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Diffstat (limited to 'third_party/rust/regex-automata/src/dfa/automaton.rs')
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diff --git a/third_party/rust/regex-automata/src/dfa/automaton.rs b/third_party/rust/regex-automata/src/dfa/automaton.rs new file mode 100644 index 0000000000..7e2be9a151 --- /dev/null +++ b/third_party/rust/regex-automata/src/dfa/automaton.rs @@ -0,0 +1,2120 @@ +#[cfg(feature = "alloc")] +use crate::util::search::PatternSet; +use crate::{ + dfa::search, + util::{ + empty, + prefilter::Prefilter, + primitives::{PatternID, StateID}, + search::{Anchored, HalfMatch, Input, MatchError}, + }, +}; + +/// A trait describing the interface of a deterministic finite automaton (DFA). +/// +/// The complexity of this trait probably means that it's unlikely for others +/// to implement it. The primary purpose of the trait is to provide for a way +/// of abstracting over different types of DFAs. In this crate, that means +/// dense DFAs and sparse DFAs. (Dense DFAs are fast but memory hungry, where +/// as sparse DFAs are slower but come with a smaller memory footprint. But +/// they otherwise provide exactly equivalent expressive power.) For example, a +/// [`dfa::regex::Regex`](crate::dfa::regex::Regex) is generic over this trait. +/// +/// Normally, a DFA's execution model is very simple. You might have a single +/// start state, zero or more final or "match" states and a function that +/// transitions from one state to the next given the next byte of input. +/// Unfortunately, the interface described by this trait is significantly +/// more complicated than this. The complexity has a number of different +/// reasons, mostly motivated by performance, functionality or space savings: +/// +/// * A DFA can search for multiple patterns simultaneously. This +/// means extra information is returned when a match occurs. Namely, +/// a match is not just an offset, but an offset plus a pattern ID. +/// [`Automaton::pattern_len`] returns the number of patterns compiled into +/// the DFA, [`Automaton::match_len`] returns the total number of patterns +/// that match in a particular state and [`Automaton::match_pattern`] permits +/// iterating over the patterns that match in a particular state. +/// * A DFA can have multiple start states, and the choice of which start +/// state to use depends on the content of the string being searched and +/// position of the search, as well as whether the search is an anchored +/// search for a specific pattern in the DFA. Moreover, computing the start +/// state also depends on whether you're doing a forward or a reverse search. +/// [`Automaton::start_state_forward`] and [`Automaton::start_state_reverse`] +/// are used to compute the start state for forward and reverse searches, +/// respectively. +/// * All matches are delayed by one byte to support things like `$` and `\b` +/// at the end of a pattern. Therefore, every use of a DFA is required to use +/// [`Automaton::next_eoi_state`] +/// at the end of the search to compute the final transition. +/// * For optimization reasons, some states are treated specially. Every +/// state is either special or not, which can be determined via the +/// [`Automaton::is_special_state`] method. If it's special, then the state +/// must be at least one of a few possible types of states. (Note that some +/// types can overlap, for example, a match state can also be an accel state. +/// But some types can't. If a state is a dead state, then it can never be any +/// other type of state.) Those types are: +/// * A dead state. A dead state means the DFA will never enter a match +/// state. This can be queried via the [`Automaton::is_dead_state`] method. +/// * A quit state. A quit state occurs if the DFA had to stop the search +/// prematurely for some reason. This can be queried via the +/// [`Automaton::is_quit_state`] method. +/// * A match state. A match state occurs when a match is found. When a DFA +/// enters a match state, the search may stop immediately (when looking +/// for the earliest match), or it may continue to find the leftmost-first +/// match. This can be queried via the [`Automaton::is_match_state`] +/// method. +/// * A start state. A start state is where a search begins. For every +/// search, there is exactly one start state that is used, however, a +/// DFA may contain many start states. When the search is in a start +/// state, it may use a prefilter to quickly skip to candidate matches +/// without executing the DFA on every byte. This can be queried via the +/// [`Automaton::is_start_state`] method. +/// * An accel state. An accel state is a state that is accelerated. +/// That is, it is a state where _most_ of its transitions loop back to +/// itself and only a small number of transitions lead to other states. +/// This kind of state is said to be accelerated because a search routine +/// can quickly look for the bytes leading out of the state instead of +/// continuing to execute the DFA on each byte. This can be queried via the +/// [`Automaton::is_accel_state`] method. And the bytes that lead out of +/// the state can be queried via the [`Automaton::accelerator`] method. +/// +/// There are a number of provided methods on this trait that implement +/// efficient searching (for forwards and backwards) with a DFA using +/// all of the above features of this trait. In particular, given the +/// complexity of all these features, implementing a search routine in +/// this trait can be a little subtle. With that said, it is possible to +/// somewhat simplify the search routine. For example, handling accelerated +/// states is strictly optional, since it is always correct to assume that +/// `Automaton::is_accel_state` returns false. However, one complex part of +/// writing a search routine using this trait is handling the 1-byte delay of a +/// match. That is not optional. +/// +/// # Safety +/// +/// This trait is not safe to implement so that code may rely on the +/// correctness of implementations of this trait to avoid undefined behavior. +/// The primary correctness guarantees are: +/// +/// * `Automaton::start_state` always returns a valid state ID or an error or +/// panics. +/// * `Automaton::next_state`, when given a valid state ID, always returns +/// a valid state ID for all values of `anchored` and `byte`, or otherwise +/// panics. +/// +/// In general, the rest of the methods on `Automaton` need to uphold their +/// contracts as well. For example, `Automaton::is_dead` should only returns +/// true if the given state ID is actually a dead state. +pub unsafe trait Automaton { + /// Transitions from the current state to the next state, given the next + /// byte of input. + /// + /// Implementations must guarantee that the returned ID is always a valid + /// ID when `current` refers to a valid ID. Moreover, the transition + /// function must be defined for all possible values of `input`. + /// + /// # Panics + /// + /// If the given ID does not refer to a valid state, then this routine + /// may panic but it also may not panic and instead return an invalid ID. + /// However, if the caller provides an invalid ID then this must never + /// sacrifice memory safety. + /// + /// # Example + /// + /// This shows a simplistic example for walking a DFA for a given haystack + /// by using the `next_state` method. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, Input}; + /// + /// let dfa = dense::DFA::new(r"[a-z]+r")?; + /// let haystack = "bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// let mut state = dfa.start_state_forward(&Input::new(haystack))?; + /// // Walk all the bytes in the haystack. + /// for &b in haystack { + /// state = dfa.next_state(state, b); + /// } + /// // Matches are always delayed by 1 byte, so we must explicitly walk the + /// // special "EOI" transition at the end of the search. + /// state = dfa.next_eoi_state(state); + /// assert!(dfa.is_match_state(state)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn next_state(&self, current: StateID, input: u8) -> StateID; + + /// Transitions from the current state to the next state, given the next + /// byte of input. + /// + /// Unlike [`Automaton::next_state`], implementations may implement this + /// more efficiently by assuming that the `current` state ID is valid. + /// Typically, this manifests by eliding bounds checks. + /// + /// # Safety + /// + /// Callers of this method must guarantee that `current` refers to a valid + /// state ID. If `current` is not a valid state ID for this automaton, then + /// calling this routine may result in undefined behavior. + /// + /// If `current` is valid, then implementations must guarantee that the ID + /// returned is valid for all possible values of `input`. + unsafe fn next_state_unchecked( + &self, + current: StateID, + input: u8, + ) -> StateID; + + /// Transitions from the current state to the next state for the special + /// EOI symbol. + /// + /// Implementations must guarantee that the returned ID is always a valid + /// ID when `current` refers to a valid ID. + /// + /// This routine must be called at the end of every search in a correct + /// implementation of search. Namely, DFAs in this crate delay matches + /// by one byte in order to support look-around operators. Thus, after + /// reaching the end of a haystack, a search implementation must follow one + /// last EOI transition. + /// + /// It is best to think of EOI as an additional symbol in the alphabet of + /// a DFA that is distinct from every other symbol. That is, the alphabet + /// of DFAs in this crate has a logical size of 257 instead of 256, where + /// 256 corresponds to every possible inhabitant of `u8`. (In practice, the + /// physical alphabet size may be smaller because of alphabet compression + /// via equivalence classes, but EOI is always represented somehow in the + /// alphabet.) + /// + /// # Panics + /// + /// If the given ID does not refer to a valid state, then this routine + /// may panic but it also may not panic and instead return an invalid ID. + /// However, if the caller provides an invalid ID then this must never + /// sacrifice memory safety. + /// + /// # Example + /// + /// This shows a simplistic example for walking a DFA for a given haystack, + /// and then finishing the search with the final EOI transition. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, Input}; + /// + /// let dfa = dense::DFA::new(r"[a-z]+r")?; + /// let haystack = "bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// // + /// // The unwrap is OK because we aren't requesting a start state for a + /// // specific pattern. + /// let mut state = dfa.start_state_forward(&Input::new(haystack))?; + /// // Walk all the bytes in the haystack. + /// for &b in haystack { + /// state = dfa.next_state(state, b); + /// } + /// // Matches are always delayed by 1 byte, so we must explicitly walk + /// // the special "EOI" transition at the end of the search. Without this + /// // final transition, the assert below will fail since the DFA will not + /// // have entered a match state yet! + /// state = dfa.next_eoi_state(state); + /// assert!(dfa.is_match_state(state)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn next_eoi_state(&self, current: StateID) -> StateID; + + /// Return the ID of the start state for this lazy DFA when executing a + /// forward search. + /// + /// Unlike typical DFA implementations, the start state for DFAs in this + /// crate is dependent on a few different factors: + /// + /// * The [`Anchored`] mode of the search. Unanchored, anchored and + /// anchored searches for a specific [`PatternID`] all use different start + /// states. + /// * The position at which the search begins, via [`Input::start`]. This + /// and the byte immediately preceding the start of the search (if one + /// exists) influence which look-behind assertions are true at the start + /// of the search. This in turn influences which start state is selected. + /// * Whether the search is a forward or reverse search. This routine can + /// only be used for forward searches. + /// + /// # Errors + /// + /// This may return a [`MatchError`] if the search needs to give up + /// when determining the start state (for example, if it sees a "quit" + /// byte). This can also return an error if the given `Input` contains an + /// unsupported [`Anchored`] configuration. + fn start_state_forward( + &self, + input: &Input<'_>, + ) -> Result<StateID, MatchError>; + + /// Return the ID of the start state for this lazy DFA when executing a + /// reverse search. + /// + /// Unlike typical DFA implementations, the start state for DFAs in this + /// crate is dependent on a few different factors: + /// + /// * The [`Anchored`] mode of the search. Unanchored, anchored and + /// anchored searches for a specific [`PatternID`] all use different start + /// states. + /// * The position at which the search begins, via [`Input::start`]. This + /// and the byte immediately preceding the start of the search (if one + /// exists) influence which look-behind assertions are true at the start + /// of the search. This in turn influences which start state is selected. + /// * Whether the search is a forward or reverse search. This routine can + /// only be used for reverse searches. + /// + /// # Errors + /// + /// This may return a [`MatchError`] if the search needs to give up + /// when determining the start state (for example, if it sees a "quit" + /// byte). This can also return an error if the given `Input` contains an + /// unsupported [`Anchored`] configuration. + fn start_state_reverse( + &self, + input: &Input<'_>, + ) -> Result<StateID, MatchError>; + + /// If this DFA has a universal starting state for the given anchor mode + /// and the DFA supports universal starting states, then this returns that + /// state's identifier. + /// + /// A DFA is said to have a universal starting state when the starting + /// state is invariant with respect to the haystack. Usually, the starting + /// state is chosen depending on the bytes immediately surrounding the + /// starting position of a search. However, the starting state only differs + /// when one or more of the patterns in the DFA have look-around assertions + /// in its prefix. + /// + /// Stated differently, if none of the patterns in a DFA have look-around + /// assertions in their prefix, then the DFA has a universal starting state + /// and _may_ be returned by this method. + /// + /// It is always correct for implementations to return `None`, and indeed, + /// this is what the default implementation does. When this returns `None`, + /// callers must use either `start_state_forward` or `start_state_reverse` + /// to get the starting state. + /// + /// # Use case + /// + /// There are a few reasons why one might want to use this: + /// + /// * If you know your regex patterns have no look-around assertions in + /// their prefix, then calling this routine is likely cheaper and perhaps + /// more semantically meaningful. + /// * When implementing prefilter support in a DFA regex implementation, + /// it is necessary to re-compute the start state after a candidate + /// is returned from the prefilter. However, this is only needed when + /// there isn't a universal start state. When one exists, one can avoid + /// re-computing the start state. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense::DFA}, + /// Anchored, + /// }; + /// + /// // There are no look-around assertions in the prefixes of any of the + /// // patterns, so we get a universal start state. + /// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+$", "[A-Z]+"])?; + /// assert!(dfa.universal_start_state(Anchored::No).is_some()); + /// assert!(dfa.universal_start_state(Anchored::Yes).is_some()); + /// + /// // One of the patterns has a look-around assertion in its prefix, + /// // so this means there is no longer a universal start state. + /// let dfa = DFA::new_many(&["[0-9]+", "^[a-z]+$", "[A-Z]+"])?; + /// assert!(!dfa.universal_start_state(Anchored::No).is_some()); + /// assert!(!dfa.universal_start_state(Anchored::Yes).is_some()); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + fn universal_start_state(&self, _mode: Anchored) -> Option<StateID> { + None + } + + /// Returns true if and only if the given identifier corresponds to a + /// "special" state. A special state is one or more of the following: + /// a dead state, a quit state, a match state, a start state or an + /// accelerated state. + /// + /// A correct implementation _may_ always return false for states that + /// are either start states or accelerated states, since that information + /// is only intended to be used for optimization purposes. Correct + /// implementations must return true if the state is a dead, quit or match + /// state. This is because search routines using this trait must be able + /// to rely on `is_special_state` as an indicator that a state may need + /// special treatment. (For example, when a search routine sees a dead + /// state, it must terminate.) + /// + /// This routine permits search implementations to use a single branch to + /// check whether a state needs special attention before executing the next + /// transition. The example below shows how to do this. + /// + /// # Example + /// + /// This example shows how `is_special_state` can be used to implement a + /// correct search routine with minimal branching. In particular, this + /// search routine implements "leftmost" matching, which means that it + /// doesn't immediately stop once a match is found. Instead, it continues + /// until it reaches a dead state. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// HalfMatch, MatchError, Input, + /// }; + /// + /// fn find<A: Automaton>( + /// dfa: &A, + /// haystack: &[u8], + /// ) -> Result<Option<HalfMatch>, MatchError> { + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. Note that start states can never + /// // be match states (since DFAs in this crate delay matches by 1 + /// // byte), so we don't need to check if the start state is a match. + /// let mut state = dfa.start_state_forward(&Input::new(haystack))?; + /// let mut last_match = None; + /// // Walk all the bytes in the haystack. We can quit early if we see + /// // a dead or a quit state. The former means the automaton will + /// // never transition to any other state. The latter means that the + /// // automaton entered a condition in which its search failed. + /// for (i, &b) in haystack.iter().enumerate() { + /// state = dfa.next_state(state, b); + /// if dfa.is_special_state(state) { + /// if dfa.is_match_state(state) { + /// last_match = Some(HalfMatch::new( + /// dfa.match_pattern(state, 0), + /// i, + /// )); + /// } else if dfa.is_dead_state(state) { + /// return Ok(last_match); + /// } else if dfa.is_quit_state(state) { + /// // It is possible to enter into a quit state after + /// // observing a match has occurred. In that case, we + /// // should return the match instead of an error. + /// if last_match.is_some() { + /// return Ok(last_match); + /// } + /// return Err(MatchError::quit(b, i)); + /// } + /// // Implementors may also want to check for start or accel + /// // states and handle them differently for performance + /// // reasons. But it is not necessary for correctness. + /// } + /// } + /// // Matches are always delayed by 1 byte, so we must explicitly walk + /// // the special "EOI" transition at the end of the search. + /// state = dfa.next_eoi_state(state); + /// if dfa.is_match_state(state) { + /// last_match = Some(HalfMatch::new( + /// dfa.match_pattern(state, 0), + /// haystack.len(), + /// )); + /// } + /// Ok(last_match) + /// } + /// + /// // We use a greedy '+' operator to show how the search doesn't just + /// // stop once a match is detected. It continues extending the match. + /// // Using '[a-z]+?' would also work as expected and stop the search + /// // early. Greediness is built into the automaton. + /// let dfa = dense::DFA::new(r"[a-z]+")?; + /// let haystack = "123 foobar 4567".as_bytes(); + /// let mat = find(&dfa, haystack)?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 0); + /// assert_eq!(mat.offset(), 10); + /// + /// // Here's another example that tests our handling of the special EOI + /// // transition. This will fail to find a match if we don't call + /// // 'next_eoi_state' at the end of the search since the match isn't + /// // found until the final byte in the haystack. + /// let dfa = dense::DFA::new(r"[0-9]{4}")?; + /// let haystack = "123 foobar 4567".as_bytes(); + /// let mat = find(&dfa, haystack)?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 0); + /// assert_eq!(mat.offset(), 15); + /// + /// // And note that our search implementation above automatically works + /// // with multi-DFAs. Namely, `dfa.match_pattern(match_state, 0)` selects + /// // the appropriate pattern ID for us. + /// let dfa = dense::DFA::new_many(&[r"[a-z]+", r"[0-9]+"])?; + /// let haystack = "123 foobar 4567".as_bytes(); + /// let mat = find(&dfa, haystack)?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 1); + /// assert_eq!(mat.offset(), 3); + /// let mat = find(&dfa, &haystack[3..])?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 0); + /// assert_eq!(mat.offset(), 7); + /// let mat = find(&dfa, &haystack[10..])?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 1); + /// assert_eq!(mat.offset(), 5); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn is_special_state(&self, id: StateID) -> bool; + + /// Returns true if and only if the given identifier corresponds to a dead + /// state. When a DFA enters a dead state, it is impossible to leave. That + /// is, every transition on a dead state by definition leads back to the + /// same dead state. + /// + /// In practice, the dead state always corresponds to the identifier `0`. + /// Moreover, in practice, there is only one dead state. + /// + /// The existence of a dead state is not strictly required in the classical + /// model of finite state machines, where one generally only cares about + /// the question of whether an input sequence matches or not. Dead states + /// are not needed to answer that question, since one can immediately quit + /// as soon as one enters a final or "match" state. However, we don't just + /// care about matches but also care about the location of matches, and + /// more specifically, care about semantics like "greedy" matching. + /// + /// For example, given the pattern `a+` and the input `aaaz`, the dead + /// state won't be entered until the state machine reaches `z` in the + /// input, at which point, the search routine can quit. But without the + /// dead state, the search routine wouldn't know when to quit. In a + /// classical representation, the search routine would stop after seeing + /// the first `a` (which is when the search would enter a match state). But + /// this wouldn't implement "greedy" matching where `a+` matches as many + /// `a`'s as possible. + /// + /// # Example + /// + /// See the example for [`Automaton::is_special_state`] for how to use this + /// method correctly. + fn is_dead_state(&self, id: StateID) -> bool; + + /// Returns true if and only if the given identifier corresponds to a quit + /// state. A quit state is like a dead state (it has no transitions other + /// than to itself), except it indicates that the DFA failed to complete + /// the search. When this occurs, callers can neither accept or reject that + /// a match occurred. + /// + /// In practice, the quit state always corresponds to the state immediately + /// following the dead state. (Which is not usually represented by `1`, + /// since state identifiers are pre-multiplied by the state machine's + /// alphabet stride, and the alphabet stride varies between DFAs.) + /// + /// The typical way in which a quit state can occur is when heuristic + /// support for Unicode word boundaries is enabled via the + /// [`dense::Config::unicode_word_boundary`](crate::dfa::dense::Config::unicode_word_boundary) + /// option. But other options, like the lower level + /// [`dense::Config::quit`](crate::dfa::dense::Config::quit) + /// configuration, can also result in a quit state being entered. The + /// purpose of the quit state is to provide a way to execute a fast DFA + /// in common cases while delegating to slower routines when the DFA quits. + /// + /// The default search implementations provided by this crate will return a + /// [`MatchError::quit`] error when a quit state is entered. + /// + /// # Example + /// + /// See the example for [`Automaton::is_special_state`] for how to use this + /// method correctly. + fn is_quit_state(&self, id: StateID) -> bool; + + /// Returns true if and only if the given identifier corresponds to a + /// match state. A match state is also referred to as a "final" state and + /// indicates that a match has been found. + /// + /// If all you care about is whether a particular pattern matches in the + /// input sequence, then a search routine can quit early as soon as the + /// machine enters a match state. However, if you're looking for the + /// standard "leftmost-first" match location, then search _must_ continue + /// until either the end of the input or until the machine enters a dead + /// state. (Since either condition implies that no other useful work can + /// be done.) Namely, when looking for the location of a match, then + /// search implementations should record the most recent location in + /// which a match state was entered, but otherwise continue executing the + /// search as normal. (The search may even leave the match state.) Once + /// the termination condition is reached, the most recently recorded match + /// location should be returned. + /// + /// Finally, one additional power given to match states in this crate + /// is that they are always associated with a specific pattern in order + /// to support multi-DFAs. See [`Automaton::match_pattern`] for more + /// details and an example for how to query the pattern associated with a + /// particular match state. + /// + /// # Example + /// + /// See the example for [`Automaton::is_special_state`] for how to use this + /// method correctly. + fn is_match_state(&self, id: StateID) -> bool; + + /// Returns true only if the given identifier corresponds to a start + /// state + /// + /// A start state is a state in which a DFA begins a search. + /// All searches begin in a start state. Moreover, since all matches are + /// delayed by one byte, a start state can never be a match state. + /// + /// The main role of a start state is, as mentioned, to be a starting + /// point for a DFA. This starting point is determined via one of + /// [`Automaton::start_state_forward`] or + /// [`Automaton::start_state_reverse`], depending on whether one is doing + /// a forward or a reverse search, respectively. + /// + /// A secondary use of start states is for prefix acceleration. Namely, + /// while executing a search, if one detects that you're in a start state, + /// then it may be faster to look for the next match of a prefix of the + /// pattern, if one exists. If a prefix exists and since all matches must + /// begin with that prefix, then skipping ahead to occurrences of that + /// prefix may be much faster than executing the DFA. + /// + /// As mentioned in the documentation for + /// [`is_special_state`](Automaton::is_special_state) implementations + /// _may_ always return false, even if the given identifier is a start + /// state. This is because knowing whether a state is a start state or not + /// is not necessary for correctness and is only treated as a potential + /// performance optimization. (For example, the implementations of this + /// trait in this crate will only return true when the given identifier + /// corresponds to a start state and when [specialization of start + /// states](crate::dfa::dense::Config::specialize_start_states) was enabled + /// during DFA construction. If start state specialization is disabled + /// (which is the default), then this method will always return false.) + /// + /// # Example + /// + /// This example shows how to implement your own search routine that does + /// a prefix search whenever the search enters a start state. + /// + /// Note that you do not need to implement your own search routine + /// to make use of prefilters like this. The search routines + /// provided by this crate already implement prefilter support via + /// the [`Prefilter`](crate::util::prefilter::Prefilter) trait. + /// A prefilter can be added to your search configuration with + /// [`dense::Config::prefilter`](crate::dfa::dense::Config::prefilter) for + /// dense and sparse DFAs in this crate. + /// + /// This example is meant to show how you might deal with prefilters in a + /// simplified case if you are implementing your own search routine. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// HalfMatch, MatchError, Input, + /// }; + /// + /// fn find_byte(slice: &[u8], at: usize, byte: u8) -> Option<usize> { + /// // Would be faster to use the memchr crate, but this is still + /// // faster than running through the DFA. + /// slice[at..].iter().position(|&b| b == byte).map(|i| at + i) + /// } + /// + /// fn find<A: Automaton>( + /// dfa: &A, + /// haystack: &[u8], + /// prefix_byte: Option<u8>, + /// ) -> Result<Option<HalfMatch>, MatchError> { + /// // See the Automaton::is_special_state example for similar code + /// // with more comments. + /// + /// let mut state = dfa.start_state_forward(&Input::new(haystack))?; + /// let mut last_match = None; + /// let mut pos = 0; + /// while pos < haystack.len() { + /// let b = haystack[pos]; + /// state = dfa.next_state(state, b); + /// pos += 1; + /// if dfa.is_special_state(state) { + /// if dfa.is_match_state(state) { + /// last_match = Some(HalfMatch::new( + /// dfa.match_pattern(state, 0), + /// pos - 1, + /// )); + /// } else if dfa.is_dead_state(state) { + /// return Ok(last_match); + /// } else if dfa.is_quit_state(state) { + /// // It is possible to enter into a quit state after + /// // observing a match has occurred. In that case, we + /// // should return the match instead of an error. + /// if last_match.is_some() { + /// return Ok(last_match); + /// } + /// return Err(MatchError::quit(b, pos - 1)); + /// } else if dfa.is_start_state(state) { + /// // If we're in a start state and know all matches begin + /// // with a particular byte, then we can quickly skip to + /// // candidate matches without running the DFA through + /// // every byte inbetween. + /// if let Some(prefix_byte) = prefix_byte { + /// pos = match find_byte(haystack, pos, prefix_byte) { + /// Some(pos) => pos, + /// None => break, + /// }; + /// } + /// } + /// } + /// } + /// // Matches are always delayed by 1 byte, so we must explicitly walk + /// // the special "EOI" transition at the end of the search. + /// state = dfa.next_eoi_state(state); + /// if dfa.is_match_state(state) { + /// last_match = Some(HalfMatch::new( + /// dfa.match_pattern(state, 0), + /// haystack.len(), + /// )); + /// } + /// Ok(last_match) + /// } + /// + /// // In this example, it's obvious that all occurrences of our pattern + /// // begin with 'Z', so we pass in 'Z'. Note also that we need to + /// // enable start state specialization, or else it won't be possible to + /// // detect start states during a search. ('is_start_state' would always + /// // return false.) + /// let dfa = dense::DFA::builder() + /// .configure(dense::DFA::config().specialize_start_states(true)) + /// .build(r"Z[a-z]+")?; + /// let haystack = "123 foobar Zbaz quux".as_bytes(); + /// let mat = find(&dfa, haystack, Some(b'Z'))?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 0); + /// assert_eq!(mat.offset(), 15); + /// + /// // But note that we don't need to pass in a prefix byte. If we don't, + /// // then the search routine does no acceleration. + /// let mat = find(&dfa, haystack, None)?.unwrap(); + /// assert_eq!(mat.pattern().as_usize(), 0); + /// assert_eq!(mat.offset(), 15); + /// + /// // However, if we pass an incorrect byte, then the prefix search will + /// // result in incorrect results. + /// assert_eq!(find(&dfa, haystack, Some(b'X'))?, None); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn is_start_state(&self, id: StateID) -> bool; + + /// Returns true if and only if the given identifier corresponds to an + /// accelerated state. + /// + /// An accelerated state is a special optimization + /// trick implemented by this crate. Namely, if + /// [`dense::Config::accelerate`](crate::dfa::dense::Config::accelerate) is + /// enabled (and it is by default), then DFAs generated by this crate will + /// tag states meeting certain characteristics as accelerated. States meet + /// this criteria whenever most of their transitions are self-transitions. + /// That is, transitions that loop back to the same state. When a small + /// number of transitions aren't self-transitions, then it follows that + /// there are only a small number of bytes that can cause the DFA to leave + /// that state. Thus, there is an opportunity to look for those bytes + /// using more optimized routines rather than continuing to run through + /// the DFA. This trick is similar to the prefilter idea described in + /// the documentation of [`Automaton::is_start_state`] with two main + /// differences: + /// + /// 1. It is more limited since acceleration only applies to single bytes. + /// This means states are rarely accelerated when Unicode mode is enabled + /// (which is enabled by default). + /// 2. It can occur anywhere in the DFA, which increases optimization + /// opportunities. + /// + /// Like the prefilter idea, the main downside (and a possible reason to + /// disable it) is that it can lead to worse performance in some cases. + /// Namely, if a state is accelerated for very common bytes, then the + /// overhead of checking for acceleration and using the more optimized + /// routines to look for those bytes can cause overall performance to be + /// worse than if acceleration wasn't enabled at all. + /// + /// A simple example of a regex that has an accelerated state is + /// `(?-u)[^a]+a`. Namely, the `[^a]+` sub-expression gets compiled down + /// into a single state where all transitions except for `a` loop back to + /// itself, and where `a` is the only transition (other than the special + /// EOI transition) that goes to some other state. Thus, this state can + /// be accelerated and implemented more efficiently by calling an + /// optimized routine like `memchr` with `a` as the needle. Notice that + /// the `(?-u)` to disable Unicode is necessary here, as without it, + /// `[^a]` will match any UTF-8 encoding of any Unicode scalar value other + /// than `a`. This more complicated expression compiles down to many DFA + /// states and the simple acceleration optimization is no longer available. + /// + /// Typically, this routine is used to guard calls to + /// [`Automaton::accelerator`], which returns the accelerated bytes for + /// the specified state. + fn is_accel_state(&self, id: StateID) -> bool; + + /// Returns the total number of patterns compiled into this DFA. + /// + /// In the case of a DFA that contains no patterns, this must return `0`. + /// + /// # Example + /// + /// This example shows the pattern length for a DFA that never matches: + /// + /// ``` + /// use regex_automata::dfa::{Automaton, dense::DFA}; + /// + /// let dfa: DFA<Vec<u32>> = DFA::never_match()?; + /// assert_eq!(dfa.pattern_len(), 0); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// And another example for a DFA that matches at every position: + /// + /// ``` + /// use regex_automata::dfa::{Automaton, dense::DFA}; + /// + /// let dfa: DFA<Vec<u32>> = DFA::always_match()?; + /// assert_eq!(dfa.pattern_len(), 1); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// And finally, a DFA that was constructed from multiple patterns: + /// + /// ``` + /// use regex_automata::dfa::{Automaton, dense::DFA}; + /// + /// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?; + /// assert_eq!(dfa.pattern_len(), 3); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn pattern_len(&self) -> usize; + + /// Returns the total number of patterns that match in this state. + /// + /// If the given state is not a match state, then implementations may + /// panic. + /// + /// If the DFA was compiled with one pattern, then this must necessarily + /// always return `1` for all match states. + /// + /// Implementations must guarantee that [`Automaton::match_pattern`] can be + /// called with indices up to (but not including) the length returned by + /// this routine without panicking. + /// + /// # Panics + /// + /// Implementations are permitted to panic if the provided state ID does + /// not correspond to a match state. + /// + /// # Example + /// + /// This example shows a simple instance of implementing overlapping + /// matches. In particular, it shows not only how to determine how many + /// patterns have matched in a particular state, but also how to access + /// which specific patterns have matched. + /// + /// Notice that we must use + /// [`MatchKind::All`](crate::MatchKind::All) + /// when building the DFA. If we used + /// [`MatchKind::LeftmostFirst`](crate::MatchKind::LeftmostFirst) + /// instead, then the DFA would not be constructed in a way that + /// supports overlapping matches. (It would only report a single pattern + /// that matches at any particular point in time.) + /// + /// Another thing to take note of is the patterns used and the order in + /// which the pattern IDs are reported. In the example below, pattern `3` + /// is yielded first. Why? Because it corresponds to the match that + /// appears first. Namely, the `@` symbol is part of `\S+` but not part + /// of any of the other patterns. Since the `\S+` pattern has a match that + /// starts to the left of any other pattern, its ID is returned before any + /// other. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{dfa::{Automaton, dense}, Input, MatchKind}; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().match_kind(MatchKind::All)) + /// .build_many(&[ + /// r"[[:word:]]+", r"[a-z]+", r"[A-Z]+", r"[[:^space:]]+", + /// ])?; + /// let haystack = "@bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// let mut state = dfa.start_state_forward(&Input::new(haystack))?; + /// // Walk all the bytes in the haystack. + /// for &b in haystack { + /// state = dfa.next_state(state, b); + /// } + /// state = dfa.next_eoi_state(state); + /// + /// assert!(dfa.is_match_state(state)); + /// assert_eq!(dfa.match_len(state), 3); + /// // The following calls are guaranteed to not panic since `match_len` + /// // returned `3` above. + /// assert_eq!(dfa.match_pattern(state, 0).as_usize(), 3); + /// assert_eq!(dfa.match_pattern(state, 1).as_usize(), 0); + /// assert_eq!(dfa.match_pattern(state, 2).as_usize(), 1); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn match_len(&self, id: StateID) -> usize; + + /// Returns the pattern ID corresponding to the given match index in the + /// given state. + /// + /// See [`Automaton::match_len`] for an example of how to use this + /// method correctly. Note that if you know your DFA is compiled with a + /// single pattern, then this routine is never necessary since it will + /// always return a pattern ID of `0` for an index of `0` when `id` + /// corresponds to a match state. + /// + /// Typically, this routine is used when implementing an overlapping + /// search, as the example for `Automaton::match_len` does. + /// + /// # Panics + /// + /// If the state ID is not a match state or if the match index is out + /// of bounds for the given state, then this routine may either panic + /// or produce an incorrect result. If the state ID is correct and the + /// match index is correct, then this routine must always produce a valid + /// `PatternID`. + fn match_pattern(&self, id: StateID, index: usize) -> PatternID; + + /// Returns true if and only if this automaton 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 DFAs 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::{dfa::{dense::DFA, Automaton}, util::syntax}; + /// + /// // The empty regex matches the empty string. + /// let dfa = DFA::new("")?; + /// assert!(dfa.has_empty(), "empty matches empty"); + /// // The '+' repetition operator requires at least one match, and so + /// // does not match the empty string. + /// let dfa = DFA::new("a+")?; + /// assert!(!dfa.has_empty(), "+ does not match empty"); + /// // But the '*' repetition operator does. + /// let dfa = DFA::new("a*")?; + /// assert!(dfa.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 dfa = DFA::new("(a+)*")?; + /// assert!(dfa.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 dfa = DFA::builder() + /// .configure(DFA::config().unicode_word_boundary(true)) + /// .syntax(syntax::Config::new().utf8(false)) + /// .build(r"^$\A\z\b\B(?-u:\b\B)")?; + /// assert!(dfa.has_empty(), "assertions match empty"); + /// // Even when an assertion is wrapped in a '+', it still matches the + /// // empty string. + /// let dfa = DFA::new(r"^+")?; + /// assert!(dfa.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 dfa = DFA::new("foo|(bar)?|quux")?; + /// assert!(dfa.has_empty(), "alternations can match empty"); + /// + /// // An NFA that matches nothing does not match the empty string. + /// let dfa = DFA::new("[a&&b]")?; + /// assert!(!dfa.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 dfa = DFA::new("[a&&b]*")?; + /// assert!(dfa.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 dfa = DFA::new("[a&&b]+")?; + /// assert!(!dfa.has_empty(), "+ on never-match still matches nothing"); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn has_empty(&self) -> bool; + + /// Whether UTF-8 mode is enabled for this DFA or not. + /// + /// When UTF-8 mode is enabled, all matches reported by a DFA are + /// guaranteed to correspond to spans of valid UTF-8. This includes + /// zero-width matches. For example, the DFA 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 [`thompson::Config::utf8`](crate::nfa::thompson::Config::utf8) for + /// more information. + /// + /// # Example + /// + /// This example shows how UTF-8 mode can impact the match spans that may + /// be reported in certain cases. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton}, + /// nfa::thompson, + /// HalfMatch, Input, + /// }; + /// + /// // UTF-8 mode is enabled by default. + /// let re = DFA::new("")?; + /// assert!(re.is_utf8()); + /// let mut input = Input::new("☃"); + /// let got = re.try_search_fwd(&input)?; + /// assert_eq!(Some(HalfMatch::must(0, 0)), got); + /// + /// // 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); + /// let got = re.try_search_fwd(&input)?; + /// assert_eq!(Some(HalfMatch::must(0, 3)), got); + /// + /// // But if we disable UTF-8, then we'll get matches at 1..1 and 2..2: + /// let re = DFA::builder() + /// .thompson(thompson::Config::new().utf8(false)) + /// .build("")?; + /// assert!(!re.is_utf8()); + /// let got = re.try_search_fwd(&input)?; + /// assert_eq!(Some(HalfMatch::must(0, 1)), got); + /// + /// input.set_start(2); + /// let got = re.try_search_fwd(&input)?; + /// assert_eq!(Some(HalfMatch::must(0, 2)), got); + /// + /// input.set_start(3); + /// let got = re.try_search_fwd(&input)?; + /// assert_eq!(Some(HalfMatch::must(0, 3)), got); + /// + /// input.set_start(4); + /// let got = re.try_search_fwd(&input)?; + /// assert_eq!(None, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn is_utf8(&self) -> bool; + + /// Returns true if and only if this DFA is limited to returning matches + /// whose start position is `0`. + /// + /// Note that if you're using DFAs provided by + /// this crate, then this is _orthogonal_ to + /// [`Config::start_kind`](crate::dfa::dense::Config::start_kind). + /// + /// This is useful in some cases because if a DFA is limited to producing + /// matches that start at offset `0`, then a reverse search is never + /// required for finding the start of a match. + /// + /// # Example + /// + /// ``` + /// use regex_automata::dfa::{dense::DFA, Automaton}; + /// + /// // The empty regex matches anywhere + /// let dfa = DFA::new("")?; + /// assert!(!dfa.is_always_start_anchored(), "empty matches anywhere"); + /// // 'a' matches anywhere. + /// let dfa = DFA::new("a")?; + /// assert!(!dfa.is_always_start_anchored(), "'a' matches anywhere"); + /// // '^' only matches at offset 0! + /// let dfa = DFA::new("^a")?; + /// assert!(dfa.is_always_start_anchored(), "'^a' matches only at 0"); + /// // But '(?m:^)' matches at 0 but at other offsets too. + /// let dfa = DFA::new("(?m:^)a")?; + /// assert!(!dfa.is_always_start_anchored(), "'(?m:^)a' matches anywhere"); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + fn is_always_start_anchored(&self) -> bool; + + /// Return a slice of bytes to accelerate for the given state, if possible. + /// + /// If the given state has no accelerator, then an empty slice must be + /// returned. If `Automaton::is_accel_state` returns true for the given ID, + /// then this routine _must_ return a non-empty slice. But note that it is + /// not required for an implementation of this trait to ever return `true` + /// for `is_accel_state`, even if the state _could_ be accelerated. That + /// is, acceleration is an optional optimization. But the return values of + /// `is_accel_state` and `accelerator` must be in sync. + /// + /// If the given ID is not a valid state ID for this automaton, then + /// implementations may panic or produce incorrect results. + /// + /// See [`Automaton::is_accel_state`] for more details on state + /// acceleration. + /// + /// By default, this method will always return an empty slice. + /// + /// # Example + /// + /// This example shows a contrived case in which we build a regex that we + /// know is accelerated and extract the accelerator from a state. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// util::{primitives::StateID, syntax}, + /// }; + /// + /// let dfa = dense::Builder::new() + /// // We disable Unicode everywhere and permit the regex to match + /// // invalid UTF-8. e.g., [^abc] matches \xFF, which is not valid + /// // UTF-8. If we left Unicode enabled, [^abc] would match any UTF-8 + /// // encoding of any Unicode scalar value except for 'a', 'b' or 'c'. + /// // That translates to a much more complicated DFA, and also + /// // inhibits the 'accelerator' optimization that we are trying to + /// // demonstrate in this example. + /// .syntax(syntax::Config::new().unicode(false).utf8(false)) + /// .build("[^abc]+a")?; + /// + /// // Here we just pluck out the state that we know is accelerated. + /// // While the stride calculations are something that can be relied + /// // on by callers, the specific position of the accelerated state is + /// // implementation defined. + /// // + /// // N.B. We get '3' by inspecting the state machine using 'regex-cli'. + /// // e.g., try `regex-cli debug dfa dense '[^abc]+a' -BbUC`. + /// let id = StateID::new(3 * dfa.stride()).unwrap(); + /// let accelerator = dfa.accelerator(id); + /// // The `[^abc]+` sub-expression permits [a, b, c] to be accelerated. + /// assert_eq!(accelerator, &[b'a', b'b', b'c']); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + fn accelerator(&self, _id: StateID) -> &[u8] { + &[] + } + + /// Returns the prefilter associated with a DFA, if one exists. + /// + /// The default implementation of this trait always returns `None`. And + /// indeed, it is always correct to return `None`. + /// + /// For DFAs in this crate, a prefilter can be attached to a DFA via + /// [`dense::Config::prefilter`](crate::dfa::dense::Config::prefilter). + /// + /// Do note that prefilters are not serialized by DFAs in this crate. + /// So if you deserialize a DFA that had a prefilter attached to it + /// at serialization time, then it will not have a prefilter after + /// deserialization. + #[inline] + fn get_prefilter(&self) -> Option<&Prefilter> { + None + } + + /// Executes a forward search and returns the end position of the leftmost + /// match that is found. If no match exists, then `None` is returned. + /// + /// In particular, this method continues searching even after it enters + /// a match state. The search only terminates once it has reached the + /// end of the input or when it has entered a dead or quit state. Upon + /// termination, the position of the last byte seen while still in a match + /// state is returned. + /// + /// # Errors + /// + /// This routine errors if the search could not complete. This can occur + /// in a number of circumstances: + /// + /// * The configuration of the DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the DFA quitting. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Notes for implementors + /// + /// Implementors of this trait are not required to implement any particular + /// match semantics (such as leftmost-first), which are instead manifest in + /// the DFA's transitions. But this search routine should behave as a + /// general "leftmost" search. + /// + /// In particular, this method must continue searching even after it enters + /// a match state. The search should only terminate once it has reached + /// the end of the input or when it has entered a dead or quit state. Upon + /// termination, the position of the last byte seen while still in a match + /// state is returned. + /// + /// Since this trait provides an implementation for this method by default, + /// it's unlikely that one will need to implement this. + /// + /// # Example + /// + /// This example shows how to use this method with a + /// [`dense::DFA`](crate::dfa::dense::DFA). + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, Input}; + /// + /// let dfa = dense::DFA::new("foo[0-9]+")?; + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new(b"foo12345"))?); + /// + /// // Even though a match is found after reading the first byte (`a`), + /// // the leftmost first match semantics demand that we find the earliest + /// // match that prefers earlier parts of the pattern over latter parts. + /// let dfa = dense::DFA::new("abc|a")?; + /// let expected = Some(HalfMatch::must(0, 3)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new(b"abc"))?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: specific pattern search + /// + /// This example shows how to build a multi-DFA that permits searching for + /// specific patterns. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// Anchored, HalfMatch, PatternID, Input, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().starts_for_each_pattern(true)) + /// .build_many(&["[a-z0-9]{6}", "[a-z][a-z0-9]{5}"])?; + /// let haystack = "foo123".as_bytes(); + /// + /// // 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(HalfMatch::must(0, 6)); + /// let got = dfa.try_search_fwd(&Input::new(haystack))?; + /// assert_eq!(expected, got); + /// + /// // But if we want to check whether some other pattern matches, then we + /// // can provide its pattern ID. + /// let input = Input::new(haystack) + /// .anchored(Anchored::Pattern(PatternID::must(1))); + /// let expected = Some(HalfMatch::must(1, 6)); + /// let got = dfa.try_search_fwd(&input)?; + /// assert_eq!(expected, got); + /// + /// # 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. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, Input}; + /// + /// // N.B. We disable Unicode here so that we use a simple ASCII word + /// // boundary. Alternatively, we could enable heuristic support for + /// // Unicode word boundaries. + /// let dfa = dense::DFA::new(r"(?-u)\b[0-9]{3}\b")?; + /// let haystack = "foo123bar".as_bytes(); + /// + /// // 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 `3` instead of `6`. + /// let input = Input::new(&haystack[3..6]); + /// let expected = Some(HalfMatch::must(0, 3)); + /// let got = dfa.try_search_fwd(&input)?; + /// assert_eq!(expected, got); + /// + /// // 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 input = Input::new(haystack).range(3..6); + /// let expected = None; + /// let got = dfa.try_search_fwd(&input)?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + fn try_search_fwd( + &self, + input: &Input<'_>, + ) -> Result<Option<HalfMatch>, MatchError> { + let utf8empty = self.has_empty() && self.is_utf8(); + let hm = match search::find_fwd(&self, input)? { + None => return Ok(None), + Some(hm) if !utf8empty => return Ok(Some(hm)), + Some(hm) => hm, + }; + // We get to this point when we know our DFA can match the empty string + // AND when UTF-8 mode is enabled. In this case, we skip any matches + // whose offset splits a codepoint. Such a match is necessarily a + // zero-width match, because UTF-8 mode requires the underlying NFA + // to be built such that all non-empty matches span valid UTF-8. + // Therefore, any match that ends in the middle of a codepoint cannot + // be part of a span of valid UTF-8 and thus must be an empty match. + // In such cases, we skip it, so as not to report matches that split a + // codepoint. + // + // Note that this is not a checked assumption. Callers *can* provide an + // NFA with UTF-8 mode enabled but produces non-empty matches that span + // invalid UTF-8. But doing so is documented to result in unspecified + // behavior. + empty::skip_splits_fwd(input, hm, hm.offset(), |input| { + let got = search::find_fwd(&self, input)?; + Ok(got.map(|hm| (hm, hm.offset()))) + }) + } + + /// Executes a reverse search and returns the start of the position of the + /// leftmost match that is found. If no match exists, then `None` is + /// returned. + /// + /// # Errors + /// + /// This routine errors if the search could not complete. This can occur + /// in a number of circumstances: + /// + /// * The configuration of the DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the DFA quitting. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// This example shows how to use this method with a + /// [`dense::DFA`](crate::dfa::dense::DFA). In particular, this + /// routine is principally useful when used in conjunction with the + /// [`nfa::thompson::Config::reverse`](crate::nfa::thompson::Config::reverse) + /// configuration. In general, it's unlikely to be correct to use + /// both `try_search_fwd` and `try_search_rev` with the same DFA since + /// any particular DFA will only support searching in one direction with + /// respect to the pattern. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson, + /// dfa::{Automaton, dense}, + /// HalfMatch, Input, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .thompson(thompson::Config::new().reverse(true)) + /// .build("foo[0-9]+")?; + /// let expected = Some(HalfMatch::must(0, 0)); + /// assert_eq!(expected, dfa.try_search_rev(&Input::new(b"foo12345"))?); + /// + /// // Even though a match is found after reading the last byte (`c`), + /// // the leftmost first match semantics demand that we find the earliest + /// // match that prefers earlier parts of the pattern over latter parts. + /// let dfa = dense::Builder::new() + /// .thompson(thompson::Config::new().reverse(true)) + /// .build("abc|c")?; + /// let expected = Some(HalfMatch::must(0, 0)); + /// assert_eq!(expected, dfa.try_search_rev(&Input::new(b"abc"))?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: UTF-8 mode + /// + /// This examples demonstrates that UTF-8 mode applies to reverse + /// DFAs. When UTF-8 mode is enabled in the underlying NFA, then all + /// matches reported must correspond to valid UTF-8 spans. This includes + /// prohibiting zero-width matches that split a codepoint. + /// + /// UTF-8 mode is enabled by default. Notice below how the only zero-width + /// matches reported are those at UTF-8 boundaries: + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton}, + /// nfa::thompson, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .thompson(thompson::Config::new().reverse(true)) + /// .build(r"")?; + /// + /// // Run the reverse DFA to collect all matches. + /// let mut input = Input::new("☃"); + /// let mut matches = vec![]; + /// loop { + /// match dfa.try_search_rev(&input)? { + /// None => break, + /// Some(hm) => { + /// matches.push(hm); + /// if hm.offset() == 0 || input.end() == 0 { + /// break; + /// } else if hm.offset() < input.end() { + /// input.set_end(hm.offset()); + /// } else { + /// // This is only necessary to handle zero-width + /// // matches, which of course occur in this example. + /// // Without this, the search would never advance + /// // backwards beyond the initial match. + /// input.set_end(input.end() - 1); + /// } + /// } + /// } + /// } + /// + /// // No matches split a codepoint. + /// let expected = vec![ + /// HalfMatch::must(0, 3), + /// HalfMatch::must(0, 0), + /// ]; + /// assert_eq!(expected, matches); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Now let's look at the same example, but with UTF-8 mode on the + /// original NFA disabled (which results in disabling UTF-8 mode on the + /// DFA): + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton}, + /// nfa::thompson, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .thompson(thompson::Config::new().reverse(true).utf8(false)) + /// .build(r"")?; + /// + /// // Run the reverse DFA to collect all matches. + /// let mut input = Input::new("☃"); + /// let mut matches = vec![]; + /// loop { + /// match dfa.try_search_rev(&input)? { + /// None => break, + /// Some(hm) => { + /// matches.push(hm); + /// if hm.offset() == 0 || input.end() == 0 { + /// break; + /// } else if hm.offset() < input.end() { + /// input.set_end(hm.offset()); + /// } else { + /// // This is only necessary to handle zero-width + /// // matches, which of course occur in this example. + /// // Without this, the search would never advance + /// // backwards beyond the initial match. + /// input.set_end(input.end() - 1); + /// } + /// } + /// } + /// } + /// + /// // No matches split a codepoint. + /// let expected = vec![ + /// HalfMatch::must(0, 3), + /// HalfMatch::must(0, 2), + /// HalfMatch::must(0, 1), + /// HalfMatch::must(0, 0), + /// ]; + /// assert_eq!(expected, matches); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + fn try_search_rev( + &self, + input: &Input<'_>, + ) -> Result<Option<HalfMatch>, MatchError> { + let utf8empty = self.has_empty() && self.is_utf8(); + let hm = match search::find_rev(self, input)? { + None => return Ok(None), + Some(hm) if !utf8empty => return Ok(Some(hm)), + Some(hm) => hm, + }; + empty::skip_splits_rev(input, hm, hm.offset(), |input| { + let got = search::find_rev(self, input)?; + Ok(got.map(|hm| (hm, hm.offset()))) + }) + } + + /// Executes an overlapping forward search. Matches, if one exists, can be + /// obtained via the [`OverlappingState::get_match`] method. + /// + /// This routine is principally only useful when searching for multiple + /// patterns on inputs where multiple patterns may match the same regions + /// of text. In particular, callers must preserve the automaton's search + /// state from prior calls so that the implementation knows where the last + /// match occurred. + /// + /// When using this routine to implement an iterator of overlapping + /// matches, the `start` of the search should always be set to the end + /// of the last match. If more patterns match at the previous location, + /// then they will be immediately returned. (This is tracked by the given + /// overlapping state.) Otherwise, the search continues at the starting + /// position given. + /// + /// If for some reason you want the search to forget about its previous + /// state and restart the search at a particular position, then setting the + /// state to [`OverlappingState::start`] will accomplish that. + /// + /// # Errors + /// + /// This routine errors if the search could not complete. This can occur + /// in a number of circumstances: + /// + /// * The configuration of the DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the DFA quitting. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// This example shows how to run a basic overlapping search with a + /// [`dense::DFA`](crate::dfa::dense::DFA). Notice that we build the + /// automaton with a `MatchKind::All` configuration. Overlapping searches + /// are unlikely to work as one would expect when using the default + /// `MatchKind::LeftmostFirst` match semantics, since leftmost-first + /// matching is fundamentally incompatible with overlapping searches. + /// Namely, overlapping searches need to report matches as they are seen, + /// where as leftmost-first searches will continue searching even after a + /// match has been observed in order to find the conventional end position + /// of the match. More concretely, leftmost-first searches use dead states + /// to terminate a search after a specific match can no longer be extended. + /// Overlapping searches instead do the opposite by continuing the search + /// to find totally new matches (potentially of other patterns). + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// dfa::{Automaton, OverlappingState, dense}, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().match_kind(MatchKind::All)) + /// .build_many(&[r"[[:word:]]+$", r"[[:^space:]]+$"])?; + /// let haystack = "@foo"; + /// let mut state = OverlappingState::start(); + /// + /// let expected = Some(HalfMatch::must(1, 4)); + /// dfa.try_search_overlapping_fwd(&Input::new(haystack), &mut state)?; + /// assert_eq!(expected, state.get_match()); + /// + /// // The first pattern also matches at the same position, so re-running + /// // the search will yield another match. Notice also that the first + /// // pattern is returned after the second. This is because the second + /// // pattern begins its match before the first, is therefore an earlier + /// // match and is thus reported first. + /// let expected = Some(HalfMatch::must(0, 4)); + /// dfa.try_search_overlapping_fwd(&Input::new(haystack), &mut state)?; + /// assert_eq!(expected, state.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + fn try_search_overlapping_fwd( + &self, + input: &Input<'_>, + state: &mut OverlappingState, + ) -> Result<(), MatchError> { + let utf8empty = self.has_empty() && self.is_utf8(); + search::find_overlapping_fwd(self, input, state)?; + match state.get_match() { + None => Ok(()), + Some(_) if !utf8empty => Ok(()), + Some(_) => skip_empty_utf8_splits_overlapping( + input, + state, + |input, state| { + search::find_overlapping_fwd(self, input, state) + }, + ), + } + } + + /// Executes a reverse overlapping forward search. Matches, if one exists, + /// can be obtained via the [`OverlappingState::get_match`] method. + /// + /// When using this routine to implement an iterator of overlapping + /// matches, the `start` of the search should remain invariant throughout + /// iteration. The `OverlappingState` given to the search will keep track + /// of the current position of the search. (This is because multiple + /// matches may be reported at the same position, so only the search + /// implementation itself knows when to advance the position.) + /// + /// If for some reason you want the search to forget about its previous + /// state and restart the search at a particular position, then setting the + /// state to [`OverlappingState::start`] will accomplish that. + /// + /// # Errors + /// + /// This routine errors if the search could not complete. This can occur + /// in a number of circumstances: + /// + /// * The configuration of the DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the DFA quitting. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example: UTF-8 mode + /// + /// This examples demonstrates that UTF-8 mode applies to reverse + /// DFAs. When UTF-8 mode is enabled in the underlying NFA, then all + /// matches reported must correspond to valid UTF-8 spans. This includes + /// prohibiting zero-width matches that split a codepoint. + /// + /// UTF-8 mode is enabled by default. Notice below how the only zero-width + /// matches reported are those at UTF-8 boundaries: + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton, OverlappingState}, + /// nfa::thompson, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .thompson(thompson::Config::new().reverse(true)) + /// .build_many(&[r"", r"☃"])?; + /// + /// // Run the reverse DFA to collect all matches. + /// let input = Input::new("☃"); + /// let mut state = OverlappingState::start(); + /// let mut matches = vec![]; + /// loop { + /// dfa.try_search_overlapping_rev(&input, &mut state)?; + /// match state.get_match() { + /// None => break, + /// Some(hm) => matches.push(hm), + /// } + /// } + /// + /// // No matches split a codepoint. + /// let expected = vec![ + /// HalfMatch::must(0, 3), + /// HalfMatch::must(1, 0), + /// HalfMatch::must(0, 0), + /// ]; + /// assert_eq!(expected, matches); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Now let's look at the same example, but with UTF-8 mode on the + /// original NFA disabled (which results in disabling UTF-8 mode on the + /// DFA): + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton, OverlappingState}, + /// nfa::thompson, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .thompson(thompson::Config::new().reverse(true).utf8(false)) + /// .build_many(&[r"", r"☃"])?; + /// + /// // Run the reverse DFA to collect all matches. + /// let input = Input::new("☃"); + /// let mut state = OverlappingState::start(); + /// let mut matches = vec![]; + /// loop { + /// dfa.try_search_overlapping_rev(&input, &mut state)?; + /// match state.get_match() { + /// None => break, + /// Some(hm) => matches.push(hm), + /// } + /// } + /// + /// // Now *all* positions match, even within a codepoint, + /// // because we lifted the requirement that matches + /// // correspond to valid UTF-8 spans. + /// let expected = vec![ + /// HalfMatch::must(0, 3), + /// HalfMatch::must(0, 2), + /// HalfMatch::must(0, 1), + /// HalfMatch::must(1, 0), + /// HalfMatch::must(0, 0), + /// ]; + /// assert_eq!(expected, matches); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + fn try_search_overlapping_rev( + &self, + input: &Input<'_>, + state: &mut OverlappingState, + ) -> Result<(), MatchError> { + let utf8empty = self.has_empty() && self.is_utf8(); + search::find_overlapping_rev(self, input, state)?; + match state.get_match() { + None => Ok(()), + Some(_) if !utf8empty => Ok(()), + Some(_) => skip_empty_utf8_splits_overlapping( + input, + state, + |input, state| { + search::find_overlapping_rev(self, input, state) + }, + ), + } + } + + /// Writes the set of patterns that match anywhere in the given search + /// configuration to `patset`. If multiple patterns match at the same + /// position and the underlying DFA supports overlapping matches, then all + /// matching patterns are written to the given set. + /// + /// Unless all of the patterns in this DFA are anchored, then generally + /// speaking, this will visit every byte in the haystack. + /// + /// This search routine *does not* clear the pattern set. This gives some + /// flexibility to the caller (e.g., running multiple searches with the + /// same pattern set), but does make the API bug-prone if you're reusing + /// the same pattern set for multiple searches but intended them to be + /// independent. + /// + /// If a pattern ID matched but the given `PatternSet` does not have + /// sufficient capacity to store it, then it is not inserted and silently + /// dropped. + /// + /// # Errors + /// + /// This routine errors if the search could not complete. This can occur + /// in a number of circumstances: + /// + /// * The configuration of the DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the DFA quitting. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// This example shows how to find all matching patterns in a haystack, + /// even when some patterns match at the same position as other patterns. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// dfa::{Automaton, dense::DFA}, + /// Input, MatchKind, PatternSet, + /// }; + /// + /// let patterns = &[ + /// r"[[:word:]]+", + /// r"[0-9]+", + /// r"[[:alpha:]]+", + /// r"foo", + /// r"bar", + /// r"barfoo", + /// r"foobar", + /// ]; + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .build_many(patterns)?; + /// + /// let input = Input::new("foobar"); + /// let mut patset = PatternSet::new(dfa.pattern_len()); + /// dfa.try_which_overlapping_matches(&input, &mut patset)?; + /// let expected = vec![0, 2, 3, 4, 6]; + /// let got: Vec<usize> = patset.iter().map(|p| p.as_usize()).collect(); + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "alloc")] + #[inline] + fn try_which_overlapping_matches( + &self, + input: &Input<'_>, + patset: &mut PatternSet, + ) -> Result<(), MatchError> { + let mut state = OverlappingState::start(); + while let Some(m) = { + self.try_search_overlapping_fwd(input, &mut state)?; + state.get_match() + } { + let _ = patset.insert(m.pattern()); + // There's nothing left to find, so we can stop. Or the caller + // asked us to. + if patset.is_full() || input.get_earliest() { + break; + } + } + Ok(()) + } +} + +unsafe impl<'a, A: Automaton + ?Sized> Automaton for &'a A { + #[inline] + fn next_state(&self, current: StateID, input: u8) -> StateID { + (**self).next_state(current, input) + } + + #[inline] + unsafe fn next_state_unchecked( + &self, + current: StateID, + input: u8, + ) -> StateID { + (**self).next_state_unchecked(current, input) + } + + #[inline] + fn next_eoi_state(&self, current: StateID) -> StateID { + (**self).next_eoi_state(current) + } + + #[inline] + fn start_state_forward( + &self, + input: &Input<'_>, + ) -> Result<StateID, MatchError> { + (**self).start_state_forward(input) + } + + #[inline] + fn start_state_reverse( + &self, + input: &Input<'_>, + ) -> Result<StateID, MatchError> { + (**self).start_state_reverse(input) + } + + #[inline] + fn universal_start_state(&self, mode: Anchored) -> Option<StateID> { + (**self).universal_start_state(mode) + } + + #[inline] + fn is_special_state(&self, id: StateID) -> bool { + (**self).is_special_state(id) + } + + #[inline] + fn is_dead_state(&self, id: StateID) -> bool { + (**self).is_dead_state(id) + } + + #[inline] + fn is_quit_state(&self, id: StateID) -> bool { + (**self).is_quit_state(id) + } + + #[inline] + fn is_match_state(&self, id: StateID) -> bool { + (**self).is_match_state(id) + } + + #[inline] + fn is_start_state(&self, id: StateID) -> bool { + (**self).is_start_state(id) + } + + #[inline] + fn is_accel_state(&self, id: StateID) -> bool { + (**self).is_accel_state(id) + } + + #[inline] + fn pattern_len(&self) -> usize { + (**self).pattern_len() + } + + #[inline] + fn match_len(&self, id: StateID) -> usize { + (**self).match_len(id) + } + + #[inline] + fn match_pattern(&self, id: StateID, index: usize) -> PatternID { + (**self).match_pattern(id, index) + } + + #[inline] + fn has_empty(&self) -> bool { + (**self).has_empty() + } + + #[inline] + fn is_utf8(&self) -> bool { + (**self).is_utf8() + } + + #[inline] + fn is_always_start_anchored(&self) -> bool { + (**self).is_always_start_anchored() + } + + #[inline] + fn accelerator(&self, id: StateID) -> &[u8] { + (**self).accelerator(id) + } + + #[inline] + fn get_prefilter(&self) -> Option<&Prefilter> { + (**self).get_prefilter() + } + + #[inline] + fn try_search_fwd( + &self, + input: &Input<'_>, + ) -> Result<Option<HalfMatch>, MatchError> { + (**self).try_search_fwd(input) + } + + #[inline] + fn try_search_rev( + &self, + input: &Input<'_>, + ) -> Result<Option<HalfMatch>, MatchError> { + (**self).try_search_rev(input) + } + + #[inline] + fn try_search_overlapping_fwd( + &self, + input: &Input<'_>, + state: &mut OverlappingState, + ) -> Result<(), MatchError> { + (**self).try_search_overlapping_fwd(input, state) + } + + #[inline] + fn try_search_overlapping_rev( + &self, + input: &Input<'_>, + state: &mut OverlappingState, + ) -> Result<(), MatchError> { + (**self).try_search_overlapping_rev(input, state) + } + + #[cfg(feature = "alloc")] + #[inline] + fn try_which_overlapping_matches( + &self, + input: &Input<'_>, + patset: &mut PatternSet, + ) -> Result<(), MatchError> { + (**self).try_which_overlapping_matches(input, patset) + } +} + +/// Represents the current state of an overlapping search. +/// +/// This is used for overlapping searches since they need to know something +/// about the previous search. For example, when multiple patterns match at the +/// same position, this state tracks the last reported pattern so that the next +/// search knows whether to report another matching pattern or continue with +/// the search at the next position. Additionally, it also tracks which state +/// the last search call terminated in. +/// +/// This type provides little introspection capabilities. The only thing a +/// caller can do is construct it and pass it around to permit search routines +/// to use it to track state, and also ask whether a match has been found. +/// +/// Callers should always provide a fresh state constructed via +/// [`OverlappingState::start`] when starting a new search. Reusing state from +/// a previous search may result in incorrect results. +#[derive(Clone, Debug, Eq, PartialEq)] +pub struct OverlappingState { + /// The match reported by the most recent overlapping search to use this + /// state. + /// + /// If a search does not find any matches, then it is expected to clear + /// this value. + pub(crate) mat: Option<HalfMatch>, + /// The state ID of the state at which the search was in when the call + /// terminated. When this is a match state, `last_match` must be set to a + /// non-None value. + /// + /// A `None` value indicates the start state of the corresponding + /// automaton. We cannot use the actual ID, since any one automaton may + /// have many start states, and which one is in use depends on several + /// search-time factors. + pub(crate) id: Option<StateID>, + /// The position of the search. + /// + /// When `id` is None (i.e., we are starting a search), this is set to + /// the beginning of the search as given by the caller regardless of its + /// current value. Subsequent calls to an overlapping search pick up at + /// this offset. + pub(crate) at: usize, + /// The index into the matching patterns of the next match to report if the + /// current state is a match state. Note that this may be 1 greater than + /// the total number of matches to report for the current match state. (In + /// which case, no more matches should be reported at the current position + /// and the search should advance to the next position.) + pub(crate) next_match_index: Option<usize>, + /// This is set to true when a reverse overlapping search has entered its + /// EOI transitions. + /// + /// This isn't used in a forward search because it knows to stop once the + /// position exceeds the end of the search range. In a reverse search, + /// since we use unsigned offsets, we don't "know" once we've gone past + /// `0`. So the only way to detect it is with this extra flag. The reverse + /// overlapping search knows to terminate specifically after it has + /// reported all matches after following the EOI transition. + pub(crate) rev_eoi: bool, +} + +impl OverlappingState { + /// Create a new overlapping state that begins at the start state of any + /// automaton. + pub fn start() -> OverlappingState { + OverlappingState { + mat: None, + id: None, + at: 0, + next_match_index: None, + rev_eoi: false, + } + } + + /// Return the match result of the most recent search to execute with this + /// state. + /// + /// A searches will clear this result automatically, such that if no + /// match is found, this will correctly report `None`. + pub fn get_match(&self) -> Option<HalfMatch> { + self.mat + } +} + +/// Runs the given overlapping `search` function (forwards or backwards) until +/// a match is found whose offset does not split a codepoint. +/// +/// This is *not* always correct to call. It should only be called when the DFA +/// has UTF-8 mode enabled *and* it can produce zero-width matches. Calling +/// this when both of those things aren't true might result in legitimate +/// matches getting skipped. +#[cold] +#[inline(never)] +fn skip_empty_utf8_splits_overlapping<F>( + input: &Input<'_>, + state: &mut OverlappingState, + mut search: F, +) -> Result<(), MatchError> +where + F: FnMut(&Input<'_>, &mut OverlappingState) -> Result<(), MatchError>, +{ + // Note that this routine works for forwards and reverse searches + // even though there's no code here to handle those cases. That's + // because overlapping searches drive themselves to completion via + // `OverlappingState`. So all we have to do is push it until no matches are + // found. + + let mut hm = match state.get_match() { + None => return Ok(()), + Some(hm) => hm, + }; + if input.get_anchored().is_anchored() { + if !input.is_char_boundary(hm.offset()) { + state.mat = None; + } + return Ok(()); + } + while !input.is_char_boundary(hm.offset()) { + search(input, state)?; + hm = match state.get_match() { + None => return Ok(()), + Some(hm) => hm, + }; + } + Ok(()) +} + +/// Write a prefix "state" indicator for fmt::Debug impls. +/// +/// Specifically, this tries to succinctly distinguish the different types of +/// states: dead states, quit states, accelerated states, start states and +/// match states. It even accounts for the possible overlappings of different +/// state types. +pub(crate) fn fmt_state_indicator<A: Automaton>( + f: &mut core::fmt::Formatter<'_>, + dfa: A, + id: StateID, +) -> core::fmt::Result { + if dfa.is_dead_state(id) { + write!(f, "D")?; + if dfa.is_start_state(id) { + write!(f, ">")?; + } else { + write!(f, " ")?; + } + } else if dfa.is_quit_state(id) { + write!(f, "Q ")?; + } else if dfa.is_start_state(id) { + if dfa.is_accel_state(id) { + write!(f, "A>")?; + } else { + write!(f, " >")?; + } + } else if dfa.is_match_state(id) { + if dfa.is_accel_state(id) { + write!(f, "A*")?; + } else { + write!(f, " *")?; + } + } else if dfa.is_accel_state(id) { + write!(f, "A ")?; + } else { + write!(f, " ")?; + } + Ok(()) +} + +#[cfg(all(test, feature = "syntax", feature = "dfa-build"))] +mod tests { + // A basic test ensuring that our Automaton trait is object safe. (This is + // the main reason why we don't define the search routines as generic over + // Into<Input>.) + #[test] + fn object_safe() { + use crate::{ + dfa::{dense, Automaton}, + HalfMatch, Input, + }; + + let dfa = dense::DFA::new("abc").unwrap(); + let dfa: &dyn Automaton = &dfa; + assert_eq!( + Ok(Some(HalfMatch::must(0, 6))), + dfa.try_search_fwd(&Input::new(b"xyzabcxyz")), + ); + } +} |