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Diffstat (limited to 'third_party/rust/regex-automata/src/nfa/thompson/backtrack.rs')
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diff --git a/third_party/rust/regex-automata/src/nfa/thompson/backtrack.rs b/third_party/rust/regex-automata/src/nfa/thompson/backtrack.rs new file mode 100644 index 0000000000..eba037c1d0 --- /dev/null +++ b/third_party/rust/regex-automata/src/nfa/thompson/backtrack.rs @@ -0,0 +1,1884 @@ +/*! +An NFA backed bounded backtracker for executing regex searches with capturing +groups. + +This module provides a [`BoundedBacktracker`] that works by simulating an NFA +using the classical backtracking algorithm with a twist: it avoids redoing +work that it has done before and thereby avoids worst case exponential time. +In exchange, it can only be used on "short" haystacks. Its advantage is that +is can be faster than the [`PikeVM`](thompson::pikevm::PikeVM) in many cases +because it does less book-keeping. +*/ + +use alloc::{vec, vec::Vec}; + +use crate::{ + nfa::thompson::{self, BuildError, State, NFA}, + util::{ + captures::Captures, + empty, iter, + prefilter::Prefilter, + primitives::{NonMaxUsize, PatternID, SmallIndex, StateID}, + search::{Anchored, HalfMatch, Input, Match, MatchError, Span}, + }, +}; + +/// Returns the minimum visited capacity for the given haystack. +/// +/// This function can be used as the argument to [`Config::visited_capacity`] +/// in order to guarantee that a backtracking search for the given `input` +/// won't return an error when using a [`BoundedBacktracker`] built from the +/// given `NFA`. +/// +/// This routine exists primarily as a way to test that the bounded backtracker +/// works correctly when its capacity is set to the smallest possible amount. +/// Still, it may be useful in cases where you know you want to use the bounded +/// backtracker for a specific input, and just need to know what visited +/// capacity to provide to make it work. +/// +/// Be warned that this number could be quite large as it is multiplicative in +/// the size the given NFA and haystack. +pub fn min_visited_capacity(nfa: &NFA, input: &Input<'_>) -> usize { + div_ceil(nfa.states().len() * (input.get_span().len() + 1), 8) +} + +/// The configuration used for building a bounded backtracker. +/// +/// A bounded backtracker configuration is a simple data object that is +/// typically used with [`Builder::configure`]. +#[derive(Clone, Debug, Default)] +pub struct Config { + pre: Option<Option<Prefilter>>, + visited_capacity: Option<usize>, +} + +impl Config { + /// Return a new default regex configuration. + pub fn new() -> Config { + Config::default() + } + + /// Set a prefilter to be used whenever a start state is entered. + /// + /// A [`Prefilter`] in this context is meant to accelerate searches by + /// looking for literal prefixes that every match for the corresponding + /// pattern (or patterns) must start with. Once a prefilter produces a + /// match, the underlying search routine continues on to try and confirm + /// the match. + /// + /// Be warned that setting a prefilter does not guarantee that the search + /// will be faster. While it's usually a good bet, if the prefilter + /// produces a lot of false positive candidates (i.e., positions matched + /// by the prefilter but not by the regex), then the overall result can + /// be slower than if you had just executed the regex engine without any + /// prefilters. + /// + /// By default no prefilter is set. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// util::prefilter::Prefilter, + /// Input, Match, MatchKind, + /// }; + /// + /// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "bar"]); + /// let re = BoundedBacktracker::builder() + /// .configure(BoundedBacktracker::config().prefilter(pre)) + /// .build(r"(foo|bar)[a-z]+")?; + /// let mut cache = re.create_cache(); + /// let input = Input::new("foo1 barfox bar"); + /// assert_eq!( + /// Some(Match::must(0, 5..11)), + /// re.try_find(&mut cache, input)?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Be warned though that an incorrect prefilter can lead to incorrect + /// results! + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// util::prefilter::Prefilter, + /// Input, HalfMatch, MatchKind, + /// }; + /// + /// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "car"]); + /// let re = BoundedBacktracker::builder() + /// .configure(BoundedBacktracker::config().prefilter(pre)) + /// .build(r"(foo|bar)[a-z]+")?; + /// let mut cache = re.create_cache(); + /// let input = Input::new("foo1 barfox bar"); + /// // No match reported even though there clearly is one! + /// assert_eq!(None, re.try_find(&mut cache, input)?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn prefilter(mut self, pre: Option<Prefilter>) -> Config { + self.pre = Some(pre); + self + } + + /// Set the visited capacity used to bound backtracking. + /// + /// The visited capacity represents the amount of heap memory (in bytes) to + /// allocate toward tracking which parts of the backtracking search have + /// been done before. The heap memory needed for any particular search is + /// proportional to `haystack.len() * nfa.states().len()`, which an be + /// quite large. Therefore, the bounded backtracker is typically only able + /// to run on shorter haystacks. + /// + /// For a given regex, increasing the visited capacity means that the + /// maximum haystack length that can be searched is increased. The + /// [`BoundedBacktracker::max_haystack_len`] method returns that maximum. + /// + /// The default capacity is a reasonable but empirically chosen size. + /// + /// # Example + /// + /// As with other regex engines, Unicode is what tends to make the bounded + /// backtracker less useful by making the maximum haystack length quite + /// small. If necessary, increasing the visited capacity using this routine + /// will increase the maximum haystack length at the cost of using more + /// memory. + /// + /// Note though that the specific maximum values here are not an API + /// guarantee. The default visited capacity is subject to change and not + /// covered by semver. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::nfa::thompson::backtrack::BoundedBacktracker; + /// + /// // Unicode inflates the size of the underlying NFA quite a bit, and + /// // thus means that the backtracker can only handle smaller haystacks, + /// // assuming that the visited capacity remains unchanged. + /// let re = BoundedBacktracker::new(r"\w+")?; + /// assert!(re.max_haystack_len() <= 7_000); + /// // But we can increase the visited capacity to handle bigger haystacks! + /// let re = BoundedBacktracker::builder() + /// .configure(BoundedBacktracker::config().visited_capacity(1<<20)) + /// .build(r"\w+")?; + /// assert!(re.max_haystack_len() >= 25_000); + /// assert!(re.max_haystack_len() <= 28_000); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn visited_capacity(mut self, capacity: usize) -> Config { + self.visited_capacity = Some(capacity); + self + } + + /// Returns the prefilter set in this configuration, if one at all. + pub fn get_prefilter(&self) -> Option<&Prefilter> { + self.pre.as_ref().unwrap_or(&None).as_ref() + } + + /// Returns the configured visited capacity. + /// + /// Note that the actual capacity used may be slightly bigger than the + /// configured capacity. + pub fn get_visited_capacity(&self) -> usize { + const DEFAULT: usize = 256 * (1 << 10); // 256 KB + self.visited_capacity.unwrap_or(DEFAULT) + } + + /// Overwrite the default configuration such that the options in `o` are + /// always used. If an option in `o` is not set, then the corresponding + /// option in `self` is used. If it's not set in `self` either, then it + /// remains not set. + pub(crate) fn overwrite(&self, o: Config) -> Config { + Config { + pre: o.pre.or_else(|| self.pre.clone()), + visited_capacity: o.visited_capacity.or(self.visited_capacity), + } + } +} + +/// A builder for a bounded backtracker. +/// +/// This builder permits configuring options for the syntax of a pattern, the +/// NFA construction and the `BoundedBacktracker` construction. 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. +/// +/// # 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. +/// +/// ``` +/// use regex_automata::{ +/// nfa::thompson::{self, backtrack::BoundedBacktracker}, +/// util::syntax, +/// Match, +/// }; +/// +/// let re = BoundedBacktracker::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(Ok(Match::must(0, 1..9))); +/// let got = re.try_find_iter(&mut cache, haystack).next(); +/// 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. +/// // +/// // N.B. This example does not show the impact of +/// // disabling UTF-8 mode on a BoundedBacktracker Config, since that +/// // only impacts regexes that can produce matches of +/// // length 0. +/// assert_eq!(b"foo\xFFarzz", &haystack[got.unwrap()?.range()]); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone, Debug)] +pub struct Builder { + config: Config, + #[cfg(feature = "syntax")] + thompson: thompson::Compiler, +} + +impl Builder { + /// Create a new BoundedBacktracker builder with its default configuration. + pub fn new() -> Builder { + Builder { + config: Config::default(), + #[cfg(feature = "syntax")] + thompson: thompson::Compiler::new(), + } + } + + /// Build a `BoundedBacktracker` 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<BoundedBacktracker, BuildError> { + self.build_many(&[pattern]) + } + + /// Build a `BoundedBacktracker` from the given patterns. + #[cfg(feature = "syntax")] + pub fn build_many<P: AsRef<str>>( + &self, + patterns: &[P], + ) -> Result<BoundedBacktracker, BuildError> { + let nfa = self.thompson.build_many(patterns)?; + self.build_from_nfa(nfa) + } + + /// Build a `BoundedBacktracker` directly from its NFA. + /// + /// Note that when using this method, any configuration that applies to the + /// construction of the NFA itself will of course be ignored, since the NFA + /// given here is already built. + pub fn build_from_nfa( + &self, + nfa: NFA, + ) -> Result<BoundedBacktracker, BuildError> { + nfa.look_set_any().available().map_err(BuildError::word)?; + Ok(BoundedBacktracker { config: self.config.clone(), nfa }) + } + + /// Apply the given `BoundedBacktracker` configuration options to this + /// builder. + pub fn configure(&mut self, config: Config) -> &mut Builder { + self.config = self.config.overwrite(config); + self + } + + /// 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. + /// + /// These settings only apply when constructing a `BoundedBacktracker` + /// directly from a pattern. + #[cfg(feature = "syntax")] + pub fn syntax( + &mut self, + config: crate::util::syntax::Config, + ) -> &mut Builder { + self.thompson.syntax(config); + self + } + + /// Set the Thompson NFA configuration for this builder using + /// [`nfa::thompson::Config`](crate::nfa::thompson::Config). + /// + /// This permits setting things like if additional time should be spent + /// shrinking the size of the NFA. + /// + /// These settings only apply when constructing a `BoundedBacktracker` + /// directly from a pattern. + #[cfg(feature = "syntax")] + pub fn thompson(&mut self, config: thompson::Config) -> &mut Builder { + self.thompson.configure(config); + self + } +} + +/// A backtracking regex engine that bounds its execution to avoid exponential +/// blow-up. +/// +/// This regex engine only implements leftmost-first match semantics and +/// only supports leftmost searches. It effectively does the same thing as a +/// [`PikeVM`](thompson::pikevm::PikeVM), but typically does it faster because +/// it doesn't have to worry about copying capturing group spans for most NFA +/// states. Instead, the backtracker can maintain one set of captures (provided +/// by the caller) and never needs to copy them. In exchange, the backtracker +/// bounds itself to ensure it doesn't exhibit worst case exponential time. +/// This results in the backtracker only being able to handle short haystacks +/// given reasonable memory usage. +/// +/// # Searches may return an error! +/// +/// By design, this backtracking regex engine is bounded. This bound is +/// implemented by not visiting any combination of NFA state ID and position +/// in a haystack more than once. Thus, the total memory required to bound +/// backtracking is proportional to `haystack.len() * nfa.states().len()`. +/// This can obviously get quite large, since large haystacks aren't terribly +/// uncommon. To avoid using exorbitant memory, the capacity is bounded by +/// a fixed limit set via [`Config::visited_capacity`]. Thus, if the total +/// capacity required for a particular regex and a haystack exceeds this +/// capacity, then the search routine will return an error. +/// +/// Unlike other regex engines that may return an error at search time (like +/// the DFA or the hybrid NFA/DFA), there is no way to guarantee that a bounded +/// backtracker will work for every haystack. Therefore, this regex engine +/// _only_ exposes fallible search routines to avoid the footgun of panicking +/// when running a search on a haystack that is too big. +/// +/// If one wants to use the fallible search APIs without handling the +/// error, the only way to guarantee an error won't occur from the +/// haystack length is to ensure the haystack length does not exceed +/// [`BoundedBacktracker::max_haystack_len`]. +/// +/// # Example: Unicode word boundaries +/// +/// This example shows that the bounded backtracker implements Unicode word +/// boundaries correctly by default. +/// +/// ``` +/// # if cfg!(miri) { return Ok(()); } // miri takes too long +/// use regex_automata::{nfa::thompson::backtrack::BoundedBacktracker, Match}; +/// +/// let re = BoundedBacktracker::new(r"\b\w+\b")?; +/// let mut cache = re.create_cache(); +/// +/// let mut it = re.try_find_iter(&mut cache, "Шерлок Холмс"); +/// assert_eq!(Some(Ok(Match::must(0, 0..12))), it.next()); +/// assert_eq!(Some(Ok(Match::must(0, 13..23))), it.next()); +/// assert_eq!(None, it.next()); +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +/// +/// # Example: multiple regex patterns +/// +/// The bounded backtracker supports searching for multiple patterns +/// simultaneously, just like other regex engines. Note though that because it +/// uses a backtracking strategy, this regex engine is unlikely to scale well +/// as more patterns are added. But then again, as more patterns are added, the +/// maximum haystack length allowed will also shorten (assuming the visited +/// capacity remains invariant). +/// +/// ``` +/// use regex_automata::{nfa::thompson::backtrack::BoundedBacktracker, Match}; +/// +/// let re = BoundedBacktracker::new_many(&["[a-z]+", "[0-9]+"])?; +/// let mut cache = re.create_cache(); +/// +/// let mut it = re.try_find_iter(&mut cache, "abc 1 foo 4567 0 quux"); +/// assert_eq!(Some(Ok(Match::must(0, 0..3))), it.next()); +/// assert_eq!(Some(Ok(Match::must(1, 4..5))), it.next()); +/// assert_eq!(Some(Ok(Match::must(0, 6..9))), it.next()); +/// assert_eq!(Some(Ok(Match::must(1, 10..14))), it.next()); +/// assert_eq!(Some(Ok(Match::must(1, 15..16))), it.next()); +/// assert_eq!(Some(Ok(Match::must(0, 17..21))), it.next()); +/// assert_eq!(None, it.next()); +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone, Debug)] +pub struct BoundedBacktracker { + config: Config, + nfa: NFA, +} + +impl BoundedBacktracker { + /// Parse the given regular expression using the default configuration and + /// return the corresponding `BoundedBacktracker`. + /// + /// If you want a non-default configuration, then use the [`Builder`] to + /// set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, + /// }; + /// + /// let re = BoundedBacktracker::new("foo[0-9]+bar")?; + /// let mut cache = re.create_cache(); + /// assert_eq!( + /// Some(Ok(Match::must(0, 3..14))), + /// re.try_find_iter(&mut cache, "zzzfoo12345barzzz").next(), + /// ); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new(pattern: &str) -> Result<BoundedBacktracker, BuildError> { + BoundedBacktracker::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::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, + /// }; + /// + /// let re = BoundedBacktracker::new_many(&["[a-z]+", "[0-9]+"])?; + /// let mut cache = re.create_cache(); + /// + /// let mut it = re.try_find_iter(&mut cache, "abc 1 foo 4567 0 quux"); + /// assert_eq!(Some(Ok(Match::must(0, 0..3))), it.next()); + /// assert_eq!(Some(Ok(Match::must(1, 4..5))), it.next()); + /// assert_eq!(Some(Ok(Match::must(0, 6..9))), it.next()); + /// assert_eq!(Some(Ok(Match::must(1, 10..14))), it.next()); + /// assert_eq!(Some(Ok(Match::must(1, 15..16))), it.next()); + /// assert_eq!(Some(Ok(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<BoundedBacktracker, BuildError> { + BoundedBacktracker::builder().build_many(patterns) + } + + /// # Example + /// + /// This shows how to hand assemble a regular expression via its HIR, + /// compile an NFA from it and build a BoundedBacktracker from the NFA. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::{NFA, backtrack::BoundedBacktracker}, + /// Match, + /// }; + /// use regex_syntax::hir::{Hir, Class, ClassBytes, ClassBytesRange}; + /// + /// let hir = Hir::class(Class::Bytes(ClassBytes::new(vec![ + /// ClassBytesRange::new(b'0', b'9'), + /// ClassBytesRange::new(b'A', b'Z'), + /// ClassBytesRange::new(b'_', b'_'), + /// ClassBytesRange::new(b'a', b'z'), + /// ]))); + /// + /// let config = NFA::config().nfa_size_limit(Some(1_000)); + /// let nfa = NFA::compiler().configure(config).build_from_hir(&hir)?; + /// + /// let re = BoundedBacktracker::new_from_nfa(nfa)?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// let expected = Some(Match::must(0, 3..4)); + /// re.try_captures(&mut cache, "!@#A#@!", &mut caps)?; + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn new_from_nfa(nfa: NFA) -> Result<BoundedBacktracker, BuildError> { + BoundedBacktracker::builder().build_from_nfa(nfa) + } + + /// Create a new `BoundedBacktracker` that matches every input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, + /// }; + /// + /// let re = BoundedBacktracker::always_match()?; + /// let mut cache = re.create_cache(); + /// + /// let expected = Some(Ok(Match::must(0, 0..0))); + /// assert_eq!(expected, re.try_find_iter(&mut cache, "").next()); + /// assert_eq!(expected, re.try_find_iter(&mut cache, "foo").next()); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn always_match() -> Result<BoundedBacktracker, BuildError> { + let nfa = thompson::NFA::always_match(); + BoundedBacktracker::new_from_nfa(nfa) + } + + /// Create a new `BoundedBacktracker` that never matches any input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::nfa::thompson::backtrack::BoundedBacktracker; + /// + /// let re = BoundedBacktracker::never_match()?; + /// let mut cache = re.create_cache(); + /// + /// assert_eq!(None, re.try_find_iter(&mut cache, "").next()); + /// assert_eq!(None, re.try_find_iter(&mut cache, "foo").next()); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn never_match() -> Result<BoundedBacktracker, BuildError> { + let nfa = thompson::NFA::never_match(); + BoundedBacktracker::new_from_nfa(nfa) + } + + /// Return a default configuration for a `BoundedBacktracker`. + /// + /// This is a convenience routine to avoid needing to import the `Config` + /// type when customizing the construction of a `BoundedBacktracker`. + /// + /// # Example + /// + /// This example shows how to disable UTF-8 mode. When UTF-8 mode is + /// disabled, zero-width matches that split a codepoint are allowed. + /// Otherwise they are never reported. + /// + /// In the code below, notice that `""` is permitted to match positions + /// that split the encoding of a codepoint. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::{self, backtrack::BoundedBacktracker}, + /// Match, + /// }; + /// + /// let re = BoundedBacktracker::builder() + /// .thompson(thompson::Config::new().utf8(false)) + /// .build(r"")?; + /// let mut cache = re.create_cache(); + /// + /// let haystack = "a☃z"; + /// let mut it = re.try_find_iter(&mut cache, haystack); + /// assert_eq!(Some(Ok(Match::must(0, 0..0))), it.next()); + /// assert_eq!(Some(Ok(Match::must(0, 1..1))), it.next()); + /// assert_eq!(Some(Ok(Match::must(0, 2..2))), it.next()); + /// assert_eq!(Some(Ok(Match::must(0, 3..3))), it.next()); + /// assert_eq!(Some(Ok(Match::must(0, 4..4))), it.next()); + /// assert_eq!(Some(Ok(Match::must(0, 5..5))), it.next()); + /// assert_eq!(None, it.next()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn config() -> Config { + Config::new() + } + + /// Return a builder for configuring the construction of a + /// `BoundedBacktracker`. + /// + /// 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::{ + /// nfa::thompson::{self, backtrack::BoundedBacktracker}, + /// util::syntax, + /// Match, + /// }; + /// + /// let re = BoundedBacktracker::builder() + /// .syntax(syntax::Config::new().utf8(false)) + /// .thompson(thompson::Config::new().utf8(false)) + /// .build(r"foo(?-u:[^b])ar.*")?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// let haystack = b"\xFEfoo\xFFarzz\xE2\x98\xFF\n"; + /// let expected = Some(Match::must(0, 1..9)); + /// re.try_captures(&mut cache, haystack, &mut caps)?; + /// assert_eq!(expected, caps.get_match()); + /// + /// # 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, + /// [`BoundedBacktracker::reset_cache`]). + pub fn create_cache(&self) -> Cache { + Cache::new(self) + } + + /// Create a new empty set of capturing groups that is guaranteed to be + /// valid for the search APIs on this `BoundedBacktracker`. + /// + /// A `Captures` value created for a specific `BoundedBacktracker` cannot + /// be used with any other `BoundedBacktracker`. + /// + /// This is a convenience function for [`Captures::all`]. See the + /// [`Captures`] documentation for an explanation of its alternative + /// constructors that permit the `BoundedBacktracker` to do less work + /// during a search, and thus might make it faster. + pub fn create_captures(&self) -> Captures { + Captures::all(self.get_nfa().group_info().clone()) + } + + /// Reset the given cache such that it can be used for searching with the + /// this `BoundedBacktracker` (and only this `BoundedBacktracker`). + /// + /// A cache reset permits reusing memory already allocated in this cache + /// with a different `BoundedBacktracker`. + /// + /// # Example + /// + /// This shows how to re-purpose a cache for use with a different + /// `BoundedBacktracker`. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, + /// }; + /// + /// let re1 = BoundedBacktracker::new(r"\w")?; + /// let re2 = BoundedBacktracker::new(r"\W")?; + /// + /// let mut cache = re1.create_cache(); + /// assert_eq!( + /// Some(Ok(Match::must(0, 0..2))), + /// re1.try_find_iter(&mut cache, "Δ").next(), + /// ); + /// + /// // 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 BoundedBacktracker 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(Ok(Match::must(0, 0..3))), + /// re2.try_find_iter(&mut cache, "☃").next(), + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn reset_cache(&self, cache: &mut Cache) { + cache.reset(self); + } + + /// Returns the total number of patterns compiled into this + /// `BoundedBacktracker`. + /// + /// In the case of a `BoundedBacktracker` that contains no patterns, this + /// returns `0`. + /// + /// # Example + /// + /// This example shows the pattern length for a `BoundedBacktracker` that + /// never matches: + /// + /// ``` + /// use regex_automata::nfa::thompson::backtrack::BoundedBacktracker; + /// + /// let re = BoundedBacktracker::never_match()?; + /// assert_eq!(re.pattern_len(), 0); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// And another example for a `BoundedBacktracker` that matches at every + /// position: + /// + /// ``` + /// use regex_automata::nfa::thompson::backtrack::BoundedBacktracker; + /// + /// let re = BoundedBacktracker::always_match()?; + /// assert_eq!(re.pattern_len(), 1); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// And finally, a `BoundedBacktracker` that was constructed from multiple + /// patterns: + /// + /// ``` + /// use regex_automata::nfa::thompson::backtrack::BoundedBacktracker; + /// + /// let re = BoundedBacktracker::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?; + /// assert_eq!(re.pattern_len(), 3); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn pattern_len(&self) -> usize { + self.nfa.pattern_len() + } + + /// Return the config for this `BoundedBacktracker`. + #[inline] + pub fn get_config(&self) -> &Config { + &self.config + } + + /// Returns a reference to the underlying NFA. + #[inline] + pub fn get_nfa(&self) -> &NFA { + &self.nfa + } + + /// Returns the maximum haystack length supported by this backtracker. + /// + /// This routine is a function of both [`Config::visited_capacity`] and the + /// internal size of the backtracker's NFA. + /// + /// # Example + /// + /// This example shows how the maximum haystack length can vary depending + /// on the size of the regex itself. Note though that the specific maximum + /// values here are not an API guarantee. The default visited capacity is + /// subject to change and not covered by semver. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, MatchError, + /// }; + /// + /// // If you're only using ASCII, you get a big budget. + /// let re = BoundedBacktracker::new(r"(?-u)\w+")?; + /// let mut cache = re.create_cache(); + /// assert_eq!(re.max_haystack_len(), 299_592); + /// // Things work up to the max. + /// let mut haystack = "a".repeat(299_592); + /// let expected = Some(Ok(Match::must(0, 0..299_592))); + /// assert_eq!(expected, re.try_find_iter(&mut cache, &haystack).next()); + /// // But you'll get an error if you provide a haystack that's too big. + /// // Notice that we use the 'try_find_iter' routine instead, which + /// // yields Result<Match, MatchError> instead of Match. + /// haystack.push('a'); + /// let expected = Some(Err(MatchError::haystack_too_long(299_593))); + /// assert_eq!(expected, re.try_find_iter(&mut cache, &haystack).next()); + /// + /// // Unicode inflates the size of the underlying NFA quite a bit, and + /// // thus means that the backtracker can only handle smaller haystacks, + /// // assuming that the visited capacity remains unchanged. + /// let re = BoundedBacktracker::new(r"\w+")?; + /// assert!(re.max_haystack_len() <= 7_000); + /// // But we can increase the visited capacity to handle bigger haystacks! + /// let re = BoundedBacktracker::builder() + /// .configure(BoundedBacktracker::config().visited_capacity(1<<20)) + /// .build(r"\w+")?; + /// assert!(re.max_haystack_len() >= 25_000); + /// assert!(re.max_haystack_len() <= 28_000); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn max_haystack_len(&self) -> usize { + // The capacity given in the config is "bytes of heap memory," but the + // capacity we use here is "number of bits." So convert the capacity in + // bytes to the capacity in bits. + let capacity = 8 * self.get_config().get_visited_capacity(); + let blocks = div_ceil(capacity, Visited::BLOCK_SIZE); + let real_capacity = blocks * Visited::BLOCK_SIZE; + (real_capacity / self.nfa.states().len()) - 1 + } +} + +impl BoundedBacktracker { + /// Returns true if and only if this regex matches the given haystack. + /// + /// In the case of a backtracking regex engine, and unlike most other + /// regex engines in this crate, short circuiting isn't practical. However, + /// this routine may still be faster because it instructs backtracking to + /// not keep track of any capturing groups. + /// + /// # Errors + /// + /// This routine only errors if the search could not complete. For this + /// backtracking regex engine, this only occurs when the haystack length + /// exceeds [`BoundedBacktracker::max_haystack_len`]. + /// + /// When a search cannot complete, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// ``` + /// use regex_automata::nfa::thompson::backtrack::BoundedBacktracker; + /// + /// let re = BoundedBacktracker::new("foo[0-9]+bar")?; + /// let mut cache = re.create_cache(); + /// + /// assert!(re.try_is_match(&mut cache, "foo12345bar")?); + /// assert!(!re.try_is_match(&mut cache, "foobar")?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: consistency with search APIs + /// + /// `is_match` is guaranteed to return `true` whenever `find` returns a + /// match. This includes searches that are executed entirely within a + /// codepoint: + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Input, + /// }; + /// + /// let re = BoundedBacktracker::new("a*")?; + /// let mut cache = re.create_cache(); + /// + /// assert!(!re.try_is_match(&mut cache, Input::new("☃").span(1..2))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Notice that when UTF-8 mode is disabled, then the above reports a + /// match because the restriction against zero-width matches that split a + /// codepoint has been lifted: + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::{backtrack::BoundedBacktracker, NFA}, + /// Input, + /// }; + /// + /// let re = BoundedBacktracker::builder() + /// .thompson(NFA::config().utf8(false)) + /// .build("a*")?; + /// let mut cache = re.create_cache(); + /// + /// assert!(re.try_is_match(&mut cache, Input::new("☃").span(1..2))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_is_match<'h, I: Into<Input<'h>>>( + &self, + cache: &mut Cache, + input: I, + ) -> Result<bool, MatchError> { + let input = input.into().earliest(true); + self.try_search_slots(cache, &input, &mut []).map(|pid| pid.is_some()) + } + + /// Executes a leftmost forward search and returns a `Match` if one exists. + /// + /// This routine only includes the overall match span. To get + /// access to the individual spans of each capturing group, use + /// [`BoundedBacktracker::try_captures`]. + /// + /// # Errors + /// + /// This routine only errors if the search could not complete. For this + /// backtracking regex engine, this only occurs when the haystack length + /// exceeds [`BoundedBacktracker::max_haystack_len`]. + /// + /// When a search cannot complete, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, + /// }; + /// + /// let re = BoundedBacktracker::new("foo[0-9]+")?; + /// let mut cache = re.create_cache(); + /// let expected = Match::must(0, 0..8); + /// assert_eq!(Some(expected), re.try_find(&mut cache, "foo12345")?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_find<'h, I: Into<Input<'h>>>( + &self, + cache: &mut Cache, + input: I, + ) -> Result<Option<Match>, MatchError> { + let input = input.into(); + if self.get_nfa().pattern_len() == 1 { + let mut slots = [None, None]; + let pid = match self.try_search_slots(cache, &input, &mut slots)? { + None => return Ok(None), + Some(pid) => pid, + }; + let start = match slots[0] { + None => return Ok(None), + Some(s) => s.get(), + }; + let end = match slots[1] { + None => return Ok(None), + Some(s) => s.get(), + }; + return Ok(Some(Match::new(pid, Span { start, end }))); + } + let ginfo = self.get_nfa().group_info(); + let slots_len = ginfo.implicit_slot_len(); + let mut slots = vec![None; slots_len]; + let pid = match self.try_search_slots(cache, &input, &mut slots)? { + None => return Ok(None), + Some(pid) => pid, + }; + let start = match slots[pid.as_usize() * 2] { + None => return Ok(None), + Some(s) => s.get(), + }; + let end = match slots[pid.as_usize() * 2 + 1] { + None => return Ok(None), + Some(s) => s.get(), + }; + Ok(Some(Match::new(pid, Span { start, end }))) + } + + /// Executes a leftmost forward search and writes the spans of capturing + /// groups that participated in a match into the provided [`Captures`] + /// value. If no match was found, then [`Captures::is_match`] is guaranteed + /// to return `false`. + /// + /// # Errors + /// + /// This routine only errors if the search could not complete. For this + /// backtracking regex engine, this only occurs when the haystack length + /// exceeds [`BoundedBacktracker::max_haystack_len`]. + /// + /// When a search cannot complete, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Span, + /// }; + /// + /// let re = BoundedBacktracker::new( + /// r"^([0-9]{4})-([0-9]{2})-([0-9]{2})$", + /// )?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// re.try_captures(&mut cache, "2010-03-14", &mut caps)?; + /// assert!(caps.is_match()); + /// assert_eq!(Some(Span::from(0..4)), caps.get_group(1)); + /// assert_eq!(Some(Span::from(5..7)), caps.get_group(2)); + /// assert_eq!(Some(Span::from(8..10)), caps.get_group(3)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_captures<'h, I: Into<Input<'h>>>( + &self, + cache: &mut Cache, + input: I, + caps: &mut Captures, + ) -> Result<(), MatchError> { + self.try_search(cache, &input.into(), caps) + } + + /// Returns an iterator over all non-overlapping leftmost matches in the + /// given bytes. If no match exists, then the iterator yields no elements. + /// + /// If the regex engine returns an error at any point, then the iterator + /// will yield that error. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, MatchError, + /// }; + /// + /// let re = BoundedBacktracker::new("foo[0-9]+")?; + /// let mut cache = re.create_cache(); + /// + /// let text = "foo1 foo12 foo123"; + /// let result: Result<Vec<Match>, MatchError> = re + /// .try_find_iter(&mut cache, text) + /// .collect(); + /// let matches = result?; + /// 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 try_find_iter<'r, 'c, 'h, I: Into<Input<'h>>>( + &'r self, + cache: &'c mut Cache, + input: I, + ) -> TryFindMatches<'r, 'c, 'h> { + let caps = Captures::matches(self.get_nfa().group_info().clone()); + let it = iter::Searcher::new(input.into()); + TryFindMatches { re: self, cache, caps, it } + } + + /// Returns an iterator over all non-overlapping `Captures` values. If no + /// match exists, then the iterator yields no elements. + /// + /// This yields the same matches as [`BoundedBacktracker::try_find_iter`], + /// but it includes the spans of all capturing groups that participate in + /// each match. + /// + /// If the regex engine returns an error at any point, then the iterator + /// will yield that error. + /// + /// **Tip:** See [`util::iter::Searcher`](crate::util::iter::Searcher) for + /// how to correctly iterate over all matches in a haystack while avoiding + /// the creation of a new `Captures` value for every match. (Which you are + /// forced to do with an `Iterator`.) + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Span, + /// }; + /// + /// let re = BoundedBacktracker::new("foo(?P<numbers>[0-9]+)")?; + /// let mut cache = re.create_cache(); + /// + /// let text = "foo1 foo12 foo123"; + /// let mut spans = vec![]; + /// for result in re.try_captures_iter(&mut cache, text) { + /// let caps = result?; + /// // The unwrap is OK since 'numbers' matches if the pattern matches. + /// spans.push(caps.get_group_by_name("numbers").unwrap()); + /// } + /// assert_eq!(spans, vec![ + /// Span::from(3..4), + /// Span::from(8..10), + /// Span::from(14..17), + /// ]); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_captures_iter<'r, 'c, 'h, I: Into<Input<'h>>>( + &'r self, + cache: &'c mut Cache, + input: I, + ) -> TryCapturesMatches<'r, 'c, 'h> { + let caps = self.create_captures(); + let it = iter::Searcher::new(input.into()); + TryCapturesMatches { re: self, cache, caps, it } + } +} + +impl BoundedBacktracker { + /// Executes a leftmost forward search and writes the spans of capturing + /// groups that participated in a match into the provided [`Captures`] + /// value. If no match was found, then [`Captures::is_match`] is guaranteed + /// to return `false`. + /// + /// This is like [`BoundedBacktracker::try_captures`], but it accepts a + /// concrete `&Input` instead of an `Into<Input>`. + /// + /// # Errors + /// + /// This routine only errors if the search could not complete. For this + /// backtracking regex engine, this only occurs when the haystack length + /// exceeds [`BoundedBacktracker::max_haystack_len`]. + /// + /// When a search cannot complete, callers cannot know whether a match + /// exists or not. + /// + /// # Example: specific pattern search + /// + /// This example shows how to build a multi bounded backtracker that + /// permits searching for specific patterns. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Anchored, Input, Match, PatternID, + /// }; + /// + /// let re = BoundedBacktracker::new_many(&[ + /// "[a-z0-9]{6}", + /// "[a-z][a-z0-9]{5}", + /// ])?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// let haystack = "foo123"; + /// + /// // Since we are using the default leftmost-first match and both + /// // patterns match at the same starting position, only the first pattern + /// // will be returned in this case when doing a search for any of the + /// // patterns. + /// let expected = Some(Match::must(0, 0..6)); + /// re.try_search(&mut cache, &Input::new(haystack), &mut caps)?; + /// assert_eq!(expected, caps.get_match()); + /// + /// // But if we want to check whether some other pattern matches, then we + /// // can provide its pattern ID. + /// let expected = Some(Match::must(1, 0..6)); + /// let input = Input::new(haystack) + /// .anchored(Anchored::Pattern(PatternID::must(1))); + /// re.try_search(&mut cache, &input, &mut caps)?; + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: specifying the bounds of a search + /// + /// This example shows how providing the bounds of a search can produce + /// different results than simply sub-slicing the haystack. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, Input, + /// }; + /// + /// let re = BoundedBacktracker::new(r"\b[0-9]{3}\b")?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// let haystack = "foo123bar"; + /// + /// // Since we sub-slice the haystack, the search doesn't know about + /// // the larger context and assumes that `123` is surrounded by word + /// // boundaries. And of course, the match position is reported relative + /// // to the sub-slice as well, which means we get `0..3` instead of + /// // `3..6`. + /// let expected = Some(Match::must(0, 0..3)); + /// re.try_search(&mut cache, &Input::new(&haystack[3..6]), &mut caps)?; + /// assert_eq!(expected, caps.get_match()); + /// + /// // But if we provide the bounds of the search within the context of the + /// // entire haystack, then the search can take the surrounding context + /// // into account. (And if we did find a match, it would be reported + /// // as a valid offset into `haystack` instead of its sub-slice.) + /// let expected = None; + /// re.try_search( + /// &mut cache, &Input::new(haystack).range(3..6), &mut caps, + /// )?; + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_search( + &self, + cache: &mut Cache, + input: &Input<'_>, + caps: &mut Captures, + ) -> Result<(), MatchError> { + caps.set_pattern(None); + let pid = self.try_search_slots(cache, input, caps.slots_mut())?; + caps.set_pattern(pid); + Ok(()) + } + + /// Executes a leftmost forward search and writes the spans of capturing + /// groups that participated in a match into the provided `slots`, and + /// returns the matching pattern ID. The contents of the slots for patterns + /// other than the matching pattern are unspecified. If no match was found, + /// then `None` is returned and the contents of all `slots` is unspecified. + /// + /// This is like [`BoundedBacktracker::try_search`], but it accepts a raw + /// slots slice instead of a `Captures` value. This is useful in contexts + /// where you don't want or need to allocate a `Captures`. + /// + /// It is legal to pass _any_ number of slots to this routine. If the regex + /// engine would otherwise write a slot offset that doesn't fit in the + /// provided slice, then it is simply skipped. In general though, there are + /// usually three slice lengths you might want to use: + /// + /// * An empty slice, if you only care about which pattern matched. + /// * A slice with + /// [`pattern_len() * 2`](crate::nfa::thompson::NFA::pattern_len) + /// slots, if you only care about the overall match spans for each matching + /// pattern. + /// * A slice with + /// [`slot_len()`](crate::util::captures::GroupInfo::slot_len) slots, which + /// permits recording match offsets for every capturing group in every + /// pattern. + /// + /// # Errors + /// + /// This routine only errors if the search could not complete. For this + /// backtracking regex engine, this only occurs when the haystack length + /// exceeds [`BoundedBacktracker::max_haystack_len`]. + /// + /// When a search cannot complete, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// This example shows how to find the overall match offsets in a + /// multi-pattern search without allocating a `Captures` value. Indeed, we + /// can put our slots right on the stack. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// PatternID, Input, + /// }; + /// + /// let re = BoundedBacktracker::new_many(&[ + /// r"\pL+", + /// r"\d+", + /// ])?; + /// let mut cache = re.create_cache(); + /// let input = Input::new("!@#123"); + /// + /// // We only care about the overall match offsets here, so we just + /// // allocate two slots for each pattern. Each slot records the start + /// // and end of the match. + /// let mut slots = [None; 4]; + /// let pid = re.try_search_slots(&mut cache, &input, &mut slots)?; + /// assert_eq!(Some(PatternID::must(1)), pid); + /// + /// // The overall match offsets are always at 'pid * 2' and 'pid * 2 + 1'. + /// // See 'GroupInfo' for more details on the mapping between groups and + /// // slot indices. + /// let slot_start = pid.unwrap().as_usize() * 2; + /// let slot_end = slot_start + 1; + /// assert_eq!(Some(3), slots[slot_start].map(|s| s.get())); + /// assert_eq!(Some(6), slots[slot_end].map(|s| s.get())); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_search_slots( + &self, + cache: &mut Cache, + input: &Input<'_>, + slots: &mut [Option<NonMaxUsize>], + ) -> Result<Option<PatternID>, MatchError> { + let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); + if !utf8empty { + let maybe_hm = self.try_search_slots_imp(cache, input, slots)?; + return Ok(maybe_hm.map(|hm| hm.pattern())); + } + // See PikeVM::try_search_slots for why we do this. + let min = self.get_nfa().group_info().implicit_slot_len(); + if slots.len() >= min { + let maybe_hm = self.try_search_slots_imp(cache, input, slots)?; + return Ok(maybe_hm.map(|hm| hm.pattern())); + } + if self.get_nfa().pattern_len() == 1 { + let mut enough = [None, None]; + let got = self.try_search_slots_imp(cache, input, &mut enough)?; + // This is OK because we know `enough_slots` is strictly bigger + // than `slots`, otherwise this special case isn't reached. + slots.copy_from_slice(&enough[..slots.len()]); + return Ok(got.map(|hm| hm.pattern())); + } + let mut enough = vec![None; min]; + let got = self.try_search_slots_imp(cache, input, &mut enough)?; + // This is OK because we know `enough_slots` is strictly bigger than + // `slots`, otherwise this special case isn't reached. + slots.copy_from_slice(&enough[..slots.len()]); + Ok(got.map(|hm| hm.pattern())) + } + + /// This is the actual implementation of `try_search_slots_imp` that + /// doesn't account for the special case when 1) the NFA has UTF-8 mode + /// enabled, 2) the NFA can match the empty string and 3) the caller has + /// provided an insufficient number of slots to record match offsets. + #[inline(never)] + fn try_search_slots_imp( + &self, + cache: &mut Cache, + input: &Input<'_>, + slots: &mut [Option<NonMaxUsize>], + ) -> Result<Option<HalfMatch>, MatchError> { + let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); + let hm = match self.search_imp(cache, input, slots)? { + None => return Ok(None), + Some(hm) if !utf8empty => return Ok(Some(hm)), + Some(hm) => hm, + }; + empty::skip_splits_fwd(input, hm, hm.offset(), |input| { + Ok(self + .search_imp(cache, input, slots)? + .map(|hm| (hm, hm.offset()))) + }) + } + + /// The implementation of standard leftmost backtracking search. + /// + /// Capturing group spans are written to 'caps', but only if requested. + /// 'caps' can be one of three things: 1) totally empty, in which case, we + /// only report the pattern that matched or 2) only has slots for recording + /// the overall match offsets for any pattern or 3) has all slots available + /// for recording the spans of any groups participating in a match. + fn search_imp( + &self, + cache: &mut Cache, + input: &Input<'_>, + slots: &mut [Option<NonMaxUsize>], + ) -> Result<Option<HalfMatch>, MatchError> { + // Unlike in the PikeVM, we write our capturing group spans directly + // into the caller's captures groups. So we have to make sure we're + // starting with a blank slate first. In the PikeVM, we avoid this + // by construction: the spans that are copied to every slot in the + // 'Captures' value already account for presence/absence. In this + // backtracker, we write directly into the caller provided slots, where + // as in the PikeVM, we write into scratch space first and only copy + // them to the caller provided slots when a match is found. + for slot in slots.iter_mut() { + *slot = None; + } + cache.setup_search(&self, input)?; + if input.is_done() { + return Ok(None); + } + let (anchored, start_id) = match input.get_anchored() { + // Only way we're unanchored is if both the caller asked for an + // unanchored search *and* the pattern is itself not anchored. + Anchored::No => ( + self.nfa.is_always_start_anchored(), + // We always use the anchored starting state here, even if + // doing an unanchored search. The "unanchored" part of it is + // implemented in the loop below, by simply trying the next + // byte offset if the previous backtracking exploration failed. + self.nfa.start_anchored(), + ), + Anchored::Yes => (true, self.nfa.start_anchored()), + Anchored::Pattern(pid) => match self.nfa.start_pattern(pid) { + None => return Ok(None), + Some(sid) => (true, sid), + }, + }; + if anchored { + let at = input.start(); + return Ok(self.backtrack(cache, input, at, start_id, slots)); + } + let pre = self.get_config().get_prefilter(); + let mut at = input.start(); + while at <= input.end() { + if let Some(ref pre) = pre { + let span = Span::from(at..input.end()); + match pre.find(input.haystack(), span) { + None => break, + Some(ref span) => at = span.start, + } + } + if let Some(hm) = self.backtrack(cache, input, at, start_id, slots) + { + return Ok(Some(hm)); + } + at += 1; + } + Ok(None) + } + + /// Look for a match starting at `at` in `input` and write the matching + /// pattern ID and group spans to `caps`. The search uses `start_id` as its + /// starting state in the underlying NFA. + /// + /// If no match was found, then the caller should increment `at` and try + /// at the next position. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn backtrack( + &self, + cache: &mut Cache, + input: &Input<'_>, + at: usize, + start_id: StateID, + slots: &mut [Option<NonMaxUsize>], + ) -> Option<HalfMatch> { + cache.stack.push(Frame::Step { sid: start_id, at }); + while let Some(frame) = cache.stack.pop() { + match frame { + Frame::Step { sid, at } => { + if let Some(hm) = self.step(cache, input, sid, at, slots) { + return Some(hm); + } + } + Frame::RestoreCapture { slot, offset } => { + slots[slot] = offset; + } + } + } + None + } + + // LAMENTATION: The actual backtracking search is implemented in about + // 75 lines below. Yet this file is over 2,000 lines long. What have I + // done? + + /// Execute a "step" in the backtracing algorithm. + /// + /// A "step" is somewhat of a misnomer, because this routine keeps going + /// until it either runs out of things to try or fins a match. In the + /// former case, it may have pushed some things on to the backtracking + /// stack, in which case, those will be tried next as part of the + /// 'backtrack' routine above. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn step( + &self, + cache: &mut Cache, + input: &Input<'_>, + mut sid: StateID, + mut at: usize, + slots: &mut [Option<NonMaxUsize>], + ) -> Option<HalfMatch> { + loop { + if !cache.visited.insert(sid, at - input.start()) { + return None; + } + match *self.nfa.state(sid) { + State::ByteRange { ref trans } => { + // Why do we need this? Unlike other regex engines in this + // crate, the backtracker can steam roll ahead in the + // haystack outside of the main loop over the bytes in the + // haystack. While 'trans.matches()' below handles the case + // of 'at' being out of bounds of 'input.haystack()', we + // also need to handle the case of 'at' going out of bounds + // of the span the caller asked to search. + // + // We should perhaps make the 'trans.matches()' API accept + // an '&Input' instead of a '&[u8]'. Or at least, add a new + // API that does it. + if at >= input.end() { + return None; + } + if !trans.matches(input.haystack(), at) { + return None; + } + sid = trans.next; + at += 1; + } + State::Sparse(ref sparse) => { + if at >= input.end() { + return None; + } + sid = sparse.matches(input.haystack(), at)?; + at += 1; + } + State::Dense(ref dense) => { + if at >= input.end() { + return None; + } + sid = dense.matches(input.haystack(), at)?; + at += 1; + } + State::Look { look, next } => { + // OK because we don't permit building a searcher with a + // Unicode word boundary if the requisite Unicode data is + // unavailable. + if !self.nfa.look_matcher().matches_inline( + look, + input.haystack(), + at, + ) { + return None; + } + sid = next; + } + State::Union { ref alternates } => { + sid = match alternates.get(0) { + None => return None, + Some(&sid) => sid, + }; + cache.stack.extend( + alternates[1..] + .iter() + .copied() + .rev() + .map(|sid| Frame::Step { sid, at }), + ); + } + State::BinaryUnion { alt1, alt2 } => { + sid = alt1; + cache.stack.push(Frame::Step { sid: alt2, at }); + } + State::Capture { next, slot, .. } => { + if slot.as_usize() < slots.len() { + cache.stack.push(Frame::RestoreCapture { + slot, + offset: slots[slot], + }); + slots[slot] = NonMaxUsize::new(at); + } + sid = next; + } + State::Fail => return None, + State::Match { pattern_id } => { + return Some(HalfMatch::new(pattern_id, at)); + } + } + } + } +} + +/// An iterator over all non-overlapping matches for a fallible search. +/// +/// The iterator yields a `Result<Match, MatchError` value until no more +/// matches could be found. +/// +/// The lifetime parameters are as follows: +/// +/// * `'r` represents the lifetime of the BoundedBacktracker. +/// * `'c` represents the lifetime of the BoundedBacktracker's cache. +/// * `'h` represents the lifetime of the haystack being searched. +/// +/// This iterator can be created with the [`BoundedBacktracker::try_find_iter`] +/// method. +#[derive(Debug)] +pub struct TryFindMatches<'r, 'c, 'h> { + re: &'r BoundedBacktracker, + cache: &'c mut Cache, + caps: Captures, + it: iter::Searcher<'h>, +} + +impl<'r, 'c, 'h> Iterator for TryFindMatches<'r, 'c, 'h> { + type Item = Result<Match, MatchError>; + + #[inline] + fn next(&mut self) -> Option<Result<Match, MatchError>> { + // Splitting 'self' apart seems necessary to appease borrowck. + let TryFindMatches { re, ref mut cache, ref mut caps, ref mut it } = + *self; + it.try_advance(|input| { + re.try_search(cache, input, caps)?; + Ok(caps.get_match()) + }) + .transpose() + } +} + +/// An iterator over all non-overlapping leftmost matches, with their capturing +/// groups, for a fallible search. +/// +/// The iterator yields a `Result<Captures, MatchError>` value until no more +/// matches could be found. +/// +/// The lifetime parameters are as follows: +/// +/// * `'r` represents the lifetime of the BoundedBacktracker. +/// * `'c` represents the lifetime of the BoundedBacktracker's cache. +/// * `'h` represents the lifetime of the haystack being searched. +/// +/// This iterator can be created with the +/// [`BoundedBacktracker::try_captures_iter`] method. +#[derive(Debug)] +pub struct TryCapturesMatches<'r, 'c, 'h> { + re: &'r BoundedBacktracker, + cache: &'c mut Cache, + caps: Captures, + it: iter::Searcher<'h>, +} + +impl<'r, 'c, 'h> Iterator for TryCapturesMatches<'r, 'c, 'h> { + type Item = Result<Captures, MatchError>; + + #[inline] + fn next(&mut self) -> Option<Result<Captures, MatchError>> { + // Splitting 'self' apart seems necessary to appease borrowck. + let TryCapturesMatches { re, ref mut cache, ref mut caps, ref mut it } = + *self; + let _ = it + .try_advance(|input| { + re.try_search(cache, input, caps)?; + Ok(caps.get_match()) + }) + .transpose()?; + if caps.is_match() { + Some(Ok(caps.clone())) + } else { + None + } + } +} + +/// A cache represents mutable state that a [`BoundedBacktracker`] requires +/// during a search. +/// +/// For a given [`BoundedBacktracker`], its corresponding cache may be created +/// either via [`BoundedBacktracker::create_cache`], or via [`Cache::new`]. +/// They are equivalent in every way, except the former does not require +/// explicitly importing `Cache`. +/// +/// A particular `Cache` is coupled with the [`BoundedBacktracker`] from which +/// it was created. It may only be used with that `BoundedBacktracker`. A cache +/// and its allocations may be re-purposed via [`Cache::reset`], in which case, +/// it can only be used with the new `BoundedBacktracker` (and not the old +/// one). +#[derive(Clone, Debug)] +pub struct Cache { + /// Stack used on the heap for doing backtracking instead of the + /// traditional recursive approach. We don't want recursion because then + /// we're likely to hit a stack overflow for bigger regexes. + stack: Vec<Frame>, + /// The set of (StateID, HaystackOffset) pairs that have been visited + /// by the backtracker within a single search. If such a pair has been + /// visited, then we avoid doing the work for that pair again. This is + /// what "bounds" the backtracking and prevents it from having worst case + /// exponential time. + visited: Visited, +} + +impl Cache { + /// Create a new [`BoundedBacktracker`] cache. + /// + /// A potentially more convenient routine to create a cache is + /// [`BoundedBacktracker::create_cache`], as it does not require also + /// importing the `Cache` type. + /// + /// If you want to reuse the returned `Cache` with some other + /// `BoundedBacktracker`, then you must call [`Cache::reset`] with the + /// desired `BoundedBacktracker`. + pub fn new(re: &BoundedBacktracker) -> Cache { + Cache { stack: vec![], visited: Visited::new(re) } + } + + /// Reset this cache such that it can be used for searching with different + /// [`BoundedBacktracker`]. + /// + /// A cache reset permits reusing memory already allocated in this cache + /// with a different `BoundedBacktracker`. + /// + /// # Example + /// + /// This shows how to re-purpose a cache for use with a different + /// `BoundedBacktracker`. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// nfa::thompson::backtrack::BoundedBacktracker, + /// Match, + /// }; + /// + /// let re1 = BoundedBacktracker::new(r"\w")?; + /// let re2 = BoundedBacktracker::new(r"\W")?; + /// + /// let mut cache = re1.create_cache(); + /// assert_eq!( + /// Some(Ok(Match::must(0, 0..2))), + /// re1.try_find_iter(&mut cache, "Δ").next(), + /// ); + /// + /// // 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 BoundedBacktracker 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(Ok(Match::must(0, 0..3))), + /// re2.try_find_iter(&mut cache, "☃").next(), + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn reset(&mut self, re: &BoundedBacktracker) { + self.visited.reset(re); + } + + /// Returns the heap memory usage, in bytes, of this cache. + /// + /// 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.stack.len() * core::mem::size_of::<Frame>() + + self.visited.memory_usage() + } + + /// Clears this cache. This should be called at the start of every search + /// to ensure we start with a clean slate. + /// + /// This also sets the length of the capturing groups used in the current + /// search. This permits an optimization where by 'SlotTable::for_state' + /// only returns the number of slots equivalent to the number of slots + /// given in the 'Captures' value. This may be less than the total number + /// of possible slots, e.g., when one only wants to track overall match + /// offsets. This in turn permits less copying of capturing group spans + /// in the BoundedBacktracker. + fn setup_search( + &mut self, + re: &BoundedBacktracker, + input: &Input<'_>, + ) -> Result<(), MatchError> { + self.stack.clear(); + self.visited.setup_search(re, input)?; + Ok(()) + } +} + +/// Represents a stack frame on the heap while doing backtracking. +/// +/// Instead of using explicit recursion for backtracking, we use a stack on +/// the heap to keep track of things that we want to explore if the current +/// backtracking branch turns out to not lead to a match. +#[derive(Clone, Debug)] +enum Frame { + /// Look for a match starting at `sid` and the given position in the + /// haystack. + Step { sid: StateID, at: usize }, + /// Reset the given `slot` to the given `offset` (which might be `None`). + /// This effectively gives a "scope" to capturing groups, such that an + /// offset for a particular group only gets returned if the match goes + /// through that capturing group. If backtracking ends up going down a + /// different branch that results in a different offset (or perhaps none at + /// all), then this "restore capture" frame will cause the offset to get + /// reset. + RestoreCapture { slot: SmallIndex, offset: Option<NonMaxUsize> }, +} + +/// A bitset that keeps track of whether a particular (StateID, offset) has +/// been considered during backtracking. If it has already been visited, then +/// backtracking skips it. This is what gives backtracking its "bound." +#[derive(Clone, Debug)] +struct Visited { + /// The actual underlying bitset. Each element in the bitset corresponds + /// to a particular (StateID, offset) pair. States correspond to the rows + /// and the offsets correspond to the columns. + /// + /// If our underlying NFA has N states and the haystack we're searching + /// has M bytes, then we have N*(M+1) entries in our bitset table. The + /// M+1 occurs because our matches are delayed by one byte (to support + /// look-around), and so we need to handle the end position itself rather + /// than stopping just before the end. (If there is no end position, then + /// it's treated as "end-of-input," which is matched by things like '$'.) + /// + /// Given BITS=N*(M+1), we wind up with div_ceil(BITS, sizeof(usize)) + /// blocks. + /// + /// We use 'usize' to represent our blocks because it makes some of the + /// arithmetic in 'insert' a bit nicer. For example, if we used 'u32' for + /// our block, we'd either need to cast u32s to usizes or usizes to u32s. + bitset: Vec<usize>, + /// The stride represents one plus length of the haystack we're searching + /// (as described above). The stride must be initialized for each search. + stride: usize, +} + +impl Visited { + /// The size of each block, in bits. + const BLOCK_SIZE: usize = 8 * core::mem::size_of::<usize>(); + + /// Create a new visited set for the given backtracker. + /// + /// The set is ready to use, but must be setup at the beginning of each + /// search by calling `setup_search`. + fn new(re: &BoundedBacktracker) -> Visited { + let mut visited = Visited { bitset: vec![], stride: 0 }; + visited.reset(re); + visited + } + + /// Insert the given (StateID, offset) pair into this set. If it already + /// exists, then this is a no-op and it returns false. Otherwise this + /// returns true. + fn insert(&mut self, sid: StateID, at: usize) -> bool { + let table_index = sid.as_usize() * self.stride + at; + let block_index = table_index / Visited::BLOCK_SIZE; + let bit = table_index % Visited::BLOCK_SIZE; + let block_with_bit = 1 << bit; + if self.bitset[block_index] & block_with_bit != 0 { + return false; + } + self.bitset[block_index] |= block_with_bit; + true + } + + /// Reset this visited set to work with the given bounded backtracker. + fn reset(&mut self, _: &BoundedBacktracker) { + self.bitset.truncate(0); + } + + /// Setup this visited set to work for a search using the given NFA + /// and input configuration. The NFA must be the same NFA used by the + /// BoundedBacktracker given to Visited::reset. Failing to call this might + /// result in panics or silently incorrect search behavior. + fn setup_search( + &mut self, + re: &BoundedBacktracker, + input: &Input<'_>, + ) -> Result<(), MatchError> { + // Our haystack length is only the length of the span of the entire + // haystack that we'll be searching. + let haylen = input.get_span().len(); + let err = || MatchError::haystack_too_long(haylen); + // Our stride is one more than the length of the input because our main + // search loop includes the position at input.end(). (And it does this + // because matches are delayed by one byte to account for look-around.) + self.stride = haylen + 1; + let needed_capacity = + match re.get_nfa().states().len().checked_mul(self.stride) { + None => return Err(err()), + Some(capacity) => capacity, + }; + let max_capacity = 8 * re.get_config().get_visited_capacity(); + if needed_capacity > max_capacity { + return Err(err()); + } + let needed_blocks = div_ceil(needed_capacity, Visited::BLOCK_SIZE); + self.bitset.truncate(needed_blocks); + for block in self.bitset.iter_mut() { + *block = 0; + } + if needed_blocks > self.bitset.len() { + self.bitset.resize(needed_blocks, 0); + } + Ok(()) + } + + /// Return the heap memory usage, in bytes, of this visited set. + fn memory_usage(&self) -> usize { + self.bitset.len() * core::mem::size_of::<usize>() + } +} + +/// Integer division, but rounds up instead of down. +fn div_ceil(lhs: usize, rhs: usize) -> usize { + if lhs % rhs == 0 { + lhs / rhs + } else { + (lhs / rhs) + 1 + } +} |