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Diffstat (limited to 'third_party/rust/regex-automata/src/nfa/thompson/nfa.rs')
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diff --git a/third_party/rust/regex-automata/src/nfa/thompson/nfa.rs b/third_party/rust/regex-automata/src/nfa/thompson/nfa.rs new file mode 100644 index 0000000000..2108fa3381 --- /dev/null +++ b/third_party/rust/regex-automata/src/nfa/thompson/nfa.rs @@ -0,0 +1,2101 @@ +use core::{fmt, mem}; + +use alloc::{boxed::Box, format, string::String, sync::Arc, vec, vec::Vec}; + +#[cfg(feature = "syntax")] +use crate::nfa::thompson::{ + compiler::{Compiler, Config}, + error::BuildError, +}; +use crate::{ + nfa::thompson::builder::Builder, + util::{ + alphabet::{self, ByteClassSet, ByteClasses}, + captures::{GroupInfo, GroupInfoError}, + look::{Look, LookMatcher, LookSet}, + primitives::{ + IteratorIndexExt, PatternID, PatternIDIter, SmallIndex, StateID, + }, + sparse_set::SparseSet, + }, +}; + +/// A byte oriented Thompson non-deterministic finite automaton (NFA). +/// +/// A Thompson NFA is a finite state machine that permits unconditional epsilon +/// transitions, but guarantees that there exists at most one non-epsilon +/// transition for each element in the alphabet for each state. +/// +/// An NFA may be used directly for searching, for analysis or to build +/// a deterministic finite automaton (DFA). +/// +/// # Cheap clones +/// +/// Since an NFA is a core data type in this crate that many other regex +/// engines are based on top of, it is convenient to give ownership of an NFA +/// to said regex engines. Because of this, an NFA uses reference counting +/// internally. Therefore, it is cheap to clone and it is encouraged to do so. +/// +/// # Capabilities +/// +/// Using an NFA for searching via the +/// [`PikeVM`](crate::nfa::thompson::pikevm::PikeVM) provides the most amount +/// of "power" of any regex engine in this crate. Namely, it supports the +/// following in all cases: +/// +/// 1. Detection of a match. +/// 2. Location of a match, including both the start and end offset, in a +/// single pass of the haystack. +/// 3. Location of matching capturing groups. +/// 4. Handles multiple patterns, including (1)-(3) when multiple patterns are +/// present. +/// +/// # Capturing Groups +/// +/// Groups refer to parenthesized expressions inside a regex pattern. They look +/// like this, where `exp` is an arbitrary regex: +/// +/// * `(exp)` - An unnamed capturing group. +/// * `(?P<name>exp)` or `(?<name>exp)` - A named capturing group. +/// * `(?:exp)` - A non-capturing group. +/// * `(?i:exp)` - A non-capturing group that sets flags. +/// +/// Only the first two forms are said to be _capturing_. Capturing +/// means that the last position at which they match is reportable. The +/// [`Captures`](crate::util::captures::Captures) type provides convenient +/// access to the match positions of capturing groups, which includes looking +/// up capturing groups by their name. +/// +/// # Byte oriented +/// +/// This NFA is byte oriented, which means that all of its transitions are +/// defined on bytes. In other words, the alphabet of an NFA consists of the +/// 256 different byte values. +/// +/// While DFAs nearly demand that they be byte oriented for performance +/// reasons, an NFA could conceivably be *Unicode codepoint* oriented. Indeed, +/// a previous version of this NFA supported both byte and codepoint oriented +/// modes. A codepoint oriented mode can work because an NFA fundamentally uses +/// a sparse representation of transitions, which works well with the large +/// sparse space of Unicode codepoints. +/// +/// Nevertheless, this NFA is only byte oriented. This choice is primarily +/// driven by implementation simplicity, and also in part memory usage. In +/// practice, performance between the two is roughly comparable. However, +/// building a DFA (including a hybrid DFA) really wants a byte oriented NFA. +/// So if we do have a codepoint oriented NFA, then we also need to generate +/// byte oriented NFA in order to build an hybrid NFA/DFA. Thus, by only +/// generating byte oriented NFAs, we can produce one less NFA. In other words, +/// if we made our NFA codepoint oriented, we'd need to *also* make it support +/// a byte oriented mode, which is more complicated. But a byte oriented mode +/// can support everything. +/// +/// # Differences with DFAs +/// +/// At the theoretical level, the precise difference between an NFA and a DFA +/// is that, in a DFA, for every state, an input symbol unambiguously refers +/// to a single transition _and_ that an input symbol is required for each +/// transition. At a practical level, this permits DFA implementations to be +/// implemented at their core with a small constant number of CPU instructions +/// for each byte of input searched. In practice, this makes them quite a bit +/// faster than NFAs _in general_. Namely, in order to execute a search for any +/// Thompson NFA, one needs to keep track of a _set_ of states, and execute +/// the possible transitions on all of those states for each input symbol. +/// Overall, this results in much more overhead. To a first approximation, one +/// can expect DFA searches to be about an order of magnitude faster. +/// +/// So why use an NFA at all? The main advantage of an NFA is that it takes +/// linear time (in the size of the pattern string after repetitions have been +/// expanded) to build and linear memory usage. A DFA, on the other hand, may +/// take exponential time and/or space to build. Even in non-pathological +/// cases, DFAs often take quite a bit more memory than their NFA counterparts, +/// _especially_ if large Unicode character classes are involved. Of course, +/// an NFA also provides additional capabilities. For example, it can match +/// Unicode word boundaries on non-ASCII text and resolve the positions of +/// capturing groups. +/// +/// Note that a [`hybrid::regex::Regex`](crate::hybrid::regex::Regex) strikes a +/// good balance between an NFA and a DFA. It avoids the exponential build time +/// of a DFA while maintaining its fast search time. The downside of a hybrid +/// NFA/DFA is that in some cases it can be slower at search time than the NFA. +/// (It also has less functionality than a pure NFA. It cannot handle Unicode +/// word boundaries on non-ASCII text and cannot resolve capturing groups.) +/// +/// # Example +/// +/// This shows how to build an NFA with the default configuration and execute a +/// search using the Pike VM. +/// +/// ``` +/// use regex_automata::{nfa::thompson::pikevm::PikeVM, Match}; +/// +/// let re = PikeVM::new(r"foo[0-9]+")?; +/// let mut cache = re.create_cache(); +/// let mut caps = re.create_captures(); +/// +/// let expected = Some(Match::must(0, 0..8)); +/// re.captures(&mut cache, b"foo12345", &mut caps); +/// assert_eq!(expected, caps.get_match()); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +/// +/// # Example: resolving capturing groups +/// +/// This example shows how to parse some simple dates and extract the +/// components of each date via capturing groups. +/// +/// ``` +/// # if cfg!(miri) { return Ok(()); } // miri takes too long +/// use regex_automata::{ +/// nfa::thompson::pikevm::PikeVM, +/// util::captures::Captures, +/// }; +/// +/// let vm = PikeVM::new(r"(?P<y>\d{4})-(?P<m>\d{2})-(?P<d>\d{2})")?; +/// let mut cache = vm.create_cache(); +/// +/// let haystack = "2012-03-14, 2013-01-01 and 2014-07-05"; +/// let all: Vec<Captures> = vm.captures_iter( +/// &mut cache, haystack.as_bytes() +/// ).collect(); +/// // There should be a total of 3 matches. +/// assert_eq!(3, all.len()); +/// // The year from the second match is '2013'. +/// let span = all[1].get_group_by_name("y").unwrap(); +/// assert_eq!("2013", &haystack[span]); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +/// +/// This example shows that only the last match of a capturing group is +/// reported, even if it had to match multiple times for an overall match +/// to occur. +/// +/// ``` +/// use regex_automata::{nfa::thompson::pikevm::PikeVM, Span}; +/// +/// let re = PikeVM::new(r"([a-z]){4}")?; +/// let mut cache = re.create_cache(); +/// let mut caps = re.create_captures(); +/// +/// let haystack = b"quux"; +/// re.captures(&mut cache, haystack, &mut caps); +/// assert!(caps.is_match()); +/// assert_eq!(Some(Span::from(3..4)), caps.get_group(1)); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone)] +pub struct NFA( + // We make NFAs reference counted primarily for two reasons. First is that + // the NFA type itself is quite large (at least 0.5KB), and so it makes + // sense to put it on the heap by default anyway. Second is that, for Arc + // specifically, this enables cheap clones. This tends to be useful because + // several structures (the backtracker, the Pike VM, the hybrid NFA/DFA) + // all want to hang on to an NFA for use during search time. We could + // provide the NFA at search time via a function argument, but this makes + // for an unnecessarily annoying API. Instead, we just let each structure + // share ownership of the NFA. Using a deep clone would not be smart, since + // the NFA can use quite a bit of heap space. + Arc<Inner>, +); + +impl NFA { + /// Parse the given regular expression using a default configuration and + /// build an NFA from it. + /// + /// If you want a non-default configuration, then use the NFA + /// [`Compiler`] with a [`Config`]. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{nfa::thompson::pikevm::PikeVM, Match}; + /// + /// let re = PikeVM::new(r"foo[0-9]+")?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// let expected = Some(Match::must(0, 0..8)); + /// re.captures(&mut cache, b"foo12345", &mut caps); + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new(pattern: &str) -> Result<NFA, BuildError> { + NFA::compiler().build(pattern) + } + + /// Parse the given regular expressions using a default configuration and + /// build a multi-NFA from them. + /// + /// If you want a non-default configuration, then use the NFA + /// [`Compiler`] with a [`Config`]. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{nfa::thompson::pikevm::PikeVM, Match}; + /// + /// let re = PikeVM::new_many(&["[0-9]+", "[a-z]+"])?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// let expected = Some(Match::must(1, 0..3)); + /// re.captures(&mut cache, b"foo12345bar", &mut caps); + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new_many<P: AsRef<str>>(patterns: &[P]) -> Result<NFA, BuildError> { + NFA::compiler().build_many(patterns) + } + + /// Returns an NFA with a single regex pattern that always matches at every + /// position. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{nfa::thompson::{NFA, pikevm::PikeVM}, Match}; + /// + /// let re = PikeVM::new_from_nfa(NFA::always_match())?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// let expected = Some(Match::must(0, 0..0)); + /// re.captures(&mut cache, b"", &mut caps); + /// assert_eq!(expected, caps.get_match()); + /// re.captures(&mut cache, b"foo", &mut caps); + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn always_match() -> NFA { + // We could use NFA::new("") here and we'd get the same semantics, but + // hand-assembling the NFA (as below) does the same thing with a fewer + // number of states. It also avoids needing the 'syntax' feature + // enabled. + // + // Technically all we need is the "match" state, but we add the + // "capture" states so that the PikeVM can use this NFA. + // + // The unwraps below are OK because we add so few states that they will + // never exhaust any default limits in any environment. + let mut builder = Builder::new(); + let pid = builder.start_pattern().unwrap(); + assert_eq!(pid.as_usize(), 0); + let start_id = + builder.add_capture_start(StateID::ZERO, 0, None).unwrap(); + let end_id = builder.add_capture_end(StateID::ZERO, 0).unwrap(); + let match_id = builder.add_match().unwrap(); + builder.patch(start_id, end_id).unwrap(); + builder.patch(end_id, match_id).unwrap(); + let pid = builder.finish_pattern(start_id).unwrap(); + assert_eq!(pid.as_usize(), 0); + builder.build(start_id, start_id).unwrap() + } + + /// Returns an NFA that never matches at any position. + /// + /// This is a convenience routine for creating an NFA with zero patterns. + /// + /// # Example + /// + /// ``` + /// use regex_automata::nfa::thompson::{NFA, pikevm::PikeVM}; + /// + /// let re = PikeVM::new_from_nfa(NFA::never_match())?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// re.captures(&mut cache, b"", &mut caps); + /// assert!(!caps.is_match()); + /// re.captures(&mut cache, b"foo", &mut caps); + /// assert!(!caps.is_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn never_match() -> NFA { + // This always succeeds because it only requires one NFA state, which + // will never exhaust any (default) limits. + let mut builder = Builder::new(); + let sid = builder.add_fail().unwrap(); + builder.build(sid, sid).unwrap() + } + + /// Return a default configuration for an `NFA`. + /// + /// This is a convenience routine to avoid needing to import the `Config` + /// type when customizing the construction of an NFA. + /// + /// # Example + /// + /// This example shows how to build an NFA with a small size limit that + /// results in a compilation error for any regex that tries to use more + /// heap memory than the configured limit. + /// + /// ``` + /// use regex_automata::nfa::thompson::{NFA, pikevm::PikeVM}; + /// + /// let result = PikeVM::builder() + /// .thompson(NFA::config().nfa_size_limit(Some(1_000))) + /// // Remember, \w is Unicode-aware by default and thus huge. + /// .build(r"\w+"); + /// assert!(result.is_err()); + /// ``` + #[cfg(feature = "syntax")] + pub fn config() -> Config { + Config::new() + } + + /// Return a compiler for configuring the construction of an `NFA`. + /// + /// This is a convenience routine to avoid needing to import the + /// [`Compiler`] type in common cases. + /// + /// # Example + /// + /// This example shows how to build an NFA that is permitted match invalid + /// UTF-8. Without the additional syntax configuration here, compilation of + /// `(?-u:.)` would fail because it is permitted to match invalid UTF-8. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::pikevm::PikeVM, + /// util::syntax, + /// Match, + /// }; + /// + /// let re = PikeVM::builder() + /// .syntax(syntax::Config::new().utf8(false)) + /// .build(r"[a-z]+(?-u:.)")?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// let expected = Some(Match::must(0, 1..5)); + /// re.captures(&mut cache, b"\xFFabc\xFF", &mut caps); + /// assert_eq!(expected, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn compiler() -> Compiler { + Compiler::new() + } + + /// Returns an iterator over all pattern identifiers in this NFA. + /// + /// Pattern IDs are allocated in sequential order starting from zero, + /// where the order corresponds to the order of patterns provided to the + /// [`NFA::new_many`] constructor. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, PatternID}; + /// + /// let nfa = NFA::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?; + /// let pids: Vec<PatternID> = nfa.patterns().collect(); + /// assert_eq!(pids, vec![ + /// PatternID::must(0), + /// PatternID::must(1), + /// PatternID::must(2), + /// ]); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn patterns(&self) -> PatternIter<'_> { + PatternIter { + it: PatternID::iter(self.pattern_len()), + _marker: core::marker::PhantomData, + } + } + + /// Returns the total number of regex patterns in this NFA. + /// + /// This may return zero if the NFA was constructed with no patterns. In + /// this case, the NFA can never produce a match for any input. + /// + /// This is guaranteed to be no bigger than [`PatternID::LIMIT`] because + /// NFA construction will fail if too many patterns are added. + /// + /// It is always true that `nfa.patterns().count() == nfa.pattern_len()`. + /// + /// # Example + /// + /// ``` + /// use regex_automata::nfa::thompson::NFA; + /// + /// let nfa = NFA::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?; + /// assert_eq!(3, nfa.pattern_len()); + /// + /// let nfa = NFA::never_match(); + /// assert_eq!(0, nfa.pattern_len()); + /// + /// let nfa = NFA::always_match(); + /// assert_eq!(1, nfa.pattern_len()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn pattern_len(&self) -> usize { + self.0.start_pattern.len() + } + + /// Return the state identifier of the initial anchored state of this NFA. + /// + /// The returned identifier is guaranteed to be a valid index into the + /// slice returned by [`NFA::states`], and is also a valid argument to + /// [`NFA::state`]. + /// + /// # Example + /// + /// This example shows a somewhat contrived example where we can easily + /// predict the anchored starting state. + /// + /// ``` + /// use regex_automata::nfa::thompson::{NFA, State, WhichCaptures}; + /// + /// let nfa = NFA::compiler() + /// .configure(NFA::config().which_captures(WhichCaptures::None)) + /// .build("a")?; + /// let state = nfa.state(nfa.start_anchored()); + /// match *state { + /// State::ByteRange { trans } => { + /// assert_eq!(b'a', trans.start); + /// assert_eq!(b'a', trans.end); + /// } + /// _ => unreachable!("unexpected state"), + /// } + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn start_anchored(&self) -> StateID { + self.0.start_anchored + } + + /// Return the state identifier of the initial unanchored state of this + /// NFA. + /// + /// This is equivalent to the identifier returned by + /// [`NFA::start_anchored`] when the NFA has no unanchored starting state. + /// + /// The returned identifier is guaranteed to be a valid index into the + /// slice returned by [`NFA::states`], and is also a valid argument to + /// [`NFA::state`]. + /// + /// # Example + /// + /// This example shows that the anchored and unanchored starting states + /// are equivalent when an anchored NFA is built. + /// + /// ``` + /// use regex_automata::nfa::thompson::NFA; + /// + /// let nfa = NFA::new("^a")?; + /// assert_eq!(nfa.start_anchored(), nfa.start_unanchored()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn start_unanchored(&self) -> StateID { + self.0.start_unanchored + } + + /// Return the state identifier of the initial anchored state for the given + /// pattern, or `None` if there is no pattern corresponding to the given + /// identifier. + /// + /// If one uses the starting state for a particular pattern, then the only + /// match that can be returned is for the corresponding pattern. + /// + /// The returned identifier is guaranteed to be a valid index into the + /// slice returned by [`NFA::states`], and is also a valid argument to + /// [`NFA::state`]. + /// + /// # Errors + /// + /// If the pattern doesn't exist in this NFA, then this returns an error. + /// This occurs when `pid.as_usize() >= nfa.pattern_len()`. + /// + /// # Example + /// + /// This example shows that the anchored and unanchored starting states + /// are equivalent when an anchored NFA is built. + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, PatternID}; + /// + /// let nfa = NFA::new_many(&["^a", "^b"])?; + /// // The anchored and unanchored states for the entire NFA are the same, + /// // since all of the patterns are anchored. + /// assert_eq!(nfa.start_anchored(), nfa.start_unanchored()); + /// // But the anchored starting states for each pattern are distinct, + /// // because these starting states can only lead to matches for the + /// // corresponding pattern. + /// let anchored = Some(nfa.start_anchored()); + /// assert_ne!(anchored, nfa.start_pattern(PatternID::must(0))); + /// assert_ne!(anchored, nfa.start_pattern(PatternID::must(1))); + /// // Requesting a pattern not in the NFA will result in None: + /// assert_eq!(None, nfa.start_pattern(PatternID::must(2))); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn start_pattern(&self, pid: PatternID) -> Option<StateID> { + self.0.start_pattern.get(pid.as_usize()).copied() + } + + /// Get the byte class set for this NFA. + /// + /// A byte class set is a partitioning of this NFA's alphabet into + /// equivalence classes. Any two bytes in the same equivalence class are + /// guaranteed to never discriminate between a match or a non-match. (The + /// partitioning may not be minimal.) + /// + /// Byte classes are used internally by this crate when building DFAs. + /// Namely, among other optimizations, they enable a space optimization + /// where the DFA's internal alphabet is defined over the equivalence + /// classes of bytes instead of all possible byte values. The former is + /// often quite a bit smaller than the latter, which permits the DFA to use + /// less space for its transition table. + #[inline] + pub(crate) fn byte_class_set(&self) -> &ByteClassSet { + &self.0.byte_class_set + } + + /// Get the byte classes for this NFA. + /// + /// Byte classes represent a partitioning of this NFA's alphabet into + /// equivalence classes. Any two bytes in the same equivalence class are + /// guaranteed to never discriminate between a match or a non-match. (The + /// partitioning may not be minimal.) + /// + /// Byte classes are used internally by this crate when building DFAs. + /// Namely, among other optimizations, they enable a space optimization + /// where the DFA's internal alphabet is defined over the equivalence + /// classes of bytes instead of all possible byte values. The former is + /// often quite a bit smaller than the latter, which permits the DFA to use + /// less space for its transition table. + /// + /// # Example + /// + /// This example shows how to query the class of various bytes. + /// + /// ``` + /// use regex_automata::nfa::thompson::NFA; + /// + /// let nfa = NFA::new("[a-z]+")?; + /// let classes = nfa.byte_classes(); + /// // 'a' and 'z' are in the same class for this regex. + /// assert_eq!(classes.get(b'a'), classes.get(b'z')); + /// // But 'a' and 'A' are not. + /// assert_ne!(classes.get(b'a'), classes.get(b'A')); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn byte_classes(&self) -> &ByteClasses { + &self.0.byte_classes + } + + /// Return a reference to the NFA state corresponding to the given ID. + /// + /// This is a convenience routine for `nfa.states()[id]`. + /// + /// # Panics + /// + /// This panics when the given identifier does not reference a valid state. + /// That is, when `id.as_usize() >= nfa.states().len()`. + /// + /// # Example + /// + /// The anchored state for a pattern will typically correspond to a + /// capturing state for that pattern. (Although, this is not an API + /// guarantee!) + /// + /// ``` + /// use regex_automata::{nfa::thompson::{NFA, State}, PatternID}; + /// + /// let nfa = NFA::new("a")?; + /// let state = nfa.state(nfa.start_pattern(PatternID::ZERO).unwrap()); + /// match *state { + /// State::Capture { slot, .. } => { + /// assert_eq!(0, slot.as_usize()); + /// } + /// _ => unreachable!("unexpected state"), + /// } + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn state(&self, id: StateID) -> &State { + &self.states()[id] + } + + /// Returns a slice of all states in this NFA. + /// + /// The slice returned is indexed by `StateID`. This provides a convenient + /// way to access states while following transitions among those states. + /// + /// # Example + /// + /// This demonstrates that disabling UTF-8 mode can shrink the size of the + /// NFA considerably in some cases, especially when using Unicode character + /// classes. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::nfa::thompson::NFA; + /// + /// let nfa_unicode = NFA::new(r"\w")?; + /// let nfa_ascii = NFA::new(r"(?-u)\w")?; + /// // Yes, a factor of 45 difference. No lie. + /// assert!(40 * nfa_ascii.states().len() < nfa_unicode.states().len()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn states(&self) -> &[State] { + &self.0.states + } + + /// Returns the capturing group info for this NFA. + /// + /// The [`GroupInfo`] provides a way to map to and from capture index + /// and capture name for each pattern. It also provides a mapping from + /// each of the capturing groups in every pattern to their corresponding + /// slot offsets encoded in [`State::Capture`] states. + /// + /// Note that `GroupInfo` uses reference counting internally, such that + /// cloning a `GroupInfo` is very cheap. + /// + /// # Example + /// + /// This example shows how to get a list of all capture group names for + /// a particular pattern. + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, PatternID}; + /// + /// let nfa = NFA::new(r"(a)(?P<foo>b)(c)(d)(?P<bar>e)")?; + /// // The first is the implicit group that is always unnammed. The next + /// // 5 groups are the explicit groups found in the concrete syntax above. + /// let expected = vec![None, None, Some("foo"), None, None, Some("bar")]; + /// let got: Vec<Option<&str>> = + /// nfa.group_info().pattern_names(PatternID::ZERO).collect(); + /// assert_eq!(expected, got); + /// + /// // Using an invalid pattern ID will result in nothing yielded. + /// let got = nfa.group_info().pattern_names(PatternID::must(999)).count(); + /// assert_eq!(0, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn group_info(&self) -> &GroupInfo { + &self.0.group_info() + } + + /// Returns true if and only if this NFA has at least one + /// [`Capture`](State::Capture) in its sequence of states. + /// + /// This is useful as a way to perform a quick test before attempting + /// something that does or does not require capture states. For example, + /// some regex engines (like the PikeVM) require capture states in order to + /// work at all. + /// + /// # Example + /// + /// This example shows a few different NFAs and whether they have captures + /// or not. + /// + /// ``` + /// use regex_automata::nfa::thompson::{NFA, WhichCaptures}; + /// + /// // Obviously has capture states. + /// let nfa = NFA::new("(a)")?; + /// assert!(nfa.has_capture()); + /// + /// // Less obviously has capture states, because every pattern has at + /// // least one anonymous capture group corresponding to the match for the + /// // entire pattern. + /// let nfa = NFA::new("a")?; + /// assert!(nfa.has_capture()); + /// + /// // Other than hand building your own NFA, this is the only way to build + /// // an NFA without capturing groups. In general, you should only do this + /// // if you don't intend to use any of the NFA-oriented regex engines. + /// // Overall, capturing groups don't have many downsides. Although they + /// // can add a bit of noise to simple NFAs, so it can be nice to disable + /// // them for debugging purposes. + /// // + /// // Notice that 'has_capture' is false here even when we have an + /// // explicit capture group in the pattern. + /// let nfa = NFA::compiler() + /// .configure(NFA::config().which_captures(WhichCaptures::None)) + /// .build("(a)")?; + /// assert!(!nfa.has_capture()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn has_capture(&self) -> bool { + self.0.has_capture + } + + /// Returns true if and only if this NFA can match the empty string. + /// When it returns false, all possible matches are guaranteed to have a + /// non-zero length. + /// + /// This is useful as cheap way to know whether code needs to handle the + /// case of a zero length match. This is particularly important when UTF-8 + /// modes are enabled, as when UTF-8 mode is enabled, empty matches that + /// split a codepoint must never be reported. This extra handling can + /// sometimes be costly, and since regexes matching an empty string are + /// somewhat rare, it can be beneficial to treat such regexes specially. + /// + /// # Example + /// + /// This example shows a few different NFAs and whether they match the + /// empty string or not. Notice the empty string isn't merely a matter + /// of a string of length literally `0`, but rather, whether a match can + /// occur between specific pairs of bytes. + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::syntax}; + /// + /// // The empty regex matches the empty string. + /// let nfa = NFA::new("")?; + /// assert!(nfa.has_empty(), "empty matches empty"); + /// // The '+' repetition operator requires at least one match, and so + /// // does not match the empty string. + /// let nfa = NFA::new("a+")?; + /// assert!(!nfa.has_empty(), "+ does not match empty"); + /// // But the '*' repetition operator does. + /// let nfa = NFA::new("a*")?; + /// assert!(nfa.has_empty(), "* does match empty"); + /// // And wrapping '+' in an operator that can match an empty string also + /// // causes it to match the empty string too. + /// let nfa = NFA::new("(a+)*")?; + /// assert!(nfa.has_empty(), "+ inside of * matches empty"); + /// + /// // If a regex is just made of a look-around assertion, even if the + /// // assertion requires some kind of non-empty string around it (such as + /// // \b), then it is still treated as if it matches the empty string. + /// // Namely, if a match occurs of just a look-around assertion, then the + /// // match returned is empty. + /// let nfa = NFA::compiler() + /// .syntax(syntax::Config::new().utf8(false)) + /// .build(r"^$\A\z\b\B(?-u:\b\B)")?; + /// assert!(nfa.has_empty(), "assertions match empty"); + /// // Even when an assertion is wrapped in a '+', it still matches the + /// // empty string. + /// let nfa = NFA::new(r"\b+")?; + /// assert!(nfa.has_empty(), "+ of an assertion matches empty"); + /// + /// // An alternation with even one branch that can match the empty string + /// // is also said to match the empty string overall. + /// let nfa = NFA::new("foo|(bar)?|quux")?; + /// assert!(nfa.has_empty(), "alternations can match empty"); + /// + /// // An NFA that matches nothing does not match the empty string. + /// let nfa = NFA::new("[a&&b]")?; + /// assert!(!nfa.has_empty(), "never matching means not matching empty"); + /// // But if it's wrapped in something that doesn't require a match at + /// // all, then it can match the empty string! + /// let nfa = NFA::new("[a&&b]*")?; + /// assert!(nfa.has_empty(), "* on never-match still matches empty"); + /// // Since a '+' requires a match, using it on something that can never + /// // match will itself produce a regex that can never match anything, + /// // and thus does not match the empty string. + /// let nfa = NFA::new("[a&&b]+")?; + /// assert!(!nfa.has_empty(), "+ on never-match still matches nothing"); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn has_empty(&self) -> bool { + self.0.has_empty + } + + /// Whether UTF-8 mode is enabled for this NFA or not. + /// + /// When UTF-8 mode is enabled, all matches reported by a regex engine + /// derived from this NFA are guaranteed to correspond to spans of valid + /// UTF-8. This includes zero-width matches. For example, the regex engine + /// must guarantee that the empty regex will not match at the positions + /// between code units in the UTF-8 encoding of a single codepoint. + /// + /// See [`Config::utf8`] for more information. + /// + /// This is enabled by default. + /// + /// # Example + /// + /// This example shows how UTF-8 mode can impact the match spans that may + /// be reported in certain cases. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::{self, pikevm::PikeVM}, + /// Match, Input, + /// }; + /// + /// let re = PikeVM::new("")?; + /// let (mut cache, mut caps) = (re.create_cache(), re.create_captures()); + /// + /// // UTF-8 mode is enabled by default. + /// let mut input = Input::new("☃"); + /// re.search(&mut cache, &input, &mut caps); + /// assert_eq!(Some(Match::must(0, 0..0)), caps.get_match()); + /// + /// // Even though an empty regex matches at 1..1, our next match is + /// // 3..3 because 1..1 and 2..2 split the snowman codepoint (which is + /// // three bytes long). + /// input.set_start(1); + /// re.search(&mut cache, &input, &mut caps); + /// assert_eq!(Some(Match::must(0, 3..3)), caps.get_match()); + /// + /// // But if we disable UTF-8, then we'll get matches at 1..1 and 2..2: + /// let re = PikeVM::builder() + /// .thompson(thompson::Config::new().utf8(false)) + /// .build("")?; + /// re.search(&mut cache, &input, &mut caps); + /// assert_eq!(Some(Match::must(0, 1..1)), caps.get_match()); + /// + /// input.set_start(2); + /// re.search(&mut cache, &input, &mut caps); + /// assert_eq!(Some(Match::must(0, 2..2)), caps.get_match()); + /// + /// input.set_start(3); + /// re.search(&mut cache, &input, &mut caps); + /// assert_eq!(Some(Match::must(0, 3..3)), caps.get_match()); + /// + /// input.set_start(4); + /// re.search(&mut cache, &input, &mut caps); + /// assert_eq!(None, caps.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn is_utf8(&self) -> bool { + self.0.utf8 + } + + /// Returns true when this NFA is meant to be matched in reverse. + /// + /// Generally speaking, when this is true, it means the NFA is supposed to + /// be used in conjunction with moving backwards through the haystack. That + /// is, from a higher memory address to a lower memory address. + /// + /// It is often the case that lower level routines dealing with an NFA + /// don't need to care about whether it is "meant" to be matched in reverse + /// or not. However, there are some specific cases where it matters. For + /// example, the implementation of CRLF-aware `^` and `$` line anchors + /// needs to know whether the search is in the forward or reverse + /// direction. In the forward direction, neither `^` nor `$` should match + /// when a `\r` has been seen previously and a `\n` is next. However, in + /// the reverse direction, neither `^` nor `$` should match when a `\n` + /// has been seen previously and a `\r` is next. This fundamentally changes + /// how the state machine is constructed, and thus needs to be altered + /// based on the direction of the search. + /// + /// This is automatically set when using a [`Compiler`] with a configuration + /// where [`Config::reverse`] is enabled. If you're building your own NFA + /// by hand via a [`Builder`] + #[inline] + pub fn is_reverse(&self) -> bool { + self.0.reverse + } + + /// Returns true if and only if all starting states for this NFA correspond + /// to the beginning of an anchored search. + /// + /// Typically, an NFA will have both an anchored and an unanchored starting + /// state. Namely, because it tends to be useful to have both and the cost + /// of having an unanchored starting state is almost zero (for an NFA). + /// However, if all patterns in the NFA are themselves anchored, then even + /// the unanchored starting state will correspond to an anchored search + /// since the pattern doesn't permit anything else. + /// + /// # Example + /// + /// This example shows a few different scenarios where this method's + /// return value varies. + /// + /// ``` + /// use regex_automata::nfa::thompson::NFA; + /// + /// // The unanchored starting state permits matching this pattern anywhere + /// // in a haystack, instead of just at the beginning. + /// let nfa = NFA::new("a")?; + /// assert!(!nfa.is_always_start_anchored()); + /// + /// // In this case, the pattern is itself anchored, so there is no way + /// // to run an unanchored search. + /// let nfa = NFA::new("^a")?; + /// assert!(nfa.is_always_start_anchored()); + /// + /// // When multiline mode is enabled, '^' can match at the start of a line + /// // in addition to the start of a haystack, so an unanchored search is + /// // actually possible. + /// let nfa = NFA::new("(?m)^a")?; + /// assert!(!nfa.is_always_start_anchored()); + /// + /// // Weird cases also work. A pattern is only considered anchored if all + /// // matches may only occur at the start of a haystack. + /// let nfa = NFA::new("(^a)|a")?; + /// assert!(!nfa.is_always_start_anchored()); + /// + /// // When multiple patterns are present, if they are all anchored, then + /// // the NFA is always anchored too. + /// let nfa = NFA::new_many(&["^a", "^b", "^c"])?; + /// assert!(nfa.is_always_start_anchored()); + /// + /// // But if one pattern is unanchored, then the NFA must permit an + /// // unanchored search. + /// let nfa = NFA::new_many(&["^a", "b", "^c"])?; + /// assert!(!nfa.is_always_start_anchored()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn is_always_start_anchored(&self) -> bool { + self.start_anchored() == self.start_unanchored() + } + + /// Returns the look-around matcher associated with this NFA. + /// + /// A look-around matcher determines how to match look-around assertions. + /// In particular, some assertions are configurable. For example, the + /// `(?m:^)` and `(?m:$)` assertions can have their line terminator changed + /// from the default of `\n` to any other byte. + /// + /// If the NFA was built using a [`Compiler`], then this matcher + /// can be set via the [`Config::look_matcher`] configuration + /// knob. Otherwise, if you've built an NFA by hand, it is set via + /// [`Builder::set_look_matcher`]. + /// + /// # Example + /// + /// This shows how to change the line terminator for multi-line assertions. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::{self, pikevm::PikeVM}, + /// util::look::LookMatcher, + /// Match, Input, + /// }; + /// + /// let mut lookm = LookMatcher::new(); + /// lookm.set_line_terminator(b'\x00'); + /// + /// let re = PikeVM::builder() + /// .thompson(thompson::Config::new().look_matcher(lookm)) + /// .build(r"(?m)^[a-z]+$")?; + /// let mut cache = re.create_cache(); + /// + /// // Multi-line assertions now use NUL as a terminator. + /// assert_eq!( + /// Some(Match::must(0, 1..4)), + /// re.find(&mut cache, b"\x00abc\x00"), + /// ); + /// // ... and \n is no longer recognized as a terminator. + /// assert_eq!( + /// None, + /// re.find(&mut cache, b"\nabc\n"), + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn look_matcher(&self) -> &LookMatcher { + &self.0.look_matcher + } + + /// Returns the union of all look-around assertions used throughout this + /// NFA. When the returned set is empty, it implies that the NFA has no + /// look-around assertions and thus zero conditional epsilon transitions. + /// + /// This is useful in some cases enabling optimizations. It is not + /// unusual, for example, for optimizations to be of the form, "for any + /// regex with zero conditional epsilon transitions, do ..." where "..." + /// is some kind of optimization. + /// + /// This isn't only helpful for optimizations either. Sometimes look-around + /// assertions are difficult to support. For example, many of the DFAs in + /// this crate don't support Unicode word boundaries or handle them using + /// heuristics. Handling that correctly typically requires some kind of + /// cheap check of whether the NFA has a Unicode word boundary in the first + /// place. + /// + /// # Example + /// + /// This example shows how this routine varies based on the regex pattern: + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::look::Look}; + /// + /// // No look-around at all. + /// let nfa = NFA::new("a")?; + /// assert!(nfa.look_set_any().is_empty()); + /// + /// // When multiple patterns are present, since this returns the union, + /// // it will include look-around assertions that only appear in one + /// // pattern. + /// let nfa = NFA::new_many(&["a", "b", "a^b", "c"])?; + /// assert!(nfa.look_set_any().contains(Look::Start)); + /// + /// // Some groups of assertions have various shortcuts. For example: + /// let nfa = NFA::new(r"(?-u:\b)")?; + /// assert!(nfa.look_set_any().contains_word()); + /// assert!(!nfa.look_set_any().contains_word_unicode()); + /// assert!(nfa.look_set_any().contains_word_ascii()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn look_set_any(&self) -> LookSet { + self.0.look_set_any + } + + /// Returns the union of all prefix look-around assertions for every + /// pattern in this NFA. When the returned set is empty, it implies none of + /// the patterns require moving through a conditional epsilon transition + /// before inspecting the first byte in the haystack. + /// + /// This can be useful for determining what kinds of assertions need to be + /// satisfied at the beginning of a search. For example, typically DFAs + /// in this crate will build a distinct starting state for each possible + /// starting configuration that might result in look-around assertions + /// being satisfied differently. However, if the set returned here is + /// empty, then you know that the start state is invariant because there + /// are no conditional epsilon transitions to consider. + /// + /// # Example + /// + /// This example shows how this routine varies based on the regex pattern: + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::look::Look}; + /// + /// // No look-around at all. + /// let nfa = NFA::new("a")?; + /// assert!(nfa.look_set_prefix_any().is_empty()); + /// + /// // When multiple patterns are present, since this returns the union, + /// // it will include look-around assertions that only appear in one + /// // pattern. But it will only include assertions that are in the prefix + /// // of a pattern. For example, this includes '^' but not '$' even though + /// // '$' does appear. + /// let nfa = NFA::new_many(&["a", "b", "^ab$", "c"])?; + /// assert!(nfa.look_set_prefix_any().contains(Look::Start)); + /// assert!(!nfa.look_set_prefix_any().contains(Look::End)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn look_set_prefix_any(&self) -> LookSet { + self.0.look_set_prefix_any + } + + // FIXME: The `look_set_prefix_all` computation was not correct, and it + // seemed a little tricky to fix it. Since I wasn't actually using it for + // anything, I just decided to remove it in the run up to the regex 1.9 + // release. If you need this, please file an issue. + /* + /// Returns the intersection of all prefix look-around assertions for every + /// pattern in this NFA. When the returned set is empty, it implies at + /// least one of the patterns does not require moving through a conditional + /// epsilon transition before inspecting the first byte in the haystack. + /// Conversely, when the set contains an assertion, it implies that every + /// pattern in the NFA also contains that assertion in its prefix. + /// + /// This can be useful for determining what kinds of assertions need to be + /// satisfied at the beginning of a search. For example, if you know that + /// [`Look::Start`] is in the prefix intersection set returned here, then + /// you know that all searches, regardless of input configuration, will be + /// anchored. + /// + /// # Example + /// + /// This example shows how this routine varies based on the regex pattern: + /// + /// ``` + /// use regex_automata::{nfa::thompson::NFA, util::look::Look}; + /// + /// // No look-around at all. + /// let nfa = NFA::new("a")?; + /// assert!(nfa.look_set_prefix_all().is_empty()); + /// + /// // When multiple patterns are present, since this returns the + /// // intersection, it will only include assertions present in every + /// // prefix, and only the prefix. + /// let nfa = NFA::new_many(&["^a$", "^b$", "$^ab$", "^c$"])?; + /// assert!(nfa.look_set_prefix_all().contains(Look::Start)); + /// assert!(!nfa.look_set_prefix_all().contains(Look::End)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn look_set_prefix_all(&self) -> LookSet { + self.0.look_set_prefix_all + } + */ + + /// Returns the memory usage, in bytes, of this NFA. + /// + /// This does **not** include the stack size used up by this NFA. To + /// compute that, use `std::mem::size_of::<NFA>()`. + /// + /// # Example + /// + /// This example shows that large Unicode character classes can use quite + /// a bit of memory. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::nfa::thompson::NFA; + /// + /// let nfa_unicode = NFA::new(r"\w")?; + /// let nfa_ascii = NFA::new(r"(?-u:\w)")?; + /// + /// assert!(10 * nfa_ascii.memory_usage() < nfa_unicode.memory_usage()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn memory_usage(&self) -> usize { + use core::mem::size_of; + + size_of::<Inner>() // allocated on the heap via Arc + + self.0.states.len() * size_of::<State>() + + self.0.start_pattern.len() * size_of::<StateID>() + + self.0.group_info.memory_usage() + + self.0.memory_extra + } +} + +impl fmt::Debug for NFA { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + self.0.fmt(f) + } +} + +/// The "inner" part of the NFA. We split this part out so that we can easily +/// wrap it in an `Arc` above in the definition of `NFA`. +/// +/// See builder.rs for the code that actually builds this type. This module +/// does provide (internal) mutable methods for adding things to this +/// NFA before finalizing it, but the high level construction process is +/// controlled by the builder abstraction. (Which is complicated enough to +/// get its own module.) +#[derive(Default)] +pub(super) struct Inner { + /// The state sequence. This sequence is guaranteed to be indexable by all + /// starting state IDs, and it is also guaranteed to contain at most one + /// `Match` state for each pattern compiled into this NFA. (A pattern may + /// not have a corresponding `Match` state if a `Match` state is impossible + /// to reach.) + states: Vec<State>, + /// The anchored starting state of this NFA. + start_anchored: StateID, + /// The unanchored starting state of this NFA. + start_unanchored: StateID, + /// The starting states for each individual pattern. Starting at any + /// of these states will result in only an anchored search for the + /// corresponding pattern. The vec is indexed by pattern ID. When the NFA + /// contains a single regex, then `start_pattern[0]` and `start_anchored` + /// are always equivalent. + start_pattern: Vec<StateID>, + /// Info about the capturing groups in this NFA. This is responsible for + /// mapping groups to slots, mapping groups to names and names to groups. + group_info: GroupInfo, + /// A representation of equivalence classes over the transitions in this + /// NFA. Two bytes in the same equivalence class must not discriminate + /// between a match or a non-match. This map can be used to shrink the + /// total size of a DFA's transition table with a small match-time cost. + /// + /// Note that the NFA's transitions are *not* defined in terms of these + /// equivalence classes. The NFA's transitions are defined on the original + /// byte values. For the most part, this is because they wouldn't really + /// help the NFA much since the NFA already uses a sparse representation + /// to represent transitions. Byte classes are most effective in a dense + /// representation. + byte_class_set: ByteClassSet, + /// This is generated from `byte_class_set`, and essentially represents the + /// same thing but supports different access patterns. Namely, this permits + /// looking up the equivalence class of a byte very cheaply. + /// + /// Ideally we would just store this, but because of annoying code + /// structure reasons, we keep both this and `byte_class_set` around for + /// now. I think I would prefer that `byte_class_set` were computed in the + /// `Builder`, but right now, we compute it as states are added to the + /// `NFA`. + byte_classes: ByteClasses, + /// Whether this NFA has a `Capture` state anywhere. + has_capture: bool, + /// When the empty string is in the language matched by this NFA. + has_empty: bool, + /// Whether UTF-8 mode is enabled for this NFA. Briefly, this means that + /// all non-empty matches produced by this NFA correspond to spans of valid + /// UTF-8, and any empty matches produced by this NFA that split a UTF-8 + /// encoded codepoint should be filtered out by the corresponding regex + /// engine. + utf8: bool, + /// Whether this NFA is meant to be matched in reverse or not. + reverse: bool, + /// The matcher to be used for look-around assertions. + look_matcher: LookMatcher, + /// The union of all look-around assertions that occur anywhere within + /// this NFA. If this set is empty, then it means there are precisely zero + /// conditional epsilon transitions in the NFA. + look_set_any: LookSet, + /// The union of all look-around assertions that occur as a zero-length + /// prefix for any of the patterns in this NFA. + look_set_prefix_any: LookSet, + /* + /// The intersection of all look-around assertions that occur as a + /// zero-length prefix for any of the patterns in this NFA. + look_set_prefix_all: LookSet, + */ + /// Heap memory used indirectly by NFA states and other things (like the + /// various capturing group representations above). Since each state + /// might use a different amount of heap, we need to keep track of this + /// incrementally. + memory_extra: usize, +} + +impl Inner { + /// Runs any last finalization bits and turns this into a full NFA. + pub(super) fn into_nfa(mut self) -> NFA { + self.byte_classes = self.byte_class_set.byte_classes(); + // Do epsilon closure from the start state of every pattern in order + // to compute various properties such as look-around assertions and + // whether the empty string can be matched. + let mut stack = vec![]; + let mut seen = SparseSet::new(self.states.len()); + for &start_id in self.start_pattern.iter() { + stack.push(start_id); + seen.clear(); + // let mut prefix_all = LookSet::full(); + let mut prefix_any = LookSet::empty(); + while let Some(sid) = stack.pop() { + if !seen.insert(sid) { + continue; + } + match self.states[sid] { + State::ByteRange { .. } + | State::Dense { .. } + | State::Fail => continue, + State::Sparse(_) => { + // This snippet below will rewrite this sparse state + // as a dense state. By doing it here, we apply this + // optimization to all hot "sparse" states since these + // are the states that are reachable from the start + // state via an epsilon closure. + // + // Unfortunately, this optimization did not seem to + // help much in some very limited ad hoc benchmarking. + // + // I left the 'Dense' state type in place in case we + // want to revisit this, but I suspect the real way + // to make forward progress is a more fundamental + // rearchitecting of how data in the NFA is laid out. + // I think we should consider a single contiguous + // allocation instead of all this indirection and + // potential heap allocations for every state. But this + // is a large re-design and will require API breaking + // changes. + // self.memory_extra -= self.states[sid].memory_usage(); + // let trans = DenseTransitions::from_sparse(sparse); + // self.states[sid] = State::Dense(trans); + // self.memory_extra += self.states[sid].memory_usage(); + continue; + } + State::Match { .. } => self.has_empty = true, + State::Look { look, next } => { + prefix_any = prefix_any.insert(look); + stack.push(next); + } + State::Union { ref alternates } => { + // Order doesn't matter here, since we're just dealing + // with look-around sets. But if we do richer analysis + // here that needs to care about preference order, then + // this should be done in reverse. + stack.extend(alternates.iter()); + } + State::BinaryUnion { alt1, alt2 } => { + stack.push(alt2); + stack.push(alt1); + } + State::Capture { next, .. } => { + stack.push(next); + } + } + } + self.look_set_prefix_any = + self.look_set_prefix_any.union(prefix_any); + } + NFA(Arc::new(self)) + } + + /// Returns the capturing group info for this NFA. + pub(super) fn group_info(&self) -> &GroupInfo { + &self.group_info + } + + /// Add the given state to this NFA after allocating a fresh identifier for + /// it. + /// + /// This panics if too many states are added such that a fresh identifier + /// could not be created. (Currently, the only caller of this routine is + /// a `Builder`, and it upholds this invariant.) + pub(super) fn add(&mut self, state: State) -> StateID { + match state { + State::ByteRange { ref trans } => { + self.byte_class_set.set_range(trans.start, trans.end); + } + State::Sparse(ref sparse) => { + for trans in sparse.transitions.iter() { + self.byte_class_set.set_range(trans.start, trans.end); + } + } + State::Dense { .. } => unreachable!(), + State::Look { look, .. } => { + self.look_matcher + .add_to_byteset(look, &mut self.byte_class_set); + self.look_set_any = self.look_set_any.insert(look); + } + State::Capture { .. } => { + self.has_capture = true; + } + State::Union { .. } + | State::BinaryUnion { .. } + | State::Fail + | State::Match { .. } => {} + } + + let id = StateID::new(self.states.len()).unwrap(); + self.memory_extra += state.memory_usage(); + self.states.push(state); + id + } + + /// Set the starting state identifiers for this NFA. + /// + /// `start_anchored` and `start_unanchored` may be equivalent. When they + /// are, then the NFA can only execute anchored searches. This might + /// occur, for example, for patterns that are unconditionally anchored. + /// e.g., `^foo`. + pub(super) fn set_starts( + &mut self, + start_anchored: StateID, + start_unanchored: StateID, + start_pattern: &[StateID], + ) { + self.start_anchored = start_anchored; + self.start_unanchored = start_unanchored; + self.start_pattern = start_pattern.to_vec(); + } + + /// Sets the UTF-8 mode of this NFA. + pub(super) fn set_utf8(&mut self, yes: bool) { + self.utf8 = yes; + } + + /// Sets the reverse mode of this NFA. + pub(super) fn set_reverse(&mut self, yes: bool) { + self.reverse = yes; + } + + /// Sets the look-around assertion matcher for this NFA. + pub(super) fn set_look_matcher(&mut self, m: LookMatcher) { + self.look_matcher = m; + } + + /// Set the capturing groups for this NFA. + /// + /// The given slice should contain the capturing groups for each pattern, + /// The capturing groups in turn should correspond to the total number of + /// capturing groups in the pattern, including the anonymous first capture + /// group for each pattern. If a capturing group does have a name, then it + /// should be provided as a Arc<str>. + /// + /// This returns an error if a corresponding `GroupInfo` could not be + /// built. + pub(super) fn set_captures( + &mut self, + captures: &[Vec<Option<Arc<str>>>], + ) -> Result<(), GroupInfoError> { + self.group_info = GroupInfo::new( + captures.iter().map(|x| x.iter().map(|y| y.as_ref())), + )?; + Ok(()) + } + + /// Remap the transitions in every state of this NFA using the given map. + /// The given map should be indexed according to state ID namespace used by + /// the transitions of the states currently in this NFA. + /// + /// This is particularly useful to the NFA builder, since it is convenient + /// to add NFA states in order to produce their final IDs. Then, after all + /// of the intermediate "empty" states (unconditional epsilon transitions) + /// have been removed from the builder's representation, we can re-map all + /// of the transitions in the states already added to their final IDs. + pub(super) fn remap(&mut self, old_to_new: &[StateID]) { + for state in &mut self.states { + state.remap(old_to_new); + } + self.start_anchored = old_to_new[self.start_anchored]; + self.start_unanchored = old_to_new[self.start_unanchored]; + for id in self.start_pattern.iter_mut() { + *id = old_to_new[*id]; + } + } +} + +impl fmt::Debug for Inner { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + writeln!(f, "thompson::NFA(")?; + for (sid, state) in self.states.iter().with_state_ids() { + let status = if sid == self.start_anchored { + '^' + } else if sid == self.start_unanchored { + '>' + } else { + ' ' + }; + writeln!(f, "{}{:06?}: {:?}", status, sid.as_usize(), state)?; + } + let pattern_len = self.start_pattern.len(); + if pattern_len > 1 { + writeln!(f, "")?; + for pid in 0..pattern_len { + let sid = self.start_pattern[pid]; + writeln!(f, "START({:06?}): {:?}", pid, sid.as_usize())?; + } + } + writeln!(f, "")?; + writeln!( + f, + "transition equivalence classes: {:?}", + self.byte_classes, + )?; + writeln!(f, ")")?; + Ok(()) + } +} + +/// A state in an NFA. +/// +/// In theory, it can help to conceptualize an `NFA` as a graph consisting of +/// `State`s. Each `State` contains its complete set of outgoing transitions. +/// +/// In practice, it can help to conceptualize an `NFA` as a sequence of +/// instructions for a virtual machine. Each `State` says what to do and where +/// to go next. +/// +/// Strictly speaking, the practical interpretation is the most correct one, +/// because of the [`Capture`](State::Capture) state. Namely, a `Capture` +/// state always forwards execution to another state unconditionally. Its only +/// purpose is to cause a side effect: the recording of the current input +/// position at a particular location in memory. In this sense, an `NFA` +/// has more power than a theoretical non-deterministic finite automaton. +/// +/// For most uses of this crate, it is likely that one may never even need to +/// be aware of this type at all. The main use cases for looking at `State`s +/// directly are if you need to write your own search implementation or if you +/// need to do some kind of analysis on the NFA. +#[derive(Clone, Eq, PartialEq)] +pub enum State { + /// A state with a single transition that can only be taken if the current + /// input symbol is in a particular range of bytes. + ByteRange { + /// The transition from this state to the next. + trans: Transition, + }, + /// A state with possibly many transitions represented in a sparse fashion. + /// Transitions are non-overlapping and ordered lexicographically by input + /// range. + /// + /// In practice, this is used for encoding UTF-8 automata. Its presence is + /// primarily an optimization that avoids many additional unconditional + /// epsilon transitions (via [`Union`](State::Union) states), and thus + /// decreases the overhead of traversing the NFA. This can improve both + /// matching time and DFA construction time. + Sparse(SparseTransitions), + /// A dense representation of a state with multiple transitions. + Dense(DenseTransitions), + /// A conditional epsilon transition satisfied via some sort of + /// look-around. Look-around is limited to anchor and word boundary + /// assertions. + /// + /// Look-around states are meant to be evaluated while performing epsilon + /// closure (computing the set of states reachable from a particular state + /// via only epsilon transitions). If the current position in the haystack + /// satisfies the look-around assertion, then you're permitted to follow + /// that epsilon transition. + Look { + /// The look-around assertion that must be satisfied before moving + /// to `next`. + look: Look, + /// The state to transition to if the look-around assertion is + /// satisfied. + next: StateID, + }, + /// An alternation such that there exists an epsilon transition to all + /// states in `alternates`, where matches found via earlier transitions + /// are preferred over later transitions. + Union { + /// An ordered sequence of unconditional epsilon transitions to other + /// states. Transitions earlier in the sequence are preferred over + /// transitions later in the sequence. + alternates: Box<[StateID]>, + }, + /// An alternation such that there exists precisely two unconditional + /// epsilon transitions, where matches found via `alt1` are preferred over + /// matches found via `alt2`. + /// + /// This state exists as a common special case of Union where there are + /// only two alternates. In this case, we don't need any allocations to + /// represent the state. This saves a bit of memory and also saves an + /// additional memory access when traversing the NFA. + BinaryUnion { + /// An unconditional epsilon transition to another NFA state. This + /// is preferred over `alt2`. + alt1: StateID, + /// An unconditional epsilon transition to another NFA state. Matches + /// reported via this transition should only be reported if no matches + /// were found by following `alt1`. + alt2: StateID, + }, + /// An empty state that records a capture location. + /// + /// From the perspective of finite automata, this is precisely equivalent + /// to an unconditional epsilon transition, but serves the purpose of + /// instructing NFA simulations to record additional state when the finite + /// state machine passes through this epsilon transition. + /// + /// `slot` in this context refers to the specific capture group slot + /// offset that is being recorded. Each capturing group has two slots + /// corresponding to the start and end of the matching portion of that + /// group. + /// + /// The pattern ID and capture group index are also included in this state + /// in case they are useful. But mostly, all you'll need is `next` and + /// `slot`. + Capture { + /// The state to transition to, unconditionally. + next: StateID, + /// The pattern ID that this capture belongs to. + pattern_id: PatternID, + /// The capture group index that this capture belongs to. Capture group + /// indices are local to each pattern. For example, when capturing + /// groups are enabled, every pattern has a capture group at index + /// `0`. + group_index: SmallIndex, + /// The slot index for this capture. Every capturing group has two + /// slots: one for the start haystack offset and one for the end + /// haystack offset. Unlike capture group indices, slot indices are + /// global across all patterns in this NFA. That is, each slot belongs + /// to a single pattern, but there is only one slot at index `i`. + slot: SmallIndex, + }, + /// A state that cannot be transitioned out of. This is useful for cases + /// where you want to prevent matching from occurring. For example, if your + /// regex parser permits empty character classes, then one could choose + /// a `Fail` state to represent them. (An empty character class can be + /// thought of as an empty set. Since nothing is in an empty set, they can + /// never match anything.) + Fail, + /// A match state. There is at least one such occurrence of this state for + /// each regex that can match that is in this NFA. + Match { + /// The matching pattern ID. + pattern_id: PatternID, + }, +} + +impl State { + /// Returns true if and only if this state contains one or more epsilon + /// transitions. + /// + /// In practice, a state has no outgoing transitions (like `Match`), has + /// only non-epsilon transitions (like `ByteRange`) or has only epsilon + /// transitions (like `Union`). + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::{State, Transition}, + /// util::primitives::{PatternID, StateID, SmallIndex}, + /// }; + /// + /// // Capture states are epsilon transitions. + /// let state = State::Capture { + /// next: StateID::ZERO, + /// pattern_id: PatternID::ZERO, + /// group_index: SmallIndex::ZERO, + /// slot: SmallIndex::ZERO, + /// }; + /// assert!(state.is_epsilon()); + /// + /// // ByteRange states are not. + /// let state = State::ByteRange { + /// trans: Transition { start: b'a', end: b'z', next: StateID::ZERO }, + /// }; + /// assert!(!state.is_epsilon()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn is_epsilon(&self) -> bool { + match *self { + State::ByteRange { .. } + | State::Sparse { .. } + | State::Dense { .. } + | State::Fail + | State::Match { .. } => false, + State::Look { .. } + | State::Union { .. } + | State::BinaryUnion { .. } + | State::Capture { .. } => true, + } + } + + /// Returns the heap memory usage of this NFA state in bytes. + fn memory_usage(&self) -> usize { + match *self { + State::ByteRange { .. } + | State::Look { .. } + | State::BinaryUnion { .. } + | State::Capture { .. } + | State::Match { .. } + | State::Fail => 0, + State::Sparse(SparseTransitions { ref transitions }) => { + transitions.len() * mem::size_of::<Transition>() + } + State::Dense { .. } => 256 * mem::size_of::<StateID>(), + State::Union { ref alternates } => { + alternates.len() * mem::size_of::<StateID>() + } + } + } + + /// Remap the transitions in this state using the given map. Namely, the + /// given map should be indexed according to the transitions currently + /// in this state. + /// + /// This is used during the final phase of the NFA compiler, which turns + /// its intermediate NFA into the final NFA. + fn remap(&mut self, remap: &[StateID]) { + match *self { + State::ByteRange { ref mut trans } => { + trans.next = remap[trans.next] + } + State::Sparse(SparseTransitions { ref mut transitions }) => { + for t in transitions.iter_mut() { + t.next = remap[t.next]; + } + } + State::Dense(DenseTransitions { ref mut transitions }) => { + for sid in transitions.iter_mut() { + *sid = remap[*sid]; + } + } + State::Look { ref mut next, .. } => *next = remap[*next], + State::Union { ref mut alternates } => { + for alt in alternates.iter_mut() { + *alt = remap[*alt]; + } + } + State::BinaryUnion { ref mut alt1, ref mut alt2 } => { + *alt1 = remap[*alt1]; + *alt2 = remap[*alt2]; + } + State::Capture { ref mut next, .. } => *next = remap[*next], + State::Fail => {} + State::Match { .. } => {} + } + } +} + +impl fmt::Debug for State { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match *self { + State::ByteRange { ref trans } => trans.fmt(f), + State::Sparse(SparseTransitions { ref transitions }) => { + let rs = transitions + .iter() + .map(|t| format!("{:?}", t)) + .collect::<Vec<String>>() + .join(", "); + write!(f, "sparse({})", rs) + } + State::Dense(ref dense) => { + write!(f, "dense(")?; + for (i, t) in dense.iter().enumerate() { + if i > 0 { + write!(f, ", ")?; + } + write!(f, "{:?}", t)?; + } + write!(f, ")") + } + State::Look { ref look, next } => { + write!(f, "{:?} => {:?}", look, next.as_usize()) + } + State::Union { ref alternates } => { + let alts = alternates + .iter() + .map(|id| format!("{:?}", id.as_usize())) + .collect::<Vec<String>>() + .join(", "); + write!(f, "union({})", alts) + } + State::BinaryUnion { alt1, alt2 } => { + write!( + f, + "binary-union({}, {})", + alt1.as_usize(), + alt2.as_usize() + ) + } + State::Capture { next, pattern_id, group_index, slot } => { + write!( + f, + "capture(pid={:?}, group={:?}, slot={:?}) => {:?}", + pattern_id.as_usize(), + group_index.as_usize(), + slot.as_usize(), + next.as_usize(), + ) + } + State::Fail => write!(f, "FAIL"), + State::Match { pattern_id } => { + write!(f, "MATCH({:?})", pattern_id.as_usize()) + } + } + } +} + +/// A sequence of transitions used to represent a sparse state. +/// +/// This is the primary representation of a [`Sparse`](State::Sparse) state. +/// It corresponds to a sorted sequence of transitions with non-overlapping +/// byte ranges. If the byte at the current position in the haystack matches +/// one of the byte ranges, then the finite state machine should take the +/// corresponding transition. +#[derive(Clone, Debug, Eq, PartialEq)] +pub struct SparseTransitions { + /// The sorted sequence of non-overlapping transitions. + pub transitions: Box<[Transition]>, +} + +impl SparseTransitions { + /// This follows the matching transition for a particular byte. + /// + /// The matching transition is found by looking for a matching byte + /// range (there is at most one) corresponding to the position `at` in + /// `haystack`. + /// + /// If `at >= haystack.len()`, then this returns `None`. + #[inline] + pub fn matches(&self, haystack: &[u8], at: usize) -> Option<StateID> { + haystack.get(at).and_then(|&b| self.matches_byte(b)) + } + + /// This follows the matching transition for any member of the alphabet. + /// + /// The matching transition is found by looking for a matching byte + /// range (there is at most one) corresponding to the position `at` in + /// `haystack`. If the given alphabet unit is [`EOI`](alphabet::Unit::eoi), + /// then this always returns `None`. + #[inline] + pub(crate) fn matches_unit( + &self, + unit: alphabet::Unit, + ) -> Option<StateID> { + unit.as_u8().map_or(None, |byte| self.matches_byte(byte)) + } + + /// This follows the matching transition for a particular byte. + /// + /// The matching transition is found by looking for a matching byte range + /// (there is at most one) corresponding to the byte given. + #[inline] + pub fn matches_byte(&self, byte: u8) -> Option<StateID> { + for t in self.transitions.iter() { + if t.start > byte { + break; + } else if t.matches_byte(byte) { + return Some(t.next); + } + } + None + + /* + // This is an alternative implementation that uses binary search. In + // some ad hoc experiments, like + // + // smallishru=OpenSubtitles2018.raw.sample.smallish.ru + // regex-cli find nfa thompson pikevm -b "@$smallishru" '\b\w+\b' + // + // I could not observe any improvement, and in fact, things seemed to + // be a bit slower. I can see an improvement in at least one benchmark: + // + // allcpssmall=all-codepoints-utf8-10x + // regex-cli find nfa thompson pikevm @$allcpssmall '\pL{100}' + // + // Where total search time goes from 3.2s to 2.4s when using binary + // search. + self.transitions + .binary_search_by(|t| { + if t.end < byte { + core::cmp::Ordering::Less + } else if t.start > byte { + core::cmp::Ordering::Greater + } else { + core::cmp::Ordering::Equal + } + }) + .ok() + .map(|i| self.transitions[i].next) + */ + } +} + +/// A sequence of transitions used to represent a dense state. +/// +/// This is the primary representation of a [`Dense`](State::Dense) state. It +/// provides constant time matching. That is, given a byte in a haystack and +/// a `DenseTransitions`, one can determine if the state matches in constant +/// time. +/// +/// This is in contrast to `SparseTransitions`, whose time complexity is +/// necessarily bigger than constant time. Also in contrast, `DenseTransitions` +/// usually requires (much) more heap memory. +#[derive(Clone, Debug, Eq, PartialEq)] +pub struct DenseTransitions { + /// A dense representation of this state's transitions on the heap. This + /// always has length 256. + pub transitions: Box<[StateID]>, +} + +impl DenseTransitions { + /// This follows the matching transition for a particular byte. + /// + /// The matching transition is found by looking for a transition that + /// doesn't correspond to `StateID::ZERO` for the byte `at` the given + /// position in `haystack`. + /// + /// If `at >= haystack.len()`, then this returns `None`. + #[inline] + pub fn matches(&self, haystack: &[u8], at: usize) -> Option<StateID> { + haystack.get(at).and_then(|&b| self.matches_byte(b)) + } + + /// This follows the matching transition for any member of the alphabet. + /// + /// The matching transition is found by looking for a transition that + /// doesn't correspond to `StateID::ZERO` for the byte `at` the given + /// position in `haystack`. + /// + /// If `at >= haystack.len()` or if the given alphabet unit is + /// [`EOI`](alphabet::Unit::eoi), then this returns `None`. + #[inline] + pub(crate) fn matches_unit( + &self, + unit: alphabet::Unit, + ) -> Option<StateID> { + unit.as_u8().map_or(None, |byte| self.matches_byte(byte)) + } + + /// This follows the matching transition for a particular byte. + /// + /// The matching transition is found by looking for a transition that + /// doesn't correspond to `StateID::ZERO` for the given `byte`. + /// + /// If `at >= haystack.len()`, then this returns `None`. + #[inline] + pub fn matches_byte(&self, byte: u8) -> Option<StateID> { + let next = self.transitions[usize::from(byte)]; + if next == StateID::ZERO { + None + } else { + Some(next) + } + } + + /* + /// The dense state optimization isn't currently enabled, so permit a + /// little bit of dead code. + pub(crate) fn from_sparse(sparse: &SparseTransitions) -> DenseTransitions { + let mut dense = vec![StateID::ZERO; 256]; + for t in sparse.transitions.iter() { + for b in t.start..=t.end { + dense[usize::from(b)] = t.next; + } + } + DenseTransitions { transitions: dense.into_boxed_slice() } + } + */ + + /// Returns an iterator over all transitions that don't point to + /// `StateID::ZERO`. + pub(crate) fn iter(&self) -> impl Iterator<Item = Transition> + '_ { + use crate::util::int::Usize; + self.transitions + .iter() + .enumerate() + .filter(|&(_, &sid)| sid != StateID::ZERO) + .map(|(byte, &next)| Transition { + start: byte.as_u8(), + end: byte.as_u8(), + next, + }) + } +} + +/// A single transition to another state. +/// +/// This transition may only be followed if the current byte in the haystack +/// falls in the inclusive range of bytes specified. +#[derive(Clone, Copy, Eq, Hash, PartialEq)] +pub struct Transition { + /// The inclusive start of the byte range. + pub start: u8, + /// The inclusive end of the byte range. + pub end: u8, + /// The identifier of the state to transition to. + pub next: StateID, +} + +impl Transition { + /// Returns true if the position `at` in `haystack` falls in this + /// transition's range of bytes. + /// + /// If `at >= haystack.len()`, then this returns `false`. + pub fn matches(&self, haystack: &[u8], at: usize) -> bool { + haystack.get(at).map_or(false, |&b| self.matches_byte(b)) + } + + /// Returns true if the given alphabet unit falls in this transition's + /// range of bytes. If the given unit is [`EOI`](alphabet::Unit::eoi), then + /// this returns `false`. + pub fn matches_unit(&self, unit: alphabet::Unit) -> bool { + unit.as_u8().map_or(false, |byte| self.matches_byte(byte)) + } + + /// Returns true if the given byte falls in this transition's range of + /// bytes. + pub fn matches_byte(&self, byte: u8) -> bool { + self.start <= byte && byte <= self.end + } +} + +impl fmt::Debug for Transition { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + use crate::util::escape::DebugByte; + + let Transition { start, end, next } = *self; + if self.start == self.end { + write!(f, "{:?} => {:?}", DebugByte(start), next.as_usize()) + } else { + write!( + f, + "{:?}-{:?} => {:?}", + DebugByte(start), + DebugByte(end), + next.as_usize(), + ) + } + } +} + +/// An iterator over all pattern IDs in an NFA. +/// +/// This iterator is created by [`NFA::patterns`]. +/// +/// The lifetime parameter `'a` refers to the lifetime of the NFA from which +/// this pattern iterator was created. +#[derive(Debug)] +pub struct PatternIter<'a> { + it: PatternIDIter, + /// We explicitly associate a lifetime with this iterator even though we + /// don't actually borrow anything from the NFA. We do this for backward + /// compatibility purposes. If we ever do need to borrow something from + /// the NFA, then we can and just get rid of this marker without breaking + /// the public API. + _marker: core::marker::PhantomData<&'a ()>, +} + +impl<'a> Iterator for PatternIter<'a> { + type Item = PatternID; + + fn next(&mut self) -> Option<PatternID> { + self.it.next() + } +} + +#[cfg(all(test, feature = "nfa-pikevm"))] +mod tests { + use super::*; + use crate::{nfa::thompson::pikevm::PikeVM, Input}; + + // This asserts that an NFA state doesn't have its size changed. It is + // *really* easy to accidentally increase the size, and thus potentially + // dramatically increase the memory usage of every NFA. + // + // This assert doesn't mean we absolutely cannot increase the size of an + // NFA state. We can. It's just here to make sure we do it knowingly and + // intentionally. + #[test] + fn state_has_small_size() { + #[cfg(target_pointer_width = "64")] + assert_eq!(24, core::mem::size_of::<State>()); + #[cfg(target_pointer_width = "32")] + assert_eq!(20, core::mem::size_of::<State>()); + } + + #[test] + fn always_match() { + let re = PikeVM::new_from_nfa(NFA::always_match()).unwrap(); + let mut cache = re.create_cache(); + let mut caps = re.create_captures(); + let mut find = |haystack, start, end| { + let input = Input::new(haystack).range(start..end); + re.search(&mut cache, &input, &mut caps); + caps.get_match().map(|m| m.end()) + }; + + assert_eq!(Some(0), find("", 0, 0)); + assert_eq!(Some(0), find("a", 0, 1)); + assert_eq!(Some(1), find("a", 1, 1)); + assert_eq!(Some(0), find("ab", 0, 2)); + assert_eq!(Some(1), find("ab", 1, 2)); + assert_eq!(Some(2), find("ab", 2, 2)); + } + + #[test] + fn never_match() { + let re = PikeVM::new_from_nfa(NFA::never_match()).unwrap(); + let mut cache = re.create_cache(); + let mut caps = re.create_captures(); + let mut find = |haystack, start, end| { + let input = Input::new(haystack).range(start..end); + re.search(&mut cache, &input, &mut caps); + caps.get_match().map(|m| m.end()) + }; + + assert_eq!(None, find("", 0, 0)); + assert_eq!(None, find("a", 0, 1)); + assert_eq!(None, find("a", 1, 1)); + assert_eq!(None, find("ab", 0, 2)); + assert_eq!(None, find("ab", 1, 2)); + assert_eq!(None, find("ab", 2, 2)); + } +} |