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Diffstat (limited to 'third_party/rust/regex-automata/src/hybrid/dfa.rs')
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diff --git a/third_party/rust/regex-automata/src/hybrid/dfa.rs b/third_party/rust/regex-automata/src/hybrid/dfa.rs new file mode 100644 index 0000000000..67261c1a30 --- /dev/null +++ b/third_party/rust/regex-automata/src/hybrid/dfa.rs @@ -0,0 +1,4381 @@ +/*! +Types and routines specific to lazy DFAs. + +This module is the home of [`hybrid::dfa::DFA`](DFA). + +This module also contains a [`hybrid::dfa::Builder`](Builder) and a +[`hybrid::dfa::Config`](Config) for configuring and building a lazy DFA. +*/ + +use core::{iter, mem::size_of}; + +use alloc::vec::Vec; + +use crate::{ + hybrid::{ + error::{BuildError, CacheError}, + id::{LazyStateID, LazyStateIDError}, + search, + }, + nfa::thompson, + util::{ + alphabet::{self, ByteClasses, ByteSet}, + determinize::{self, State, StateBuilderEmpty, StateBuilderNFA}, + empty, + prefilter::Prefilter, + primitives::{PatternID, StateID as NFAStateID}, + search::{ + Anchored, HalfMatch, Input, MatchError, MatchKind, PatternSet, + }, + sparse_set::SparseSets, + start::{Start, StartByteMap}, + }, +}; + +/// The minimum number of states that a lazy DFA's cache size must support. +/// +/// This is checked at time of construction to ensure that at least some small +/// number of states can fit in the given capacity allotment. If we can't fit +/// at least this number of states, then the thinking is that it's pretty +/// senseless to use the lazy DFA. More to the point, parts of the code do +/// assume that the cache can fit at least some small number of states. +const MIN_STATES: usize = SENTINEL_STATES + 2; + +/// The number of "sentinel" states that get added to every lazy DFA. +/// +/// These are special states indicating status conditions of a search: unknown, +/// dead and quit. These states in particular also use zero NFA states, so +/// their memory usage is quite small. This is relevant for computing the +/// minimum memory needed for a lazy DFA cache. +const SENTINEL_STATES: usize = 3; + +/// A hybrid NFA/DFA (also called a "lazy DFA") for regex searching. +/// +/// A lazy DFA is a DFA that builds itself at search time. It otherwise has +/// very similar characteristics as a [`dense::DFA`](crate::dfa::dense::DFA). +/// Indeed, both support precisely the same regex features with precisely the +/// same semantics. +/// +/// Where as a `dense::DFA` must be completely built to handle any input before +/// it may be used for search, a lazy DFA starts off effectively empty. During +/// a search, a lazy DFA will build itself depending on whether it has already +/// computed the next transition or not. If it has, then it looks a lot like +/// a `dense::DFA` internally: it does a very fast table based access to find +/// the next transition. Otherwise, if the state hasn't been computed, then it +/// does determinization _for that specific transition_ to compute the next DFA +/// state. +/// +/// The main selling point of a lazy DFA is that, in practice, it has +/// the performance profile of a `dense::DFA` without the weakness of it +/// taking worst case exponential time to build. Indeed, for each byte of +/// input, the lazy DFA will construct as most one new DFA state. Thus, a +/// lazy DFA achieves worst case `O(mn)` time for regex search (where `m ~ +/// pattern.len()` and `n ~ haystack.len()`). +/// +/// The main downsides of a lazy DFA are: +/// +/// 1. It requires mutable "cache" space during search. This is where the +/// transition table, among other things, is stored. +/// 2. In pathological cases (e.g., if the cache is too small), it will run +/// out of room and either require a bigger cache capacity or will repeatedly +/// clear the cache and thus repeatedly regenerate DFA states. Overall, this +/// will tend to be slower than a typical NFA simulation. +/// +/// # Capabilities +/// +/// Like a `dense::DFA`, a single lazy DFA fundamentally supports the following +/// operations: +/// +/// 1. Detection of a match. +/// 2. Location of the end of a match. +/// 3. In the case of a lazy DFA with multiple patterns, which pattern matched +/// is reported as well. +/// +/// A notable absence from the above list of capabilities is the location of +/// the *start* of a match. In order to provide both the start and end of +/// a match, *two* lazy DFAs are required. This functionality is provided by a +/// [`Regex`](crate::hybrid::regex::Regex). +/// +/// # Example +/// +/// This shows how to build a lazy DFA with the default configuration and +/// execute a search. Notice how, in contrast to a `dense::DFA`, we must create +/// a cache and pass it to our search routine. +/// +/// ``` +/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; +/// +/// let dfa = DFA::new("foo[0-9]+")?; +/// let mut cache = dfa.create_cache(); +/// +/// let expected = Some(HalfMatch::must(0, 8)); +/// assert_eq!(expected, dfa.try_search_fwd( +/// &mut cache, &Input::new("foo12345"))?, +/// ); +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone, Debug)] +pub struct DFA { + config: Config, + nfa: thompson::NFA, + stride2: usize, + start_map: StartByteMap, + classes: ByteClasses, + quitset: ByteSet, + cache_capacity: usize, +} + +impl DFA { + /// Parse the given regular expression using a default configuration and + /// return the corresponding lazy DFA. + /// + /// If you want a non-default configuration, then use the [`Builder`] to + /// set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let dfa = DFA::new("foo[0-9]+bar")?; + /// let mut cache = dfa.create_cache(); + /// + /// let expected = HalfMatch::must(0, 11); + /// assert_eq!( + /// Some(expected), + /// dfa.try_search_fwd(&mut cache, &Input::new("foo12345bar"))?, + /// ); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new(pattern: &str) -> Result<DFA, BuildError> { + DFA::builder().build(pattern) + } + + /// Parse the given regular expressions using a default configuration and + /// return the corresponding lazy multi-DFA. + /// + /// If you want a non-default configuration, then use the [`Builder`] to + /// set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+"])?; + /// let mut cache = dfa.create_cache(); + /// + /// let expected = HalfMatch::must(1, 3); + /// assert_eq!( + /// Some(expected), + /// dfa.try_search_fwd(&mut cache, &Input::new("foo12345bar"))?, + /// ); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new_many<P: AsRef<str>>(patterns: &[P]) -> Result<DFA, BuildError> { + DFA::builder().build_many(patterns) + } + + /// Create a new lazy DFA that matches every input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let dfa = DFA::always_match()?; + /// let mut cache = dfa.create_cache(); + /// + /// let expected = HalfMatch::must(0, 0); + /// assert_eq!(Some(expected), dfa.try_search_fwd( + /// &mut cache, &Input::new(""))?, + /// ); + /// assert_eq!(Some(expected), dfa.try_search_fwd( + /// &mut cache, &Input::new("foo"))?, + /// ); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn always_match() -> Result<DFA, BuildError> { + let nfa = thompson::NFA::always_match(); + Builder::new().build_from_nfa(nfa) + } + + /// Create a new lazy DFA that never matches any input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, Input}; + /// + /// let dfa = DFA::never_match()?; + /// let mut cache = dfa.create_cache(); + /// + /// assert_eq!(None, dfa.try_search_fwd(&mut cache, &Input::new(""))?); + /// assert_eq!(None, dfa.try_search_fwd(&mut cache, &Input::new("foo"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn never_match() -> Result<DFA, BuildError> { + let nfa = thompson::NFA::never_match(); + Builder::new().build_from_nfa(nfa) + } + + /// Return a default configuration for a `DFA`. + /// + /// This is a convenience routine to avoid needing to import the [`Config`] + /// type when customizing the construction of a lazy DFA. + /// + /// # Example + /// + /// This example shows how to build a lazy DFA that heuristically supports + /// Unicode word boundaries. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, MatchError, Input}; + /// + /// let re = DFA::builder() + /// .configure(DFA::config().unicode_word_boundary(true)) + /// .build(r"\b\w+\b")?; + /// let mut cache = re.create_cache(); + /// + /// // Since our haystack is all ASCII, the DFA search sees then and knows + /// // it is legal to interpret Unicode word boundaries as ASCII word + /// // boundaries. + /// let input = Input::new("!!foo!!"); + /// let expected = HalfMatch::must(0, 5); + /// assert_eq!(Some(expected), re.try_search_fwd(&mut cache, &input)?); + /// + /// // But if our haystack contains non-ASCII, then the search will fail + /// // with an error. + /// let input = Input::new("!!βββ!!"); + /// let expected = MatchError::quit(b'\xCE', 2); + /// assert_eq!(Err(expected), re.try_search_fwd(&mut cache, &input)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn config() -> Config { + Config::new() + } + + /// Return a builder for configuring the construction of a `Regex`. + /// + /// This is a convenience routine to avoid needing to import the + /// [`Builder`] type in common cases. + /// + /// # Example + /// + /// This example shows how to use the builder to disable UTF-8 mode + /// everywhere for lazy DFAs. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, util::syntax, HalfMatch, Input}; + /// + /// let re = DFA::builder() + /// .syntax(syntax::Config::new().utf8(false)) + /// .build(r"foo(?-u:[^b])ar.*")?; + /// let mut cache = re.create_cache(); + /// + /// let input = Input::new(b"\xFEfoo\xFFarzz\xE2\x98\xFF\n"); + /// let expected = Some(HalfMatch::must(0, 9)); + /// let got = re.try_search_fwd(&mut cache, &input)?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn builder() -> Builder { + Builder::new() + } + + /// Create a new cache for this lazy DFA. + /// + /// The cache returned should only be used for searches for this + /// lazy DFA. If you want to reuse the cache for another DFA, then + /// you must call [`Cache::reset`] with that DFA (or, equivalently, + /// [`DFA::reset_cache`]). + pub fn create_cache(&self) -> Cache { + Cache::new(self) + } + + /// Reset the given cache such that it can be used for searching with the + /// this lazy DFA (and only this DFA). + /// + /// A cache reset permits reusing memory already allocated in this cache + /// with a different lazy DFA. + /// + /// Resetting a cache sets its "clear count" to 0. This is relevant if the + /// lazy DFA has been configured to "give up" after it has cleared the + /// cache a certain number of times. + /// + /// Any lazy state ID generated by the cache prior to resetting it is + /// invalid after the reset. + /// + /// # Example + /// + /// This shows how to re-purpose a cache for use with a different DFA. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let dfa1 = DFA::new(r"\w")?; + /// let dfa2 = DFA::new(r"\W")?; + /// + /// let mut cache = dfa1.create_cache(); + /// assert_eq!( + /// Some(HalfMatch::must(0, 2)), + /// dfa1.try_search_fwd(&mut cache, &Input::new("Δ"))?, + /// ); + /// + /// // Using 'cache' with dfa2 is not allowed. It may result in panics or + /// // incorrect results. In order to re-purpose the cache, we must reset + /// // it with the DFA we'd like to use it with. + /// // + /// // Similarly, after this reset, using the cache with 'dfa1' is also not + /// // allowed. + /// dfa2.reset_cache(&mut cache); + /// assert_eq!( + /// Some(HalfMatch::must(0, 3)), + /// dfa2.try_search_fwd(&mut cache, &Input::new("☃"))?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn reset_cache(&self, cache: &mut Cache) { + Lazy::new(self, cache).reset_cache() + } + + /// Returns the total number of patterns compiled into this lazy DFA. + /// + /// In the case of a DFA that contains no patterns, this returns `0`. + /// + /// # Example + /// + /// This example shows the pattern length for a DFA that never matches: + /// + /// ``` + /// use regex_automata::hybrid::dfa::DFA; + /// + /// let dfa = 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::hybrid::dfa::DFA; + /// + /// let dfa = 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::hybrid::dfa::DFA; + /// + /// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?; + /// assert_eq!(dfa.pattern_len(), 3); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn pattern_len(&self) -> usize { + self.nfa.pattern_len() + } + + /// Returns the equivalence classes that make up the alphabet for this DFA. + /// + /// Unless [`Config::byte_classes`] was disabled, it is possible that + /// multiple distinct bytes are grouped into the same equivalence class + /// if it is impossible for them to discriminate between a match and a + /// non-match. This has the effect of reducing the overall alphabet size + /// and in turn potentially substantially reducing the size of the DFA's + /// transition table. + /// + /// The downside of using equivalence classes like this is that every state + /// transition will automatically use this map to convert an arbitrary + /// byte to its corresponding equivalence class. In practice this has a + /// negligible impact on performance. + pub fn byte_classes(&self) -> &ByteClasses { + &self.classes + } + + /// Returns this lazy DFA's configuration. + pub fn get_config(&self) -> &Config { + &self.config + } + + /// Returns a reference to the underlying NFA. + pub fn get_nfa(&self) -> &thompson::NFA { + &self.nfa + } + + /// Returns the stride, as a base-2 exponent, required for these + /// equivalence classes. + /// + /// The stride is always the smallest power of 2 that is greater than or + /// equal to the alphabet length. This is done so that converting between + /// state IDs and indices can be done with shifts alone, which is much + /// faster than integer division. + fn stride2(&self) -> usize { + self.stride2 + } + + /// Returns the total stride for every state in this lazy DFA. This + /// corresponds to the total number of transitions used by each state in + /// this DFA's transition table. + fn stride(&self) -> usize { + 1 << self.stride2() + } + + /// Returns the memory usage, in bytes, of this lazy DFA. + /// + /// This does **not** include the stack size used up by this lazy DFA. To + /// compute that, use `std::mem::size_of::<DFA>()`. This also does not + /// include the size of the `Cache` used. + /// + /// This also does not include any heap memory used by the NFA inside of + /// this hybrid NFA/DFA. This is because the NFA's ownership is shared, and + /// thus not owned by this hybrid NFA/DFA. More practically, several regex + /// engines in this crate embed an NFA, and reporting the NFA's memory + /// usage in all of them would likely result in reporting higher heap + /// memory than is actually used. + pub fn memory_usage(&self) -> usize { + // The only thing that uses heap memory in a DFA is the NFA. But the + // NFA has shared ownership, so reporting its memory as part of the + // hybrid DFA is likely to lead to double-counting the NFA memory + // somehow. In particular, this DFA does not really own an NFA, so + // including it in the DFA's memory usage doesn't seem semantically + // correct. + 0 + } +} + +impl DFA { + /// 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 lazy DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the lazy DFA quitting. + /// * The configuration of the lazy DFA may also permit it to "give up" + /// on a search if it makes ineffective use of its transition table + /// cache. The default configuration does not enable this by default, + /// although it is typically a good idea to. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// This example shows how to run a basic search. + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let dfa = DFA::new("foo[0-9]+")?; + /// let mut cache = dfa.create_cache(); + /// let expected = HalfMatch::must(0, 8); + /// assert_eq!(Some(expected), dfa.try_search_fwd( + /// &mut cache, &Input::new("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 later parts. + /// let dfa = DFA::new("abc|a")?; + /// let mut cache = dfa.create_cache(); + /// let expected = HalfMatch::must(0, 3); + /// assert_eq!(Some(expected), dfa.try_search_fwd( + /// &mut cache, &Input::new("abc"))?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: specific pattern search + /// + /// This example shows how to build a lazy multi-DFA that permits searching + /// for specific patterns. + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// Anchored, HalfMatch, PatternID, Input, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().starts_for_each_pattern(true)) + /// .build_many(&["[a-z0-9]{6}", "[a-z][a-z0-9]{5}"])?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "foo123"; + /// + /// // Since we are using the default leftmost-first match and both + /// // patterns match at the same starting position, only the first pattern + /// // will be returned in this case when doing a search for any of the + /// // patterns. + /// let expected = Some(HalfMatch::must(0, 6)); + /// let got = dfa.try_search_fwd(&mut cache, &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 expected = Some(HalfMatch::must(1, 6)); + /// let input = Input::new(haystack) + /// .anchored(Anchored::Pattern(PatternID::must(1))); + /// let got = dfa.try_search_fwd(&mut cache, &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::{hybrid::dfa::DFA, 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 since our haystack is pure ASCII. + /// let dfa = DFA::new(r"(?-u)\b[0-9]{3}\b")?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "foo123bar"; + /// + /// // Since we sub-slice the haystack, the search doesn't know about the + /// // larger context and assumes that `123` is surrounded by word + /// // boundaries. And of course, the match position is reported relative + /// // to the sub-slice as well, which means we get `3` instead of `6`. + /// let expected = Some(HalfMatch::must(0, 3)); + /// let got = dfa.try_search_fwd( + /// &mut cache, + /// &Input::new(&haystack[3..6]), + /// )?; + /// 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 expected = None; + /// let got = dfa.try_search_fwd( + /// &mut cache, + /// &Input::new(haystack).range(3..6), + /// )?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_search_fwd( + &self, + cache: &mut Cache, + input: &Input<'_>, + ) -> Result<Option<HalfMatch>, MatchError> { + let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); + let hm = match search::find_fwd(self, cache, 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, cache, 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 lazy DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the lazy DFA quitting. + /// * The configuration of the lazy DFA may also permit it to "give up" + /// on a search if it makes ineffective use of its transition table + /// cache. The default configuration does not enable this by default, + /// although it is typically a good idea to. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// 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, + /// hybrid::dfa::DFA, + /// HalfMatch, Input, + /// }; + /// + /// let dfa = DFA::builder() + /// .thompson(thompson::Config::new().reverse(true)) + /// .build("foo[0-9]+")?; + /// let mut cache = dfa.create_cache(); + /// let expected = HalfMatch::must(0, 0); + /// assert_eq!( + /// Some(expected), + /// dfa.try_search_rev(&mut cache, &Input::new("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 = DFA::builder() + /// .thompson(thompson::Config::new().reverse(true)) + /// .build("abc|c")?; + /// let mut cache = dfa.create_cache(); + /// let expected = HalfMatch::must(0, 0); + /// assert_eq!(Some(expected), dfa.try_search_rev( + /// &mut cache, &Input::new("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::{ + /// hybrid::dfa::DFA, + /// nfa::thompson, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .thompson(thompson::Config::new().reverse(true)) + /// .build(r"")?; + /// let mut cache = dfa.create_cache(); + /// + /// // Run the reverse DFA to collect all matches. + /// let mut input = Input::new("☃"); + /// let mut matches = vec![]; + /// loop { + /// match dfa.try_search_rev(&mut cache, &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 + /// underlying NFA disabled: + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// nfa::thompson, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .thompson(thompson::Config::new().reverse(true).utf8(false)) + /// .build(r"")?; + /// let mut cache = dfa.create_cache(); + /// + /// // Run the reverse DFA to collect all matches. + /// let mut input = Input::new("☃"); + /// let mut matches = vec![]; + /// loop { + /// match dfa.try_search_rev(&mut cache, &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] + pub fn try_search_rev( + &self, + cache: &mut Cache, + input: &Input<'_>, + ) -> Result<Option<HalfMatch>, MatchError> { + let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); + let hm = match search::find_rev(self, cache, 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, cache, input)?; + Ok(got.map(|hm| (hm, hm.offset()))) + }) + } + + /// Executes an overlapping forward search and returns the end position of + /// matches as they are found. If no match exists, then `None` is returned. + /// + /// 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 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 lazy DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the lazy DFA quitting. + /// * The configuration of the lazy DFA may also permit it to "give up" + /// on a search if it makes ineffective use of its transition table + /// cache. The default configuration does not enable this by default, + /// although it is typically a good idea to. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # Example + /// + /// This example shows how to run a basic overlapping search. 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::{ + /// hybrid::dfa::{DFA, OverlappingState}, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .build_many(&[r"\w+$", r"\S+$"])?; + /// let mut cache = dfa.create_cache(); + /// + /// let haystack = "@foo"; + /// let mut state = OverlappingState::start(); + /// + /// let expected = Some(HalfMatch::must(1, 4)); + /// dfa.try_search_overlapping_fwd( + /// &mut cache, &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( + /// &mut cache, &Input::new(haystack), &mut state, + /// )?; + /// assert_eq!(expected, state.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn try_search_overlapping_fwd( + &self, + cache: &mut Cache, + input: &Input<'_>, + state: &mut OverlappingState, + ) -> Result<(), MatchError> { + let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); + search::find_overlapping_fwd(self, cache, 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, cache, input, state) + }, + ), + } + } + + /// Executes a reverse overlapping search and returns the start of the + /// position of the leftmost match that is found. If no match exists, then + /// `None` is returned. + /// + /// 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 lazy DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the lazy DFA quitting. + /// * The configuration of the lazy DFA may also permit it to "give up" + /// on a search if it makes ineffective use of its transition table + /// cache. The default configuration does not enable this by default, + /// although it is typically a good idea to. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # 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::{ + /// hybrid::dfa::{DFA, 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"☃"])?; + /// let mut cache = dfa.create_cache(); + /// + /// // 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(&mut cache, &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 + /// underlying NFA disabled: + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::{DFA, 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"☃"])?; + /// let mut cache = dfa.create_cache(); + /// + /// // 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(&mut cache, &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] + pub fn try_search_overlapping_rev( + &self, + cache: &mut Cache, + input: &Input<'_>, + state: &mut OverlappingState, + ) -> Result<(), MatchError> { + let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8(); + search::find_overlapping_rev(self, cache, 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, cache, 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 lazy DFA may permit it to "quit" the search. + /// For example, setting quit bytes or enabling heuristic support for + /// Unicode word boundaries. The default configuration does not enable any + /// option that could result in the lazy DFA quitting. + /// * The configuration of the lazy DFA may also permit it to "give up" + /// on a search if it makes ineffective use of its transition table + /// cache. The default configuration does not enable this by default, + /// although it is typically a good idea to. + /// * When the provided `Input` configuration is not supported. For + /// example, by providing an unsupported anchor mode. + /// + /// When a search returns an error, callers cannot know whether a match + /// exists or not. + /// + /// # 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::{ + /// hybrid::dfa::DFA, + /// Input, MatchKind, PatternSet, + /// }; + /// + /// let patterns = &[ + /// r"\w+", r"\d+", r"\pL+", r"foo", r"bar", r"barfoo", r"foobar", + /// ]; + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .build_many(patterns)?; + /// let mut cache = dfa.create_cache(); + /// + /// let input = Input::new("foobar"); + /// let mut patset = PatternSet::new(dfa.pattern_len()); + /// dfa.try_which_overlapping_matches(&mut cache, &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>>(()) + /// ``` + #[inline] + pub fn try_which_overlapping_matches( + &self, + cache: &mut Cache, + input: &Input<'_>, + patset: &mut PatternSet, + ) -> Result<(), MatchError> { + let mut state = OverlappingState::start(); + while let Some(m) = { + self.try_search_overlapping_fwd(cache, input, &mut state)?; + state.get_match() + } { + let _ = patset.try_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(()) + } +} + +impl DFA { + /// Transitions from the current state to the next state, given the next + /// byte of input. + /// + /// The given cache is used to either reuse pre-computed state + /// transitions, or to store this newly computed transition for future + /// reuse. Thus, this routine guarantees that it will never return a state + /// ID that has an "unknown" tag. + /// + /// # State identifier validity + /// + /// The only valid value for `current` is the lazy state ID returned + /// by the most recent call to `next_state`, `next_state_untagged`, + /// `next_state_untagged_unchecked`, `start_state_forward` or + /// `state_state_reverse` for the given `cache`. Any state ID returned from + /// prior calls to these routines (with the same `cache`) is considered + /// invalid (even if it gives an appearance of working). State IDs returned + /// from _any_ prior call for different `cache` values are also always + /// invalid. + /// + /// The returned ID is always a valid ID when `current` refers to a valid + /// ID. Moreover, this routine is defined for all possible values of + /// `input`. + /// + /// These validity rules are not checked, even in debug mode. Callers are + /// required to uphold these rules themselves. + /// + /// Violating these state ID validity rules will not sacrifice memory + /// safety, but _may_ produce an incorrect result or a panic. + /// + /// # 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 or + /// incorrect ID. + /// + /// # Example + /// + /// This shows a simplistic example for walking a lazy DFA for a given + /// haystack by using the `next_state` method. + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, Input}; + /// + /// let dfa = DFA::new(r"[a-z]+r")?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// let mut sid = dfa.start_state_forward( + /// &mut cache, &Input::new(haystack), + /// )?; + /// // Walk all the bytes in the haystack. + /// for &b in haystack { + /// sid = dfa.next_state(&mut cache, sid, b)?; + /// } + /// // Matches are always delayed by 1 byte, so we must explicitly walk the + /// // special "EOI" transition at the end of the search. + /// sid = dfa.next_eoi_state(&mut cache, sid)?; + /// assert!(sid.is_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn next_state( + &self, + cache: &mut Cache, + current: LazyStateID, + input: u8, + ) -> Result<LazyStateID, CacheError> { + let class = usize::from(self.classes.get(input)); + let offset = current.as_usize_untagged() + class; + let sid = cache.trans[offset]; + if !sid.is_unknown() { + return Ok(sid); + } + let unit = alphabet::Unit::u8(input); + Lazy::new(self, cache).cache_next_state(current, unit) + } + + /// Transitions from the current state to the next state, given the next + /// byte of input and a state ID that is not tagged. + /// + /// The only reason to use this routine is performance. In particular, the + /// `next_state` method needs to do some additional checks, among them is + /// to account for identifiers to states that are not yet computed. In + /// such a case, the transition is computed on the fly. However, if it is + /// known that the `current` state ID is untagged, then these checks can be + /// omitted. + /// + /// Since this routine does not compute states on the fly, it does not + /// modify the cache and thus cannot return an error. Consequently, `cache` + /// does not need to be mutable and it is possible for this routine to + /// return a state ID corresponding to the special "unknown" state. In + /// this case, it is the caller's responsibility to use the prior state + /// ID and `input` with `next_state` in order to force the computation of + /// the unknown transition. Otherwise, trying to use the "unknown" state + /// ID will just result in transitioning back to itself, and thus never + /// terminating. (This is technically a special exemption to the state ID + /// validity rules, but is permissible since this routine is guarateed to + /// never mutate the given `cache`, and thus the identifier is guaranteed + /// to remain valid.) + /// + /// See [`LazyStateID`] for more details on what it means for a state ID + /// to be tagged. Also, see + /// [`next_state_untagged_unchecked`](DFA::next_state_untagged_unchecked) + /// for this same idea, but with bounds checks forcefully elided. + /// + /// # State identifier validity + /// + /// The only valid value for `current` is an **untagged** lazy + /// state ID returned by the most recent call to `next_state`, + /// `next_state_untagged`, `next_state_untagged_unchecked`, + /// `start_state_forward` or `state_state_reverse` for the given `cache`. + /// Any state ID returned from prior calls to these routines (with the + /// same `cache`) is considered invalid (even if it gives an appearance + /// of working). State IDs returned from _any_ prior call for different + /// `cache` values are also always invalid. + /// + /// The returned ID is always a valid ID when `current` refers to a valid + /// ID, although it may be tagged. Moreover, this routine is defined for + /// all possible values of `input`. + /// + /// Not all validity rules are checked, even in debug mode. Callers are + /// required to uphold these rules themselves. + /// + /// Violating these state ID validity rules will not sacrifice memory + /// safety, but _may_ produce an incorrect result or a panic. + /// + /// # 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 or + /// incorrect ID. + /// + /// # Example + /// + /// This shows a simplistic example for walking a lazy DFA for a given + /// haystack by using the `next_state_untagged` method where possible. + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, Input}; + /// + /// let dfa = DFA::new(r"[a-z]+r")?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// let mut sid = dfa.start_state_forward( + /// &mut cache, &Input::new(haystack), + /// )?; + /// // Walk all the bytes in the haystack. + /// let mut at = 0; + /// while at < haystack.len() { + /// if sid.is_tagged() { + /// sid = dfa.next_state(&mut cache, sid, haystack[at])?; + /// } else { + /// let mut prev_sid = sid; + /// // We attempt to chew through as much as we can while moving + /// // through untagged state IDs. Thus, the transition function + /// // does less work on average per byte. (Unrolling this loop + /// // may help even more.) + /// while at < haystack.len() { + /// prev_sid = sid; + /// sid = dfa.next_state_untagged( + /// &mut cache, sid, haystack[at], + /// ); + /// at += 1; + /// if sid.is_tagged() { + /// break; + /// } + /// } + /// // We must ensure that we never proceed to the next iteration + /// // with an unknown state ID. If we don't account for this + /// // case, then search isn't guaranteed to terminate since all + /// // transitions on unknown states loop back to itself. + /// if sid.is_unknown() { + /// sid = dfa.next_state( + /// &mut cache, prev_sid, haystack[at - 1], + /// )?; + /// } + /// } + /// } + /// // Matches are always delayed by 1 byte, so we must explicitly walk the + /// // special "EOI" transition at the end of the search. + /// sid = dfa.next_eoi_state(&mut cache, sid)?; + /// assert!(sid.is_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn next_state_untagged( + &self, + cache: &Cache, + current: LazyStateID, + input: u8, + ) -> LazyStateID { + debug_assert!(!current.is_tagged()); + let class = usize::from(self.classes.get(input)); + let offset = current.as_usize_unchecked() + class; + cache.trans[offset] + } + + /// Transitions from the current state to the next state, eliding bounds + /// checks, given the next byte of input and a state ID that is not tagged. + /// + /// The only reason to use this routine is performance. In particular, the + /// `next_state` method needs to do some additional checks, among them is + /// to account for identifiers to states that are not yet computed. In + /// such a case, the transition is computed on the fly. However, if it is + /// known that the `current` state ID is untagged, then these checks can be + /// omitted. + /// + /// Since this routine does not compute states on the fly, it does not + /// modify the cache and thus cannot return an error. Consequently, `cache` + /// does not need to be mutable and it is possible for this routine to + /// return a state ID corresponding to the special "unknown" state. In + /// this case, it is the caller's responsibility to use the prior state + /// ID and `input` with `next_state` in order to force the computation of + /// the unknown transition. Otherwise, trying to use the "unknown" state + /// ID will just result in transitioning back to itself, and thus never + /// terminating. (This is technically a special exemption to the state ID + /// validity rules, but is permissible since this routine is guarateed to + /// never mutate the given `cache`, and thus the identifier is guaranteed + /// to remain valid.) + /// + /// See [`LazyStateID`] for more details on what it means for a state ID + /// to be tagged. Also, see + /// [`next_state_untagged`](DFA::next_state_untagged) + /// for this same idea, but with memory safety guaranteed by retaining + /// bounds checks. + /// + /// # State identifier validity + /// + /// The only valid value for `current` is an **untagged** lazy + /// state ID returned by the most recent call to `next_state`, + /// `next_state_untagged`, `next_state_untagged_unchecked`, + /// `start_state_forward` or `state_state_reverse` for the given `cache`. + /// Any state ID returned from prior calls to these routines (with the + /// same `cache`) is considered invalid (even if it gives an appearance + /// of working). State IDs returned from _any_ prior call for different + /// `cache` values are also always invalid. + /// + /// The returned ID is always a valid ID when `current` refers to a valid + /// ID, although it may be tagged. Moreover, this routine is defined for + /// all possible values of `input`. + /// + /// Not all validity rules are checked, even in debug mode. Callers are + /// required to uphold these rules themselves. + /// + /// Violating these state ID validity rules will not sacrifice memory + /// safety, but _may_ produce an incorrect result or a panic. + /// + /// # Safety + /// + /// Callers of this method must guarantee that `current` refers to a valid + /// state ID according to the rules described above. 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 the ID returned is valid for all possible + /// values of `input`. + #[inline] + pub unsafe fn next_state_untagged_unchecked( + &self, + cache: &Cache, + current: LazyStateID, + input: u8, + ) -> LazyStateID { + debug_assert!(!current.is_tagged()); + let class = usize::from(self.classes.get(input)); + let offset = current.as_usize_unchecked() + class; + *cache.trans.get_unchecked(offset) + } + + /// Transitions from the current state to the next state for the special + /// EOI symbol. + /// + /// The given cache is used to either reuse pre-computed state + /// transitions, or to store this newly computed transition for future + /// reuse. Thus, this routine guarantees that it will never return a state + /// ID that has an "unknown" tag. + /// + /// This routine must be called at the end of every search in a correct + /// implementation of search. Namely, lazy 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 + /// lazy 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.) + /// + /// # State identifier validity + /// + /// The only valid value for `current` is the lazy state ID returned + /// by the most recent call to `next_state`, `next_state_untagged`, + /// `next_state_untagged_unchecked`, `start_state_forward` or + /// `state_state_reverse` for the given `cache`. Any state ID returned from + /// prior calls to these routines (with the same `cache`) is considered + /// invalid (even if it gives an appearance of working). State IDs returned + /// from _any_ prior call for different `cache` values are also always + /// invalid. + /// + /// The returned ID is always a valid ID when `current` refers to a valid + /// ID. + /// + /// These validity rules are not checked, even in debug mode. Callers are + /// required to uphold these rules themselves. + /// + /// Violating these state ID validity rules will not sacrifice memory + /// safety, but _may_ produce an incorrect result or a panic. + /// + /// # 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 or + /// incorrect ID. + /// + /// # 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::{hybrid::dfa::DFA, Input}; + /// + /// let dfa = DFA::new(r"[a-z]+r")?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// let mut sid = dfa.start_state_forward( + /// &mut cache, &Input::new(haystack), + /// )?; + /// // Walk all the bytes in the haystack. + /// for &b in haystack { + /// sid = dfa.next_state(&mut cache, sid, 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! + /// sid = dfa.next_eoi_state(&mut cache, sid)?; + /// assert!(sid.is_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn next_eoi_state( + &self, + cache: &mut Cache, + current: LazyStateID, + ) -> Result<LazyStateID, CacheError> { + let eoi = self.classes.eoi().as_usize(); + let offset = current.as_usize_untagged() + eoi; + let sid = cache.trans[offset]; + if !sid.is_unknown() { + return Ok(sid); + } + let unit = self.classes.eoi(); + Lazy::new(self, cache).cache_next_state(current, unit) + } + + /// 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`] (not a [`CacheError`]!) if the search + /// needs to give up when determining the start state (for example, if + /// it sees a "quit" byte or if the cache has been cleared too many + /// times). This can also return an error if the given `Input` contains an + /// unsupported [`Anchored`] configuration. + #[cfg_attr(feature = "perf-inline", inline(always))] + pub fn start_state_forward( + &self, + cache: &mut Cache, + input: &Input<'_>, + ) -> Result<LazyStateID, MatchError> { + if !self.quitset.is_empty() && input.start() > 0 { + let offset = input.start() - 1; + let byte = input.haystack()[offset]; + if self.quitset.contains(byte) { + return Err(MatchError::quit(byte, offset)); + } + } + let start_type = self.start_map.fwd(input); + let start = LazyRef::new(self, cache) + .get_cached_start_id(input, start_type)?; + if !start.is_unknown() { + return Ok(start); + } + Lazy::new(self, cache).cache_start_group(input, start_type) + } + + /// 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`] (not a [`CacheError`]!) if the search + /// needs to give up when determining the start state (for example, if + /// it sees a "quit" byte or if the cache has been cleared too many + /// times). This can also return an error if the given `Input` contains an + /// unsupported [`Anchored`] configuration. + #[cfg_attr(feature = "perf-inline", inline(always))] + pub fn start_state_reverse( + &self, + cache: &mut Cache, + input: &Input<'_>, + ) -> Result<LazyStateID, MatchError> { + if !self.quitset.is_empty() && input.end() < input.haystack().len() { + let offset = input.end(); + let byte = input.haystack()[offset]; + if self.quitset.contains(byte) { + return Err(MatchError::quit(byte, offset)); + } + } + let start_type = self.start_map.rev(input); + let start = LazyRef::new(self, cache) + .get_cached_start_id(input, start_type)?; + if !start.is_unknown() { + return Ok(start); + } + Lazy::new(self, cache).cache_start_group(input, start_type) + } + + /// Returns the total number of patterns that match in this state. + /// + /// If the lazy DFA was compiled with one pattern, then this must + /// necessarily always return `1` for all match states. + /// + /// A lazy DFA guarantees that [`DFA::match_pattern`] can be called with + /// indices up to (but not including) the length returned by this routine + /// without panicking. + /// + /// # Panics + /// + /// If the given state is not a match state, then this may either panic + /// or return an incorrect result. + /// + /// # 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`] when building the DFA. If we + /// used [`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::{hybrid::dfa::DFA, Input, MatchKind}; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .build_many(&[ + /// r"\w+", r"[a-z]+", r"[A-Z]+", r"\S+", + /// ])?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "@bar".as_bytes(); + /// + /// // The start state is determined by inspecting the position and the + /// // initial bytes of the haystack. + /// let mut sid = dfa.start_state_forward( + /// &mut cache, &Input::new(haystack), + /// )?; + /// // Walk all the bytes in the haystack. + /// for &b in haystack { + /// sid = dfa.next_state(&mut cache, sid, b)?; + /// } + /// sid = dfa.next_eoi_state(&mut cache, sid)?; + /// + /// assert!(sid.is_match()); + /// assert_eq!(dfa.match_len(&mut cache, sid), 3); + /// // The following calls are guaranteed to not panic since `match_len` + /// // returned `3` above. + /// assert_eq!(dfa.match_pattern(&mut cache, sid, 0).as_usize(), 3); + /// assert_eq!(dfa.match_pattern(&mut cache, sid, 1).as_usize(), 0); + /// assert_eq!(dfa.match_pattern(&mut cache, sid, 2).as_usize(), 1); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[inline] + pub fn match_len(&self, cache: &Cache, id: LazyStateID) -> usize { + assert!(id.is_match()); + LazyRef::new(self, cache).get_cached_state(id).match_len() + } + + /// Returns the pattern ID corresponding to the given match index in the + /// given state. + /// + /// See [`DFA::match_len`] for an example of how to use this method + /// correctly. Note that if you know your lazy DFA is configured 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 `DFA::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 always produces a valid + /// `PatternID`. + #[inline] + pub fn match_pattern( + &self, + cache: &Cache, + id: LazyStateID, + match_index: usize, + ) -> PatternID { + // This is an optimization for the very common case of a DFA with a + // single pattern. This conditional avoids a somewhat more costly path + // that finds the pattern ID from the corresponding `State`, which + // requires a bit of slicing/pointer-chasing. This optimization tends + // to only matter when matches are frequent. + if self.pattern_len() == 1 { + return PatternID::ZERO; + } + LazyRef::new(self, cache) + .get_cached_state(id) + .match_pattern(match_index) + } +} + +/// A cache represents a partially computed DFA. +/// +/// A cache is the key component that differentiates a classical DFA and a +/// hybrid NFA/DFA (also called a "lazy DFA"). Where a classical DFA builds a +/// complete transition table that can handle all possible inputs, a hybrid +/// NFA/DFA starts with an empty transition table and builds only the parts +/// required during search. The parts that are built are stored in a cache. For +/// this reason, a cache is a required parameter for nearly every operation on +/// a [`DFA`]. +/// +/// Caches can be created from their corresponding DFA via +/// [`DFA::create_cache`]. A cache can only be used with either the DFA that +/// created it, or the DFA that was most recently used to reset it with +/// [`Cache::reset`]. Using a cache with any other DFA may result in panics +/// or incorrect results. +#[derive(Clone, Debug)] +pub struct Cache { + // N.B. If you're looking to understand how determinization works, it + // is probably simpler to first grok src/dfa/determinize.rs, since that + // doesn't have the "laziness" component. + /// The transition table. + /// + /// Given a `current` LazyStateID and an `input` byte, the next state can + /// be computed via `trans[untagged(current) + equiv_class(input)]`. Notice + /// that no multiplication is used. That's because state identifiers are + /// "premultiplied." + /// + /// Note that the next state may be the "unknown" state. In this case, the + /// next state is not known and determinization for `current` on `input` + /// must be performed. + trans: Vec<LazyStateID>, + /// The starting states for this DFA. + /// + /// These are computed lazily. Initially, these are all set to "unknown" + /// lazy state IDs. + /// + /// When 'starts_for_each_pattern' is disabled (the default), then the size + /// of this is constrained to the possible starting configurations based + /// on the search parameters. (At time of writing, that's 4.) However, + /// when starting states for each pattern is enabled, then there are N + /// additional groups of starting states, where each group reflects the + /// different possible configurations and N is the number of patterns. + starts: Vec<LazyStateID>, + /// A sequence of NFA/DFA powerset states that have been computed for this + /// lazy DFA. This sequence is indexable by untagged LazyStateIDs. (Every + /// tagged LazyStateID can be used to index this sequence by converting it + /// to its untagged form.) + states: Vec<State>, + /// A map from states to their corresponding IDs. This map may be accessed + /// via the raw byte representation of a state, which means that a `State` + /// does not need to be allocated to determine whether it already exists + /// in this map. Indeed, the existence of such a state is what determines + /// whether we allocate a new `State` or not. + /// + /// The higher level idea here is that we do just enough determinization + /// for a state to check whether we've already computed it. If we have, + /// then we can save a little (albeit not much) work. The real savings is + /// in memory usage. If we never checked for trivially duplicate states, + /// then our memory usage would explode to unreasonable levels. + states_to_id: StateMap, + /// Sparse sets used to track which NFA states have been visited during + /// various traversals. + sparses: SparseSets, + /// Scratch space for traversing the NFA graph. (We use space on the heap + /// instead of the call stack.) + stack: Vec<NFAStateID>, + /// Scratch space for building a NFA/DFA powerset state. This is used to + /// help amortize allocation since not every powerset state generated is + /// added to the cache. In particular, if it already exists in the cache, + /// then there is no need to allocate a new `State` for it. + scratch_state_builder: StateBuilderEmpty, + /// A simple abstraction for handling the saving of at most a single state + /// across a cache clearing. This is required for correctness. Namely, if + /// adding a new state after clearing the cache fails, then the caller + /// must retain the ability to continue using the state ID given. The + /// state corresponding to the state ID is what we preserve across cache + /// clearings. + state_saver: StateSaver, + /// The memory usage, in bytes, used by 'states' and 'states_to_id'. We + /// track this as new states are added since states use a variable amount + /// of heap. Tracking this as we add states makes it possible to compute + /// the total amount of memory used by the determinizer in constant time. + memory_usage_state: usize, + /// The number of times the cache has been cleared. When a minimum cache + /// clear count is set, then the cache will return an error instead of + /// clearing the cache if the count has been exceeded. + clear_count: usize, + /// The total number of bytes searched since the last time this cache was + /// cleared, not including the current search. + /// + /// This can be added to the length of the current search to get the true + /// total number of bytes searched. + /// + /// This is generally only non-zero when the + /// `Cache::search_{start,update,finish}` APIs are used to track search + /// progress. + bytes_searched: usize, + /// The progress of the current search. + /// + /// This is only non-`None` when callers utlize the `Cache::search_start`, + /// `Cache::search_update` and `Cache::search_finish` APIs. + /// + /// The purpose of recording search progress is to be able to make a + /// determination about the efficiency of the cache. Namely, by keeping + /// track of the + progress: Option<SearchProgress>, +} + +impl Cache { + /// Create a new cache for the given lazy DFA. + /// + /// The cache returned should only be used for searches for the given DFA. + /// If you want to reuse the cache for another DFA, then you must call + /// [`Cache::reset`] with that DFA. + pub fn new(dfa: &DFA) -> Cache { + let mut cache = Cache { + trans: alloc::vec![], + starts: alloc::vec![], + states: alloc::vec![], + states_to_id: StateMap::new(), + sparses: SparseSets::new(dfa.get_nfa().states().len()), + stack: alloc::vec![], + scratch_state_builder: StateBuilderEmpty::new(), + state_saver: StateSaver::none(), + memory_usage_state: 0, + clear_count: 0, + bytes_searched: 0, + progress: None, + }; + debug!("pre-init lazy DFA cache size: {}", cache.memory_usage()); + Lazy { dfa, cache: &mut cache }.init_cache(); + debug!("post-init lazy DFA cache size: {}", cache.memory_usage()); + cache + } + + /// Reset this cache such that it can be used for searching with the given + /// lazy DFA (and only that DFA). + /// + /// A cache reset permits reusing memory already allocated in this cache + /// with a different lazy DFA. + /// + /// Resetting a cache sets its "clear count" to 0. This is relevant if the + /// lazy DFA has been configured to "give up" after it has cleared the + /// cache a certain number of times. + /// + /// Any lazy state ID generated by the cache prior to resetting it is + /// invalid after the reset. + /// + /// # Example + /// + /// This shows how to re-purpose a cache for use with a different DFA. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let dfa1 = DFA::new(r"\w")?; + /// let dfa2 = DFA::new(r"\W")?; + /// + /// let mut cache = dfa1.create_cache(); + /// assert_eq!( + /// Some(HalfMatch::must(0, 2)), + /// dfa1.try_search_fwd(&mut cache, &Input::new("Δ"))?, + /// ); + /// + /// // Using 'cache' with dfa2 is not allowed. It may result in panics or + /// // incorrect results. In order to re-purpose the cache, we must reset + /// // it with the DFA we'd like to use it with. + /// // + /// // Similarly, after this reset, using the cache with 'dfa1' is also not + /// // allowed. + /// cache.reset(&dfa2); + /// assert_eq!( + /// Some(HalfMatch::must(0, 3)), + /// dfa2.try_search_fwd(&mut cache, &Input::new("☃"))?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn reset(&mut self, dfa: &DFA) { + Lazy::new(dfa, self).reset_cache() + } + + /// Initializes a new search starting at the given position. + /// + /// If a previous search was unfinished, then it is finished automatically + /// and a new search is begun. + /// + /// Note that keeping track of search progress is _not necessary_ + /// for correct implementations of search using a lazy DFA. Keeping + /// track of search progress is only necessary if you want the + /// [`Config::minimum_bytes_per_state`] configuration knob to work. + #[inline] + pub fn search_start(&mut self, at: usize) { + // If a previous search wasn't marked as finished, then finish it + // now automatically. + if let Some(p) = self.progress.take() { + self.bytes_searched += p.len(); + } + self.progress = Some(SearchProgress { start: at, at }); + } + + /// Updates the current search to indicate that it has search to the + /// current position. + /// + /// No special care needs to be taken for reverse searches. Namely, the + /// position given may be _less than_ the starting position of the search. + /// + /// # Panics + /// + /// This panics if no search has been started by [`Cache::search_start`]. + #[inline] + pub fn search_update(&mut self, at: usize) { + let p = + self.progress.as_mut().expect("no in-progress search to update"); + p.at = at; + } + + /// Indicates that a search has finished at the given position. + /// + /// # Panics + /// + /// This panics if no search has been started by [`Cache::search_start`]. + #[inline] + pub fn search_finish(&mut self, at: usize) { + let mut p = + self.progress.take().expect("no in-progress search to finish"); + p.at = at; + self.bytes_searched += p.len(); + } + + /// Returns the total number of bytes that have been searched since this + /// cache was last cleared. + /// + /// This is useful for determining the efficiency of the cache. For + /// example, the lazy DFA uses this value in conjunction with the + /// [`Config::minimum_bytes_per_state`] knob to help determine whether it + /// should quit searching. + /// + /// This always returns `0` if search progress isn't being tracked. Note + /// that the lazy DFA search routines in this crate always track search + /// progress. + pub fn search_total_len(&self) -> usize { + self.bytes_searched + self.progress.as_ref().map_or(0, |p| p.len()) + } + + /// Returns the total number of times this cache has been cleared since it + /// was either created or last reset. + /// + /// This is useful for informational purposes or if you want to change + /// search strategies based on the number of times the cache has been + /// cleared. + pub fn clear_count(&self) -> usize { + self.clear_count + } + + /// Returns the heap memory usage, in bytes, of this cache. + /// + /// This does **not** include the stack size used up by this cache. To + /// compute that, use `std::mem::size_of::<Cache>()`. + pub fn memory_usage(&self) -> usize { + const ID_SIZE: usize = size_of::<LazyStateID>(); + const STATE_SIZE: usize = size_of::<State>(); + + // NOTE: If you make changes to the below, then + // 'minimum_cache_capacity' should be updated correspondingly. + + self.trans.len() * ID_SIZE + + self.starts.len() * ID_SIZE + + self.states.len() * STATE_SIZE + // Maps likely use more memory than this, but it's probably close. + + self.states_to_id.len() * (STATE_SIZE + ID_SIZE) + + self.sparses.memory_usage() + + self.stack.capacity() * ID_SIZE + + self.scratch_state_builder.capacity() + // Heap memory used by 'State' in both 'states' and 'states_to_id'. + + self.memory_usage_state + } +} + +/// Keeps track of the progress of the current search. +/// +/// This is updated via the `Cache::search_{start,update,finish}` APIs to +/// record how many bytes have been searched. This permits computing a +/// heuristic that represents the efficiency of a cache, and thus helps inform +/// whether the lazy DFA should give up or not. +#[derive(Clone, Debug)] +struct SearchProgress { + start: usize, + at: usize, +} + +impl SearchProgress { + /// Returns the length, in bytes, of this search so far. + /// + /// This automatically handles the case of a reverse search, where `at` + /// is likely to be less than `start`. + fn len(&self) -> usize { + if self.start <= self.at { + self.at - self.start + } else { + self.start - self.at + } + } +} + +/// A map from states to state identifiers. When using std, we use a standard +/// hashmap, since it's a bit faster for this use case. (Other maps, like +/// one's based on FNV, have not yet been benchmarked.) +/// +/// The main purpose of this map is to reuse states where possible. This won't +/// fully minimize the DFA, but it works well in a lot of cases. +#[cfg(feature = "std")] +type StateMap = std::collections::HashMap<State, LazyStateID>; +#[cfg(not(feature = "std"))] +type StateMap = alloc::collections::BTreeMap<State, LazyStateID>; + +/// A type that groups methods that require the base NFA/DFA and writable +/// access to the cache. +#[derive(Debug)] +struct Lazy<'i, 'c> { + dfa: &'i DFA, + cache: &'c mut Cache, +} + +impl<'i, 'c> Lazy<'i, 'c> { + /// Creates a new 'Lazy' wrapper for a DFA and its corresponding cache. + fn new(dfa: &'i DFA, cache: &'c mut Cache) -> Lazy<'i, 'c> { + Lazy { dfa, cache } + } + + /// Return an immutable view by downgrading a writable cache to a read-only + /// cache. + fn as_ref<'a>(&'a self) -> LazyRef<'i, 'a> { + LazyRef::new(self.dfa, self.cache) + } + + /// This is marked as 'inline(never)' to avoid bloating methods on 'DFA' + /// like 'next_state' and 'next_eoi_state' that are called in critical + /// areas. The idea is to let the optimizer focus on the other areas of + /// those methods as the hot path. + /// + /// Here's an example that justifies 'inline(never)' + /// + /// ```ignore + /// regex-cli find hybrid dfa \ + /// @all-codepoints-utf8-100x '\pL{100}' --cache-capacity 10000000 + /// ``` + /// + /// Where 'all-codepoints-utf8-100x' is the UTF-8 encoding of every + /// codepoint, in sequence, repeated 100 times. + /// + /// With 'inline(never)' hyperfine reports 1.1s per run. With + /// 'inline(always)', hyperfine reports 1.23s. So that's a 10% improvement. + #[cold] + #[inline(never)] + fn cache_next_state( + &mut self, + mut current: LazyStateID, + unit: alphabet::Unit, + ) -> Result<LazyStateID, CacheError> { + let stride2 = self.dfa.stride2(); + let empty_builder = self.get_state_builder(); + let builder = determinize::next( + self.dfa.get_nfa(), + self.dfa.get_config().get_match_kind(), + &mut self.cache.sparses, + &mut self.cache.stack, + &self.cache.states[current.as_usize_untagged() >> stride2], + unit, + empty_builder, + ); + let save_state = !self.as_ref().state_builder_fits_in_cache(&builder); + if save_state { + self.save_state(current); + } + let next = self.add_builder_state(builder, |sid| sid)?; + if save_state { + current = self.saved_state_id(); + } + // This is the payoff. The next time 'next_state' is called with this + // state and alphabet unit, it will find this transition and avoid + // having to re-determinize this transition. + self.set_transition(current, unit, next); + Ok(next) + } + + /// Compute and cache the starting state for the given pattern ID (if + /// present) and the starting configuration. + /// + /// This panics if a pattern ID is given and the DFA isn't configured to + /// build anchored start states for each pattern. + /// + /// This will never return an unknown lazy state ID. + /// + /// If caching this state would otherwise result in a cache that has been + /// cleared too many times, then an error is returned. + #[cold] + #[inline(never)] + fn cache_start_group( + &mut self, + input: &Input<'_>, + start: Start, + ) -> Result<LazyStateID, MatchError> { + let mode = input.get_anchored(); + let nfa_start_id = match mode { + Anchored::No => self.dfa.get_nfa().start_unanchored(), + Anchored::Yes => self.dfa.get_nfa().start_anchored(), + Anchored::Pattern(pid) => { + if !self.dfa.get_config().get_starts_for_each_pattern() { + return Err(MatchError::unsupported_anchored(mode)); + } + match self.dfa.get_nfa().start_pattern(pid) { + None => return Ok(self.as_ref().dead_id()), + Some(sid) => sid, + } + } + }; + + let id = self + .cache_start_one(nfa_start_id, start) + .map_err(|_| MatchError::gave_up(input.start()))?; + self.set_start_state(input, start, id); + Ok(id) + } + + /// Compute and cache the starting state for the given NFA state ID and the + /// starting configuration. The NFA state ID might be one of the following: + /// + /// 1) An unanchored start state to match any pattern. + /// 2) An anchored start state to match any pattern. + /// 3) An anchored start state for a particular pattern. + /// + /// This will never return an unknown lazy state ID. + /// + /// If caching this state would otherwise result in a cache that has been + /// cleared too many times, then an error is returned. + fn cache_start_one( + &mut self, + nfa_start_id: NFAStateID, + start: Start, + ) -> Result<LazyStateID, CacheError> { + let mut builder_matches = self.get_state_builder().into_matches(); + determinize::set_lookbehind_from_start( + self.dfa.get_nfa(), + &start, + &mut builder_matches, + ); + self.cache.sparses.set1.clear(); + determinize::epsilon_closure( + self.dfa.get_nfa(), + nfa_start_id, + builder_matches.look_have(), + &mut self.cache.stack, + &mut self.cache.sparses.set1, + ); + let mut builder = builder_matches.into_nfa(); + determinize::add_nfa_states( + &self.dfa.get_nfa(), + &self.cache.sparses.set1, + &mut builder, + ); + let tag_starts = self.dfa.get_config().get_specialize_start_states(); + self.add_builder_state(builder, |id| { + if tag_starts { + id.to_start() + } else { + id + } + }) + } + + /// Either add the given builder state to this cache, or return an ID to an + /// equivalent state already in this cache. + /// + /// In the case where no equivalent state exists, the idmap function given + /// may be used to transform the identifier allocated. This is useful if + /// the caller needs to tag the ID with additional information. + /// + /// This will never return an unknown lazy state ID. + /// + /// If caching this state would otherwise result in a cache that has been + /// cleared too many times, then an error is returned. + fn add_builder_state( + &mut self, + builder: StateBuilderNFA, + idmap: impl Fn(LazyStateID) -> LazyStateID, + ) -> Result<LazyStateID, CacheError> { + if let Some(&cached_id) = + self.cache.states_to_id.get(builder.as_bytes()) + { + // Since we have a cached state, put the constructed state's + // memory back into our scratch space, so that it can be reused. + self.put_state_builder(builder); + return Ok(cached_id); + } + let result = self.add_state(builder.to_state(), idmap); + self.put_state_builder(builder); + result + } + + /// Allocate a new state ID and add the given state to this cache. + /// + /// The idmap function given may be used to transform the identifier + /// allocated. This is useful if the caller needs to tag the ID with + /// additional information. + /// + /// This will never return an unknown lazy state ID. + /// + /// If caching this state would otherwise result in a cache that has been + /// cleared too many times, then an error is returned. + fn add_state( + &mut self, + state: State, + idmap: impl Fn(LazyStateID) -> LazyStateID, + ) -> Result<LazyStateID, CacheError> { + if !self.as_ref().state_fits_in_cache(&state) { + self.try_clear_cache()?; + } + // It's important for this to come second, since the above may clear + // the cache. If we clear the cache after ID generation, then the ID + // is likely bunk since it would have been generated based on a larger + // transition table. + let mut id = idmap(self.next_state_id()?); + if state.is_match() { + id = id.to_match(); + } + // Add room in the transition table. Since this is a fresh state, all + // of its transitions are unknown. + self.cache.trans.extend( + iter::repeat(self.as_ref().unknown_id()).take(self.dfa.stride()), + ); + // When we add a sentinel state, we never want to set any quit + // transitions. Technically, this is harmless, since sentinel states + // have all of their transitions set to loop back to themselves. But + // when creating sentinel states before the quit sentinel state, + // this will try to call 'set_transition' on a state ID that doesn't + // actually exist yet, which isn't allowed. So we just skip doing so + // entirely. + if !self.dfa.quitset.is_empty() && !self.as_ref().is_sentinel(id) { + let quit_id = self.as_ref().quit_id(); + for b in self.dfa.quitset.iter() { + self.set_transition(id, alphabet::Unit::u8(b), quit_id); + } + } + self.cache.memory_usage_state += state.memory_usage(); + self.cache.states.push(state.clone()); + self.cache.states_to_id.insert(state, id); + Ok(id) + } + + /// Allocate a new state ID. + /// + /// This will never return an unknown lazy state ID. + /// + /// If caching this state would otherwise result in a cache that has been + /// cleared too many times, then an error is returned. + fn next_state_id(&mut self) -> Result<LazyStateID, CacheError> { + let sid = match LazyStateID::new(self.cache.trans.len()) { + Ok(sid) => sid, + Err(_) => { + self.try_clear_cache()?; + // This has to pass since we check that ID capacity at + // construction time can fit at least MIN_STATES states. + LazyStateID::new(self.cache.trans.len()).unwrap() + } + }; + Ok(sid) + } + + /// Attempt to clear the cache used by this lazy DFA. + /// + /// If clearing the cache exceeds the minimum number of required cache + /// clearings, then this will return a cache error. In this case, + /// callers should bubble this up as the cache can't be used until it is + /// reset. Implementations of search should convert this error into a + /// [`MatchError::gave_up`]. + /// + /// If 'self.state_saver' is set to save a state, then this state is + /// persisted through cache clearing. Otherwise, the cache is returned to + /// its state after initialization with two exceptions: its clear count + /// is incremented and some of its memory likely has additional capacity. + /// That is, clearing a cache does _not_ release memory. + /// + /// Otherwise, any lazy state ID generated by the cache prior to resetting + /// it is invalid after the reset. + fn try_clear_cache(&mut self) -> Result<(), CacheError> { + let c = self.dfa.get_config(); + if let Some(min_count) = c.get_minimum_cache_clear_count() { + if self.cache.clear_count >= min_count { + if let Some(min_bytes_per) = c.get_minimum_bytes_per_state() { + let len = self.cache.search_total_len(); + let min_bytes = + min_bytes_per.saturating_mul(self.cache.states.len()); + // If we've searched 0 bytes then probably something has + // gone wrong and the lazy DFA search implementation isn't + // correctly updating the search progress state. + if len == 0 { + trace!( + "number of bytes searched is 0, but \ + a minimum bytes per state searched ({}) is \ + enabled, maybe Cache::search_update \ + is not being used?", + min_bytes_per, + ); + } + if len < min_bytes { + trace!( + "lazy DFA cache has been cleared {} times, \ + which exceeds the limit of {}, \ + AND its bytes searched per state is less \ + than the configured minimum of {}, \ + therefore lazy DFA is giving up \ + (bytes searched since cache clear = {}, \ + number of states = {})", + self.cache.clear_count, + min_count, + min_bytes_per, + len, + self.cache.states.len(), + ); + return Err(CacheError::bad_efficiency()); + } else { + trace!( + "lazy DFA cache has been cleared {} times, \ + which exceeds the limit of {}, \ + AND its bytes searched per state is greater \ + than the configured minimum of {}, \ + therefore lazy DFA is continuing! \ + (bytes searched since cache clear = {}, \ + number of states = {})", + self.cache.clear_count, + min_count, + min_bytes_per, + len, + self.cache.states.len(), + ); + } + } else { + trace!( + "lazy DFA cache has been cleared {} times, \ + which exceeds the limit of {}, \ + since there is no configured bytes per state \ + minimum, lazy DFA is giving up", + self.cache.clear_count, + min_count, + ); + return Err(CacheError::too_many_cache_clears()); + } + } + } + self.clear_cache(); + Ok(()) + } + + /// Clears _and_ resets the cache. Resetting the cache means that no + /// states are persisted and the clear count is reset to 0. No heap memory + /// is released. + /// + /// Note that the caller may reset a cache with a different DFA than what + /// it was created from. In which case, the cache can now be used with the + /// new DFA (and not the old DFA). + fn reset_cache(&mut self) { + self.cache.state_saver = StateSaver::none(); + self.clear_cache(); + // If a new DFA is used, it might have a different number of NFA + // states, so we need to make sure our sparse sets have the appropriate + // size. + self.cache.sparses.resize(self.dfa.get_nfa().states().len()); + self.cache.clear_count = 0; + self.cache.progress = None; + } + + /// Clear the cache used by this lazy DFA. + /// + /// If 'self.state_saver' is set to save a state, then this state is + /// persisted through cache clearing. Otherwise, the cache is returned to + /// its state after initialization with two exceptions: its clear count + /// is incremented and some of its memory likely has additional capacity. + /// That is, clearing a cache does _not_ release memory. + /// + /// Otherwise, any lazy state ID generated by the cache prior to resetting + /// it is invalid after the reset. + fn clear_cache(&mut self) { + self.cache.trans.clear(); + self.cache.starts.clear(); + self.cache.states.clear(); + self.cache.states_to_id.clear(); + self.cache.memory_usage_state = 0; + self.cache.clear_count += 1; + self.cache.bytes_searched = 0; + if let Some(ref mut progress) = self.cache.progress { + progress.start = progress.at; + } + trace!( + "lazy DFA cache has been cleared (count: {})", + self.cache.clear_count + ); + self.init_cache(); + // If the state we want to save is one of the sentinel + // (unknown/dead/quit) states, then 'init_cache' adds those back, and + // their identifier values remains invariant. So there's no need to add + // it again. (And indeed, doing so would be incorrect!) + if let Some((old_id, state)) = self.cache.state_saver.take_to_save() { + // If the state is one of the special sentinel states, then it is + // automatically added by cache initialization and its ID always + // remains the same. With that said, this should never occur since + // the sentinel states are all loop states back to themselves. So + // we should never be in a position where we're attempting to save + // a sentinel state since we never compute transitions out of a + // sentinel state. + assert!( + !self.as_ref().is_sentinel(old_id), + "cannot save sentinel state" + ); + let new_id = self + .add_state(state, |id| { + if old_id.is_start() { + // We don't need to consult the + // 'specialize_start_states' config knob here, because + // if it's disabled, old_id.is_start() will never + // return true. + id.to_start() + } else { + id + } + }) + // The unwrap here is OK because lazy DFA creation ensures that + // we have room in the cache to add MIN_STATES states. Since + // 'init_cache' above adds 3, this adds a 4th. + .expect("adding one state after cache clear must work"); + self.cache.state_saver = StateSaver::Saved(new_id); + } + } + + /// Initialize this cache from emptiness to a place where it can be used + /// for search. + /// + /// This is called both at cache creation time and after the cache has been + /// cleared. + /// + /// Primarily, this adds the three sentinel states and allocates some + /// initial memory. + fn init_cache(&mut self) { + // Why multiply by 2 here? Because we make room for both the unanchored + // and anchored start states. Unanchored is first and then anchored. + let mut starts_len = Start::len().checked_mul(2).unwrap(); + // ... but if we also want start states for every pattern, we make room + // for that too. + if self.dfa.get_config().get_starts_for_each_pattern() { + starts_len += Start::len() * self.dfa.pattern_len(); + } + self.cache + .starts + .extend(iter::repeat(self.as_ref().unknown_id()).take(starts_len)); + // This is the set of NFA states that corresponds to each of our three + // sentinel states: the empty set. + let dead = State::dead(); + // This sets up some states that we use as sentinels that are present + // in every DFA. While it would be technically possible to implement + // this DFA without explicitly putting these states in the transition + // table, this is convenient to do to make `next_state` correct for all + // valid state IDs without needing explicit conditionals to special + // case these sentinel states. + // + // All three of these states are "dead" states. That is, all of + // them transition only to themselves. So once you enter one of + // these states, it's impossible to leave them. Thus, any correct + // search routine must explicitly check for these state types. (Sans + // `unknown`, since that is only used internally to represent missing + // states.) + let unk_id = + self.add_state(dead.clone(), |id| id.to_unknown()).unwrap(); + let dead_id = self.add_state(dead.clone(), |id| id.to_dead()).unwrap(); + let quit_id = self.add_state(dead.clone(), |id| id.to_quit()).unwrap(); + assert_eq!(unk_id, self.as_ref().unknown_id()); + assert_eq!(dead_id, self.as_ref().dead_id()); + assert_eq!(quit_id, self.as_ref().quit_id()); + // The idea here is that if you start in an unknown/dead/quit state and + // try to transition on them, then you should end up where you started. + self.set_all_transitions(unk_id, unk_id); + self.set_all_transitions(dead_id, dead_id); + self.set_all_transitions(quit_id, quit_id); + // All of these states are technically equivalent from the FSM + // perspective, so putting all three of them in the cache isn't + // possible. (They are distinct merely because we use their + // identifiers as sentinels to mean something, as indicated by the + // names.) Moreover, we wouldn't want to do that. Unknown and quit + // states are special in that they are artificial constructions + // this implementation. But dead states are a natural part of + // determinization. When you reach a point in the NFA where you cannot + // go anywhere else, a dead state will naturally arise and we MUST + // reuse the canonical dead state that we've created here. Why? Because + // it is the state ID that tells the search routine whether a state is + // dead or not, and thus, whether to stop the search. Having a bunch of + // distinct dead states would be quite wasteful! + self.cache.states_to_id.insert(dead, dead_id); + } + + /// Save the state corresponding to the ID given such that the state + /// persists through a cache clearing. + /// + /// While the state may persist, the ID may not. In order to discover the + /// new state ID, one must call 'saved_state_id' after a cache clearing. + fn save_state(&mut self, id: LazyStateID) { + let state = self.as_ref().get_cached_state(id).clone(); + self.cache.state_saver = StateSaver::ToSave { id, state }; + } + + /// Returns the updated lazy state ID for a state that was persisted + /// through a cache clearing. + /// + /// It is only correct to call this routine when both a state has been + /// saved and the cache has just been cleared. Otherwise, this panics. + fn saved_state_id(&mut self) -> LazyStateID { + self.cache + .state_saver + .take_saved() + .expect("state saver does not have saved state ID") + } + + /// Set all transitions on the state 'from' to 'to'. + fn set_all_transitions(&mut self, from: LazyStateID, to: LazyStateID) { + for unit in self.dfa.classes.representatives(..) { + self.set_transition(from, unit, to); + } + } + + /// Set the transition on 'from' for 'unit' to 'to'. + /// + /// This panics if either 'from' or 'to' is invalid. + /// + /// All unit values are OK. + fn set_transition( + &mut self, + from: LazyStateID, + unit: alphabet::Unit, + to: LazyStateID, + ) { + assert!(self.as_ref().is_valid(from), "invalid 'from' id: {:?}", from); + assert!(self.as_ref().is_valid(to), "invalid 'to' id: {:?}", to); + let offset = + from.as_usize_untagged() + self.dfa.classes.get_by_unit(unit); + self.cache.trans[offset] = to; + } + + /// Set the start ID for the given pattern ID (if given) and starting + /// configuration to the ID given. + /// + /// This panics if 'id' is not valid or if a pattern ID is given and + /// 'starts_for_each_pattern' is not enabled. + fn set_start_state( + &mut self, + input: &Input<'_>, + start: Start, + id: LazyStateID, + ) { + assert!(self.as_ref().is_valid(id)); + let start_index = start.as_usize(); + let index = match input.get_anchored() { + Anchored::No => start_index, + Anchored::Yes => Start::len() + start_index, + Anchored::Pattern(pid) => { + assert!( + self.dfa.get_config().get_starts_for_each_pattern(), + "attempted to search for a specific pattern \ + without enabling starts_for_each_pattern", + ); + let pid = pid.as_usize(); + (2 * Start::len()) + (Start::len() * pid) + start_index + } + }; + self.cache.starts[index] = id; + } + + /// Returns a state builder from this DFA that might have existing + /// capacity. This helps avoid allocs in cases where a state is built that + /// turns out to already be cached. + /// + /// Callers must put the state builder back with 'put_state_builder', + /// otherwise the allocation reuse won't work. + fn get_state_builder(&mut self) -> StateBuilderEmpty { + core::mem::replace( + &mut self.cache.scratch_state_builder, + StateBuilderEmpty::new(), + ) + } + + /// Puts the given state builder back into this DFA for reuse. + /// + /// Note that building a 'State' from a builder always creates a new alloc, + /// so callers should always put the builder back. + fn put_state_builder(&mut self, builder: StateBuilderNFA) { + let _ = core::mem::replace( + &mut self.cache.scratch_state_builder, + builder.clear(), + ); + } +} + +/// A type that groups methods that require the base NFA/DFA and read-only +/// access to the cache. +#[derive(Debug)] +struct LazyRef<'i, 'c> { + dfa: &'i DFA, + cache: &'c Cache, +} + +impl<'i, 'c> LazyRef<'i, 'c> { + /// Creates a new 'Lazy' wrapper for a DFA and its corresponding cache. + fn new(dfa: &'i DFA, cache: &'c Cache) -> LazyRef<'i, 'c> { + LazyRef { dfa, cache } + } + + /// Return the ID of the start state for the given configuration. + /// + /// If the start state has not yet been computed, then this returns an + /// unknown lazy state ID. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn get_cached_start_id( + &self, + input: &Input<'_>, + start: Start, + ) -> Result<LazyStateID, MatchError> { + let start_index = start.as_usize(); + let mode = input.get_anchored(); + let index = match mode { + Anchored::No => start_index, + Anchored::Yes => Start::len() + start_index, + Anchored::Pattern(pid) => { + if !self.dfa.get_config().get_starts_for_each_pattern() { + return Err(MatchError::unsupported_anchored(mode)); + } + if pid.as_usize() >= self.dfa.pattern_len() { + return Ok(self.dead_id()); + } + (2 * Start::len()) + + (Start::len() * pid.as_usize()) + + start_index + } + }; + Ok(self.cache.starts[index]) + } + + /// Return the cached NFA/DFA powerset state for the given ID. + /// + /// This panics if the given ID does not address a valid state. + fn get_cached_state(&self, sid: LazyStateID) -> &State { + let index = sid.as_usize_untagged() >> self.dfa.stride2(); + &self.cache.states[index] + } + + /// Returns true if and only if the given ID corresponds to a "sentinel" + /// state. + /// + /// A sentinel state is a state that signifies a special condition of + /// search, and where every transition maps back to itself. See LazyStateID + /// for more details. Note that start and match states are _not_ sentinels + /// since they may otherwise be real states with non-trivial transitions. + /// The purposes of sentinel states is purely to indicate something. Their + /// transitions are not meant to be followed. + fn is_sentinel(&self, id: LazyStateID) -> bool { + id == self.unknown_id() || id == self.dead_id() || id == self.quit_id() + } + + /// Returns the ID of the unknown state for this lazy DFA. + fn unknown_id(&self) -> LazyStateID { + // This unwrap is OK since 0 is always a valid state ID. + LazyStateID::new(0).unwrap().to_unknown() + } + + /// Returns the ID of the dead state for this lazy DFA. + fn dead_id(&self) -> LazyStateID { + // This unwrap is OK since the maximum value here is 1 * 512 = 512, + // which is <= 2047 (the maximum state ID on 16-bit systems). Where + // 512 is the worst case for our equivalence classes (every byte is a + // distinct class). + LazyStateID::new(1 << self.dfa.stride2()).unwrap().to_dead() + } + + /// Returns the ID of the quit state for this lazy DFA. + fn quit_id(&self) -> LazyStateID { + // This unwrap is OK since the maximum value here is 2 * 512 = 1024, + // which is <= 2047 (the maximum state ID on 16-bit systems). Where + // 512 is the worst case for our equivalence classes (every byte is a + // distinct class). + LazyStateID::new(2 << self.dfa.stride2()).unwrap().to_quit() + } + + /// Returns true if and only if the given ID is valid. + /// + /// An ID is valid if it is both a valid index into the transition table + /// and is a multiple of the DFA's stride. + fn is_valid(&self, id: LazyStateID) -> bool { + let id = id.as_usize_untagged(); + id < self.cache.trans.len() && id % self.dfa.stride() == 0 + } + + /// Returns true if adding the state given would fit in this cache. + fn state_fits_in_cache(&self, state: &State) -> bool { + let needed = self.cache.memory_usage() + + self.memory_usage_for_one_more_state(state.memory_usage()); + trace!( + "lazy DFA cache capacity check: {:?} ?<=? {:?}", + needed, + self.dfa.cache_capacity + ); + needed <= self.dfa.cache_capacity + } + + /// Returns true if adding the state to be built by the given builder would + /// fit in this cache. + fn state_builder_fits_in_cache(&self, state: &StateBuilderNFA) -> bool { + let needed = self.cache.memory_usage() + + self.memory_usage_for_one_more_state(state.as_bytes().len()); + needed <= self.dfa.cache_capacity + } + + /// Returns the additional memory usage, in bytes, required to add one more + /// state to this cache. The given size should be the heap size, in bytes, + /// that would be used by the new state being added. + fn memory_usage_for_one_more_state( + &self, + state_heap_size: usize, + ) -> usize { + const ID_SIZE: usize = size_of::<LazyStateID>(); + const STATE_SIZE: usize = size_of::<State>(); + + self.dfa.stride() * ID_SIZE // additional space needed in trans table + + STATE_SIZE // space in cache.states + + (STATE_SIZE + ID_SIZE) // space in cache.states_to_id + + state_heap_size // heap memory used by state itself + } +} + +/// A simple type that encapsulates the saving of a state ID through a cache +/// clearing. +/// +/// A state ID can be marked for saving with ToSave, while a state ID can be +/// saved itself with Saved. +#[derive(Clone, Debug)] +enum StateSaver { + /// An empty state saver. In this case, no states (other than the special + /// sentinel states) are preserved after clearing the cache. + None, + /// An ID of a state (and the state itself) that should be preserved after + /// the lazy DFA's cache has been cleared. After clearing, the updated ID + /// is stored in 'Saved' since it may have changed. + ToSave { id: LazyStateID, state: State }, + /// An ID that of a state that has been persisted through a lazy DFA + /// cache clearing. The ID recorded here corresponds to an ID that was + /// once marked as ToSave. The IDs are likely not equivalent even though + /// the states they point to are. + Saved(LazyStateID), +} + +impl StateSaver { + /// Create an empty state saver. + fn none() -> StateSaver { + StateSaver::None + } + + /// Replace this state saver with an empty saver, and if this saver is a + /// request to save a state, return that request. + fn take_to_save(&mut self) -> Option<(LazyStateID, State)> { + match core::mem::replace(self, StateSaver::None) { + StateSaver::None | StateSaver::Saved(_) => None, + StateSaver::ToSave { id, state } => Some((id, state)), + } + } + + /// Replace this state saver with an empty saver, and if this saver is a + /// saved state (or a request to save a state), return that state's ID. + /// + /// The idea here is that a request to save a state isn't necessarily + /// honored because it might not be needed. e.g., Some higher level code + /// might request a state to be saved on the off chance that the cache gets + /// cleared when a new state is added at a lower level. But if that new + /// state is never added, then the cache is never cleared and the state and + /// its ID remain unchanged. + fn take_saved(&mut self) -> Option<LazyStateID> { + match core::mem::replace(self, StateSaver::None) { + StateSaver::None => None, + StateSaver::Saved(id) | StateSaver::ToSave { id, .. } => Some(id), + } + } +} + +/// The configuration used for building a lazy DFA. +/// +/// As a convenience, [`DFA::config`] is an alias for [`Config::new`]. The +/// advantage of the former is that it often lets you avoid importing the +/// `Config` type directly. +/// +/// A lazy DFA configuration is a simple data object that is typically used +/// with [`Builder::configure`]. +/// +/// The default configuration guarantees that a search will never return a +/// "gave up" or "quit" error, although it is possible for a search to fail +/// if [`Config::starts_for_each_pattern`] wasn't enabled (which it is not by +/// default) and an [`Anchored::Pattern`] mode is requested via [`Input`]. +#[derive(Clone, Debug, Default)] +pub struct Config { + // As with other configuration types in this crate, we put all our knobs + // in options so that we can distinguish between "default" and "not set." + // This makes it possible to easily combine multiple configurations + // without default values overwriting explicitly specified values. See the + // 'overwrite' method. + // + // For docs on the fields below, see the corresponding method setters. + match_kind: Option<MatchKind>, + pre: Option<Option<Prefilter>>, + starts_for_each_pattern: Option<bool>, + byte_classes: Option<bool>, + unicode_word_boundary: Option<bool>, + quitset: Option<ByteSet>, + specialize_start_states: Option<bool>, + cache_capacity: Option<usize>, + skip_cache_capacity_check: Option<bool>, + minimum_cache_clear_count: Option<Option<usize>>, + minimum_bytes_per_state: Option<Option<usize>>, +} + +impl Config { + /// Return a new default lazy DFA builder configuration. + pub fn new() -> Config { + Config::default() + } + + /// Set the desired match semantics. + /// + /// The default is [`MatchKind::LeftmostFirst`], which corresponds to the + /// match semantics of Perl-like regex engines. That is, when multiple + /// patterns would match at the same leftmost position, the pattern that + /// appears first in the concrete syntax is chosen. + /// + /// Currently, the only other kind of match semantics supported is + /// [`MatchKind::All`]. This corresponds to classical DFA construction + /// where all possible matches are added to the lazy DFA. + /// + /// Typically, `All` is used when one wants to execute an overlapping + /// search and `LeftmostFirst` otherwise. In particular, it rarely makes + /// sense to use `All` with the various "leftmost" find routines, since the + /// leftmost routines depend on the `LeftmostFirst` automata construction + /// strategy. Specifically, `LeftmostFirst` adds dead states to the + /// lazy DFA as a way to terminate the search and report a match. + /// `LeftmostFirst` also supports non-greedy matches using this strategy + /// where as `All` does not. + /// + /// # Example: overlapping search + /// + /// This example shows the typical use of `MatchKind::All`, which is to + /// report overlapping matches. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{ + /// hybrid::dfa::{DFA, OverlappingState}, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .build_many(&[r"\w+$", r"\S+$"])?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "@foo"; + /// let mut state = OverlappingState::start(); + /// + /// let expected = Some(HalfMatch::must(1, 4)); + /// dfa.try_search_overlapping_fwd( + /// &mut cache, &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( + /// &mut cache, &Input::new(haystack), &mut state, + /// )?; + /// assert_eq!(expected, state.get_match()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: reverse automaton to find start of match + /// + /// Another example for using `MatchKind::All` is for constructing a + /// reverse automaton to find the start of a match. `All` semantics are + /// used for this in order to find the longest possible match, which + /// corresponds to the leftmost starting position. + /// + /// Note that if you need the starting position then + /// [`hybrid::regex::Regex`](crate::hybrid::regex::Regex) will handle this + /// for you, so it's usually not necessary to do this yourself. + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// nfa::thompson::NFA, + /// Anchored, HalfMatch, Input, MatchKind, + /// }; + /// + /// let input = Input::new("123foobar456"); + /// let pattern = r"[a-z]+r"; + /// + /// let dfa_fwd = DFA::new(pattern)?; + /// let dfa_rev = DFA::builder() + /// .thompson(NFA::config().reverse(true)) + /// .configure(DFA::config().match_kind(MatchKind::All)) + /// .build(pattern)?; + /// let mut cache_fwd = dfa_fwd.create_cache(); + /// let mut cache_rev = dfa_rev.create_cache(); + /// + /// let expected_fwd = HalfMatch::must(0, 9); + /// let expected_rev = HalfMatch::must(0, 3); + /// let got_fwd = dfa_fwd.try_search_fwd(&mut cache_fwd, &input)?.unwrap(); + /// // Here we don't specify the pattern to search for since there's only + /// // one pattern and we're doing a leftmost search. But if this were an + /// // overlapping search, you'd need to specify the pattern that matched + /// // in the forward direction. (Otherwise, you might wind up finding the + /// // starting position of a match of some other pattern.) That in turn + /// // requires building the reverse automaton with starts_for_each_pattern + /// // enabled. + /// let input = input + /// .clone() + /// .range(..got_fwd.offset()) + /// .anchored(Anchored::Yes); + /// let got_rev = dfa_rev.try_search_rev(&mut cache_rev, &input)?.unwrap(); + /// assert_eq!(expected_fwd, got_fwd); + /// assert_eq!(expected_rev, got_rev); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn match_kind(mut self, kind: MatchKind) -> Config { + self.match_kind = Some(kind); + self + } + + /// Set a prefilter to be used whenever a start state is entered. + /// + /// A [`Prefilter`] in this context is meant to accelerate searches by + /// looking for literal prefixes that every match for the corresponding + /// pattern (or patterns) must start with. Once a prefilter produces a + /// match, the underlying search routine continues on to try and confirm + /// the match. + /// + /// Be warned that setting a prefilter does not guarantee that the search + /// will be faster. While it's usually a good bet, if the prefilter + /// produces a lot of false positive candidates (i.e., positions matched + /// by the prefilter but not by the regex), then the overall result can + /// be slower than if you had just executed the regex engine without any + /// prefilters. + /// + /// Note that unless [`Config::specialize_start_states`] has been + /// explicitly set, then setting this will also enable (when `pre` is + /// `Some`) or disable (when `pre` is `None`) start state specialization. + /// This occurs because without start state specialization, a prefilter + /// is likely to be less effective. And without a prefilter, start state + /// specialization is usually pointless. + /// + /// By default no prefilter is set. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// util::prefilter::Prefilter, + /// Input, HalfMatch, MatchKind, + /// }; + /// + /// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "bar"]); + /// let re = DFA::builder() + /// .configure(DFA::config().prefilter(pre)) + /// .build(r"(foo|bar)[a-z]+")?; + /// let mut cache = re.create_cache(); + /// let input = Input::new("foo1 barfox bar"); + /// assert_eq!( + /// Some(HalfMatch::must(0, 11)), + /// re.try_search_fwd(&mut cache, &input)?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Be warned though that an incorrect prefilter can lead to incorrect + /// results! + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// util::prefilter::Prefilter, + /// Input, HalfMatch, MatchKind, + /// }; + /// + /// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "car"]); + /// let re = DFA::builder() + /// .configure(DFA::config().prefilter(pre)) + /// .build(r"(foo|bar)[a-z]+")?; + /// let mut cache = re.create_cache(); + /// let input = Input::new("foo1 barfox bar"); + /// assert_eq!( + /// // No match reported even though there clearly is one! + /// None, + /// re.try_search_fwd(&mut cache, &input)?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn prefilter(mut self, pre: Option<Prefilter>) -> Config { + self.pre = Some(pre); + if self.specialize_start_states.is_none() { + self.specialize_start_states = + Some(self.get_prefilter().is_some()); + } + self + } + + /// Whether to compile a separate start state for each pattern in the + /// lazy DFA. + /// + /// When enabled, a separate **anchored** start state is added for each + /// pattern in the lazy DFA. When this start state is used, then the DFA + /// will only search for matches for the pattern specified, even if there + /// are other patterns in the DFA. + /// + /// The main downside of this option is that it can potentially increase + /// the size of the DFA and/or increase the time it takes to build the + /// DFA at search time. However, since this is configuration for a lazy + /// DFA, these states aren't actually built unless they're used. Enabling + /// this isn't necessarily free, however, as it may result in higher cache + /// usage. + /// + /// There are a few reasons one might want to enable this (it's disabled + /// by default): + /// + /// 1. When looking for the start of an overlapping match (using a reverse + /// DFA), doing it correctly requires starting the reverse search using the + /// starting state of the pattern that matched in the forward direction. + /// Indeed, when building a [`Regex`](crate::hybrid::regex::Regex), it + /// will automatically enable this option when building the reverse DFA + /// internally. + /// 2. When you want to use a DFA with multiple patterns to both search + /// for matches of any pattern or to search for anchored matches of one + /// particular pattern while using the same DFA. (Otherwise, you would need + /// to compile a new DFA for each pattern.) + /// + /// By default this is disabled. + /// + /// # Example + /// + /// This example shows how to use this option to permit the same lazy DFA + /// to run both general searches for any pattern and anchored searches for + /// a specific pattern. + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// Anchored, HalfMatch, Input, PatternID, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().starts_for_each_pattern(true)) + /// .build_many(&[r"[a-z0-9]{6}", r"[a-z][a-z0-9]{5}"])?; + /// let mut cache = dfa.create_cache(); + /// let haystack = "bar foo123"; + /// + /// // Here's a normal unanchored search that looks for any pattern. + /// let expected = HalfMatch::must(0, 10); + /// let input = Input::new(haystack); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?); + /// // We can also do a normal anchored search for any pattern. Since it's + /// // an anchored search, we position the start of the search where we + /// // know the match will begin. + /// let expected = HalfMatch::must(0, 10); + /// let input = Input::new(haystack).range(4..); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?); + /// // Since we compiled anchored start states for each pattern, we can + /// // also look for matches of other patterns explicitly, even if a + /// // different pattern would have normally matched. + /// let expected = HalfMatch::must(1, 10); + /// let input = Input::new(haystack) + /// .range(4..) + /// .anchored(Anchored::Pattern(PatternID::must(1))); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn starts_for_each_pattern(mut self, yes: bool) -> Config { + self.starts_for_each_pattern = Some(yes); + self + } + + /// Whether to attempt to shrink the size of the lazy DFA's alphabet or + /// not. + /// + /// This option is enabled by default and should never be disabled unless + /// one is debugging the lazy DFA. + /// + /// When enabled, the lazy DFA will use a map from all possible bytes + /// to their corresponding equivalence class. Each equivalence class + /// represents a set of bytes that does not discriminate between a match + /// and a non-match in the DFA. For example, the pattern `[ab]+` has at + /// least two equivalence classes: a set containing `a` and `b` and a set + /// containing every byte except for `a` and `b`. `a` and `b` are in the + /// same equivalence classes because they never discriminate between a + /// match and a non-match. + /// + /// The advantage of this map is that the size of the transition table + /// can be reduced drastically from `#states * 256 * sizeof(LazyStateID)` + /// to `#states * k * sizeof(LazyStateID)` where `k` is the number of + /// equivalence classes (rounded up to the nearest power of 2). As a + /// result, total space usage can decrease substantially. Moreover, since a + /// smaller alphabet is used, DFA compilation during search becomes faster + /// as well since it will potentially be able to reuse a single transition + /// for multiple bytes. + /// + /// **WARNING:** This is only useful for debugging lazy DFAs. Disabling + /// this does not yield any speed advantages. Namely, even when this is + /// disabled, a byte class map is still used while searching. The only + /// difference is that every byte will be forced into its own distinct + /// equivalence class. This is useful for debugging the actual generated + /// transitions because it lets one see the transitions defined on actual + /// bytes instead of the equivalence classes. + pub fn byte_classes(mut self, yes: bool) -> Config { + self.byte_classes = Some(yes); + self + } + + /// Heuristically enable Unicode word boundaries. + /// + /// When set, this will attempt to implement Unicode word boundaries as if + /// they were ASCII word boundaries. This only works when the search input + /// is ASCII only. If a non-ASCII byte is observed while searching, then a + /// [`MatchError::quit`] error is returned. + /// + /// A possible alternative to enabling this option is to simply use an + /// ASCII word boundary, e.g., via `(?-u:\b)`. The main reason to use this + /// option is if you absolutely need Unicode support. This option lets one + /// use a fast search implementation (a DFA) for some potentially very + /// common cases, while providing the option to fall back to some other + /// regex engine to handle the general case when an error is returned. + /// + /// If the pattern provided has no Unicode word boundary in it, then this + /// option has no effect. (That is, quitting on a non-ASCII byte only + /// occurs when this option is enabled _and_ a Unicode word boundary is + /// present in the pattern.) + /// + /// This is almost equivalent to setting all non-ASCII bytes to be quit + /// bytes. The only difference is that this will cause non-ASCII bytes to + /// be quit bytes _only_ when a Unicode word boundary is present in the + /// pattern. + /// + /// When enabling this option, callers _must_ be prepared to handle + /// a [`MatchError`](crate::MatchError) error during search. + /// When using a [`Regex`](crate::hybrid::regex::Regex), this + /// corresponds to using the `try_` suite of methods. Alternatively, + /// if callers can guarantee that their input is ASCII only, then a + /// [`MatchError::quit`] error will never be returned while searching. + /// + /// This is disabled by default. + /// + /// # Example + /// + /// This example shows how to heuristically enable Unicode word boundaries + /// in a pattern. It also shows what happens when a search comes across a + /// non-ASCII byte. + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// HalfMatch, Input, MatchError, + /// }; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().unicode_word_boundary(true)) + /// .build(r"\b[0-9]+\b")?; + /// let mut cache = dfa.create_cache(); + /// + /// // The match occurs before the search ever observes the snowman + /// // character, so no error occurs. + /// let haystack = "foo 123 ☃"; + /// let expected = Some(HalfMatch::must(0, 7)); + /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; + /// assert_eq!(expected, got); + /// + /// // Notice that this search fails, even though the snowman character + /// // occurs after the ending match offset. This is because search + /// // routines read one byte past the end of the search to account for + /// // look-around, and indeed, this is required here to determine whether + /// // the trailing \b matches. + /// let haystack = "foo 123 ☃"; + /// let expected = MatchError::quit(0xE2, 8); + /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack)); + /// assert_eq!(Err(expected), got); + /// + /// // Another example is executing a search where the span of the haystack + /// // we specify is all ASCII, but there is non-ASCII just before it. This + /// // correctly also reports an error. + /// let input = Input::new("β123").range(2..); + /// let expected = MatchError::quit(0xB2, 1); + /// let got = dfa.try_search_fwd(&mut cache, &input); + /// assert_eq!(Err(expected), got); + /// + /// // And similarly for the trailing word boundary. + /// let input = Input::new("123β").range(..3); + /// let expected = MatchError::quit(0xCE, 3); + /// let got = dfa.try_search_fwd(&mut cache, &input); + /// assert_eq!(Err(expected), got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn unicode_word_boundary(mut self, yes: bool) -> Config { + // We have a separate option for this instead of just setting the + // appropriate quit bytes here because we don't want to set quit bytes + // for every regex. We only want to set them when the regex contains a + // Unicode word boundary. + self.unicode_word_boundary = Some(yes); + self + } + + /// Add a "quit" byte to the lazy DFA. + /// + /// When a quit byte is seen during search time, then search will return a + /// [`MatchError::quit`] error indicating the offset at which the search + /// stopped. + /// + /// A quit byte will always overrule any other aspects of a regex. For + /// example, if the `x` byte is added as a quit byte and the regex `\w` is + /// used, then observing `x` will cause the search to quit immediately + /// despite the fact that `x` is in the `\w` class. + /// + /// This mechanism is primarily useful for heuristically enabling certain + /// features like Unicode word boundaries in a DFA. Namely, if the input + /// to search is ASCII, then a Unicode word boundary can be implemented + /// via an ASCII word boundary with no change in semantics. Thus, a DFA + /// can attempt to match a Unicode word boundary but give up as soon as it + /// observes a non-ASCII byte. Indeed, if callers set all non-ASCII bytes + /// to be quit bytes, then Unicode word boundaries will be permitted when + /// building lazy DFAs. Of course, callers should enable + /// [`Config::unicode_word_boundary`] if they want this behavior instead. + /// (The advantage being that non-ASCII quit bytes will only be added if a + /// Unicode word boundary is in the pattern.) + /// + /// When enabling this option, callers _must_ be prepared to handle a + /// [`MatchError`](crate::MatchError) error during search. When using a + /// [`Regex`](crate::hybrid::regex::Regex), this corresponds to using the + /// `try_` suite of methods. + /// + /// By default, there are no quit bytes set. + /// + /// # Panics + /// + /// This panics if heuristic Unicode word boundaries are enabled and any + /// non-ASCII byte is removed from the set of quit bytes. Namely, enabling + /// Unicode word boundaries requires setting every non-ASCII byte to a quit + /// byte. So if the caller attempts to undo any of that, then this will + /// panic. + /// + /// # Example + /// + /// This example shows how to cause a search to terminate if it sees a + /// `\n` byte. This could be useful if, for example, you wanted to prevent + /// a user supplied pattern from matching across a line boundary. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, MatchError, Input}; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().quit(b'\n', true)) + /// .build(r"foo\p{any}+bar")?; + /// let mut cache = dfa.create_cache(); + /// + /// let haystack = "foo\nbar"; + /// // Normally this would produce a match, since \p{any} contains '\n'. + /// // But since we instructed the automaton to enter a quit state if a + /// // '\n' is observed, this produces a match error instead. + /// let expected = MatchError::quit(b'\n', 3); + /// let got = dfa.try_search_fwd( + /// &mut cache, + /// &Input::new(haystack), + /// ).unwrap_err(); + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn quit(mut self, byte: u8, yes: bool) -> Config { + if self.get_unicode_word_boundary() && !byte.is_ascii() && !yes { + panic!( + "cannot set non-ASCII byte to be non-quit when \ + Unicode word boundaries are enabled" + ); + } + if self.quitset.is_none() { + self.quitset = Some(ByteSet::empty()); + } + if yes { + self.quitset.as_mut().unwrap().add(byte); + } else { + self.quitset.as_mut().unwrap().remove(byte); + } + self + } + + /// Enable specializing start states in the lazy DFA. + /// + /// When start states are specialized, an implementor of a search routine + /// using a lazy DFA can tell when the search has entered a starting state. + /// When start states aren't specialized, then it is impossible to know + /// whether the search has entered a start state. + /// + /// Ideally, this option wouldn't need to exist and we could always + /// specialize start states. The problem is that start states can be quite + /// active. This in turn means that an efficient search routine is likely + /// to ping-pong between a heavily optimized hot loop that handles most + /// states and to a less optimized specialized handling of start states. + /// This causes branches to get heavily mispredicted and overall can + /// materially decrease throughput. Therefore, specializing start states + /// should only be enabled when it is needed. + /// + /// Knowing whether a search is in a start state is typically useful when a + /// prefilter is active for the search. A prefilter is typically only run + /// when in a start state and a prefilter can greatly accelerate a search. + /// Therefore, the possible cost of specializing start states is worth it + /// in this case. Otherwise, if you have no prefilter, there is likely no + /// reason to specialize start states. + /// + /// This is disabled by default, but note that it is automatically + /// enabled (or disabled) if [`Config::prefilter`] is set. Namely, unless + /// `specialize_start_states` has already been set, [`Config::prefilter`] + /// will automatically enable or disable it based on whether a prefilter + /// is present or not, respectively. This is done because a prefilter's + /// effectiveness is rooted in being executed whenever the DFA is in a + /// start state, and that's only possible to do when they are specialized. + /// + /// Note that it is plausibly reasonable to _disable_ this option + /// explicitly while _enabling_ a prefilter. In that case, a prefilter + /// will still be run at the beginning of a search, but never again. This + /// in theory could strike a good balance if you're in a situation where a + /// prefilter is likely to produce many false positive candidates. + /// + /// # Example + /// + /// This example shows how to enable start state specialization and then + /// shows how to check whether a state is a start state or not. + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, MatchError, Input}; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().specialize_start_states(true)) + /// .build(r"[a-z]+")?; + /// let mut cache = dfa.create_cache(); + /// + /// let haystack = "123 foobar 4567".as_bytes(); + /// let sid = dfa.start_state_forward(&mut cache, &Input::new(haystack))?; + /// // The ID returned by 'start_state_forward' will always be tagged as + /// // a start state when start state specialization is enabled. + /// assert!(sid.is_tagged()); + /// assert!(sid.is_start()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Compare the above with the default lazy DFA configuration where + /// start states are _not_ specialized. In this case, the start state + /// is not tagged and `sid.is_start()` returns false. + /// + /// ``` + /// use regex_automata::{hybrid::dfa::DFA, MatchError, Input}; + /// + /// let dfa = DFA::new(r"[a-z]+")?; + /// let mut cache = dfa.create_cache(); + /// + /// let haystack = "123 foobar 4567".as_bytes(); + /// let sid = dfa.start_state_forward(&mut cache, &Input::new(haystack))?; + /// // Start states are not tagged in the default configuration! + /// assert!(!sid.is_tagged()); + /// assert!(!sid.is_start()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn specialize_start_states(mut self, yes: bool) -> Config { + self.specialize_start_states = Some(yes); + self + } + + /// Sets the maximum amount of heap memory, in bytes, to allocate to the + /// cache for use during a lazy DFA search. If the lazy DFA would otherwise + /// use more heap memory, then, depending on other configuration knobs, + /// either stop the search and return an error or clear the cache and + /// continue the search. + /// + /// The default cache capacity is some "reasonable" number that will + /// accommodate most regular expressions. You may find that if you need + /// to build a large DFA then it may be necessary to increase the cache + /// capacity. + /// + /// Note that while building a lazy DFA will do a "minimum" check to ensure + /// the capacity is big enough, this is more or less about correctness. + /// If the cache is bigger than the minimum but still "too small," then the + /// lazy DFA could wind up spending a lot of time clearing the cache and + /// recomputing transitions, thus negating the performance benefits of a + /// lazy DFA. Thus, setting the cache capacity is mostly an experimental + /// endeavor. For most common patterns, however, the default should be + /// sufficient. + /// + /// For more details on how the lazy DFA's cache is used, see the + /// documentation for [`Cache`]. + /// + /// # Example + /// + /// This example shows what happens if the configured cache capacity is + /// too small. In such cases, one can override the cache capacity to make + /// it bigger. Alternatively, one might want to use less memory by setting + /// a smaller cache capacity. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let pattern = r"\p{L}{1000}"; + /// + /// // The default cache capacity is likely too small to deal with regexes + /// // that are very large. Large repetitions of large Unicode character + /// // classes are a common way to make very large regexes. + /// let _ = DFA::new(pattern).unwrap_err(); + /// // Bump up the capacity to something bigger. + /// let dfa = DFA::builder() + /// .configure(DFA::config().cache_capacity(100 * (1<<20))) // 100 MB + /// .build(pattern)?; + /// let mut cache = dfa.create_cache(); + /// + /// let haystack = "ͰͲͶͿΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙ".repeat(50); + /// let expected = Some(HalfMatch::must(0, 2000)); + /// let got = dfa.try_search_fwd(&mut cache, &Input::new(&haystack))?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn cache_capacity(mut self, bytes: usize) -> Config { + self.cache_capacity = Some(bytes); + self + } + + /// Configures construction of a lazy DFA to use the minimum cache capacity + /// if the configured capacity is otherwise too small for the provided NFA. + /// + /// This is useful if you never want lazy DFA construction to fail because + /// of a capacity that is too small. + /// + /// In general, this option is typically not a good idea. In particular, + /// while a minimum cache capacity does permit the lazy DFA to function + /// where it otherwise couldn't, it's plausible that it may not function + /// well if it's constantly running out of room. In that case, the speed + /// advantages of the lazy DFA may be negated. On the other hand, the + /// "minimum" cache capacity computed may not be completely accurate and + /// could actually be bigger than what is really necessary. Therefore, it + /// is plausible that using the minimum cache capacity could still result + /// in very good performance. + /// + /// This is disabled by default. + /// + /// # Example + /// + /// This example shows what happens if the configured cache capacity is + /// too small. In such cases, one could override the capacity explicitly. + /// An alternative, demonstrated here, let's us force construction to use + /// the minimum cache capacity if the configured capacity is otherwise + /// too small. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input}; + /// + /// let pattern = r"\p{L}{1000}"; + /// + /// // The default cache capacity is likely too small to deal with regexes + /// // that are very large. Large repetitions of large Unicode character + /// // classes are a common way to make very large regexes. + /// let _ = DFA::new(pattern).unwrap_err(); + /// // Configure construction such it automatically selects the minimum + /// // cache capacity if it would otherwise be too small. + /// let dfa = DFA::builder() + /// .configure(DFA::config().skip_cache_capacity_check(true)) + /// .build(pattern)?; + /// let mut cache = dfa.create_cache(); + /// + /// let haystack = "ͰͲͶͿΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙ".repeat(50); + /// let expected = Some(HalfMatch::must(0, 2000)); + /// let got = dfa.try_search_fwd(&mut cache, &Input::new(&haystack))?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn skip_cache_capacity_check(mut self, yes: bool) -> Config { + self.skip_cache_capacity_check = Some(yes); + self + } + + /// Configure a lazy DFA search to quit after a certain number of cache + /// clearings. + /// + /// When a minimum is set, then a lazy DFA search will *possibly* "give + /// up" after the minimum number of cache clearings has occurred. This is + /// typically useful in scenarios where callers want to detect whether the + /// lazy DFA search is "efficient" or not. If the cache is cleared too many + /// times, this is a good indicator that it is not efficient, and thus, the + /// caller may wish to use some other regex engine. + /// + /// Note that the number of times a cache is cleared is a property of + /// the cache itself. Thus, if a cache is used in a subsequent search + /// with a similarly configured lazy DFA, then it could cause the + /// search to "give up" if the cache needed to be cleared, depending + /// on its internal count and configured minimum. The cache clear + /// count can only be reset to `0` via [`DFA::reset_cache`] (or + /// [`Regex::reset_cache`](crate::hybrid::regex::Regex::reset_cache) if + /// you're using the `Regex` API). + /// + /// By default, no minimum is configured. Thus, a lazy DFA search will + /// never give up due to cache clearings. If you do set this option, you + /// might consider also setting [`Config::minimum_bytes_per_state`] in + /// order for the lazy DFA to take efficiency into account before giving + /// up. + /// + /// # Example + /// + /// This example uses a somewhat pathological configuration to demonstrate + /// the _possible_ behavior of cache clearing and how it might result + /// in a search that returns an error. + /// + /// It is important to note that the precise mechanics of how and when + /// a cache gets cleared is an implementation detail. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{hybrid::dfa::DFA, Input, MatchError, MatchErrorKind}; + /// + /// // This is a carefully chosen regex. The idea is to pick one + /// // that requires some decent number of states (hence the bounded + /// // repetition). But we specifically choose to create a class with an + /// // ASCII letter and a non-ASCII letter so that we can check that no new + /// // states are created once the cache is full. Namely, if we fill up the + /// // cache on a haystack of 'a's, then in order to match one 'β', a new + /// // state will need to be created since a 'β' is encoded with multiple + /// // bytes. Since there's no room for this state, the search should quit + /// // at the very first position. + /// let pattern = r"[aβ]{100}"; + /// let dfa = DFA::builder() + /// .configure( + /// // Configure it so that we have the minimum cache capacity + /// // possible. And that if any clearings occur, the search quits. + /// DFA::config() + /// .skip_cache_capacity_check(true) + /// .cache_capacity(0) + /// .minimum_cache_clear_count(Some(0)), + /// ) + /// .build(pattern)?; + /// let mut cache = dfa.create_cache(); + /// + /// // Our search will give up before reaching the end! + /// let haystack = "a".repeat(101).into_bytes(); + /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); + /// assert!(matches!( + /// *result.unwrap_err().kind(), + /// MatchErrorKind::GaveUp { .. }, + /// )); + /// + /// // Now that we know the cache is full, if we search a haystack that we + /// // know will require creating at least one new state, it should not + /// // be able to make much progress. + /// let haystack = "β".repeat(101).into_bytes(); + /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); + /// assert!(matches!( + /// *result.unwrap_err().kind(), + /// MatchErrorKind::GaveUp { .. }, + /// )); + /// + /// // If we reset the cache, then we should be able to create more states + /// // and make more progress with searching for betas. + /// cache.reset(&dfa); + /// let haystack = "β".repeat(101).into_bytes(); + /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); + /// assert!(matches!( + /// *result.unwrap_err().kind(), + /// MatchErrorKind::GaveUp { .. }, + /// )); + /// + /// // ... switching back to ASCII still makes progress since it just needs + /// // to set transitions on existing states! + /// let haystack = "a".repeat(101).into_bytes(); + /// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack)); + /// assert!(matches!( + /// *result.unwrap_err().kind(), + /// MatchErrorKind::GaveUp { .. }, + /// )); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn minimum_cache_clear_count(mut self, min: Option<usize>) -> Config { + self.minimum_cache_clear_count = Some(min); + self + } + + /// Configure a lazy DFA search to quit only when its efficiency drops + /// below the given minimum. + /// + /// The efficiency of the cache is determined by the number of DFA states + /// compiled per byte of haystack searched. For example, if the efficiency + /// is 2, then it means the lazy DFA is creating a new DFA state after + /// searching approximately 2 bytes in a haystack. Generally speaking, 2 + /// is quite bad and it's likely that even a slower regex engine like the + /// [`PikeVM`](crate::nfa::thompson::pikevm::PikeVM) would be faster. + /// + /// This has no effect if [`Config::minimum_cache_clear_count`] is not set. + /// Namely, this option only kicks in when the cache has been cleared more + /// than the minimum number. If no minimum is set, then the cache is simply + /// cleared whenever it fills up and it is impossible for the lazy DFA to + /// quit due to ineffective use of the cache. + /// + /// In general, if one is setting [`Config::minimum_cache_clear_count`], + /// then one should probably also set this knob as well. The reason is + /// that the absolute number of times the cache is cleared is generally + /// not a great predictor of efficiency. For example, if a new DFA state + /// is created for every 1,000 bytes searched, then it wouldn't be hard + /// for the cache to get cleared more than `N` times and then cause the + /// lazy DFA to quit. But a new DFA state every 1,000 bytes is likely quite + /// good from a performance perspective, and it's likely that the lazy + /// DFA should continue searching, even if it requires clearing the cache + /// occasionally. + /// + /// Finally, note that if you're implementing your own lazy DFA search + /// routine and also want this efficiency check to work correctly, then + /// you'll need to use the following routines to record search progress: + /// + /// * Call [`Cache::search_start`] at the beginning of every search. + /// * Call [`Cache::search_update`] whenever [`DFA::next_state`] is + /// called. + /// * Call [`Cache::search_finish`] before completing a search. (It is + /// not strictly necessary to call this when an error is returned, as + /// `Cache::search_start` will automatically finish the previous search + /// for you. But calling it where possible before returning helps improve + /// the accuracy of how many bytes have actually been searched.) + pub fn minimum_bytes_per_state(mut self, min: Option<usize>) -> Config { + self.minimum_bytes_per_state = Some(min); + self + } + + /// Returns the match semantics set in this configuration. + pub fn get_match_kind(&self) -> MatchKind { + self.match_kind.unwrap_or(MatchKind::LeftmostFirst) + } + + /// Returns the prefilter set in this configuration, if one at all. + pub fn get_prefilter(&self) -> Option<&Prefilter> { + self.pre.as_ref().unwrap_or(&None).as_ref() + } + + /// Returns whether this configuration has enabled anchored starting states + /// for every pattern in the DFA. + pub fn get_starts_for_each_pattern(&self) -> bool { + self.starts_for_each_pattern.unwrap_or(false) + } + + /// Returns whether this configuration has enabled byte classes or not. + /// This is typically a debugging oriented option, as disabling it confers + /// no speed benefit. + pub fn get_byte_classes(&self) -> bool { + self.byte_classes.unwrap_or(true) + } + + /// Returns whether this configuration has enabled heuristic Unicode word + /// boundary support. When enabled, it is possible for a search to return + /// an error. + pub fn get_unicode_word_boundary(&self) -> bool { + self.unicode_word_boundary.unwrap_or(false) + } + + /// Returns whether this configuration will instruct the lazy DFA to enter + /// a quit state whenever the given byte is seen during a search. When at + /// least one byte has this enabled, it is possible for a search to return + /// an error. + pub fn get_quit(&self, byte: u8) -> bool { + self.quitset.map_or(false, |q| q.contains(byte)) + } + + /// Returns whether this configuration will instruct the lazy DFA to + /// "specialize" start states. When enabled, the lazy DFA will tag start + /// states so that search routines using the lazy DFA can detect when + /// it's in a start state and do some kind of optimization (like run a + /// prefilter). + pub fn get_specialize_start_states(&self) -> bool { + self.specialize_start_states.unwrap_or(false) + } + + /// Returns the cache capacity set on this configuration. + pub fn get_cache_capacity(&self) -> usize { + self.cache_capacity.unwrap_or(2 * (1 << 20)) + } + + /// Returns whether the cache capacity check should be skipped. + pub fn get_skip_cache_capacity_check(&self) -> bool { + self.skip_cache_capacity_check.unwrap_or(false) + } + + /// Returns, if set, the minimum number of times the cache must be cleared + /// before a lazy DFA search can give up. When no minimum is set, then a + /// search will never quit and will always clear the cache whenever it + /// fills up. + pub fn get_minimum_cache_clear_count(&self) -> Option<usize> { + self.minimum_cache_clear_count.unwrap_or(None) + } + + /// Returns, if set, the minimum number of bytes per state that need to be + /// processed in order for the lazy DFA to keep going. If the minimum falls + /// below this number (and the cache has been cleared a minimum number of + /// times), then the lazy DFA will return a "gave up" error. + pub fn get_minimum_bytes_per_state(&self) -> Option<usize> { + self.minimum_bytes_per_state.unwrap_or(None) + } + + /// Returns the minimum lazy DFA cache capacity required for the given NFA. + /// + /// The cache capacity required for a particular NFA may change without + /// notice. Callers should not rely on it being stable. + /// + /// This is useful for informational purposes, but can also be useful for + /// other reasons. For example, if one wants to check the minimum cache + /// capacity themselves or if one wants to set the capacity based on the + /// minimum. + /// + /// This may return an error if this configuration does not support all of + /// the instructions used in the given NFA. For example, if the NFA has a + /// Unicode word boundary but this configuration does not enable heuristic + /// support for Unicode word boundaries. + pub fn get_minimum_cache_capacity( + &self, + nfa: &thompson::NFA, + ) -> Result<usize, BuildError> { + let quitset = self.quit_set_from_nfa(nfa)?; + let classes = self.byte_classes_from_nfa(nfa, &quitset); + let starts = self.get_starts_for_each_pattern(); + Ok(minimum_cache_capacity(nfa, &classes, starts)) + } + + /// Returns the byte class map used during search from the given NFA. + /// + /// If byte classes are disabled on this configuration, then a map is + /// returned that puts each byte in its own equivalent class. + fn byte_classes_from_nfa( + &self, + nfa: &thompson::NFA, + quit: &ByteSet, + ) -> ByteClasses { + if !self.get_byte_classes() { + // The lazy DFA will always use the equivalence class map, but + // enabling this option is useful for debugging. Namely, this will + // cause all transitions to be defined over their actual bytes + // instead of an opaque equivalence class identifier. The former is + // much easier to grok as a human. + ByteClasses::singletons() + } else { + let mut set = nfa.byte_class_set().clone(); + // It is important to distinguish any "quit" bytes from all other + // bytes. Otherwise, a non-quit byte may end up in the same class + // as a quit byte, and thus cause the DFA stop when it shouldn't. + // + // Test case: + // + // regex-cli find hybrid regex -w @conn.json.1000x.log \ + // '^#' '\b10\.55\.182\.100\b' + if !quit.is_empty() { + set.add_set(&quit); + } + set.byte_classes() + } + } + + /// Return the quit set for this configuration and the given NFA. + /// + /// This may return an error if the NFA is incompatible with this + /// configuration's quit set. For example, if the NFA has a Unicode word + /// boundary and the quit set doesn't include non-ASCII bytes. + fn quit_set_from_nfa( + &self, + nfa: &thompson::NFA, + ) -> Result<ByteSet, BuildError> { + let mut quit = self.quitset.unwrap_or(ByteSet::empty()); + if nfa.look_set_any().contains_word_unicode() { + if self.get_unicode_word_boundary() { + for b in 0x80..=0xFF { + quit.add(b); + } + } else { + // If heuristic support for Unicode word boundaries wasn't + // enabled, then we can still check if our quit set is correct. + // If the caller set their quit bytes in a way that causes the + // DFA to quit on at least all non-ASCII bytes, then that's all + // we need for heuristic support to work. + if !quit.contains_range(0x80, 0xFF) { + return Err( + BuildError::unsupported_dfa_word_boundary_unicode(), + ); + } + } + } + Ok(quit) + } + + /// Overwrite the default configuration such that the options in `o` are + /// always used. If an option in `o` is not set, then the corresponding + /// option in `self` is used. If it's not set in `self` either, then it + /// remains not set. + fn overwrite(&self, o: Config) -> Config { + Config { + match_kind: o.match_kind.or(self.match_kind), + pre: o.pre.or_else(|| self.pre.clone()), + starts_for_each_pattern: o + .starts_for_each_pattern + .or(self.starts_for_each_pattern), + byte_classes: o.byte_classes.or(self.byte_classes), + unicode_word_boundary: o + .unicode_word_boundary + .or(self.unicode_word_boundary), + quitset: o.quitset.or(self.quitset), + specialize_start_states: o + .specialize_start_states + .or(self.specialize_start_states), + cache_capacity: o.cache_capacity.or(self.cache_capacity), + skip_cache_capacity_check: o + .skip_cache_capacity_check + .or(self.skip_cache_capacity_check), + minimum_cache_clear_count: o + .minimum_cache_clear_count + .or(self.minimum_cache_clear_count), + minimum_bytes_per_state: o + .minimum_bytes_per_state + .or(self.minimum_bytes_per_state), + } + } +} + +/// A builder for constructing a lazy deterministic finite automaton from +/// regular expressions. +/// +/// As a convenience, [`DFA::builder`] is an alias for [`Builder::new`]. The +/// advantage of the former is that it often lets you avoid importing the +/// `Builder` type directly. +/// +/// This builder provides two main things: +/// +/// 1. It provides a few different `build` routines for actually constructing +/// a DFA from different kinds of inputs. The most convenient is +/// [`Builder::build`], which builds a DFA directly from a pattern string. The +/// most flexible is [`Builder::build_from_nfa`], which builds a DFA straight +/// from an NFA. +/// 2. The builder permits configuring a number of things. +/// [`Builder::configure`] is used with [`Config`] to configure aspects of +/// the DFA and the construction process itself. [`Builder::syntax`] and +/// [`Builder::thompson`] permit configuring the regex parser and Thompson NFA +/// construction, respectively. The syntax and thompson configurations only +/// apply when building from a pattern string. +/// +/// This builder always constructs a *single* lazy DFA. As such, this builder +/// can only be used to construct regexes that either detect the presence +/// of a match or find the end location of a match. A single DFA cannot +/// produce both the start and end of a match. For that information, use a +/// [`Regex`](crate::hybrid::regex::Regex), which can be similarly configured +/// using [`regex::Builder`](crate::hybrid::regex::Builder). The main reason +/// to use a DFA directly is if the end location of a match is enough for your +/// use case. Namely, a `Regex` will construct two lazy DFAs instead of one, +/// since a second reverse DFA is needed to find the start of a match. +/// +/// # Example +/// +/// This example shows how to build a lazy DFA that uses a tiny cache capacity +/// and completely disables Unicode. That is: +/// +/// * Things such as `\w`, `.` and `\b` are no longer Unicode-aware. `\w` +/// and `\b` are ASCII-only while `.` matches any byte except for `\n` +/// (instead of any UTF-8 encoding of a Unicode scalar value except for +/// `\n`). Things that are Unicode only, such as `\pL`, are not allowed. +/// * The pattern itself is permitted to match invalid UTF-8. For example, +/// things like `[^a]` that match any byte except for `a` are permitted. +/// +/// ``` +/// use regex_automata::{ +/// hybrid::dfa::DFA, +/// nfa::thompson, +/// util::syntax, +/// HalfMatch, Input, +/// }; +/// +/// let dfa = DFA::builder() +/// .configure(DFA::config().cache_capacity(5_000)) +/// .thompson(thompson::Config::new().utf8(false)) +/// .syntax(syntax::Config::new().unicode(false).utf8(false)) +/// .build(r"foo[^b]ar.*")?; +/// let mut cache = dfa.create_cache(); +/// +/// let haystack = b"\xFEfoo\xFFar\xE2\x98\xFF\n"; +/// let expected = Some(HalfMatch::must(0, 10)); +/// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; +/// assert_eq!(expected, got); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone, Debug)] +pub struct Builder { + config: Config, + #[cfg(feature = "syntax")] + thompson: thompson::Compiler, +} + +impl Builder { + /// Create a new lazy DFA builder with the default configuration. + pub fn new() -> Builder { + Builder { + config: Config::default(), + #[cfg(feature = "syntax")] + thompson: thompson::Compiler::new(), + } + } + + /// Build a lazy DFA from the given pattern. + /// + /// If there was a problem parsing or compiling the pattern, then an error + /// is returned. + #[cfg(feature = "syntax")] + pub fn build(&self, pattern: &str) -> Result<DFA, BuildError> { + self.build_many(&[pattern]) + } + + /// Build a lazy DFA from the given patterns. + /// + /// When matches are returned, the pattern ID corresponds to the index of + /// the pattern in the slice given. + #[cfg(feature = "syntax")] + pub fn build_many<P: AsRef<str>>( + &self, + patterns: &[P], + ) -> Result<DFA, BuildError> { + let nfa = self + .thompson + .clone() + // We can always forcefully disable captures because DFAs do not + // support them. + .configure( + thompson::Config::new() + .which_captures(thompson::WhichCaptures::None), + ) + .build_many(patterns) + .map_err(BuildError::nfa)?; + self.build_from_nfa(nfa) + } + + /// Build a DFA from the given NFA. + /// + /// Note that this requires owning a `thompson::NFA`. While this may force + /// you to clone the NFA, such a clone is not a deep clone. Namely, NFAs + /// are defined internally to support shared ownership such that cloning is + /// very cheap. + /// + /// # Example + /// + /// This example shows how to build a lazy DFA if you already have an NFA + /// in hand. + /// + /// ``` + /// use regex_automata::{ + /// hybrid::dfa::DFA, + /// nfa::thompson, + /// HalfMatch, Input, + /// }; + /// + /// let haystack = "foo123bar"; + /// + /// // This shows how to set non-default options for building an NFA. + /// let nfa = thompson::Compiler::new() + /// .configure(thompson::Config::new().shrink(true)) + /// .build(r"[0-9]+")?; + /// let dfa = DFA::builder().build_from_nfa(nfa)?; + /// let mut cache = dfa.create_cache(); + /// let expected = Some(HalfMatch::must(0, 6)); + /// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn build_from_nfa( + &self, + nfa: thompson::NFA, + ) -> Result<DFA, BuildError> { + let quitset = self.config.quit_set_from_nfa(&nfa)?; + let classes = self.config.byte_classes_from_nfa(&nfa, &quitset); + // Check that we can fit at least a few states into our cache, + // otherwise it's pretty senseless to use the lazy DFA. This does have + // a possible failure mode though. This assumes the maximum size of a + // state in powerset space (so, the total number of NFA states), which + // may never actually materialize, and could be quite a bit larger + // than the actual biggest state. If this turns out to be a problem, + // we could expose a knob that disables this check. But if so, we have + // to be careful not to panic in other areas of the code (the cache + // clearing and init code) that tend to assume some minimum useful + // cache capacity. + let min_cache = minimum_cache_capacity( + &nfa, + &classes, + self.config.get_starts_for_each_pattern(), + ); + let mut cache_capacity = self.config.get_cache_capacity(); + if cache_capacity < min_cache { + // When the caller has asked us to skip the cache capacity check, + // then we simply force the cache capacity to its minimum amount + // and mush on. + if self.config.get_skip_cache_capacity_check() { + debug!( + "given capacity ({}) is too small, \ + since skip_cache_capacity_check is enabled, \ + setting cache capacity to minimum ({})", + cache_capacity, min_cache, + ); + cache_capacity = min_cache; + } else { + return Err(BuildError::insufficient_cache_capacity( + min_cache, + cache_capacity, + )); + } + } + // We also need to check that we can fit at least some small number + // of states in our state ID space. This is unlikely to trigger in + // >=32-bit systems, but 16-bit systems have a pretty small state ID + // space since a number of bits are used up as sentinels. + if let Err(err) = minimum_lazy_state_id(&classes) { + return Err(BuildError::insufficient_state_id_capacity(err)); + } + let stride2 = classes.stride2(); + let start_map = StartByteMap::new(nfa.look_matcher()); + Ok(DFA { + config: self.config.clone(), + nfa, + stride2, + start_map, + classes, + quitset, + cache_capacity, + }) + } + + /// Apply the given lazy DFA configuration options to this builder. + pub fn configure(&mut self, config: Config) -> &mut Builder { + self.config = self.config.overwrite(config); + self + } + + /// Set the syntax configuration for this builder using + /// [`syntax::Config`](crate::util::syntax::Config). + /// + /// This permits setting things like case insensitivity, Unicode and multi + /// line mode. + /// + /// These settings only apply when constructing a lazy DFA directly from a + /// pattern. + #[cfg(feature = "syntax")] + pub fn syntax( + &mut self, + config: crate::util::syntax::Config, + ) -> &mut Builder { + self.thompson.syntax(config); + self + } + + /// Set the Thompson NFA configuration for this builder using + /// [`nfa::thompson::Config`](crate::nfa::thompson::Config). + /// + /// This permits setting things like whether the DFA should match the regex + /// in reverse or if additional time should be spent shrinking the size of + /// the NFA. + /// + /// These settings only apply when constructing a DFA directly from a + /// pattern. + #[cfg(feature = "syntax")] + pub fn thompson(&mut self, config: thompson::Config) -> &mut Builder { + self.thompson.configure(config); + self + } +} + +/// 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<LazyStateID>, + /// 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 +/// underlying NFA 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(()) +} + +/// Based on the minimum number of states required for a useful lazy DFA cache, +/// this returns the minimum lazy state ID that must be representable. +/// +/// It's not likely for this to have any impact 32-bit systems (or higher), but +/// on 16-bit systems, the lazy state ID space is quite constrained and thus +/// may be insufficient if our MIN_STATES value is (for some reason) too high. +fn minimum_lazy_state_id( + classes: &ByteClasses, +) -> Result<LazyStateID, LazyStateIDError> { + let stride = 1 << classes.stride2(); + let min_state_index = MIN_STATES.checked_sub(1).unwrap(); + LazyStateID::new(min_state_index * stride) +} + +/// Based on the minimum number of states required for a useful lazy DFA cache, +/// this returns a heuristic minimum number of bytes of heap space required. +/// +/// This is a "heuristic" because the minimum it returns is likely bigger than +/// the true minimum. Namely, it assumes that each powerset NFA/DFA state uses +/// the maximum number of NFA states (all of them). This is likely bigger +/// than what is required in practice. Computing the true minimum effectively +/// requires determinization, which is probably too much work to do for a +/// simple check like this. +/// +/// One of the issues with this approach IMO is that it requires that this +/// be in sync with the calculation above for computing how much heap memory +/// the DFA cache uses. If we get it wrong, it's possible for example for the +/// minimum to be smaller than the computed heap memory, and thus, it may be +/// the case that we can't add the required minimum number of states. That in +/// turn will make lazy DFA panic because we assume that we can add at least a +/// minimum number of states. +/// +/// Another approach would be to always allow the minimum number of states to +/// be added to the lazy DFA cache, even if it exceeds the configured cache +/// limit. This does mean that the limit isn't really a limit in all cases, +/// which is unfortunate. But it does at least guarantee that the lazy DFA can +/// always make progress, even if it is slow. (This approach is very similar to +/// enabling the 'skip_cache_capacity_check' config knob, except it wouldn't +/// rely on cache size calculation. Instead, it would just always permit a +/// minimum number of states to be added.) +fn minimum_cache_capacity( + nfa: &thompson::NFA, + classes: &ByteClasses, + starts_for_each_pattern: bool, +) -> usize { + const ID_SIZE: usize = size_of::<LazyStateID>(); + const STATE_SIZE: usize = size_of::<State>(); + + let stride = 1 << classes.stride2(); + let states_len = nfa.states().len(); + let sparses = 2 * states_len * NFAStateID::SIZE; + let trans = MIN_STATES * stride * ID_SIZE; + + let mut starts = Start::len() * ID_SIZE; + if starts_for_each_pattern { + starts += (Start::len() * nfa.pattern_len()) * ID_SIZE; + } + + // The min number of states HAS to be at least 4: we have 3 sentinel states + // and then we need space for one more when we save a state after clearing + // the cache. We also need space for one more, otherwise we get stuck in a + // loop where we try to add a 5th state, which gets rejected, which clears + // the cache, which adds back a saved state (4th total state) which then + // tries to add the 5th state again. + assert!(MIN_STATES >= 5, "minimum number of states has to be at least 5"); + // The minimum number of non-sentinel states. We consider this separately + // because sentinel states are much smaller in that they contain no NFA + // states. Given our aggressive calculation here, it's worth being more + // precise with the number of states we need. + let non_sentinel = MIN_STATES.checked_sub(SENTINEL_STATES).unwrap(); + + // Every `State` has 5 bytes for flags, 4 bytes (max) for the number of + // patterns, followed by 32-bit encodings of patterns and then delta + // varint encodings of NFA state IDs. We use the worst case (which isn't + // technically possible) of 5 bytes for each NFA state ID. + // + // HOWEVER, three of the states needed by a lazy DFA are just the sentinel + // unknown, dead and quit states. Those states have a known size and it is + // small. + let dead_state_size = State::dead().memory_usage(); + let max_state_size = 5 + 4 + (nfa.pattern_len() * 4) + (states_len * 5); + let states = (SENTINEL_STATES * (STATE_SIZE + dead_state_size)) + + (non_sentinel * (STATE_SIZE + max_state_size)); + // NOTE: We don't double count heap memory used by State for this map since + // we use reference counting to avoid doubling memory usage. (This tends to + // be where most memory is allocated in the cache.) + let states_to_sid = (MIN_STATES * STATE_SIZE) + (MIN_STATES * ID_SIZE); + let stack = states_len * NFAStateID::SIZE; + let scratch_state_builder = max_state_size; + + trans + + starts + + states + + states_to_sid + + sparses + + stack + + scratch_state_builder +} + +#[cfg(all(test, feature = "syntax"))] +mod tests { + use super::*; + + // Tests that we handle heuristic Unicode word boundary support in reverse + // DFAs in the specific case of contextual searches. + // + // I wrote this test when I discovered a bug in how heuristic word + // boundaries were handled. Namely, that the starting state selection + // didn't consider the DFA's quit byte set when looking at the byte + // immediately before the start of the search (or immediately after the + // end of the search in the case of a reverse search). As a result, it was + // possible for '\bfoo\b' to match 'β123' because the trailing \xB2 byte + // in the 'β' codepoint would be treated as a non-word character. But of + // course, this search should trigger the DFA to quit, since there is a + // non-ASCII byte in consideration. + // + // Thus, I fixed 'start_state_{forward,reverse}' to check the quit byte set + // if it wasn't empty. The forward case is tested in the doc test for the + // Config::unicode_word_boundary API. We test the reverse case here, which + // is sufficiently niche that it doesn't really belong in a doc test. + #[test] + fn heuristic_unicode_reverse() { + let dfa = DFA::builder() + .configure(DFA::config().unicode_word_boundary(true)) + .thompson(thompson::Config::new().reverse(true)) + .build(r"\b[0-9]+\b") + .unwrap(); + let mut cache = dfa.create_cache(); + + let input = Input::new("β123").range(2..); + let expected = MatchError::quit(0xB2, 1); + let got = dfa.try_search_rev(&mut cache, &input); + assert_eq!(Err(expected), got); + + let input = Input::new("123β").range(..3); + let expected = MatchError::quit(0xCE, 3); + let got = dfa.try_search_rev(&mut cache, &input); + assert_eq!(Err(expected), got); + } +} |