Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 895 insertions, 0 deletions

diff --git a/third_party/rust/regex-automata/src/hybrid/regex.rs b/third_party/rust/regex-automata/src/hybrid/regex.rs
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+/*!
+A lazy DFA backed `Regex`.
+
+This module provides a [`Regex`] backed by a lazy DFA. A `Regex` implements
+convenience routines you might have come to expect, such as finding a match
+and iterating over all non-overlapping matches. This `Regex` type is limited
+in its capabilities to what a lazy DFA can provide. Therefore, APIs involving
+capturing groups, for example, are not provided.
+
+Internally, a `Regex` is composed of two DFAs. One is a "forward" DFA that
+finds the end offset of a match, where as the other is a "reverse" DFA that
+find the start offset of a match.
+
+See the [parent module](crate::hybrid) for examples.
+*/
+
+use crate::{
+    hybrid::{
+        dfa::{self, DFA},
+        error::BuildError,
+    },
+    nfa::thompson,
+    util::{
+        iter,
+        search::{Anchored, Input, Match, MatchError, MatchKind},
+    },
+};
+
+/// A regular expression that uses hybrid NFA/DFAs (also called "lazy DFAs")
+/// for searching.
+///
+/// A regular expression is comprised of two lazy DFAs, a "forward" DFA and a
+/// "reverse" DFA. The forward DFA is responsible for detecting the end of
+/// a match while the reverse DFA is responsible for detecting the start
+/// of a match. Thus, in order to find the bounds of any given match, a
+/// forward search must first be run followed by a reverse search. A match
+/// found by the forward DFA guarantees that the reverse DFA will also find
+/// a match.
+///
+/// # Fallibility
+///
+/// Most of the search routines defined on this type will _panic_ when the
+/// underlying search fails. This might be because the DFA gave up because it
+/// saw a quit byte, whether configured explicitly or via heuristic Unicode
+/// word boundary support, although neither are enabled by default. It might
+/// also fail if the underlying DFA determines it isn't making effective use of
+/// the cache (which also never happens by default). Or it might fail because
+/// an invalid `Input` configuration is given, for example, with an unsupported
+/// [`Anchored`] mode.
+///
+/// If you need to handle these error cases instead of allowing them to trigger
+/// a panic, then the lower level [`Regex::try_search`] provides a fallible API
+/// that never panics.
+///
+/// # Example
+///
+/// This example shows how to cause a search to terminate if it sees a
+/// `\n` byte, and handle the error returned. This could be useful if, for
+/// example, you wanted to prevent a user supplied pattern from matching
+/// across a line boundary.
+///
+/// ```
+/// # if cfg!(miri) { return Ok(()); } // miri takes too long
+/// use regex_automata::{hybrid::{dfa, regex::Regex}, Input, MatchError};
+///
+/// let re = Regex::builder()
+///     .dfa(dfa::Config::new().quit(b'\n', true))
+///     .build(r"foo\p{any}+bar")?;
+/// let mut cache = re.create_cache();
+///
+/// let input = Input::new("foo\nbar");
+/// // Normally this would produce a match, since \p{any} contains '\n'.
+/// // But since we instructed the automaton to enter a quit state if a
+/// // '\n' is observed, this produces a match error instead.
+/// let expected = MatchError::quit(b'\n', 3);
+/// let got = re.try_search(&mut cache, &input).unwrap_err();
+/// assert_eq!(expected, got);
+///
+/// # Ok::<(), Box<dyn std::error::Error>>(())
+/// ```
+#[derive(Debug)]
+pub struct Regex {
+    /// The forward lazy DFA. This can only find the end of a match.
+    forward: DFA,
+    /// The reverse lazy DFA. This can only find the start of a match.
+    ///
+    /// This is built with 'all' match semantics (instead of leftmost-first)
+    /// so that it always finds the longest possible match (which corresponds
+    /// to the leftmost starting position). It is also compiled as an anchored
+    /// matcher and has 'starts_for_each_pattern' enabled. Including starting
+    /// states for each pattern is necessary to ensure that we only look for
+    /// matches of a pattern that matched in the forward direction. Otherwise,
+    /// we might wind up finding the "leftmost" starting position of a totally
+    /// different pattern!
+    reverse: DFA,
+}
+
+/// Convenience routines for regex and cache construction.
+impl Regex {
+    /// Parse the given regular expression using the default configuration and
+    /// return the corresponding regex.
+    ///
+    /// If you want a non-default configuration, then use the [`Builder`] to
+    /// set your own configuration.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use regex_automata::{hybrid::regex::Regex, Match};
+    ///
+    /// let re = Regex::new("foo[0-9]+bar")?;
+    /// let mut cache = re.create_cache();
+    /// assert_eq!(
+    ///     Some(Match::must(0, 3..14)),
+    ///     re.find(&mut cache, "zzzfoo12345barzzz"),
+    /// );
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    #[cfg(feature = "syntax")]
+    pub fn new(pattern: &str) -> Result<Regex, BuildError> {
+        Regex::builder().build(pattern)
+    }
+
+    /// Like `new`, but parses multiple patterns into a single "multi regex."
+    /// This similarly uses the default regex configuration.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use regex_automata::{hybrid::regex::Regex, Match};
+    ///
+    /// let re = Regex::new_many(&["[a-z]+", "[0-9]+"])?;
+    /// let mut cache = re.create_cache();
+    ///
+    /// let mut it = re.find_iter(&mut cache, "abc 1 foo 4567 0 quux");
+    /// assert_eq!(Some(Match::must(0, 0..3)), it.next());
+    /// assert_eq!(Some(Match::must(1, 4..5)), it.next());
+    /// assert_eq!(Some(Match::must(0, 6..9)), it.next());
+    /// assert_eq!(Some(Match::must(1, 10..14)), it.next());
+    /// assert_eq!(Some(Match::must(1, 15..16)), it.next());
+    /// assert_eq!(Some(Match::must(0, 17..21)), it.next());
+    /// assert_eq!(None, it.next());
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    #[cfg(feature = "syntax")]
+    pub fn new_many<P: AsRef<str>>(
+        patterns: &[P],
+    ) -> Result<Regex, BuildError> {
+        Regex::builder().build_many(patterns)
+    }
+
+    /// Return a builder for configuring the construction of a `Regex`.
+    ///
+    /// This is a convenience routine to avoid needing to import the
+    /// [`Builder`] type in common cases.
+    ///
+    /// # Example
+    ///
+    /// This example shows how to use the builder to disable UTF-8 mode
+    /// everywhere.
+    ///
+    /// ```
+    /// # if cfg!(miri) { return Ok(()); } // miri takes too long
+    /// use regex_automata::{
+    ///     hybrid::regex::Regex, nfa::thompson, util::syntax, Match,
+    /// };
+    ///
+    /// let re = Regex::builder()
+    ///     .syntax(syntax::Config::new().utf8(false))
+    ///     .thompson(thompson::Config::new().utf8(false))
+    ///     .build(r"foo(?-u:[^b])ar.*")?;
+    /// let mut cache = re.create_cache();
+    ///
+    /// let haystack = b"\xFEfoo\xFFarzz\xE2\x98\xFF\n";
+    /// let expected = Some(Match::must(0, 1..9));
+    /// let got = re.find(&mut cache, haystack);
+    /// assert_eq!(expected, got);
+    ///
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    pub fn builder() -> Builder {
+        Builder::new()
+    }
+
+    /// Create a new cache for this `Regex`.
+    ///
+    /// The cache returned should only be used for searches for this
+    /// `Regex`. If you want to reuse the cache for another `Regex`, then
+    /// you must call [`Cache::reset`] with that `Regex` (or, equivalently,
+    /// [`Regex::reset_cache`]).
+    pub fn create_cache(&self) -> Cache {
+        Cache::new(self)
+    }
+
+    /// Reset the given cache such that it can be used for searching with the
+    /// this `Regex` (and only this `Regex`).
+    ///
+    /// A cache reset permits reusing memory already allocated in this cache
+    /// with a different `Regex`.
+    ///
+    /// Resetting a cache sets its "clear count" to 0. This is relevant if the
+    /// `Regex` has been configured to "give up" after it has cleared the cache
+    /// a certain number of times.
+    ///
+    /// # Example
+    ///
+    /// This shows how to re-purpose a cache for use with a different `Regex`.
+    ///
+    /// ```
+    /// # if cfg!(miri) { return Ok(()); } // miri takes too long
+    /// use regex_automata::{hybrid::regex::Regex, Match};
+    ///
+    /// let re1 = Regex::new(r"\w")?;
+    /// let re2 = Regex::new(r"\W")?;
+    ///
+    /// let mut cache = re1.create_cache();
+    /// assert_eq!(
+    ///     Some(Match::must(0, 0..2)),
+    ///     re1.find(&mut cache, "Δ"),
+    /// );
+    ///
+    /// // Using 'cache' with re2 is not allowed. It may result in panics or
+    /// // incorrect results. In order to re-purpose the cache, we must reset
+    /// // it with the Regex we'd like to use it with.
+    /// //
+    /// // Similarly, after this reset, using the cache with 're1' is also not
+    /// // allowed.
+    /// re2.reset_cache(&mut cache);
+    /// assert_eq!(
+    ///     Some(Match::must(0, 0..3)),
+    ///     re2.find(&mut cache, "☃"),
+    /// );
+    ///
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    pub fn reset_cache(&self, cache: &mut Cache) {
+        self.forward().reset_cache(&mut cache.forward);
+        self.reverse().reset_cache(&mut cache.reverse);
+    }
+}
+
+/// Standard infallible search routines for finding and iterating over matches.
+impl Regex {
+    /// Returns true if and only if this regex matches the given haystack.
+    ///
+    /// This routine may short circuit if it knows that scanning future input
+    /// will never lead to a different result. In particular, if the underlying
+    /// DFA enters a match state or a dead state, then this routine will return
+    /// `true` or `false`, respectively, without inspecting any future input.
+    ///
+    /// # Panics
+    ///
+    /// This routine panics if the search could not complete. This can occur
+    /// in a number of circumstances:
+    ///
+    /// * The configuration of the lazy DFA may permit it to "quit" the search.
+    /// For example, setting quit bytes or enabling heuristic support for
+    /// Unicode word boundaries. The default configuration does not enable any
+    /// option that could result in the lazy DFA quitting.
+    /// * The configuration of the lazy DFA may also permit it to "give up"
+    /// on a search if it makes ineffective use of its transition table
+    /// cache. The default configuration does not enable this by default,
+    /// although it is typically a good idea to.
+    /// * When the provided `Input` configuration is not supported. For
+    /// example, by providing an unsupported anchor mode.
+    ///
+    /// When a search panics, callers cannot know whether a match exists or
+    /// not.
+    ///
+    /// Use [`Regex::try_search`] if you want to handle these error conditions.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use regex_automata::hybrid::regex::Regex;
+    ///
+    /// let re = Regex::new("foo[0-9]+bar")?;
+    /// let mut cache = re.create_cache();
+    ///
+    /// assert!(re.is_match(&mut cache, "foo12345bar"));
+    /// assert!(!re.is_match(&mut cache, "foobar"));
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    #[inline]
+    pub fn is_match<'h, I: Into<Input<'h>>>(
+        &self,
+        cache: &mut Cache,
+        input: I,
+    ) -> bool {
+        // Not only can we do an "earliest" search, but we can avoid doing a
+        // reverse scan too.
+        self.forward()
+            .try_search_fwd(&mut cache.forward, &input.into().earliest(true))
+            .unwrap()
+            .is_some()
+    }
+
+    /// Returns the start and end offset of the leftmost match. If no match
+    /// exists, then `None` is returned.
+    ///
+    /// # Panics
+    ///
+    /// This routine panics if the search could not complete. This can occur
+    /// in a number of circumstances:
+    ///
+    /// * The configuration of the lazy DFA may permit it to "quit" the search.
+    /// For example, setting quit bytes or enabling heuristic support for
+    /// Unicode word boundaries. The default configuration does not enable any
+    /// option that could result in the lazy DFA quitting.
+    /// * The configuration of the lazy DFA may also permit it to "give up"
+    /// on a search if it makes ineffective use of its transition table
+    /// cache. The default configuration does not enable this by default,
+    /// although it is typically a good idea to.
+    /// * When the provided `Input` configuration is not supported. For
+    /// example, by providing an unsupported anchor mode.
+    ///
+    /// When a search panics, callers cannot know whether a match exists or
+    /// not.
+    ///
+    /// Use [`Regex::try_search`] if you want to handle these error conditions.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use regex_automata::{Match, hybrid::regex::Regex};
+    ///
+    /// let re = Regex::new("foo[0-9]+")?;
+    /// let mut cache = re.create_cache();
+    /// assert_eq!(
+    ///     Some(Match::must(0, 3..11)),
+    ///     re.find(&mut cache, "zzzfoo12345zzz"),
+    /// );
+    ///
+    /// // Even though a match is found after reading the first byte (`a`),
+    /// // the default leftmost-first match semantics demand that we find the
+    /// // earliest match that prefers earlier parts of the pattern over latter
+    /// // parts.
+    /// let re = Regex::new("abc|a")?;
+    /// let mut cache = re.create_cache();
+    /// assert_eq!(Some(Match::must(0, 0..3)), re.find(&mut cache, "abc"));
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    #[inline]
+    pub fn find<'h, I: Into<Input<'h>>>(
+        &self,
+        cache: &mut Cache,
+        input: I,
+    ) -> Option<Match> {
+        self.try_search(cache, &input.into()).unwrap()
+    }
+
+    /// Returns an iterator over all non-overlapping leftmost matches in the
+    /// given bytes. If no match exists, then the iterator yields no elements.
+    ///
+    /// # Panics
+    ///
+    /// This routine panics if the search could not complete. This can occur
+    /// in a number of circumstances:
+    ///
+    /// * The configuration of the lazy DFA may permit it to "quit" the search.
+    /// For example, setting quit bytes or enabling heuristic support for
+    /// Unicode word boundaries. The default configuration does not enable any
+    /// option that could result in the lazy DFA quitting.
+    /// * The configuration of the lazy DFA may also permit it to "give up"
+    /// on a search if it makes ineffective use of its transition table
+    /// cache. The default configuration does not enable this by default,
+    /// although it is typically a good idea to.
+    /// * When the provided `Input` configuration is not supported. For
+    /// example, by providing an unsupported anchor mode.
+    ///
+    /// When a search panics, callers cannot know whether a match exists or
+    /// not.
+    ///
+    /// The above conditions also apply to the iterator returned as well. For
+    /// example, if the lazy DFA gives up or quits during a search using this
+    /// method, then a panic will occur during iteration.
+    ///
+    /// Use [`Regex::try_search`] with [`util::iter::Searcher`](iter::Searcher)
+    /// if you want to handle these error conditions.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use regex_automata::{hybrid::regex::Regex, Match};
+    ///
+    /// let re = Regex::new("foo[0-9]+")?;
+    /// let mut cache = re.create_cache();
+    ///
+    /// let text = "foo1 foo12 foo123";
+    /// let matches: Vec<Match> = re.find_iter(&mut cache, text).collect();
+    /// assert_eq!(matches, vec![
+    ///     Match::must(0, 0..4),
+    ///     Match::must(0, 5..10),
+    ///     Match::must(0, 11..17),
+    /// ]);
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    #[inline]
+    pub fn find_iter<'r, 'c, 'h, I: Into<Input<'h>>>(
+        &'r self,
+        cache: &'c mut Cache,
+        input: I,
+    ) -> FindMatches<'r, 'c, 'h> {
+        let it = iter::Searcher::new(input.into());
+        FindMatches { re: self, cache, it }
+    }
+}
+
+/// Lower level "search" primitives that accept a `&Input` for cheap reuse
+/// and return an error if one occurs instead of panicking.
+impl Regex {
+    /// Returns the start and end offset of the leftmost match. If no match
+    /// exists, then `None` is returned.
+    ///
+    /// This is like [`Regex::find`] but with two differences:
+    ///
+    /// 1. It is not generic over `Into<Input>` and instead accepts a
+    /// `&Input`. This permits reusing the same `Input` for multiple searches
+    /// without needing to create a new one. This _may_ help with latency.
+    /// 2. It returns an error if the search could not complete where as
+    /// [`Regex::find`] will panic.
+    ///
+    /// # Errors
+    ///
+    /// This routine errors if the search could not complete. This can occur
+    /// in a number of circumstances:
+    ///
+    /// * The configuration of the lazy DFA may permit it to "quit" the search.
+    /// For example, setting quit bytes or enabling heuristic support for
+    /// Unicode word boundaries. The default configuration does not enable any
+    /// option that could result in the lazy DFA quitting.
+    /// * The configuration of the lazy DFA may also permit it to "give up"
+    /// on a search if it makes ineffective use of its transition table
+    /// cache. The default configuration does not enable this by default,
+    /// although it is typically a good idea to.
+    /// * When the provided `Input` configuration is not supported. For
+    /// example, by providing an unsupported anchor mode.
+    ///
+    /// When a search returns an error, callers cannot know whether a match
+    /// exists or not.
+    #[inline]
+    pub fn try_search(
+        &self,
+        cache: &mut Cache,
+        input: &Input<'_>,
+    ) -> Result<Option<Match>, MatchError> {
+        let (fcache, rcache) = (&mut cache.forward, &mut cache.reverse);
+        let end = match self.forward().try_search_fwd(fcache, input)? {
+            None => return Ok(None),
+            Some(end) => end,
+        };
+        // This special cases an empty match at the beginning of the search. If
+        // our end matches our start, then since a reverse DFA can't match past
+        // the start, it must follow that our starting position is also our end
+        // position. So short circuit and skip the reverse search.
+        if input.start() == end.offset() {
+            return Ok(Some(Match::new(
+                end.pattern(),
+                end.offset()..end.offset(),
+            )));
+        }
+        // We can also skip the reverse search if we know our search was
+        // anchored. This occurs either when the input config is anchored or
+        // when we know the regex itself is anchored. In this case, we know the
+        // start of the match, if one is found, must be the start of the
+        // search.
+        if self.is_anchored(input) {
+            return Ok(Some(Match::new(
+                end.pattern(),
+                input.start()..end.offset(),
+            )));
+        }
+        // N.B. I have tentatively convinced myself that it isn't necessary
+        // to specify the specific pattern for the reverse search since the
+        // reverse search will always find the same pattern to match as the
+        // forward search. But I lack a rigorous proof. Why not just provide
+        // the pattern anyway? Well, if it is needed, then leaving it out
+        // gives us a chance to find a witness. (Also, if we don't need to
+        // specify the pattern, then we don't need to build the reverse DFA
+        // with 'starts_for_each_pattern' enabled. It doesn't matter too much
+        // for the lazy DFA, but does make the overall DFA bigger.)
+        //
+        // We also need to be careful to disable 'earliest' for the reverse
+        // search, since it could be enabled for the forward search. In the
+        // reverse case, to satisfy "leftmost" criteria, we need to match as
+        // much as we can. We also need to be careful to make the search
+        // anchored. We don't want the reverse search to report any matches
+        // other than the one beginning at the end of our forward search.
+        let revsearch = input
+            .clone()
+            .span(input.start()..end.offset())
+            .anchored(Anchored::Yes)
+            .earliest(false);
+        let start = self
+            .reverse()
+            .try_search_rev(rcache, &revsearch)?
+            .expect("reverse search must match if forward search does");
+        debug_assert_eq!(
+            start.pattern(),
+            end.pattern(),
+            "forward and reverse search must match same pattern",
+        );
+        debug_assert!(start.offset() <= end.offset());
+        Ok(Some(Match::new(end.pattern(), start.offset()..end.offset())))
+    }
+
+    /// Returns true if either the given input specifies an anchored search
+    /// or if the underlying NFA is always anchored.
+    fn is_anchored(&self, input: &Input<'_>) -> bool {
+        match input.get_anchored() {
+            Anchored::No => {
+                self.forward().get_nfa().is_always_start_anchored()
+            }
+            Anchored::Yes | Anchored::Pattern(_) => true,
+        }
+    }
+}
+
+/// Non-search APIs for querying information about the regex and setting a
+/// prefilter.
+impl Regex {
+    /// Return the underlying lazy DFA responsible for forward matching.
+    ///
+    /// This is useful for accessing the underlying lazy DFA and using it
+    /// directly if the situation calls for it.
+    pub fn forward(&self) -> &DFA {
+        &self.forward
+    }
+
+    /// Return the underlying lazy DFA responsible for reverse matching.
+    ///
+    /// This is useful for accessing the underlying lazy DFA and using it
+    /// directly if the situation calls for it.
+    pub fn reverse(&self) -> &DFA {
+        &self.reverse
+    }
+
+    /// Returns the total number of patterns matched by this regex.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # if cfg!(miri) { return Ok(()); } // miri takes too long
+    /// use regex_automata::hybrid::regex::Regex;
+    ///
+    /// let re = Regex::new_many(&[r"[a-z]+", r"[0-9]+", r"\w+"])?;
+    /// assert_eq!(3, re.pattern_len());
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    pub fn pattern_len(&self) -> usize {
+        assert_eq!(self.forward().pattern_len(), self.reverse().pattern_len());
+        self.forward().pattern_len()
+    }
+}
+
+/// An iterator over all non-overlapping matches for an infallible search.
+///
+/// The iterator yields a [`Match`] value until no more matches could be found.
+/// If the underlying regex engine returns an error, then a panic occurs.
+///
+/// The lifetime parameters are as follows:
+///
+/// * `'r` represents the lifetime of the regex object.
+/// * `'h` represents the lifetime of the haystack being searched.
+/// * `'c` represents the lifetime of the regex cache.
+///
+/// This iterator can be created with the [`Regex::find_iter`] method.
+#[derive(Debug)]
+pub struct FindMatches<'r, 'c, 'h> {
+    re: &'r Regex,
+    cache: &'c mut Cache,
+    it: iter::Searcher<'h>,
+}
+
+impl<'r, 'c, 'h> Iterator for FindMatches<'r, 'c, 'h> {
+    type Item = Match;
+
+    #[inline]
+    fn next(&mut self) -> Option<Match> {
+        let FindMatches { re, ref mut cache, ref mut it } = *self;
+        it.advance(|input| re.try_search(cache, input))
+    }
+}
+
+/// A cache represents a partially computed forward and reverse DFA.
+///
+/// A cache is the key component that differentiates a classical DFA and a
+/// hybrid NFA/DFA (also called a "lazy DFA"). Where a classical DFA builds a
+/// complete transition table that can handle all possible inputs, a hybrid
+/// NFA/DFA starts with an empty transition table and builds only the parts
+/// required during search. The parts that are built are stored in a cache. For
+/// this reason, a cache is a required parameter for nearly every operation on
+/// a [`Regex`].
+///
+/// Caches can be created from their corresponding `Regex` via
+/// [`Regex::create_cache`]. A cache can only be used with either the `Regex`
+/// that created it, or the `Regex` that was most recently used to reset it
+/// with [`Cache::reset`]. Using a cache with any other `Regex` may result in
+/// panics or incorrect results.
+#[derive(Debug, Clone)]
+pub struct Cache {
+    forward: dfa::Cache,
+    reverse: dfa::Cache,
+}
+
+impl Cache {
+    /// Create a new cache for the given `Regex`.
+    ///
+    /// The cache returned should only be used for searches for the given
+    /// `Regex`. If you want to reuse the cache for another `Regex`, then you
+    /// must call [`Cache::reset`] with that `Regex`.
+    pub fn new(re: &Regex) -> Cache {
+        let forward = dfa::Cache::new(re.forward());
+        let reverse = dfa::Cache::new(re.reverse());
+        Cache { forward, reverse }
+    }
+
+    /// Reset this cache such that it can be used for searching with the given
+    /// `Regex` (and only that `Regex`).
+    ///
+    /// A cache reset permits reusing memory already allocated in this cache
+    /// with a different `Regex`.
+    ///
+    /// Resetting a cache sets its "clear count" to 0. This is relevant if the
+    /// `Regex` has been configured to "give up" after it has cleared the cache
+    /// a certain number of times.
+    ///
+    /// # Example
+    ///
+    /// This shows how to re-purpose a cache for use with a different `Regex`.
+    ///
+    /// ```
+    /// # if cfg!(miri) { return Ok(()); } // miri takes too long
+    /// use regex_automata::{hybrid::regex::Regex, Match};
+    ///
+    /// let re1 = Regex::new(r"\w")?;
+    /// let re2 = Regex::new(r"\W")?;
+    ///
+    /// let mut cache = re1.create_cache();
+    /// assert_eq!(
+    ///     Some(Match::must(0, 0..2)),
+    ///     re1.find(&mut cache, "Δ"),
+    /// );
+    ///
+    /// // Using 'cache' with re2 is not allowed. It may result in panics or
+    /// // incorrect results. In order to re-purpose the cache, we must reset
+    /// // it with the Regex we'd like to use it with.
+    /// //
+    /// // Similarly, after this reset, using the cache with 're1' is also not
+    /// // allowed.
+    /// cache.reset(&re2);
+    /// assert_eq!(
+    ///     Some(Match::must(0, 0..3)),
+    ///     re2.find(&mut cache, "☃"),
+    /// );
+    ///
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    pub fn reset(&mut self, re: &Regex) {
+        self.forward.reset(re.forward());
+        self.reverse.reset(re.reverse());
+    }
+
+    /// Return a reference to the forward cache.
+    pub fn forward(&mut self) -> &dfa::Cache {
+        &self.forward
+    }
+
+    /// Return a reference to the reverse cache.
+    pub fn reverse(&mut self) -> &dfa::Cache {
+        &self.reverse
+    }
+
+    /// Return a mutable reference to the forward cache.
+    ///
+    /// If you need mutable references to both the forward and reverse caches,
+    /// then use [`Cache::as_parts_mut`].
+    pub fn forward_mut(&mut self) -> &mut dfa::Cache {
+        &mut self.forward
+    }
+
+    /// Return a mutable reference to the reverse cache.
+    ///
+    /// If you need mutable references to both the forward and reverse caches,
+    /// then use [`Cache::as_parts_mut`].
+    pub fn reverse_mut(&mut self) -> &mut dfa::Cache {
+        &mut self.reverse
+    }
+
+    /// Return references to the forward and reverse caches, respectively.
+    pub fn as_parts(&self) -> (&dfa::Cache, &dfa::Cache) {
+        (&self.forward, &self.reverse)
+    }
+
+    /// Return mutable references to the forward and reverse caches,
+    /// respectively.
+    pub fn as_parts_mut(&mut self) -> (&mut dfa::Cache, &mut dfa::Cache) {
+        (&mut self.forward, &mut self.reverse)
+    }
+
+    /// Returns the heap memory usage, in bytes, as a sum of the forward and
+    /// reverse lazy DFA caches.
+    ///
+    /// This does **not** include the stack size used up by this cache. To
+    /// compute that, use `std::mem::size_of::<Cache>()`.
+    pub fn memory_usage(&self) -> usize {
+        self.forward.memory_usage() + self.reverse.memory_usage()
+    }
+}
+
+/// A builder for a regex based on a hybrid NFA/DFA.
+///
+/// This builder permits configuring options for the syntax of a pattern, the
+/// NFA construction, the lazy DFA construction and finally the regex searching
+/// itself. This builder is different from a general purpose regex builder
+/// in that it permits fine grain configuration of the construction process.
+/// The trade off for this is complexity, and the possibility of setting a
+/// configuration that might not make sense. For example, there are two
+/// different UTF-8 modes:
+///
+/// * [`syntax::Config::utf8`](crate::util::syntax::Config::utf8) controls
+/// whether the pattern itself can contain sub-expressions that match invalid
+/// UTF-8.
+/// * [`thompson::Config::utf8`] controls how the regex iterators themselves
+/// advance the starting position of the next search when a match with zero
+/// length is found.
+///
+/// Generally speaking, callers will want to either enable all of these or
+/// disable all of these.
+///
+/// Internally, building a regex requires building two hybrid NFA/DFAs,
+/// where one is responsible for finding the end of a match and the other is
+/// responsible for finding the start of a match. If you only need to detect
+/// whether something matched, or only the end of a match, then you should use
+/// a [`dfa::Builder`] to construct a single hybrid NFA/DFA, which is cheaper
+/// than building two of them.
+///
+/// # Example
+///
+/// This example shows how to disable UTF-8 mode in the syntax and the regex
+/// itself. This is generally what you want for matching on arbitrary bytes.
+///
+/// ```
+/// # if cfg!(miri) { return Ok(()); } // miri takes too long
+/// use regex_automata::{
+///     hybrid::regex::Regex, nfa::thompson, util::syntax, Match,
+/// };
+///
+/// let re = Regex::builder()
+///     .syntax(syntax::Config::new().utf8(false))
+///     .thompson(thompson::Config::new().utf8(false))
+///     .build(r"foo(?-u:[^b])ar.*")?;
+/// let mut cache = re.create_cache();
+///
+/// let haystack = b"\xFEfoo\xFFarzz\xE2\x98\xFF\n";
+/// let expected = Some(Match::must(0, 1..9));
+/// let got = re.find(&mut cache, haystack);
+/// assert_eq!(expected, got);
+/// // Notice that `(?-u:[^b])` matches invalid UTF-8,
+/// // but the subsequent `.*` does not! Disabling UTF-8
+/// // on the syntax permits this.
+/// assert_eq!(b"foo\xFFarzz", &haystack[got.unwrap().range()]);
+///
+/// # Ok::<(), Box<dyn std::error::Error>>(())
+/// ```
+#[derive(Clone, Debug)]
+pub struct Builder {
+    dfa: dfa::Builder,
+}
+
+impl Builder {
+    /// Create a new regex builder with the default configuration.
+    pub fn new() -> Builder {
+        Builder { dfa: DFA::builder() }
+    }
+
+    /// Build a regex from the given pattern.
+    ///
+    /// If there was a problem parsing or compiling the pattern, then an error
+    /// is returned.
+    #[cfg(feature = "syntax")]
+    pub fn build(&self, pattern: &str) -> Result<Regex, BuildError> {
+        self.build_many(&[pattern])
+    }
+
+    /// Build a regex from the given patterns.
+    #[cfg(feature = "syntax")]
+    pub fn build_many<P: AsRef<str>>(
+        &self,
+        patterns: &[P],
+    ) -> Result<Regex, BuildError> {
+        let forward = self.dfa.build_many(patterns)?;
+        let reverse = self
+            .dfa
+            .clone()
+            .configure(
+                DFA::config()
+                    .prefilter(None)
+                    .specialize_start_states(false)
+                    .match_kind(MatchKind::All),
+            )
+            .thompson(thompson::Config::new().reverse(true))
+            .build_many(patterns)?;
+        Ok(self.build_from_dfas(forward, reverse))
+    }
+
+    /// Build a regex from its component forward and reverse hybrid NFA/DFAs.
+    ///
+    /// This is useful when you've built a forward and reverse lazy DFA
+    /// separately, and want to combine them into a single regex. Once build,
+    /// the individual DFAs given can still be accessed via [`Regex::forward`]
+    /// and [`Regex::reverse`].
+    ///
+    /// It is important that the reverse lazy DFA be compiled under the
+    /// following conditions:
+    ///
+    /// * It should use [`MatchKind::All`] semantics.
+    /// * It should match in reverse.
+    /// * Otherwise, its configuration should match the forward DFA.
+    ///
+    /// If these conditions aren't satisfied, then the behavior of searches is
+    /// unspecified.
+    ///
+    /// Note that when using this constructor, no configuration is applied.
+    /// Since this routine provides the DFAs to the builder, there is no
+    /// opportunity to apply other configuration options.
+    ///
+    /// # Example
+    ///
+    /// This shows how to build individual lazy forward and reverse DFAs, and
+    /// then combine them into a single `Regex`.
+    ///
+    /// ```
+    /// use regex_automata::{
+    ///     hybrid::{dfa::DFA, regex::Regex},
+    ///     nfa::thompson,
+    ///     MatchKind,
+    /// };
+    ///
+    /// let fwd = DFA::new(r"foo[0-9]+")?;
+    /// let rev = DFA::builder()
+    ///     .configure(DFA::config().match_kind(MatchKind::All))
+    ///     .thompson(thompson::Config::new().reverse(true))
+    ///     .build(r"foo[0-9]+")?;
+    ///
+    /// let re = Regex::builder().build_from_dfas(fwd, rev);
+    /// let mut cache = re.create_cache();
+    /// assert_eq!(true, re.is_match(&mut cache, "foo123"));
+    /// # Ok::<(), Box<dyn std::error::Error>>(())
+    /// ```
+    pub fn build_from_dfas(&self, forward: DFA, reverse: DFA) -> Regex {
+        Regex { forward, reverse }
+    }
+
+    /// Set the syntax configuration for this builder using
+    /// [`syntax::Config`](crate::util::syntax::Config).
+    ///
+    /// This permits setting things like case insensitivity, Unicode and multi
+    /// line mode.
+    #[cfg(feature = "syntax")]
+    pub fn syntax(
+        &mut self,
+        config: crate::util::syntax::Config,
+    ) -> &mut Builder {
+        self.dfa.syntax(config);
+        self
+    }
+
+    /// Set the Thompson NFA configuration for this builder using
+    /// [`nfa::thompson::Config`](thompson::Config).
+    ///
+    /// This permits setting things like whether additional time should be
+    /// spent shrinking the size of the NFA.
+    #[cfg(feature = "syntax")]
+    pub fn thompson(&mut self, config: thompson::Config) -> &mut Builder {
+        self.dfa.thompson(config);
+        self
+    }
+
+    /// Set the lazy DFA compilation configuration for this builder using
+    /// [`dfa::Config`](dfa::Config).
+    ///
+    /// This permits setting things like whether Unicode word boundaries should
+    /// be heuristically supported or settings how the behavior of the cache.
+    pub fn dfa(&mut self, config: dfa::Config) -> &mut Builder {
+        self.dfa.configure(config);
+        self
+    }
+}
+
+impl Default for Builder {
+    fn default() -> Builder {
+        Builder::new()
+    }
+}