mode is disabled, only ASCII case insensitive rules
        /// // are used.
        /// assert!(!re.is_match("ſ".as_bytes()));
        /// ```
        ///
        /// Since this builder is for constructing a [`bytes::Regex`](Regex),
        /// one can disable Unicode mode even if it would match invalid UTF-8:
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r".")
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally greek letters would be included in \w, but since
        /// // Unicode mode is disabled, it only matches ASCII letters.
        /// assert!(re.is_match(b"\xFF"));
        /// ```
        pub fn unicode(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.unicode(yes);
            self
        }

        /// This configures whether to enable case insensitive matching for the
        /// entire pattern.
        ///
        /// This setting can also be configured using the inline flag `i`
        /// in the pattern. For example, `(?i:foo)` matches `foo` case
        /// insensitively while `(?-i:foo)` matches `foo` case sensitively.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"foo(?-i:bar)quux")
        ///     .case_insensitive(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"FoObarQuUx"));
        /// // Even though case insensitive matching is enabled in the builder,
        /// // it can be locally disabled within the pattern. In this case,
        /// // `bar` is matched case sensitively.
        /// assert!(!re.is_match(b"fooBARquux"));
        /// ```
        pub fn case_insensitive(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.case_insensitive(yes);
            self
        }

        /// This configures multi-line mode for the entire pattern.
        ///
        /// Enabling multi-line mode changes the behavior of the `^` and `$`
        /// anchor assertions. Instead of only matching at the beginning and
        /// end of a haystack, respectively, multi-line mode causes them to
        /// match at the beginning and end of a line *in addition* to the
        /// beginning and end of a haystack. More precisely, `^` will match at
        /// the position immediately following a `\n` and `$` will match at the
        /// position immediately preceding a `\n`.
        ///
        /// The behavior of this option can be impacted by other settings too:
        ///
        /// * The [`RegexBuilder::line_terminator`] option changes `\n` above
        /// to any ASCII byte.
        /// * The [`RegexBuilder::crlf`] option changes the line terminator to
        /// be either `\r` or `\n`, but never at the position between a `\r`
        /// and `\n`.
        ///
        /// This setting can also be configured using the inline flag `m` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^foo$")
        ///     .multi_line(true)
        ///     .build()
        ///     .unwrap();
        /// assert_eq!(Some(1..4), re.find(b"\nfoo\n").map(|m| m.range()));
        /// ```
        pub fn multi_line(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.multi_line(yes);
            self
        }

        /// This configures dot-matches-new-line mode for the entire pattern.
        ///
        /// Perhaps surprisingly, the default behavior for `.` is not to match
        /// any character, but rather, to match any character except for the
        /// line terminator (which is `\n` by default). When this mode is
        /// enabled, the behavior changes such that `.` truly matches any
        /// character.
        ///
        /// This setting can also be configured using the inline flag `s` in
        /// the pattern. For example, `(?s:.)` and `\p{any}` are equivalent
        /// regexes.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"foo.bar")
        ///     .dot_matches_new_line(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = b"foo\nbar";
        /// assert_eq!(Some(&b"foo\nbar"[..]), re.find(hay).map(|m| m.as_bytes()));
        /// ```
        pub fn dot_matches_new_line(
            &mut self,
            yes: bool,
        ) -> &mut RegexBuilder {
            self.builder.dot_matches_new_line(yes);
            self
        }

        /// This configures CRLF mode for the entire pattern.
        ///
        /// When CRLF mode is enabled, both `\r` ("carriage return" or CR for
        /// short) and `\n` ("line feed" or LF for short) are treated as line
        /// terminators. This results in the following:
        ///
        /// * Unless dot-matches-new-line mode is enabled, `.` will now match
        /// any character except for `\n` and `\r`.
        /// * When multi-line mode is enabled, `^` will match immediately
        /// following a `\n` or a `\r`. Similarly, `$` will match immediately
        /// preceding a `\n` or a `\r`. Neither `^` nor `$` will ever match
        /// between `\r` and `\n`.
        ///
        /// This setting can also be configured using the inline flag `R` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^foo$")
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = b"\r\nfoo\r\n";
        /// // If CRLF mode weren't enabled here, then '$' wouldn't match
        /// // immediately after 'foo', and thus no match would be found.
        /// assert_eq!(Some(&b"foo"[..]), re.find(hay).map(|m| m.as_bytes()));
        /// ```
        ///
        /// This example demonstrates that `^` will never match at a position
        /// between `\r` and `\n`. (`$` will similarly not match between a `\r`
        /// and a `\n`.)
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^")
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = b"\r\n\r\n";
        /// let ranges: Vec<_> = re.find_iter(hay).map(|m| m.range()).collect();
        /// assert_eq!(ranges, vec![0..0, 2..2, 4..4]);
        /// ```
        pub fn crlf(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.crlf(yes);
            self
        }

        /// Configures the line terminator to be used by the regex.
        ///
        /// The line terminator is relevant in two ways for a particular regex:
        ///
        /// * When dot-matches-new-line mode is *not* enabled (the default),
        /// then `.` will match any character except for the configured line
        /// terminator.
        /// * When multi-line mode is enabled (not the default), then `^` and
        /// `$` will match immediately after and before, respectively, a line
        /// terminator.
        ///
        /// In both cases, if CRLF mode is enabled in a particular context,
        /// then it takes precedence over any configured line terminator.
        ///
        /// This option cannot be configured from within the pattern.
        ///
        /// The default line terminator is `\n`.
        ///
        /// # Example
        ///
        /// This shows how to treat the NUL byte as a line terminator. This can
        /// be a useful heuristic when searching binary data.
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"^foo$")
        ///     .multi_line(true)
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// let hay = b"\x00foo\x00";
        /// assert_eq!(Some(1..4), re.find(hay).map(|m| m.range()));
        /// ```
        ///
        /// This example shows that the behavior of `.` is impacted by this
        /// setting as well:
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r".")
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"\n"));
        /// assert!(!re.is_match(b"\x00"));
        /// ```
        ///
        /// This shows that building a regex will work even when the byte
        /// given is not ASCII. This is unlike the top-level `Regex` API where
        /// matching invalid UTF-8 is not allowed.
        ///
        /// Note though that you must disable Unicode mode. This is required
        /// because Unicode mode requires matching one codepoint at a time,
        /// and there is no way to match a non-ASCII byte as if it were a
        /// codepoint.
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// assert!(
        ///     RegexBuilder::new(r".")
        ///         .unicode(false)
        ///         .line_terminator(0x80)
        ///         .build()
        ///         .is_ok(),
        /// );
        /// ```
        pub fn line_terminator(&mut self, byte: u8) -> &mut RegexBuilder {
            self.builder.line_terminator(byte);
            self
        }

        /// This configures swap-greed mode for the entire pattern.
        ///
        /// When swap-greed mode is enabled, patterns like `a+` will become
        /// non-greedy and patterns like `a+?` will become greedy. In other
        /// words, the meanings of `a+` and `a+?` are switched.
        ///
        /// This setting can also be configured using the inline flag `U` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let re = RegexBuilder::new(r"a+")
        ///     .swap_greed(true)
        ///     .build()
        ///     .unwrap();
        /// assert_eq!(Some(&b"a"[..]), re.find(b"aaa").map(|m| m.as_bytes()));
        /// ```
        pub fn swap_greed(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.swap_greed(yes);
            self
        }

        /// This configures verbose mode for the entire pattern.
        ///
        /// When enabled, whitespace will treated as insignifcant in the
        /// pattern and `#` can be used to start a comment until the next new
        /// line.
        ///
        /// Normally, in most places in a pattern, whitespace is treated
        /// literally. For example ` +` will match one or more ASCII whitespace
        /// characters.
        ///
        /// When verbose mode is enabled, `\#` can be used to match a literal
        /// `#` and `\ ` can be used to match a literal ASCII whitespace
        /// character.
        ///
        /// Verbose mode is useful for permitting regexes to be formatted and
        /// broken up more nicely. This may make them more easily readable.
        ///
        /// This setting can also be configured using the inline flag `x` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// let pat = r"
        ///     \b
        ///     (?<first>\p{Uppercase}\w*)  # always start with uppercase letter
        ///     [\s--\n]+                   # whitespace should separate names
        ///     (?: # middle name can be an initial!
        ///         (?:(?<initial>\p{Uppercase})\.|(?<middle>\p{Uppercase}\w*))
        ///         [\s--\n]+
        ///     )?
        ///     (?<last>\p{Uppercase}\w*)
        ///     \b
        /// ";
        /// let re = RegexBuilder::new(pat)
        ///     .ignore_whitespace(true)
        ///     .build()
        ///     .unwrap();
        ///
        /// let caps = re.captures(b"Harry Potter").unwrap();
        /// assert_eq!(&b"Harry"[..], &caps["first"]);
        /// assert_eq!(&b"Potter"[..], &caps["last"]);
        ///
        /// let caps = re.captures(b"Harry J. Potter").unwrap();
        /// assert_eq!(&b"Harry"[..], &caps["first"]);
        /// // Since a middle name/initial isn't required for an overall match,
        /// // we can't assume that 'initial' or 'middle' will be populated!
        /// assert_eq!(
        ///     Some(&b"J"[..]),
        ///     caps.name("initial").map(|m| m.as_bytes()),
        /// );
        /// assert_eq!(None, caps.name("middle").map(|m| m.as_bytes()));
        /// assert_eq!(&b"Potter"[..], &caps["last"]);
        ///
        /// let caps = re.captures(b"Harry James Potter").unwrap();
        /// assert_eq!(&b"Harry"[..], &caps["first"]);
        /// // Since a middle name/initial isn't required for an overall match,
        /// // we can't assume that 'initial' or 'middle' will be populated!
        /// assert_eq!(None, caps.name("initial").map(|m| m.as_bytes()));
        /// assert_eq!(
        ///     Some(&b"James"[..]),
        ///     caps.name("middle").map(|m| m.as_bytes()),
        /// );
        /// assert_eq!(&b"Potter"[..], &caps["last"]);
        /// ```
        pub fn ignore_whitespace(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.ignore_whitespace(yes);
            self
        }

        /// This configures octal mode for the entire pattern.
        ///
        /// Octal syntax is a little-known way of uttering Unicode codepoints
        /// in a pattern. For example, `a`, `\x61`, `\u0061` and `\141` are all
        /// equivalent patterns, where the last example shows octal syntax.
        ///
        /// While supporting octal syntax isn't in and of itself a problem,
        /// it does make good error messages harder. That is, in PCRE based
        /// regex engines, syntax like `\1` invokes a backreference, which is
        /// explicitly unsupported this library. However, many users expect
        /// backreferences to be supported. Therefore, when octal support
        /// is disabled, the error message will explicitly mention that
        /// backreferences aren't supported.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// // Normally this pattern would not compile, with an error message
        /// // about backreferences not being supported. But with octal mode
        /// // enabled, octal escape sequences work.
        /// let re = RegexBuilder::new(r"\141")
        ///     .octal(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"a"));
        /// ```
        pub fn octal(&mut self, yes: bool) -> &mut RegexBuilder {
            self.builder.octal(yes);
            self
        }

        /// Sets the approximate size limit, in bytes, of the compiled regex.
        ///
        /// This roughly corresponds to the number of heap memory, in
        /// bytes, occupied by a single regex. If the regex would otherwise
        /// approximately exceed this limit, then compiling that regex will
        /// fail.
        ///
        /// The main utility of a method like this is to avoid compiling
        /// regexes that use an unexpected amount of resources, such as
        /// time and memory. Even if the memory usage of a large regex is
        /// acceptable, its search time may not be. Namely, worst case time
        /// complexity for search is `O(m * n)`, where `m ~ len(pattern)` and
        /// `n ~ len(haystack)`. That is, search time depends, in part, on the
        /// size of the compiled regex. This means that putting a limit on the
        /// size of the regex limits how much a regex can impact search time.
        ///
        /// For more information about regex size limits, see the section on
        /// [untrusted inputs](crate#untrusted-input) in the top-level crate
        /// documentation.
        ///
        /// The default for this is some reasonable number that permits most
        /// patterns to compile successfully.
        ///
        /// # Example
        ///
        /// ```
        /// # if !cfg!(target_pointer_width = "64") { return; } // see #1041
        /// use regex::bytes::RegexBuilder;
        ///
        /// // It may surprise you how big some seemingly small patterns can
        /// // be! Since \w is Unicode aware, this generates a regex that can
        /// // match approximately 140,000 distinct codepoints.
        /// assert!(RegexBuilder::new(r"\w").size_limit(45_000).build().is_err());
        /// ```
        pub fn size_limit(&mut self, bytes: usize) -> &mut RegexBuilder {
            self.builder.size_limit(bytes);
            self
        }

        /// Set the approximate capacity, in bytes, of the cache of transitions
        /// used by the lazy DFA.
        ///
        /// While the lazy DFA isn't always used, in tends to be the most
        /// commonly use regex engine in default configurations. It tends to
        /// adopt the performance profile of a fully build DFA, but without the
        /// downside of taking worst case exponential time to build.
        ///
        /// The downside is that it needs to keep a cache of transitions and
        /// states that are built while running a search, and this cache
        /// can fill up. When it fills up, the cache will reset itself. Any
        /// previously generated states and transitions will then need to be
        /// re-generated. If this happens too many times, then this library
        /// will bail out of using the lazy DFA and switch to a different regex
        /// engine.
        ///
        /// If your regex provokes this particular downside of the lazy DFA,
        /// then it may be beneficial to increase its cache capacity. This will
        /// potentially reduce the frequency of cache resetting (ideally to
        /// `0`). While it won't fix all potential performance problems with
        /// the lazy DFA, increasing the cache capacity does fix some.
        ///
        /// There is no easy way to determine, a priori, whether increasing
        /// this cache capacity will help. In general, the larger your regex,
        /// the more cache it's likely to use. But that isn't an ironclad rule.
        /// For example, a regex like `[01]*1[01]{N}` would normally produce a
        /// fully build DFA that is exponential in size with respect to `N`.
        /// The lazy DFA will prevent exponential space blow-up, but it cache
        /// is likely to fill up, even when it's large and even for smallish
        /// values of `N`.
        ///
        /// If you aren't sure whether this helps or not, it is sensible to
        /// set this to some arbitrarily large number in testing, such as
        /// `usize::MAX`. Namely, this represents the amount of capacity that
        /// *may* be used. It's probably not a good idea to use `usize::MAX` in
        /// production though, since it implies there are no controls on heap
        /// memory used by this library during a search. In effect, set it to
        /// whatever you're willing to allocate for a single regex search.
        pub fn dfa_size_limit(&mut self, bytes: usize) -> &mut RegexBuilder {
            self.builder.dfa_size_limit(bytes);
            self
        }

        /// Set the nesting limit for this parser.
        ///
        /// The nesting limit controls how deep the abstract syntax tree is
        /// allowed to be. If the AST exceeds the given limit (e.g., with too
        /// many nested groups), then an error is returned by the parser.
        ///
        /// The purpose of this limit is to act as a heuristic to prevent stack
        /// overflow for consumers that do structural induction on an AST using
        /// explicit recursion. While this crate never does this (instead using
        /// constant stack space and moving the call stack to the heap), other
        /// crates may.
        ///
        /// This limit is not checked until the entire AST is parsed.
        /// Therefore, if callers want to put a limit on the amount of heap
        /// space used, then they should impose a limit on the length, in
        /// bytes, of the concrete pattern string. In particular, this is
        /// viable since this parser implementation will limit itself to heap
        /// space proportional to the length of the pattern string. See also
        /// the [untrusted inputs](crate#untrusted-input) section in the
        /// top-level crate documentation for more information about this.
        ///
        /// Note that a nest limit of `0` will return a nest limit error for
        /// most patterns but not all. For example, a nest limit of `0` permits
        /// `a` but not `ab`, since `ab` requires an explicit concatenation,
        /// which results in a nest depth of `1`. In general, a nest limit is
        /// not something that manifests in an obvious way in the concrete
        /// syntax, therefore, it should not be used in a granular way.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexBuilder;
        ///
        /// assert!(RegexBuilder::new(r"a").nest_limit(0).build().is_ok());
        /// assert!(RegexBuilder::new(r"ab").nest_limit(0).build().is_err());
        /// ```
        pub fn nest_limit(&mut self, limit: u32) -> &mut RegexBuilder {
            self.builder.nest_limit(limit);
            self
        }
    }

    /// A configurable builder for a [`RegexSet`].
    ///
    /// This builder can be used to programmatically set flags such as `i`
    /// (case insensitive) and `x` (for verbose mode). This builder can also be
    /// used to configure things like the line terminator and a size limit on
    /// the compiled regular expression.
    #[derive(Clone, Debug)]
    pub struct RegexSetBuilder {
        builder: Builder,
    }

    impl RegexSetBuilder {
        /// Create a new builder with a default configuration for the given
        /// patterns.
        ///
        /// If the patterns are invalid or exceed the configured size limits,
        /// then an error will be returned when [`RegexSetBuilder::build`] is
        /// called.
        pub fn new<I, S>(patterns: I) -> RegexSetBuilder
        where
            I: IntoIterator<Item = S>,
            S: AsRef<str>,
        {
            RegexSetBuilder { builder: Builder::new(patterns) }
        }

        /// Compiles the patterns given to `RegexSetBuilder::new` with the
        /// configuration set on this builder.
        ///
        /// If the patterns aren't valid regexes or if a configured size limit
        /// was exceeded, then an error is returned.
        pub fn build(&self) -> Result<RegexSet, Error> {
            self.builder.build_many_bytes()
        }

        /// This configures Unicode mode for the all of the patterns.
        ///
        /// Enabling Unicode mode does a number of things:
        ///
        /// * Most fundamentally, it causes the fundamental atom of matching
        /// to be a single codepoint. When Unicode mode is disabled, it's a
        /// single byte. For example, when Unicode mode is enabled, `.` will
        /// match `💩` once, where as it will match 4 times when Unicode mode
        /// is disabled. (Since the UTF-8 encoding of `💩` is 4 bytes long.)
        /// * Case insensitive matching uses Unicode simple case folding rules.
        /// * Unicode character classes like `\p{Letter}` and `\p{Greek}` are
        /// available.
        /// * Perl character classes are Unicode aware. That is, `\w`, `\s` and
        /// `\d`.
        /// * The word boundary assertions, `\b` and `\B`, use the Unicode
        /// definition of a word character.
        ///
        /// Note that unlike the top-level `RegexSet` for searching `&str`,
        /// it is permitted to disable Unicode mode even if the resulting
        /// pattern could match invalid UTF-8. For example, `(?-u:.)` is not
        /// a valid pattern for a top-level `RegexSet`, but is valid for a
        /// `bytes::RegexSet`.
        ///
        /// For more details on the Unicode support in this crate, see the
        /// [Unicode section](crate#unicode) in this crate's top-level
        /// documentation.
        ///
        /// The default for this is `true`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"\w"])
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally greek letters would be included in \w, but since
        /// // Unicode mode is disabled, it only matches ASCII letters.
        /// assert!(!re.is_match("δ".as_bytes()));
        ///
        /// let re = RegexSetBuilder::new([r"s"])
        ///     .case_insensitive(true)
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally 'ſ' is included when searching for 's' case
        /// // insensitively due to Unicode's simple case folding rules. But
        /// // when Unicode mode is disabled, only ASCII case insensitive rules
        /// // are used.
        /// assert!(!re.is_match("ſ".as_bytes()));
        /// ```
        ///
        /// Since this builder is for constructing a
        /// [`bytes::RegexSet`](RegexSet), one can disable Unicode mode even if
        /// it would match invalid UTF-8:
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"."])
        ///     .unicode(false)
        ///     .build()
        ///     .unwrap();
        /// // Normally greek letters would be included in \w, but since
        /// // Unicode mode is disabled, it only matches ASCII letters.
        /// assert!(re.is_match(b"\xFF"));
        /// ```
        pub fn unicode(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.unicode(yes);
            self
        }

        /// This configures whether to enable case insensitive matching for all
        /// of the patterns.
        ///
        /// This setting can also be configured using the inline flag `i`
        /// in the pattern. For example, `(?i:foo)` matches `foo` case
        /// insensitively while `(?-i:foo)` matches `foo` case sensitively.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"foo(?-i:bar)quux"])
        ///     .case_insensitive(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"FoObarQuUx"));
        /// // Even though case insensitive matching is enabled in the builder,
        /// // it can be locally disabled within the pattern. In this case,
        /// // `bar` is matched case sensitively.
        /// assert!(!re.is_match(b"fooBARquux"));
        /// ```
        pub fn case_insensitive(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.case_insensitive(yes);
            self
        }

        /// This configures multi-line mode for all of the patterns.
        ///
        /// Enabling multi-line mode changes the behavior of the `^` and `$`
        /// anchor assertions. Instead of only matching at the beginning and
        /// end of a haystack, respectively, multi-line mode causes them to
        /// match at the beginning and end of a line *in addition* to the
        /// beginning and end of a haystack. More precisely, `^` will match at
        /// the position immediately following a `\n` and `$` will match at the
        /// position immediately preceding a `\n`.
        ///
        /// The behavior of this option can be impacted by other settings too:
        ///
        /// * The [`RegexSetBuilder::line_terminator`] option changes `\n`
        /// above to any ASCII byte.
        /// * The [`RegexSetBuilder::crlf`] option changes the line terminator
        /// to be either `\r` or `\n`, but never at the position between a `\r`
        /// and `\n`.
        ///
        /// This setting can also be configured using the inline flag `m` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^foo$"])
        ///     .multi_line(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"\nfoo\n"));
        /// ```
        pub fn multi_line(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.multi_line(yes);
            self
        }

        /// This configures dot-matches-new-line mode for the entire pattern.
        ///
        /// Perhaps surprisingly, the default behavior for `.` is not to match
        /// any character, but rather, to match any character except for the
        /// line terminator (which is `\n` by default). When this mode is
        /// enabled, the behavior changes such that `.` truly matches any
        /// character.
        ///
        /// This setting can also be configured using the inline flag `s` in
        /// the pattern. For example, `(?s:.)` and `\p{any}` are equivalent
        /// regexes.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"foo.bar"])
        ///     .dot_matches_new_line(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = b"foo\nbar";
        /// assert!(re.is_match(hay));
        /// ```
        pub fn dot_matches_new_line(
            &mut self,
            yes: bool,
        ) -> &mut RegexSetBuilder {
            self.builder.dot_matches_new_line(yes);
            self
        }

        /// This configures CRLF mode for all of the patterns.
        ///
        /// When CRLF mode is enabled, both `\r` ("carriage return" or CR for
        /// short) and `\n` ("line feed" or LF for short) are treated as line
        /// terminators. This results in the following:
        ///
        /// * Unless dot-matches-new-line mode is enabled, `.` will now match
        /// any character except for `\n` and `\r`.
        /// * When multi-line mode is enabled, `^` will match immediately
        /// following a `\n` or a `\r`. Similarly, `$` will match immediately
        /// preceding a `\n` or a `\r`. Neither `^` nor `$` will ever match
        /// between `\r` and `\n`.
        ///
        /// This setting can also be configured using the inline flag `R` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^foo$"])
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// let hay = b"\r\nfoo\r\n";
        /// // If CRLF mode weren't enabled here, then '$' wouldn't match
        /// // immediately after 'foo', and thus no match would be found.
        /// assert!(re.is_match(hay));
        /// ```
        ///
        /// This example demonstrates that `^` will never match at a position
        /// between `\r` and `\n`. (`$` will similarly not match between a `\r`
        /// and a `\n`.)
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^\n"])
        ///     .multi_line(true)
        ///     .crlf(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(!re.is_match(b"\r\n"));
        /// ```
        pub fn crlf(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.crlf(yes);
            self
        }

        /// Configures the line terminator to be used by the regex.
        ///
        /// The line terminator is relevant in two ways for a particular regex:
        ///
        /// * When dot-matches-new-line mode is *not* enabled (the default),
        /// then `.` will match any character except for the configured line
        /// terminator.
        /// * When multi-line mode is enabled (not the default), then `^` and
        /// `$` will match immediately after and before, respectively, a line
        /// terminator.
        ///
        /// In both cases, if CRLF mode is enabled in a particular context,
        /// then it takes precedence over any configured line terminator.
        ///
        /// This option cannot be configured from within the pattern.
        ///
        /// The default line terminator is `\n`.
        ///
        /// # Example
        ///
        /// This shows how to treat the NUL byte as a line terminator. This can
        /// be a useful heuristic when searching binary data.
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"^foo$"])
        ///     .multi_line(true)
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// let hay = b"\x00foo\x00";
        /// assert!(re.is_match(hay));
        /// ```
        ///
        /// This example shows that the behavior of `.` is impacted by this
        /// setting as well:
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let re = RegexSetBuilder::new([r"."])
        ///     .line_terminator(b'\x00')
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"\n"));
        /// assert!(!re.is_match(b"\x00"));
        /// ```
        ///
        /// This shows that building a regex will work even when the byte given
        /// is not ASCII. This is unlike the top-level `RegexSet` API where
        /// matching invalid UTF-8 is not allowed.
        ///
        /// Note though that you must disable Unicode mode. This is required
        /// because Unicode mode requires matching one codepoint at a time,
        /// and there is no way to match a non-ASCII byte as if it were a
        /// codepoint.
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// assert!(
        ///     RegexSetBuilder::new([r"."])
        ///         .unicode(false)
        ///         .line_terminator(0x80)
        ///         .build()
        ///         .is_ok(),
        /// );
        /// ```
        pub fn line_terminator(&mut self, byte: u8) -> &mut RegexSetBuilder {
            self.builder.line_terminator(byte);
            self
        }

        /// This configures swap-greed mode for all of the patterns.
        ///
        /// When swap-greed mode is enabled, patterns like `a+` will become
        /// non-greedy and patterns like `a+?` will become greedy. In other
        /// words, the meanings of `a+` and `a+?` are switched.
        ///
        /// This setting can also be configured using the inline flag `U` in
        /// the pattern.
        ///
        /// Note that this is generally not useful for a `RegexSet` since a
        /// `RegexSet` can only report whether a pattern matches or not. Since
        /// greediness never impacts whether a match is found or not (only the
        /// offsets of the match), it follows that whether parts of a pattern
        /// are greedy or not doesn't matter for a `RegexSet`.
        ///
        /// The default for this is `false`.
        pub fn swap_greed(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.swap_greed(yes);
            self
        }

        /// This configures verbose mode for all of the patterns.
        ///
        /// When enabled, whitespace will treated as insignifcant in the
        /// pattern and `#` can be used to start a comment until the next new
        /// line.
        ///
        /// Normally, in most places in a pattern, whitespace is treated
        /// literally. For example ` +` will match one or more ASCII whitespace
        /// characters.
        ///
        /// When verbose mode is enabled, `\#` can be used to match a literal
        /// `#` and `\ ` can be used to match a literal ASCII whitespace
        /// character.
        ///
        /// Verbose mode is useful for permitting regexes to be formatted and
        /// broken up more nicely. This may make them more easily readable.
        ///
        /// This setting can also be configured using the inline flag `x` in
        /// the pattern.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// let pat = r"
        ///     \b
        ///     (?<first>\p{Uppercase}\w*)  # always start with uppercase letter
        ///     [\s--\n]+                   # whitespace should separate names
        ///     (?: # middle name can be an initial!
        ///         (?:(?<initial>\p{Uppercase})\.|(?<middle>\p{Uppercase}\w*))
        ///         [\s--\n]+
        ///     )?
        ///     (?<last>\p{Uppercase}\w*)
        ///     \b
        /// ";
        /// let re = RegexSetBuilder::new([pat])
        ///     .ignore_whitespace(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"Harry Potter"));
        /// assert!(re.is_match(b"Harry J. Potter"));
        /// assert!(re.is_match(b"Harry James Potter"));
        /// assert!(!re.is_match(b"harry J. Potter"));
        /// ```
        pub fn ignore_whitespace(
            &mut self,
            yes: bool,
        ) -> &mut RegexSetBuilder {
            self.builder.ignore_whitespace(yes);
            self
        }

        /// This configures octal mode for all of the patterns.
        ///
        /// Octal syntax is a little-known way of uttering Unicode codepoints
        /// in a pattern. For example, `a`, `\x61`, `\u0061` and `\141` are all
        /// equivalent patterns, where the last example shows octal syntax.
        ///
        /// While supporting octal syntax isn't in and of itself a problem,
        /// it does make good error messages harder. That is, in PCRE based
        /// regex engines, syntax like `\1` invokes a backreference, which is
        /// explicitly unsupported this library. However, many users expect
        /// backreferences to be supported. Therefore, when octal support
        /// is disabled, the error message will explicitly mention that
        /// backreferences aren't supported.
        ///
        /// The default for this is `false`.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// // Normally this pattern would not compile, with an error message
        /// // about backreferences not being supported. But with octal mode
        /// // enabled, octal escape sequences work.
        /// let re = RegexSetBuilder::new([r"\141"])
        ///     .octal(true)
        ///     .build()
        ///     .unwrap();
        /// assert!(re.is_match(b"a"));
        /// ```
        pub fn octal(&mut self, yes: bool) -> &mut RegexSetBuilder {
            self.builder.octal(yes);
            self
        }

        /// Sets the approximate size limit, in bytes, of the compiled regex.
        ///
        /// This roughly corresponds to the number of heap memory, in
        /// bytes, occupied by a single regex. If the regex would otherwise
        /// approximately exceed this limit, then compiling that regex will
        /// fail.
        ///
        /// The main utility of a method like this is to avoid compiling
        /// regexes that use an unexpected amount of resources, such as
        /// time and memory. Even if the memory usage of a large regex is
        /// acceptable, its search time may not be. Namely, worst case time
        /// complexity for search is `O(m * n)`, where `m ~ len(pattern)` and
        /// `n ~ len(haystack)`. That is, search time depends, in part, on the
        /// size of the compiled regex. This means that putting a limit on the
        /// size of the regex limits how much a regex can impact search time.
        ///
        /// For more information about regex size limits, see the section on
        /// [untrusted inputs](crate#untrusted-input) in the top-level crate
        /// documentation.
        ///
        /// The default for this is some reasonable number that permits most
        /// patterns to compile successfully.
        ///
        /// # Example
        ///
        /// ```
        /// # if !cfg!(target_pointer_width = "64") { return; } // see #1041
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// // It may surprise you how big some seemingly small patterns can
        /// // be! Since \w is Unicode aware, this generates a regex that can
        /// // match approximately 140,000 distinct codepoints.
        /// assert!(
        ///     RegexSetBuilder::new([r"\w"])
        ///         .size_limit(45_000)
        ///         .build()
        ///         .is_err()
        /// );
        /// ```
        pub fn size_limit(&mut self, bytes: usize) -> &mut RegexSetBuilder {
            self.builder.size_limit(bytes);
            self
        }

        /// Set the approximate capacity, in bytes, of the cache of transitions
        /// used by the lazy DFA.
        ///
        /// While the lazy DFA isn't always used, in tends to be the most
        /// commonly use regex engine in default configurations. It tends to
        /// adopt the performance profile of a fully build DFA, but without the
        /// downside of taking worst case exponential time to build.
        ///
        /// The downside is that it needs to keep a cache of transitions and
        /// states that are built while running a search, and this cache
        /// can fill up. When it fills up, the cache will reset itself. Any
        /// previously generated states and transitions will then need to be
        /// re-generated. If this happens too many times, then this library
        /// will bail out of using the lazy DFA and switch to a different regex
        /// engine.
        ///
        /// If your regex provokes this particular downside of the lazy DFA,
        /// then it may be beneficial to increase its cache capacity. This will
        /// potentially reduce the frequency of cache resetting (ideally to
        /// `0`). While it won't fix all potential performance problems with
        /// the lazy DFA, increasing the cache capacity does fix some.
        ///
        /// There is no easy way to determine, a priori, whether increasing
        /// this cache capacity will help. In general, the larger your regex,
        /// the more cache it's likely to use. But that isn't an ironclad rule.
        /// For example, a regex like `[01]*1[01]{N}` would normally produce a
        /// fully build DFA that is exponential in size with respect to `N`.
        /// The lazy DFA will prevent exponential space blow-up, but it cache
        /// is likely to fill up, even when it's large and even for smallish
        /// values of `N`.
        ///
        /// If you aren't sure whether this helps or not, it is sensible to
        /// set this to some arbitrarily large number in testing, such as
        /// `usize::MAX`. Namely, this represents the amount of capacity that
        /// *may* be used. It's probably not a good idea to use `usize::MAX` in
        /// production though, since it implies there are no controls on heap
        /// memory used by this library during a search. In effect, set it to
        /// whatever you're willing to allocate for a single regex search.
        pub fn dfa_size_limit(
            &mut self,
            bytes: usize,
        ) -> &mut RegexSetBuilder {
            self.builder.dfa_size_limit(bytes);
            self
        }

        /// Set the nesting limit for this parser.
        ///
        /// The nesting limit controls how deep the abstract syntax tree is
        /// allowed to be. If the AST exceeds the given limit (e.g., with too
        /// many nested groups), then an error is returned by the parser.
        ///
        /// The purpose of this limit is to act as a heuristic to prevent stack
        /// overflow for consumers that do structural induction on an AST using
        /// explicit recursion. While this crate never does this (instead using
        /// constant stack space and moving the call stack to the heap), other
        /// crates may.
        ///
        /// This limit is not checked until the entire AST is parsed.
        /// Therefore, if callers want to put a limit on the amount of heap
        /// space used, then they should impose a limit on the length, in
        /// bytes, of the concrete pattern string. In particular, this is
        /// viable since this parser implementation will limit itself to heap
        /// space proportional to the length of the pattern string. See also
        /// the [untrusted inputs](crate#untrusted-input) section in the
        /// top-level crate documentation for more information about this.
        ///
        /// Note that a nest limit of `0` will return a nest limit error for
        /// most patterns but not all. For example, a nest limit of `0` permits
        /// `a` but not `ab`, since `ab` requires an explicit concatenation,
        /// which results in a nest depth of `1`. In general, a nest limit is
        /// not something that manifests in an obvious way in the concrete
        /// syntax, therefore, it should not be used in a granular way.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::RegexSetBuilder;
        ///
        /// assert!(RegexSetBuilder::new([r"a"]).nest_limit(0).build().is_ok());
        /// assert!(RegexSetBuilder::new([r"ab"]).nest_limit(0).build().is_err());
        /// ```
        pub fn nest_limit(&mut self, limit: u32) -> &mut RegexSetBuilder {
            self.builder.nest_limit(limit);
            self
        }
    }
}