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Diffstat (limited to 'third_party/rust/regex-automata/src/dfa/dense.rs')
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diff --git a/third_party/rust/regex-automata/src/dfa/dense.rs b/third_party/rust/regex-automata/src/dfa/dense.rs new file mode 100644 index 0000000000..6da865f977 --- /dev/null +++ b/third_party/rust/regex-automata/src/dfa/dense.rs @@ -0,0 +1,5139 @@ +/*! +Types and routines specific to dense DFAs. + +This module is the home of [`dense::DFA`](DFA). + +This module also contains a [`dense::Builder`](Builder) and a +[`dense::Config`](Config) for building and configuring a dense DFA. +*/ + +#[cfg(feature = "dfa-build")] +use core::cmp; +use core::{convert::TryFrom, fmt, iter, mem::size_of, slice}; + +#[cfg(feature = "dfa-build")] +use alloc::{ + collections::{BTreeMap, BTreeSet}, + vec, + vec::Vec, +}; + +#[cfg(feature = "dfa-build")] +use crate::{ + dfa::{ + accel::Accel, determinize, minimize::Minimizer, remapper::Remapper, + sparse, + }, + nfa::thompson, + util::{look::LookMatcher, search::MatchKind}, +}; +use crate::{ + dfa::{ + accel::Accels, + automaton::{fmt_state_indicator, Automaton}, + special::Special, + start::StartKind, + DEAD, + }, + util::{ + alphabet::{self, ByteClasses, ByteSet}, + int::{Pointer, Usize}, + prefilter::Prefilter, + primitives::{PatternID, StateID}, + search::{Anchored, Input, MatchError}, + start::{Start, StartByteMap}, + wire::{self, DeserializeError, Endian, SerializeError}, + }, +}; + +/// The label that is pre-pended to a serialized DFA. +const LABEL: &str = "rust-regex-automata-dfa-dense"; + +/// The format version of dense regexes. This version gets incremented when a +/// change occurs. A change may not necessarily be a breaking change, but the +/// version does permit good error messages in the case where a breaking change +/// is made. +const VERSION: u32 = 2; + +/// The configuration used for compiling a dense 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 dense DFA configuration is a simple data object that is typically used +/// with [`dense::Builder::configure`](self::Builder::configure). +/// +/// The default configuration guarantees that a search will never return +/// a "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`]. +#[cfg(feature = "dfa-build")] +#[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. + accelerate: Option<bool>, + pre: Option<Option<Prefilter>>, + minimize: Option<bool>, + match_kind: Option<MatchKind>, + start_kind: Option<StartKind>, + starts_for_each_pattern: Option<bool>, + byte_classes: Option<bool>, + unicode_word_boundary: Option<bool>, + quitset: Option<ByteSet>, + specialize_start_states: Option<bool>, + dfa_size_limit: Option<Option<usize>>, + determinize_size_limit: Option<Option<usize>>, +} + +#[cfg(feature = "dfa-build")] +impl Config { + /// Return a new default dense DFA compiler configuration. + pub fn new() -> Config { + Config::default() + } + + /// Enable state acceleration. + /// + /// When enabled, DFA construction will analyze each state to determine + /// whether it is eligible for simple acceleration. Acceleration typically + /// occurs when most of a state's transitions loop back to itself, leaving + /// only a select few bytes that will exit the state. When this occurs, + /// other routines like `memchr` can be used to look for those bytes which + /// may be much faster than traversing the DFA. + /// + /// Callers may elect to disable this if consistent performance is more + /// desirable than variable performance. Namely, acceleration can sometimes + /// make searching slower than it otherwise would be if the transitions + /// that leave accelerated states are traversed frequently. + /// + /// See [`Automaton::accelerator`](crate::dfa::Automaton::accelerator) for + /// an example. + /// + /// This is enabled by default. + pub fn accelerate(mut self, yes: bool) -> Config { + self.accelerate = Some(yes); + 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. + /// + /// **WARNING:** Note that prefilters are not preserved as part of + /// serialization. Serializing a DFA will drop its prefilter. + /// + /// By default no prefilter is set. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton}, + /// 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 input = Input::new("foo1 barfox bar"); + /// assert_eq!( + /// Some(HalfMatch::must(0, 11)), + /// re.try_search_fwd(&input)?, + /// ); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Be warned though that an incorrect prefilter can lead to incorrect + /// results! + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton}, + /// 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 input = Input::new("foo1 barfox bar"); + /// assert_eq!( + /// // No match reported even though there clearly is one! + /// None, + /// re.try_search_fwd(&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 + } + + /// Minimize the DFA. + /// + /// When enabled, the DFA built will be minimized such that it is as small + /// as possible. + /// + /// Whether one enables minimization or not depends on the types of costs + /// you're willing to pay and how much you care about its benefits. In + /// particular, minimization has worst case `O(n*k*logn)` time and `O(k*n)` + /// space, where `n` is the number of DFA states and `k` is the alphabet + /// size. In practice, minimization can be quite costly in terms of both + /// space and time, so it should only be done if you're willing to wait + /// longer to produce a DFA. In general, you might want a minimal DFA in + /// the following circumstances: + /// + /// 1. You would like to optimize for the size of the automaton. This can + /// manifest in one of two ways. Firstly, if you're converting the + /// DFA into Rust code (or a table embedded in the code), then a minimal + /// DFA will translate into a corresponding reduction in code size, and + /// thus, also the final compiled binary size. Secondly, if you are + /// building many DFAs and putting them on the heap, you'll be able to + /// fit more if they are smaller. Note though that building a minimal + /// DFA itself requires additional space; you only realize the space + /// savings once the minimal DFA is constructed (at which point, the + /// space used for minimization is freed). + /// 2. You've observed that a smaller DFA results in faster match + /// performance. Naively, this isn't guaranteed since there is no + /// inherent difference between matching with a bigger-than-minimal + /// DFA and a minimal DFA. However, a smaller DFA may make use of your + /// CPU's cache more efficiently. + /// 3. You are trying to establish an equivalence between regular + /// languages. The standard method for this is to build a minimal DFA + /// for each language and then compare them. If the DFAs are equivalent + /// (up to state renaming), then the languages are equivalent. + /// + /// Typically, minimization only makes sense as an offline process. That + /// is, one might minimize a DFA before serializing it to persistent + /// storage. In practical terms, minimization can take around an order of + /// magnitude more time than compiling the initial DFA via determinization. + /// + /// This option is disabled by default. + pub fn minimize(mut self, yes: bool) -> Config { + self.minimize = Some(yes); + self + } + + /// 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 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 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::{ + /// dfa::{Automaton, OverlappingState, dense}, + /// HalfMatch, Input, MatchKind, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().match_kind(MatchKind::All)) + /// .build_many(&[r"\w+$", r"\S+$"])?; + /// let input = Input::new("@foo"); + /// let mut state = OverlappingState::start(); + /// + /// let expected = Some(HalfMatch::must(1, 4)); + /// dfa.try_search_overlapping_fwd(&input, &mut state)?; + /// assert_eq!(expected, state.get_match()); + /// + /// // The first pattern also matches at the same position, so re-running + /// // the search will yield another match. Notice also that the first + /// // pattern is returned after the second. This is because the second + /// // pattern begins its match before the first, is therefore an earlier + /// // match and is thus reported first. + /// let expected = Some(HalfMatch::must(0, 4)); + /// dfa.try_search_overlapping_fwd(&input, &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 + /// [`dfa::regex::Regex`](crate::dfa::regex::Regex) will handle this for + /// you, so it's usually not necessary to do this yourself. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense, Automaton, StartKind}, + /// nfa::thompson::NFA, + /// Anchored, HalfMatch, Input, MatchKind, + /// }; + /// + /// let haystack = "123foobar456".as_bytes(); + /// let pattern = r"[a-z]+r"; + /// + /// let dfa_fwd = dense::DFA::new(pattern)?; + /// let dfa_rev = dense::Builder::new() + /// .thompson(NFA::config().reverse(true)) + /// .configure(dense::Config::new() + /// // This isn't strictly necessary since both anchored and + /// // unanchored searches are supported by default. But since + /// // finding the start-of-match only requires anchored searches, + /// // we can get rid of the unanchored configuration and possibly + /// // slim down our DFA considerably. + /// .start_kind(StartKind::Anchored) + /// .match_kind(MatchKind::All) + /// ) + /// .build(pattern)?; + /// let expected_fwd = HalfMatch::must(0, 9); + /// let expected_rev = HalfMatch::must(0, 3); + /// let got_fwd = dfa_fwd.try_search_fwd(&Input::new(haystack))?.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. Indeed, this is what Regex does internally. + /// let input = Input::new(haystack) + /// .range(..got_fwd.offset()) + /// .anchored(Anchored::Yes); + /// let got_rev = dfa_rev.try_search_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 + } + + /// The type of starting state configuration to use for a DFA. + /// + /// By default, the starting state configuration is [`StartKind::Both`]. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense::DFA, Automaton, StartKind}, + /// Anchored, HalfMatch, Input, + /// }; + /// + /// let haystack = "quux foo123"; + /// let expected = HalfMatch::must(0, 11); + /// + /// // By default, DFAs support both anchored and unanchored searches. + /// let dfa = DFA::new(r"[0-9]+")?; + /// let input = Input::new(haystack); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&input)?); + /// + /// // But if we only need anchored searches, then we can build a DFA + /// // that only supports anchored searches. This leads to a smaller DFA + /// // (potentially significantly smaller in some cases), but a DFA that + /// // will panic if you try to use it with an unanchored search. + /// let dfa = DFA::builder() + /// .configure(DFA::config().start_kind(StartKind::Anchored)) + /// .build(r"[0-9]+")?; + /// let input = Input::new(haystack) + /// .range(8..) + /// .anchored(Anchored::Yes); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&input)?); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn start_kind(mut self, kind: StartKind) -> Config { + self.start_kind = Some(kind); + self + } + + /// Whether to compile a separate start state for each pattern in the + /// automaton. + /// + /// When enabled, a separate **anchored** start state is added for each + /// pattern in the 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. + /// + /// 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::dfa::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.) + /// 3. Since the start states added for each pattern are anchored, if you + /// compile an unanchored DFA with one pattern while also enabling this + /// option, then you can use the same DFA to perform anchored or unanchored + /// searches. The latter you get with the standard search APIs. The former + /// you get from the various `_at` search methods that allow you specify a + /// pattern ID to search for. + /// + /// By default this is disabled. + /// + /// # Example + /// + /// This example shows how to use this option to permit the same DFA to + /// run both anchored and unanchored searches for a single pattern. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{dense, Automaton}, + /// Anchored, HalfMatch, PatternID, Input, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().starts_for_each_pattern(true)) + /// .build(r"foo[0-9]+")?; + /// let haystack = "quux foo123"; + /// + /// // Here's a normal unanchored search. Notice that we use 'None' for the + /// // pattern ID. Since the DFA was built as an unanchored machine, it + /// // use its default unanchored starting state. + /// let expected = HalfMatch::must(0, 11); + /// let input = Input::new(haystack); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&input)?); + /// // But now if we explicitly specify the pattern to search ('0' being + /// // the only pattern in the DFA), then it will use the starting state + /// // for that specific pattern which is always anchored. Since the + /// // pattern doesn't have a match at the beginning of the haystack, we + /// // find nothing. + /// let input = Input::new(haystack) + /// .anchored(Anchored::Pattern(PatternID::must(0))); + /// assert_eq!(None, dfa.try_search_fwd(&input)?); + /// // And finally, an anchored search is not the same as putting a '^' at + /// // beginning of the pattern. An anchored search can only match at the + /// // beginning of the *search*, which we can change: + /// let input = Input::new(haystack) + /// .anchored(Anchored::Pattern(PatternID::must(0))) + /// .range(5..); + /// assert_eq!(Some(expected), dfa.try_search_fwd(&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 DFA's alphabet or not. + /// + /// This option is enabled by default and should never be disabled unless + /// one is debugging a generated DFA. + /// + /// When enabled, the 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 class 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(StateID)` to + /// `#states * k * sizeof(StateID)` 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 becomes faster as well. + /// + /// **WARNING:** This is only useful for debugging 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`](crate::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::dfa::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`](crate::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::{ + /// dfa::{Automaton, dense}, + /// HalfMatch, Input, MatchError, + /// }; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().unicode_word_boundary(true)) + /// .build(r"\b[0-9]+\b")?; + /// + /// // The match occurs before the search ever observes the snowman + /// // character, so no error occurs. + /// let haystack = "foo 123 ☃".as_bytes(); + /// let expected = Some(HalfMatch::must(0, 7)); + /// let got = dfa.try_search_fwd(&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 ☃".as_bytes(); + /// let expected = MatchError::quit(0xE2, 8); + /// let got = dfa.try_search_fwd(&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(&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(&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 DFA. + /// + /// When a quit byte is seen during search time, then search will return + /// a [`MatchError::quit`](crate::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 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::dfa::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::{dfa::{Automaton, dense}, Input, MatchError}; + /// + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().quit(b'\n', true)) + /// .build(r"foo\p{any}+bar")?; + /// + /// let haystack = "foo\nbar".as_bytes(); + /// // 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(&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 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::{dfa::{Automaton, dense::DFA}, Input}; + /// + /// let dfa = DFA::builder() + /// .configure(DFA::config().specialize_start_states(true)) + /// .build(r"[a-z]+")?; + /// + /// let haystack = "123 foobar 4567".as_bytes(); + /// let sid = dfa.start_state_forward(&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!(dfa.is_special_state(sid)); + /// assert!(dfa.is_start_state(sid)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Compare the above with the default DFA configuration where start states + /// are _not_ specialized. In this case, the start state is not tagged at + /// all: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, Input}; + /// + /// let dfa = DFA::new(r"[a-z]+")?; + /// + /// let haystack = "123 foobar 4567"; + /// let sid = dfa.start_state_forward(&Input::new(haystack))?; + /// // Start states are not special in the default configuration! + /// assert!(!dfa.is_special_state(sid)); + /// assert!(!dfa.is_start_state(sid)); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn specialize_start_states(mut self, yes: bool) -> Config { + self.specialize_start_states = Some(yes); + self + } + + /// Set a size limit on the total heap used by a DFA. + /// + /// This size limit is expressed in bytes and is applied during + /// determinization of an NFA into a DFA. If the DFA's heap usage, and only + /// the DFA, exceeds this configured limit, then determinization is stopped + /// and an error is returned. + /// + /// This limit does not apply to auxiliary storage used during + /// determinization that isn't part of the generated DFA. + /// + /// This limit is only applied during determinization. Currently, there is + /// no way to post-pone this check to after minimization if minimization + /// was enabled. + /// + /// The total limit on heap used during determinization is the sum of the + /// DFA and determinization size limits. + /// + /// The default is no limit. + /// + /// # Example + /// + /// This example shows a DFA that fails to build because of a configured + /// size limit. This particular example also serves as a cautionary tale + /// demonstrating just how big DFAs with large Unicode character classes + /// can get. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{dfa::{dense, Automaton}, Input}; + /// + /// // 6MB isn't enough! + /// dense::Builder::new() + /// .configure(dense::Config::new().dfa_size_limit(Some(6_000_000))) + /// .build(r"\w{20}") + /// .unwrap_err(); + /// + /// // ... but 7MB probably is! + /// // (Note that DFA sizes aren't necessarily stable between releases.) + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new().dfa_size_limit(Some(7_000_000))) + /// .build(r"\w{20}")?; + /// let haystack = "A".repeat(20).into_bytes(); + /// assert!(dfa.try_search_fwd(&Input::new(&haystack))?.is_some()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// While one needs a little more than 6MB to represent `\w{20}`, it + /// turns out that you only need a little more than 6KB to represent + /// `(?-u:\w{20})`. So only use Unicode if you need it! + /// + /// As with [`Config::determinize_size_limit`], the size of a DFA is + /// influenced by other factors, such as what start state configurations + /// to support. For example, if you only need unanchored searches and not + /// anchored searches, then configuring the DFA to only support unanchored + /// searches can reduce its size. By default, DFAs support both unanchored + /// and anchored searches. + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// use regex_automata::{dfa::{dense, Automaton, StartKind}, Input}; + /// + /// // 3MB isn't enough! + /// dense::Builder::new() + /// .configure(dense::Config::new() + /// .dfa_size_limit(Some(3_000_000)) + /// .start_kind(StartKind::Unanchored) + /// ) + /// .build(r"\w{20}") + /// .unwrap_err(); + /// + /// // ... but 4MB probably is! + /// // (Note that DFA sizes aren't necessarily stable between releases.) + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new() + /// .dfa_size_limit(Some(4_000_000)) + /// .start_kind(StartKind::Unanchored) + /// ) + /// .build(r"\w{20}")?; + /// let haystack = "A".repeat(20).into_bytes(); + /// assert!(dfa.try_search_fwd(&Input::new(&haystack))?.is_some()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn dfa_size_limit(mut self, bytes: Option<usize>) -> Config { + self.dfa_size_limit = Some(bytes); + self + } + + /// Set a size limit on the total heap used by determinization. + /// + /// This size limit is expressed in bytes and is applied during + /// determinization of an NFA into a DFA. If the heap used for auxiliary + /// storage during determinization (memory that is not in the DFA but + /// necessary for building the DFA) exceeds this configured limit, then + /// determinization is stopped and an error is returned. + /// + /// This limit does not apply to heap used by the DFA itself. + /// + /// The total limit on heap used during determinization is the sum of the + /// DFA and determinization size limits. + /// + /// The default is no limit. + /// + /// # Example + /// + /// This example shows a DFA that fails to build because of a + /// configured size limit on the amount of heap space used by + /// determinization. This particular example complements the example for + /// [`Config::dfa_size_limit`] by demonstrating that not only does Unicode + /// potentially make DFAs themselves big, but it also results in more + /// auxiliary storage during determinization. (Although, auxiliary storage + /// is still not as much as the DFA itself.) + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// # if !cfg!(target_pointer_width = "64") { return Ok(()); } // see #1039 + /// use regex_automata::{dfa::{dense, Automaton}, Input}; + /// + /// // 600KB isn't enough! + /// dense::Builder::new() + /// .configure(dense::Config::new() + /// .determinize_size_limit(Some(600_000)) + /// ) + /// .build(r"\w{20}") + /// .unwrap_err(); + /// + /// // ... but 700KB probably is! + /// // (Note that auxiliary storage sizes aren't necessarily stable between + /// // releases.) + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new() + /// .determinize_size_limit(Some(700_000)) + /// ) + /// .build(r"\w{20}")?; + /// let haystack = "A".repeat(20).into_bytes(); + /// assert!(dfa.try_search_fwd(&Input::new(&haystack))?.is_some()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Note that some parts of the configuration on a DFA can have a + /// big impact on how big the DFA is, and thus, how much memory is + /// used. For example, the default setting for [`Config::start_kind`] is + /// [`StartKind::Both`]. But if you only need an anchored search, for + /// example, then it can be much cheaper to build a DFA that only supports + /// anchored searches. (Running an unanchored search with it would panic.) + /// + /// ``` + /// # if cfg!(miri) { return Ok(()); } // miri takes too long + /// # if !cfg!(target_pointer_width = "64") { return Ok(()); } // see #1039 + /// use regex_automata::{ + /// dfa::{dense, Automaton, StartKind}, + /// Anchored, Input, + /// }; + /// + /// // 200KB isn't enough! + /// dense::Builder::new() + /// .configure(dense::Config::new() + /// .determinize_size_limit(Some(200_000)) + /// .start_kind(StartKind::Anchored) + /// ) + /// .build(r"\w{20}") + /// .unwrap_err(); + /// + /// // ... but 300KB probably is! + /// // (Note that auxiliary storage sizes aren't necessarily stable between + /// // releases.) + /// let dfa = dense::Builder::new() + /// .configure(dense::Config::new() + /// .determinize_size_limit(Some(300_000)) + /// .start_kind(StartKind::Anchored) + /// ) + /// .build(r"\w{20}")?; + /// let haystack = "A".repeat(20).into_bytes(); + /// let input = Input::new(&haystack).anchored(Anchored::Yes); + /// assert!(dfa.try_search_fwd(&input)?.is_some()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn determinize_size_limit(mut self, bytes: Option<usize>) -> Config { + self.determinize_size_limit = Some(bytes); + self + } + + /// Returns whether this configuration has enabled simple state + /// acceleration. + pub fn get_accelerate(&self) -> bool { + self.accelerate.unwrap_or(true) + } + + /// Returns the prefilter attached to this configuration, if any. + pub fn get_prefilter(&self) -> Option<&Prefilter> { + self.pre.as_ref().unwrap_or(&None).as_ref() + } + + /// Returns whether this configuration has enabled the expensive process + /// of minimizing a DFA. + pub fn get_minimize(&self) -> bool { + self.minimize.unwrap_or(false) + } + + /// Returns the match semantics set in this configuration. + pub fn get_match_kind(&self) -> MatchKind { + self.match_kind.unwrap_or(MatchKind::LeftmostFirst) + } + + /// Returns the starting state configuration for a DFA. + pub fn get_starts(&self) -> StartKind { + self.start_kind.unwrap_or(StartKind::Both) + } + + /// 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 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 DFA to + /// "specialize" start states. When enabled, the DFA will mark start states + /// as "special" so that search routines using the 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 DFA size limit of this configuration if one was set. + /// The size limit is total number of bytes on the heap that a DFA is + /// permitted to use. If the DFA exceeds this limit during construction, + /// then construction is stopped and an error is returned. + pub fn get_dfa_size_limit(&self) -> Option<usize> { + self.dfa_size_limit.unwrap_or(None) + } + + /// Returns the determinization size limit of this configuration if one + /// was set. The size limit is total number of bytes on the heap that + /// determinization is permitted to use. If determinization exceeds this + /// limit during construction, then construction is stopped and an error is + /// returned. + /// + /// This is different from the DFA size limit in that this only applies to + /// the auxiliary storage used during determinization. Once determinization + /// is complete, this memory is freed. + /// + /// The limit on the total heap memory used is the sum of the DFA and + /// determinization size limits. + pub fn get_determinize_size_limit(&self) -> Option<usize> { + self.determinize_size_limit.unwrap_or(None) + } + + /// Overwrite the default configuration such that the options in `o` are + /// always used. If an option in `o` is not set, then the corresponding + /// option in `self` is used. If it's not set in `self` either, then it + /// remains not set. + pub(crate) fn overwrite(&self, o: Config) -> Config { + Config { + accelerate: o.accelerate.or(self.accelerate), + pre: o.pre.or_else(|| self.pre.clone()), + minimize: o.minimize.or(self.minimize), + match_kind: o.match_kind.or(self.match_kind), + start_kind: o.start_kind.or(self.start_kind), + 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), + dfa_size_limit: o.dfa_size_limit.or(self.dfa_size_limit), + determinize_size_limit: o + .determinize_size_limit + .or(self.determinize_size_limit), + } + } +} + +/// A builder for constructing a deterministic finite automaton from regular +/// expressions. +/// +/// 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* 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::dfa::regex::Regex), which can be similarly configured +/// using [`regex::Builder`](crate::dfa::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 DFAs instead of one, since a +/// second reverse DFA is needed to find the start of a match. +/// +/// Note that if one wants to build a sparse DFA, you must first build a dense +/// DFA and convert that to a sparse DFA. There is no way to build a sparse +/// DFA without first building a dense DFA. +/// +/// # Example +/// +/// This example shows how to build a minimized DFA that 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::{ +/// dfa::{Automaton, dense}, +/// util::syntax, +/// HalfMatch, Input, +/// }; +/// +/// let dfa = dense::Builder::new() +/// .configure(dense::Config::new().minimize(false)) +/// .syntax(syntax::Config::new().unicode(false).utf8(false)) +/// .build(r"foo[^b]ar.*")?; +/// +/// let haystack = b"\xFEfoo\xFFar\xE2\x98\xFF\n"; +/// let expected = Some(HalfMatch::must(0, 10)); +/// let got = dfa.try_search_fwd(&Input::new(haystack))?; +/// assert_eq!(expected, got); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[cfg(feature = "dfa-build")] +#[derive(Clone, Debug)] +pub struct Builder { + config: Config, + #[cfg(feature = "syntax")] + thompson: thompson::Compiler, +} + +#[cfg(feature = "dfa-build")] +impl Builder { + /// Create a new dense DFA builder with the default configuration. + pub fn new() -> Builder { + Builder { + config: Config::default(), + #[cfg(feature = "syntax")] + thompson: thompson::Compiler::new(), + } + } + + /// Build a 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<OwnedDFA, BuildError> { + self.build_many(&[pattern]) + } + + /// Build a 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<OwnedDFA, 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. + /// + /// # Example + /// + /// This example shows how to build a DFA if you already have an NFA in + /// hand. + /// + /// ``` + /// use regex_automata::{ + /// dfa::{Automaton, dense}, + /// nfa::thompson::NFA, + /// HalfMatch, Input, + /// }; + /// + /// let haystack = "foo123bar".as_bytes(); + /// + /// // This shows how to set non-default options for building an NFA. + /// let nfa = NFA::compiler() + /// .configure(NFA::config().shrink(true)) + /// .build(r"[0-9]+")?; + /// let dfa = dense::Builder::new().build_from_nfa(&nfa)?; + /// let expected = Some(HalfMatch::must(0, 6)); + /// let got = dfa.try_search_fwd(&Input::new(haystack))?; + /// assert_eq!(expected, got); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn build_from_nfa( + &self, + nfa: &thompson::NFA, + ) -> Result<OwnedDFA, BuildError> { + let mut quitset = self.config.quitset.unwrap_or(ByteSet::empty()); + if self.config.get_unicode_word_boundary() + && nfa.look_set_any().contains_word_unicode() + { + for b in 0x80..=0xFF { + quitset.add(b); + } + } + let classes = if !self.config.get_byte_classes() { + // DFAs 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 !quitset.is_empty() { + set.add_set(&quitset); + } + set.byte_classes() + }; + + let mut dfa = DFA::initial( + classes, + nfa.pattern_len(), + self.config.get_starts(), + nfa.look_matcher(), + self.config.get_starts_for_each_pattern(), + self.config.get_prefilter().map(|p| p.clone()), + quitset, + Flags::from_nfa(&nfa), + )?; + determinize::Config::new() + .match_kind(self.config.get_match_kind()) + .quit(quitset) + .dfa_size_limit(self.config.get_dfa_size_limit()) + .determinize_size_limit(self.config.get_determinize_size_limit()) + .run(nfa, &mut dfa)?; + if self.config.get_minimize() { + dfa.minimize(); + } + if self.config.get_accelerate() { + dfa.accelerate(); + } + // The state shuffling done before this point always assumes that start + // states should be marked as "special," even though it isn't the + // default configuration. State shuffling is complex enough as it is, + // so it's simpler to just "fix" our special state ID ranges to not + // include starting states after-the-fact. + if !self.config.get_specialize_start_states() { + dfa.special.set_no_special_start_states(); + } + // Look for and set the universal starting states. + dfa.set_universal_starts(); + Ok(dfa) + } + + /// Apply the given dense 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 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 + } +} + +#[cfg(feature = "dfa-build")] +impl Default for Builder { + fn default() -> Builder { + Builder::new() + } +} + +/// A convenience alias for an owned DFA. We use this particular instantiation +/// a lot in this crate, so it's worth giving it a name. This instantiation +/// is commonly used for mutable APIs on the DFA while building it. The main +/// reason for making DFAs generic is no_std support, and more generally, +/// making it possible to load a DFA from an arbitrary slice of bytes. +#[cfg(feature = "alloc")] +pub(crate) type OwnedDFA = DFA<alloc::vec::Vec<u32>>; + +/// A dense table-based deterministic finite automaton (DFA). +/// +/// All dense DFAs have one or more start states, zero or more match states +/// and a transition table that maps the current state and the current byte +/// of input to the next state. A DFA can use this information to implement +/// fast searching. In particular, the use of a dense DFA generally makes the +/// trade off that match speed is the most valuable characteristic, even if +/// building the DFA may take significant time *and* space. (More concretely, +/// building a DFA takes time and space that is exponential in the size of the +/// pattern in the worst case.) As such, the processing of every byte of input +/// is done with a small constant number of operations that does not vary with +/// the pattern, its size or the size of the alphabet. If your needs don't line +/// up with this trade off, then a dense DFA may not be an adequate solution to +/// your problem. +/// +/// In contrast, a [`sparse::DFA`] makes the opposite +/// trade off: it uses less space but will execute a variable number of +/// instructions per byte at match time, which makes it slower for matching. +/// (Note that space usage is still exponential in the size of the pattern in +/// the worst case.) +/// +/// A DFA can be built using the default configuration via the +/// [`DFA::new`] constructor. Otherwise, one can +/// configure various aspects via [`dense::Builder`](Builder). +/// +/// A single 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 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* DFAs are required. This functionality is provided by a +/// [`Regex`](crate::dfa::regex::Regex). +/// +/// # Type parameters +/// +/// A `DFA` has one type parameter, `T`, which is used to represent state IDs, +/// pattern IDs and accelerators. `T` is typically a `Vec<u32>` or a `&[u32]`. +/// +/// # The `Automaton` trait +/// +/// This type implements the [`Automaton`] trait, which means it can be used +/// for searching. For example: +/// +/// ``` +/// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; +/// +/// let dfa = DFA::new("foo[0-9]+")?; +/// let expected = HalfMatch::must(0, 8); +/// assert_eq!(Some(expected), dfa.try_search_fwd(&Input::new("foo12345"))?); +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone)] +pub struct DFA<T> { + /// The transition table for this DFA. This includes the transitions + /// themselves, along with the stride, number of states and the equivalence + /// class mapping. + tt: TransitionTable<T>, + /// The set of starting state identifiers for this DFA. The starting state + /// IDs act as pointers into the transition table. The specific starting + /// state chosen for each search is dependent on the context at which the + /// search begins. + st: StartTable<T>, + /// The set of match states and the patterns that match for each + /// corresponding match state. + /// + /// This structure is technically only needed because of support for + /// multi-regexes. Namely, multi-regexes require answering not just whether + /// a match exists, but _which_ patterns match. So we need to store the + /// matching pattern IDs for each match state. We do this even when there + /// is only one pattern for the sake of simplicity. In practice, this uses + /// up very little space for the case of one pattern. + ms: MatchStates<T>, + /// Information about which states are "special." Special states are states + /// that are dead, quit, matching, starting or accelerated. For more info, + /// see the docs for `Special`. + special: Special, + /// The accelerators for this DFA. + /// + /// If a state is accelerated, then there exist only a small number of + /// bytes that can cause the DFA to leave the state. This permits searching + /// to use optimized routines to find those specific bytes instead of using + /// the transition table. + /// + /// All accelerated states exist in a contiguous range in the DFA's + /// transition table. See dfa/special.rs for more details on how states are + /// arranged. + accels: Accels<T>, + /// Any prefilter attached to this DFA. + /// + /// Note that currently prefilters are not serialized. When deserializing + /// a DFA from bytes, this is always set to `None`. + pre: Option<Prefilter>, + /// The set of "quit" bytes for this DFA. + /// + /// This is only used when computing the start state for a particular + /// position in a haystack. Namely, in the case where there is a quit + /// byte immediately before the start of the search, this set needs to be + /// explicitly consulted. In all other cases, quit bytes are detected by + /// the DFA itself, by transitioning all quit bytes to a special "quit + /// state." + quitset: ByteSet, + /// Various flags describing the behavior of this DFA. + flags: Flags, +} + +#[cfg(feature = "dfa-build")] +impl OwnedDFA { + /// Parse the given regular expression using a default configuration and + /// return the corresponding DFA. + /// + /// If you want a non-default configuration, then use the + /// [`dense::Builder`](Builder) to set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, Input}; + /// + /// let dfa = dense::DFA::new("foo[0-9]+bar")?; + /// let expected = Some(HalfMatch::must(0, 11)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345bar"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new(pattern: &str) -> Result<OwnedDFA, BuildError> { + Builder::new().build(pattern) + } + + /// Parse the given regular expressions using a default configuration and + /// return the corresponding multi-DFA. + /// + /// If you want a non-default configuration, then use the + /// [`dense::Builder`](Builder) to set your own configuration. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, Input}; + /// + /// let dfa = dense::DFA::new_many(&["[0-9]+", "[a-z]+"])?; + /// let expected = Some(HalfMatch::must(1, 3)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345bar"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "syntax")] + pub fn new_many<P: AsRef<str>>( + patterns: &[P], + ) -> Result<OwnedDFA, BuildError> { + Builder::new().build_many(patterns) + } +} + +#[cfg(feature = "dfa-build")] +impl OwnedDFA { + /// Create a new DFA that matches every input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, Input}; + /// + /// let dfa = dense::DFA::always_match()?; + /// + /// let expected = Some(HalfMatch::must(0, 0)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new(""))?); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn always_match() -> Result<OwnedDFA, BuildError> { + let nfa = thompson::NFA::always_match(); + Builder::new().build_from_nfa(&nfa) + } + + /// Create a new DFA that never matches any input. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, Input}; + /// + /// let dfa = dense::DFA::never_match()?; + /// assert_eq!(None, dfa.try_search_fwd(&Input::new(""))?); + /// assert_eq!(None, dfa.try_search_fwd(&Input::new("foo"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn never_match() -> Result<OwnedDFA, BuildError> { + let nfa = thompson::NFA::never_match(); + Builder::new().build_from_nfa(&nfa) + } + + /// Create an initial DFA with the given equivalence classes, pattern + /// length and whether anchored starting states are enabled for each + /// pattern. An initial DFA can be further mutated via determinization. + fn initial( + classes: ByteClasses, + pattern_len: usize, + starts: StartKind, + lookm: &LookMatcher, + starts_for_each_pattern: bool, + pre: Option<Prefilter>, + quitset: ByteSet, + flags: Flags, + ) -> Result<OwnedDFA, BuildError> { + let start_pattern_len = + if starts_for_each_pattern { Some(pattern_len) } else { None }; + Ok(DFA { + tt: TransitionTable::minimal(classes), + st: StartTable::dead(starts, lookm, start_pattern_len)?, + ms: MatchStates::empty(pattern_len), + special: Special::new(), + accels: Accels::empty(), + pre, + quitset, + flags, + }) + } +} + +#[cfg(feature = "dfa-build")] +impl DFA<&[u32]> { + /// Return a new default dense DFA compiler configuration. + /// + /// This is a convenience routine to avoid needing to import the [`Config`] + /// type when customizing the construction of a dense DFA. + pub fn config() -> Config { + Config::new() + } + + /// Create a new dense DFA builder with the default configuration. + /// + /// This is a convenience routine to avoid needing to import the + /// [`Builder`] type in common cases. + pub fn builder() -> Builder { + Builder::new() + } +} + +impl<T: AsRef<[u32]>> DFA<T> { + /// Cheaply return a borrowed version of this dense DFA. Specifically, + /// the DFA returned always uses `&[u32]` for its transition table. + pub fn as_ref(&self) -> DFA<&'_ [u32]> { + DFA { + tt: self.tt.as_ref(), + st: self.st.as_ref(), + ms: self.ms.as_ref(), + special: self.special, + accels: self.accels(), + pre: self.pre.clone(), + quitset: self.quitset, + flags: self.flags, + } + } + + /// Return an owned version of this sparse DFA. Specifically, the DFA + /// returned always uses `Vec<u32>` for its transition table. + /// + /// Effectively, this returns a dense DFA whose transition table lives on + /// the heap. + #[cfg(feature = "alloc")] + pub fn to_owned(&self) -> OwnedDFA { + DFA { + tt: self.tt.to_owned(), + st: self.st.to_owned(), + ms: self.ms.to_owned(), + special: self.special, + accels: self.accels().to_owned(), + pre: self.pre.clone(), + quitset: self.quitset, + flags: self.flags, + } + } + + /// Returns the starting state configuration for this DFA. + /// + /// The default is [`StartKind::Both`], which means the DFA supports both + /// unanchored and anchored searches. However, this can generally lead to + /// bigger DFAs. Therefore, a DFA might be compiled with support for just + /// unanchored or anchored searches. In that case, running a search with + /// an unsupported configuration will panic. + pub fn start_kind(&self) -> StartKind { + self.st.kind + } + + /// Returns the start byte map used for computing the `Start` configuration + /// at the beginning of a search. + pub(crate) fn start_map(&self) -> &StartByteMap { + &self.st.start_map + } + + /// Returns true only if this DFA has starting states for each pattern. + /// + /// When a DFA has starting states for each pattern, then a search with the + /// DFA can be configured to only look for anchored matches of a specific + /// pattern. Specifically, APIs like [`Automaton::try_search_fwd`] can + /// accept a non-None `pattern_id` if and only if this method returns true. + /// Otherwise, calling `try_search_fwd` will panic. + /// + /// Note that if the DFA has no patterns, this always returns false. + pub fn starts_for_each_pattern(&self) -> bool { + self.st.pattern_len.is_some() + } + + /// 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.tt.classes + } + + /// Returns the total number of elements in the alphabet for this DFA. + /// + /// That is, this returns the total number of transitions that each state + /// in this DFA must have. Typically, a normal byte oriented DFA would + /// always have an alphabet size of 256, corresponding to the number of + /// unique values in a single byte. However, this implementation has two + /// peculiarities that impact the alphabet length: + /// + /// * Every state has a special "EOI" transition that is only followed + /// after the end of some haystack is reached. This EOI transition is + /// necessary to account for one byte of look-ahead when implementing + /// things like `\b` and `$`. + /// * Bytes are grouped into equivalence classes such that no two bytes in + /// the same class can distinguish a match from a non-match. For example, + /// in the regex `^[a-z]+$`, the ASCII bytes `a-z` could all be in the + /// same equivalence class. This leads to a massive space savings. + /// + /// Note though that the alphabet length does _not_ necessarily equal the + /// total stride space taken up by a single DFA state in the transition + /// table. Namely, for performance reasons, the stride is always the + /// smallest power of two that is greater than or equal to the alphabet + /// length. For this reason, [`DFA::stride`] or [`DFA::stride2`] are + /// often more useful. The alphabet length is typically useful only for + /// informational purposes. + pub fn alphabet_len(&self) -> usize { + self.tt.alphabet_len() + } + + /// Returns the total stride for every state in this DFA, expressed as the + /// exponent of a power of 2. The stride is the amount of space each state + /// takes up in the transition table, expressed as a number of transitions. + /// (Unused transitions map to dead states.) + /// + /// The stride of a DFA is always equivalent to the smallest power of 2 + /// that is greater than or equal to the DFA's alphabet length. This + /// definition uses extra space, but permits faster translation between + /// premultiplied state identifiers and contiguous indices (by using shifts + /// instead of relying on integer division). + /// + /// For example, if the DFA's stride is 16 transitions, then its `stride2` + /// is `4` since `2^4 = 16`. + /// + /// The minimum `stride2` value is `1` (corresponding to a stride of `2`) + /// while the maximum `stride2` value is `9` (corresponding to a stride of + /// `512`). The maximum is not `8` since the maximum alphabet size is `257` + /// when accounting for the special EOI transition. However, an alphabet + /// length of that size is exceptionally rare since the alphabet is shrunk + /// into equivalence classes. + pub fn stride2(&self) -> usize { + self.tt.stride2 + } + + /// Returns the total stride for every state in this DFA. This corresponds + /// to the total number of transitions used by each state in this DFA's + /// transition table. + /// + /// Please see [`DFA::stride2`] for more information. In particular, this + /// returns the stride as the number of transitions, where as `stride2` + /// returns it as the exponent of a power of 2. + pub fn stride(&self) -> usize { + self.tt.stride() + } + + /// Returns the memory usage, in bytes, of this DFA. + /// + /// The memory usage is computed based on the number of bytes used to + /// represent this DFA. + /// + /// This does **not** include the stack size used up by this DFA. To + /// compute that, use `std::mem::size_of::<dense::DFA>()`. + pub fn memory_usage(&self) -> usize { + self.tt.memory_usage() + + self.st.memory_usage() + + self.ms.memory_usage() + + self.accels.memory_usage() + } +} + +/// Routines for converting a dense DFA to other representations, such as +/// sparse DFAs or raw bytes suitable for persistent storage. +impl<T: AsRef<[u32]>> DFA<T> { + /// Convert this dense DFA to a sparse DFA. + /// + /// If a `StateID` is too small to represent all states in the sparse + /// DFA, then this returns an error. In most cases, if a dense DFA is + /// constructable with `StateID` then a sparse DFA will be as well. + /// However, it is not guaranteed. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense}, HalfMatch, Input}; + /// + /// let dense = dense::DFA::new("foo[0-9]+")?; + /// let sparse = dense.to_sparse()?; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, sparse.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "dfa-build")] + pub fn to_sparse(&self) -> Result<sparse::DFA<Vec<u8>>, BuildError> { + sparse::DFA::from_dense(self) + } + + /// Serialize this DFA as raw bytes to a `Vec<u8>` in little endian + /// format. Upon success, the `Vec<u8>` and the initial padding length are + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// The padding returned is non-zero if the returned `Vec<u8>` starts at + /// an address that does not have the same alignment as `u32`. The padding + /// corresponds to the number of leading bytes written to the returned + /// `Vec<u8>`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // N.B. We use native endianness here to make the example work, but + /// // using to_bytes_little_endian would work on a little endian target. + /// let (buf, _) = original_dfa.to_bytes_native_endian(); + /// // Even if buf has initial padding, DFA::from_bytes will automatically + /// // ignore it. + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf)?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "dfa-build")] + pub fn to_bytes_little_endian(&self) -> (Vec<u8>, usize) { + self.to_bytes::<wire::LE>() + } + + /// Serialize this DFA as raw bytes to a `Vec<u8>` in big endian + /// format. Upon success, the `Vec<u8>` and the initial padding length are + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// The padding returned is non-zero if the returned `Vec<u8>` starts at + /// an address that does not have the same alignment as `u32`. The padding + /// corresponds to the number of leading bytes written to the returned + /// `Vec<u8>`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // N.B. We use native endianness here to make the example work, but + /// // using to_bytes_big_endian would work on a big endian target. + /// let (buf, _) = original_dfa.to_bytes_native_endian(); + /// // Even if buf has initial padding, DFA::from_bytes will automatically + /// // ignore it. + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf)?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "dfa-build")] + pub fn to_bytes_big_endian(&self) -> (Vec<u8>, usize) { + self.to_bytes::<wire::BE>() + } + + /// Serialize this DFA as raw bytes to a `Vec<u8>` in native endian + /// format. Upon success, the `Vec<u8>` and the initial padding length are + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// The padding returned is non-zero if the returned `Vec<u8>` starts at + /// an address that does not have the same alignment as `u32`. The padding + /// corresponds to the number of leading bytes written to the returned + /// `Vec<u8>`. + /// + /// Generally speaking, native endian format should only be used when + /// you know that the target you're compiling the DFA for matches the + /// endianness of the target on which you're compiling DFA. For example, + /// if serialization and deserialization happen in the same process or on + /// the same machine. Otherwise, when serializing a DFA for use in a + /// portable environment, you'll almost certainly want to serialize _both_ + /// a little endian and a big endian version and then load the correct one + /// based on the target's configuration. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// let (buf, _) = original_dfa.to_bytes_native_endian(); + /// // Even if buf has initial padding, DFA::from_bytes will automatically + /// // ignore it. + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf)?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + #[cfg(feature = "dfa-build")] + pub fn to_bytes_native_endian(&self) -> (Vec<u8>, usize) { + self.to_bytes::<wire::NE>() + } + + /// The implementation of the public `to_bytes` serialization methods, + /// which is generic over endianness. + #[cfg(feature = "dfa-build")] + fn to_bytes<E: Endian>(&self) -> (Vec<u8>, usize) { + let len = self.write_to_len(); + let (mut buf, padding) = wire::alloc_aligned_buffer::<u32>(len); + // This should always succeed since the only possible serialization + // error is providing a buffer that's too small, but we've ensured that + // `buf` is big enough here. + self.as_ref().write_to::<E>(&mut buf[padding..]).unwrap(); + (buf, padding) + } + + /// Serialize this DFA as raw bytes to the given slice, in little endian + /// format. Upon success, the total number of bytes written to `dst` is + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// Note that unlike the various `to_byte_*` routines, this does not write + /// any padding. Callers are responsible for handling alignment correctly. + /// + /// # Errors + /// + /// This returns an error if the given destination slice is not big enough + /// to contain the full serialized DFA. If an error occurs, then nothing + /// is written to `dst`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA without + /// dynamic memory allocation. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // Create a 4KB buffer on the stack to store our serialized DFA. We + /// // need to use a special type to force the alignment of our [u8; N] + /// // array to be aligned to a 4 byte boundary. Otherwise, deserializing + /// // the DFA may fail because of an alignment mismatch. + /// #[repr(C)] + /// struct Aligned<B: ?Sized> { + /// _align: [u32; 0], + /// bytes: B, + /// } + /// let mut buf = Aligned { _align: [], bytes: [0u8; 4 * (1<<10)] }; + /// // N.B. We use native endianness here to make the example work, but + /// // using write_to_little_endian would work on a little endian target. + /// let written = original_dfa.write_to_native_endian(&mut buf.bytes)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf.bytes[..written])?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn write_to_little_endian( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + self.as_ref().write_to::<wire::LE>(dst) + } + + /// Serialize this DFA as raw bytes to the given slice, in big endian + /// format. Upon success, the total number of bytes written to `dst` is + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// Note that unlike the various `to_byte_*` routines, this does not write + /// any padding. Callers are responsible for handling alignment correctly. + /// + /// # Errors + /// + /// This returns an error if the given destination slice is not big enough + /// to contain the full serialized DFA. If an error occurs, then nothing + /// is written to `dst`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA without + /// dynamic memory allocation. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // Create a 4KB buffer on the stack to store our serialized DFA. We + /// // need to use a special type to force the alignment of our [u8; N] + /// // array to be aligned to a 4 byte boundary. Otherwise, deserializing + /// // the DFA may fail because of an alignment mismatch. + /// #[repr(C)] + /// struct Aligned<B: ?Sized> { + /// _align: [u32; 0], + /// bytes: B, + /// } + /// let mut buf = Aligned { _align: [], bytes: [0u8; 4 * (1<<10)] }; + /// // N.B. We use native endianness here to make the example work, but + /// // using write_to_big_endian would work on a big endian target. + /// let written = original_dfa.write_to_native_endian(&mut buf.bytes)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf.bytes[..written])?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn write_to_big_endian( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + self.as_ref().write_to::<wire::BE>(dst) + } + + /// Serialize this DFA as raw bytes to the given slice, in native endian + /// format. Upon success, the total number of bytes written to `dst` is + /// returned. + /// + /// The written bytes are guaranteed to be deserialized correctly and + /// without errors in a semver compatible release of this crate by a + /// `DFA`'s deserialization APIs (assuming all other criteria for the + /// deserialization APIs has been satisfied): + /// + /// * [`DFA::from_bytes`] + /// * [`DFA::from_bytes_unchecked`] + /// + /// Generally speaking, native endian format should only be used when + /// you know that the target you're compiling the DFA for matches the + /// endianness of the target on which you're compiling DFA. For example, + /// if serialization and deserialization happen in the same process or on + /// the same machine. Otherwise, when serializing a DFA for use in a + /// portable environment, you'll almost certainly want to serialize _both_ + /// a little endian and a big endian version and then load the correct one + /// based on the target's configuration. + /// + /// Note that unlike the various `to_byte_*` routines, this does not write + /// any padding. Callers are responsible for handling alignment correctly. + /// + /// # Errors + /// + /// This returns an error if the given destination slice is not big enough + /// to contain the full serialized DFA. If an error occurs, then nothing + /// is written to `dst`. + /// + /// # Example + /// + /// This example shows how to serialize and deserialize a DFA without + /// dynamic memory allocation. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// // Compile our original DFA. + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// // Create a 4KB buffer on the stack to store our serialized DFA. We + /// // need to use a special type to force the alignment of our [u8; N] + /// // array to be aligned to a 4 byte boundary. Otherwise, deserializing + /// // the DFA may fail because of an alignment mismatch. + /// #[repr(C)] + /// struct Aligned<B: ?Sized> { + /// _align: [u32; 0], + /// bytes: B, + /// } + /// let mut buf = Aligned { _align: [], bytes: [0u8; 4 * (1<<10)] }; + /// let written = original_dfa.write_to_native_endian(&mut buf.bytes)?; + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&buf.bytes[..written])?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn write_to_native_endian( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + self.as_ref().write_to::<wire::NE>(dst) + } + + /// Return the total number of bytes required to serialize this DFA. + /// + /// This is useful for determining the size of the buffer required to pass + /// to one of the serialization routines: + /// + /// * [`DFA::write_to_little_endian`] + /// * [`DFA::write_to_big_endian`] + /// * [`DFA::write_to_native_endian`] + /// + /// Passing a buffer smaller than the size returned by this method will + /// result in a serialization error. Serialization routines are guaranteed + /// to succeed when the buffer is big enough. + /// + /// # Example + /// + /// This example shows how to dynamically allocate enough room to serialize + /// a DFA. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// let original_dfa = DFA::new("foo[0-9]+")?; + /// + /// let mut buf = vec![0; original_dfa.write_to_len()]; + /// // This is guaranteed to succeed, because the only serialization error + /// // that can occur is when the provided buffer is too small. But + /// // write_to_len guarantees a correct size. + /// let written = original_dfa.write_to_native_endian(&mut buf).unwrap(); + /// // But this is not guaranteed to succeed! In particular, + /// // deserialization requires proper alignment for &[u32], but our buffer + /// // was allocated as a &[u8] whose required alignment is smaller than + /// // &[u32]. However, it's likely to work in practice because of how most + /// // allocators work. So if you write code like this, make sure to either + /// // handle the error correctly and/or run it under Miri since Miri will + /// // likely provoke the error by returning Vec<u8> buffers with alignment + /// // less than &[u32]. + /// let dfa: DFA<&[u32]> = match DFA::from_bytes(&buf[..written]) { + /// // As mentioned above, it is legal for an error to be returned + /// // here. It is quite difficult to get a Vec<u8> with a guaranteed + /// // alignment equivalent to Vec<u32>. + /// Err(_) => return Ok(()), + /// Ok((dfa, _)) => dfa, + /// }; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// Note that this example isn't actually guaranteed to work! In + /// particular, if `buf` is not aligned to a 4-byte boundary, then the + /// `DFA::from_bytes` call will fail. If you need this to work, then you + /// either need to deal with adding some initial padding yourself, or use + /// one of the `to_bytes` methods, which will do it for you. + pub fn write_to_len(&self) -> usize { + wire::write_label_len(LABEL) + + wire::write_endianness_check_len() + + wire::write_version_len() + + size_of::<u32>() // unused, intended for future flexibility + + self.flags.write_to_len() + + self.tt.write_to_len() + + self.st.write_to_len() + + self.ms.write_to_len() + + self.special.write_to_len() + + self.accels.write_to_len() + + self.quitset.write_to_len() + } +} + +impl<'a> DFA<&'a [u32]> { + /// Safely deserialize a DFA with a specific state identifier + /// representation. Upon success, this returns both the deserialized DFA + /// and the number of bytes read from the given slice. Namely, the contents + /// of the slice beyond the DFA are not read. + /// + /// Deserializing a DFA using this routine will never allocate heap memory. + /// For safety purposes, the DFA's transition table will be verified such + /// that every transition points to a valid state. If this verification is + /// too costly, then a [`DFA::from_bytes_unchecked`] API is provided, which + /// will always execute in constant time. + /// + /// The bytes given must be generated by one of the serialization APIs + /// of a `DFA` using a semver compatible release of this crate. Those + /// include: + /// + /// * [`DFA::to_bytes_little_endian`] + /// * [`DFA::to_bytes_big_endian`] + /// * [`DFA::to_bytes_native_endian`] + /// * [`DFA::write_to_little_endian`] + /// * [`DFA::write_to_big_endian`] + /// * [`DFA::write_to_native_endian`] + /// + /// The `to_bytes` methods allocate and return a `Vec<u8>` for you, along + /// with handling alignment correctly. The `write_to` methods do not + /// allocate and write to an existing slice (which may be on the stack). + /// Since deserialization always uses the native endianness of the target + /// platform, the serialization API you use should match the endianness of + /// the target platform. (It's often a good idea to generate serialized + /// DFAs for both forms of endianness and then load the correct one based + /// on endianness.) + /// + /// # Errors + /// + /// Generally speaking, it's easier to state the conditions in which an + /// error is _not_ returned. All of the following must be true: + /// + /// * The bytes given must be produced by one of the serialization APIs + /// on this DFA, as mentioned above. + /// * The endianness of the target platform matches the endianness used to + /// serialized the provided DFA. + /// * The slice given must have the same alignment as `u32`. + /// + /// If any of the above are not true, then an error will be returned. + /// + /// # Panics + /// + /// This routine will never panic for any input. + /// + /// # Example + /// + /// This example shows how to serialize a DFA to raw bytes, deserialize it + /// and then use it for searching. + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// let initial = DFA::new("foo[0-9]+")?; + /// let (bytes, _) = initial.to_bytes_native_endian(); + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&bytes)?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// # Example: dealing with alignment and padding + /// + /// In the above example, we used the `to_bytes_native_endian` method to + /// serialize a DFA, but we ignored part of its return value corresponding + /// to padding added to the beginning of the serialized DFA. This is OK + /// because deserialization will skip this initial padding. What matters + /// is that the address immediately following the padding has an alignment + /// that matches `u32`. That is, the following is an equivalent but + /// alternative way to write the above example: + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// let initial = DFA::new("foo[0-9]+")?; + /// // Serialization returns the number of leading padding bytes added to + /// // the returned Vec<u8>. + /// let (bytes, pad) = initial.to_bytes_native_endian(); + /// let dfa: DFA<&[u32]> = DFA::from_bytes(&bytes[pad..])?.0; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// This padding is necessary because Rust's standard library does + /// not expose any safe and robust way of creating a `Vec<u8>` with a + /// guaranteed alignment other than 1. Now, in practice, the underlying + /// allocator is likely to provide a `Vec<u8>` that meets our alignment + /// requirements, which means `pad` is zero in practice most of the time. + /// + /// The purpose of exposing the padding like this is flexibility for the + /// caller. For example, if one wants to embed a serialized DFA into a + /// compiled program, then it's important to guarantee that it starts at a + /// `u32`-aligned address. The simplest way to do this is to discard the + /// padding bytes and set it up so that the serialized DFA itself begins at + /// a properly aligned address. We can show this in two parts. The first + /// part is serializing the DFA to a file: + /// + /// ```no_run + /// use regex_automata::dfa::dense::DFA; + /// + /// let dfa = DFA::new("foo[0-9]+")?; + /// + /// let (bytes, pad) = dfa.to_bytes_big_endian(); + /// // Write the contents of the DFA *without* the initial padding. + /// std::fs::write("foo.bigendian.dfa", &bytes[pad..])?; + /// + /// // Do it again, but this time for little endian. + /// let (bytes, pad) = dfa.to_bytes_little_endian(); + /// std::fs::write("foo.littleendian.dfa", &bytes[pad..])?; + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// And now the second part is embedding the DFA into the compiled program + /// and deserializing it at runtime on first use. We use conditional + /// compilation to choose the correct endianness. + /// + /// ```no_run + /// use regex_automata::{ + /// dfa::{Automaton, dense::DFA}, + /// util::{lazy::Lazy, wire::AlignAs}, + /// HalfMatch, Input, + /// }; + /// + /// // This crate provides its own "lazy" type, kind of like + /// // lazy_static! or once_cell::sync::Lazy. But it works in no-alloc + /// // no-std environments and let's us write this using completely + /// // safe code. + /// static RE: Lazy<DFA<&'static [u32]>> = Lazy::new(|| { + /// # const _: &str = stringify! { + /// // This assignment is made possible (implicitly) via the + /// // CoerceUnsized trait. This is what guarantees that our + /// // bytes are stored in memory on a 4 byte boundary. You + /// // *must* do this or something equivalent for correct + /// // deserialization. + /// static ALIGNED: &AlignAs<[u8], u32> = &AlignAs { + /// _align: [], + /// #[cfg(target_endian = "big")] + /// bytes: *include_bytes!("foo.bigendian.dfa"), + /// #[cfg(target_endian = "little")] + /// bytes: *include_bytes!("foo.littleendian.dfa"), + /// }; + /// # }; + /// # static ALIGNED: &AlignAs<[u8], u32> = &AlignAs { + /// # _align: [], + /// # bytes: [], + /// # }; + /// + /// let (dfa, _) = DFA::from_bytes(&ALIGNED.bytes) + /// .expect("serialized DFA should be valid"); + /// dfa + /// }); + /// + /// let expected = Ok(Some(HalfMatch::must(0, 8))); + /// assert_eq!(expected, RE.try_search_fwd(&Input::new("foo12345"))); + /// ``` + /// + /// An alternative to [`util::lazy::Lazy`](crate::util::lazy::Lazy) + /// is [`lazy_static`](https://crates.io/crates/lazy_static) or + /// [`once_cell`](https://crates.io/crates/once_cell), which provide + /// stronger guarantees (like the initialization function only being + /// executed once). And `once_cell` in particular provides a more + /// expressive API. But a `Lazy` value from this crate is likely just fine + /// in most circumstances. + /// + /// Note that regardless of which initialization method you use, you + /// will still need to use the [`AlignAs`](crate::util::wire::AlignAs) + /// trick above to force correct alignment, but this is safe to do and + /// `from_bytes` will return an error if you get it wrong. + pub fn from_bytes( + slice: &'a [u8], + ) -> Result<(DFA<&'a [u32]>, usize), DeserializeError> { + // SAFETY: This is safe because we validate the transition table, start + // table, match states and accelerators below. If any validation fails, + // then we return an error. + let (dfa, nread) = unsafe { DFA::from_bytes_unchecked(slice)? }; + dfa.tt.validate(&dfa.special)?; + dfa.st.validate(&dfa.tt)?; + dfa.ms.validate(&dfa)?; + dfa.accels.validate()?; + // N.B. dfa.special doesn't have a way to do unchecked deserialization, + // so it has already been validated. + Ok((dfa, nread)) + } + + /// Deserialize a DFA with a specific state identifier representation in + /// constant time by omitting the verification of the validity of the + /// transition table and other data inside the DFA. + /// + /// This is just like [`DFA::from_bytes`], except it can potentially return + /// a DFA that exhibits undefined behavior if its transition table contains + /// invalid state identifiers. + /// + /// This routine is useful if you need to deserialize a DFA cheaply + /// and cannot afford the transition table validation performed by + /// `from_bytes`. + /// + /// # Example + /// + /// ``` + /// use regex_automata::{dfa::{Automaton, dense::DFA}, HalfMatch, Input}; + /// + /// let initial = DFA::new("foo[0-9]+")?; + /// let (bytes, _) = initial.to_bytes_native_endian(); + /// // SAFETY: This is guaranteed to be safe since the bytes given come + /// // directly from a compatible serialization routine. + /// let dfa: DFA<&[u32]> = unsafe { DFA::from_bytes_unchecked(&bytes)?.0 }; + /// + /// let expected = Some(HalfMatch::must(0, 8)); + /// assert_eq!(expected, dfa.try_search_fwd(&Input::new("foo12345"))?); + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub unsafe fn from_bytes_unchecked( + slice: &'a [u8], + ) -> Result<(DFA<&'a [u32]>, usize), DeserializeError> { + let mut nr = 0; + + nr += wire::skip_initial_padding(slice); + wire::check_alignment::<StateID>(&slice[nr..])?; + nr += wire::read_label(&slice[nr..], LABEL)?; + nr += wire::read_endianness_check(&slice[nr..])?; + nr += wire::read_version(&slice[nr..], VERSION)?; + + let _unused = wire::try_read_u32(&slice[nr..], "unused space")?; + nr += size_of::<u32>(); + + let (flags, nread) = Flags::from_bytes(&slice[nr..])?; + nr += nread; + + let (tt, nread) = TransitionTable::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (st, nread) = StartTable::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (ms, nread) = MatchStates::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (special, nread) = Special::from_bytes(&slice[nr..])?; + nr += nread; + special.validate_state_len(tt.len(), tt.stride2)?; + + let (accels, nread) = Accels::from_bytes_unchecked(&slice[nr..])?; + nr += nread; + + let (quitset, nread) = ByteSet::from_bytes(&slice[nr..])?; + nr += nread; + + // Prefilters don't support serialization, so they're always absent. + let pre = None; + Ok((DFA { tt, st, ms, special, accels, pre, quitset, flags }, nr)) + } + + /// The implementation of the public `write_to` serialization methods, + /// which is generic over endianness. + /// + /// This is defined only for &[u32] to reduce binary size/compilation time. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("dense DFA")); + } + dst = &mut dst[..nwrite]; + + let mut nw = 0; + nw += wire::write_label(LABEL, &mut dst[nw..])?; + nw += wire::write_endianness_check::<E>(&mut dst[nw..])?; + nw += wire::write_version::<E>(VERSION, &mut dst[nw..])?; + nw += { + // Currently unused, intended for future flexibility + E::write_u32(0, &mut dst[nw..]); + size_of::<u32>() + }; + nw += self.flags.write_to::<E>(&mut dst[nw..])?; + nw += self.tt.write_to::<E>(&mut dst[nw..])?; + nw += self.st.write_to::<E>(&mut dst[nw..])?; + nw += self.ms.write_to::<E>(&mut dst[nw..])?; + nw += self.special.write_to::<E>(&mut dst[nw..])?; + nw += self.accels.write_to::<E>(&mut dst[nw..])?; + nw += self.quitset.write_to::<E>(&mut dst[nw..])?; + Ok(nw) + } +} + +// The following methods implement mutable routines on the internal +// representation of a DFA. As such, we must fix the first type parameter to a +// `Vec<u32>` since a generic `T: AsRef<[u32]>` does not permit mutation. We +// can get away with this because these methods are internal to the crate and +// are exclusively used during construction of the DFA. +#[cfg(feature = "dfa-build")] +impl OwnedDFA { + /// Add a start state of this DFA. + pub(crate) fn set_start_state( + &mut self, + anchored: Anchored, + start: Start, + id: StateID, + ) { + assert!(self.tt.is_valid(id), "invalid start state"); + self.st.set_start(anchored, start, id); + } + + /// Set the given transition to this DFA. Both the `from` and `to` states + /// must already exist. + pub(crate) fn set_transition( + &mut self, + from: StateID, + byte: alphabet::Unit, + to: StateID, + ) { + self.tt.set(from, byte, to); + } + + /// An an empty state (a state where all transitions lead to a dead state) + /// and return its identifier. The identifier returned is guaranteed to + /// not point to any other existing state. + /// + /// If adding a state would exceed `StateID::LIMIT`, then this returns an + /// error. + pub(crate) fn add_empty_state(&mut self) -> Result<StateID, BuildError> { + self.tt.add_empty_state() + } + + /// Swap the two states given in the transition table. + /// + /// This routine does not do anything to check the correctness of this + /// swap. Callers must ensure that other states pointing to id1 and id2 are + /// updated appropriately. + pub(crate) fn swap_states(&mut self, id1: StateID, id2: StateID) { + self.tt.swap(id1, id2); + } + + /// Remap all of the state identifiers in this DFA according to the map + /// function given. This includes all transitions and all starting state + /// identifiers. + pub(crate) fn remap(&mut self, map: impl Fn(StateID) -> StateID) { + // We could loop over each state ID and call 'remap_state' here, but + // this is more direct: just map every transition directly. This + // technically might do a little extra work since the alphabet length + // is likely less than the stride, but if that is indeed an issue we + // should benchmark it and fix it. + for sid in self.tt.table_mut().iter_mut() { + *sid = map(*sid); + } + for sid in self.st.table_mut().iter_mut() { + *sid = map(*sid); + } + } + + /// Remap the transitions for the state given according to the function + /// given. This applies the given map function to every transition in the + /// given state and changes the transition in place to the result of the + /// map function for that transition. + pub(crate) fn remap_state( + &mut self, + id: StateID, + map: impl Fn(StateID) -> StateID, + ) { + self.tt.remap(id, map); + } + + /// Truncate the states in this DFA to the given length. + /// + /// This routine does not do anything to check the correctness of this + /// truncation. Callers must ensure that other states pointing to truncated + /// states are updated appropriately. + pub(crate) fn truncate_states(&mut self, len: usize) { + self.tt.truncate(len); + } + + /// Minimize this DFA in place using Hopcroft's algorithm. + pub(crate) fn minimize(&mut self) { + Minimizer::new(self).run(); + } + + /// Updates the match state pattern ID map to use the one provided. + /// + /// This is useful when it's convenient to manipulate matching states + /// (and their corresponding pattern IDs) as a map. In particular, the + /// representation used by a DFA for this map is not amenable to mutation, + /// so if things need to be changed (like when shuffling states), it's + /// often easier to work with the map form. + pub(crate) fn set_pattern_map( + &mut self, + map: &BTreeMap<StateID, Vec<PatternID>>, + ) -> Result<(), BuildError> { + self.ms = self.ms.new_with_map(map)?; + Ok(()) + } + + /// Find states that have a small number of non-loop transitions and mark + /// them as candidates for acceleration during search. + pub(crate) fn accelerate(&mut self) { + // dead and quit states can never be accelerated. + if self.state_len() <= 2 { + return; + } + + // Go through every state and record their accelerator, if possible. + let mut accels = BTreeMap::new(); + // Count the number of accelerated match, start and non-match/start + // states. + let (mut cmatch, mut cstart, mut cnormal) = (0, 0, 0); + for state in self.states() { + if let Some(accel) = state.accelerate(self.byte_classes()) { + debug!( + "accelerating full DFA state {}: {:?}", + state.id().as_usize(), + accel, + ); + accels.insert(state.id(), accel); + if self.is_match_state(state.id()) { + cmatch += 1; + } else if self.is_start_state(state.id()) { + cstart += 1; + } else { + assert!(!self.is_dead_state(state.id())); + assert!(!self.is_quit_state(state.id())); + cnormal += 1; + } + } + } + // If no states were able to be accelerated, then we're done. + if accels.is_empty() { + return; + } + let original_accels_len = accels.len(); + + // A remapper keeps track of state ID changes. Once we're done + // shuffling, the remapper is used to rewrite all transitions in the + // DFA based on the new positions of states. + let mut remapper = Remapper::new(self); + + // As we swap states, if they are match states, we need to swap their + // pattern ID lists too (for multi-regexes). We do this by converting + // the lists to an easily swappable map, and then convert back to + // MatchStates once we're done. + let mut new_matches = self.ms.to_map(self); + + // There is at least one state that gets accelerated, so these are + // guaranteed to get set to sensible values below. + self.special.min_accel = StateID::MAX; + self.special.max_accel = StateID::ZERO; + let update_special_accel = + |special: &mut Special, accel_id: StateID| { + special.min_accel = cmp::min(special.min_accel, accel_id); + special.max_accel = cmp::max(special.max_accel, accel_id); + }; + + // Start by shuffling match states. Any match states that are + // accelerated get moved to the end of the match state range. + if cmatch > 0 && self.special.matches() { + // N.B. special.{min,max}_match do not need updating, since the + // range/number of match states does not change. Only the ordering + // of match states may change. + let mut next_id = self.special.max_match; + let mut cur_id = next_id; + while cur_id >= self.special.min_match { + if let Some(accel) = accels.remove(&cur_id) { + accels.insert(next_id, accel); + update_special_accel(&mut self.special, next_id); + + // No need to do any actual swapping for equivalent IDs. + if cur_id != next_id { + remapper.swap(self, cur_id, next_id); + + // Swap pattern IDs for match states. + let cur_pids = new_matches.remove(&cur_id).unwrap(); + let next_pids = new_matches.remove(&next_id).unwrap(); + new_matches.insert(cur_id, next_pids); + new_matches.insert(next_id, cur_pids); + } + next_id = self.tt.prev_state_id(next_id); + } + cur_id = self.tt.prev_state_id(cur_id); + } + } + + // This is where it gets tricky. Without acceleration, start states + // normally come right after match states. But we want accelerated + // states to be a single contiguous range (to make it very fast + // to determine whether a state *is* accelerated), while also keeping + // match and starting states as contiguous ranges for the same reason. + // So what we do here is shuffle states such that it looks like this: + // + // DQMMMMAAAAASSSSSSNNNNNNN + // | | + // |---------| + // accelerated states + // + // Where: + // D - dead state + // Q - quit state + // M - match state (may be accelerated) + // A - normal state that is accelerated + // S - start state (may be accelerated) + // N - normal state that is NOT accelerated + // + // We implement this by shuffling states, which is done by a sequence + // of pairwise swaps. We start by looking at all normal states to be + // accelerated. When we find one, we swap it with the earliest starting + // state, and then swap that with the earliest normal state. This + // preserves the contiguous property. + // + // Once we're done looking for accelerated normal states, now we look + // for accelerated starting states by moving them to the beginning + // of the starting state range (just like we moved accelerated match + // states to the end of the matching state range). + // + // For a more detailed/different perspective on this, see the docs + // in dfa/special.rs. + if cnormal > 0 { + // our next available starting and normal states for swapping. + let mut next_start_id = self.special.min_start; + let mut cur_id = self.to_state_id(self.state_len() - 1); + // This is guaranteed to exist since cnormal > 0. + let mut next_norm_id = + self.tt.next_state_id(self.special.max_start); + while cur_id >= next_norm_id { + if let Some(accel) = accels.remove(&cur_id) { + remapper.swap(self, next_start_id, cur_id); + remapper.swap(self, next_norm_id, cur_id); + // Keep our accelerator map updated with new IDs if the + // states we swapped were also accelerated. + if let Some(accel2) = accels.remove(&next_norm_id) { + accels.insert(cur_id, accel2); + } + if let Some(accel2) = accels.remove(&next_start_id) { + accels.insert(next_norm_id, accel2); + } + accels.insert(next_start_id, accel); + update_special_accel(&mut self.special, next_start_id); + // Our start range shifts one to the right now. + self.special.min_start = + self.tt.next_state_id(self.special.min_start); + self.special.max_start = + self.tt.next_state_id(self.special.max_start); + next_start_id = self.tt.next_state_id(next_start_id); + next_norm_id = self.tt.next_state_id(next_norm_id); + } + // This is pretty tricky, but if our 'next_norm_id' state also + // happened to be accelerated, then the result is that it is + // now in the position of cur_id, so we need to consider it + // again. This loop is still guaranteed to terminate though, + // because when accels contains cur_id, we're guaranteed to + // increment next_norm_id even if cur_id remains unchanged. + if !accels.contains_key(&cur_id) { + cur_id = self.tt.prev_state_id(cur_id); + } + } + } + // Just like we did for match states, but we want to move accelerated + // start states to the beginning of the range instead of the end. + if cstart > 0 { + // N.B. special.{min,max}_start do not need updating, since the + // range/number of start states does not change at this point. Only + // the ordering of start states may change. + let mut next_id = self.special.min_start; + let mut cur_id = next_id; + while cur_id <= self.special.max_start { + if let Some(accel) = accels.remove(&cur_id) { + remapper.swap(self, cur_id, next_id); + accels.insert(next_id, accel); + update_special_accel(&mut self.special, next_id); + next_id = self.tt.next_state_id(next_id); + } + cur_id = self.tt.next_state_id(cur_id); + } + } + + // Remap all transitions in our DFA and assert some things. + remapper.remap(self); + // This unwrap is OK because acceleration never changes the number of + // match states or patterns in those match states. Since acceleration + // runs after the pattern map has been set at least once, we know that + // our match states cannot error. + self.set_pattern_map(&new_matches).unwrap(); + self.special.set_max(); + self.special.validate().expect("special state ranges should validate"); + self.special + .validate_state_len(self.state_len(), self.stride2()) + .expect( + "special state ranges should be consistent with state length", + ); + assert_eq!( + self.special.accel_len(self.stride()), + // We record the number of accelerated states initially detected + // since the accels map is itself mutated in the process above. + // If mutated incorrectly, its size may change, and thus can't be + // trusted as a source of truth of how many accelerated states we + // expected there to be. + original_accels_len, + "mismatch with expected number of accelerated states", + ); + + // And finally record our accelerators. We kept our accels map updated + // as we shuffled states above, so the accelerators should now + // correspond to a contiguous range in the state ID space. (Which we + // assert.) + let mut prev: Option<StateID> = None; + for (id, accel) in accels { + assert!(prev.map_or(true, |p| self.tt.next_state_id(p) == id)); + prev = Some(id); + self.accels.add(accel); + } + } + + /// Shuffle the states in this DFA so that starting states, match + /// states and accelerated states are all contiguous. + /// + /// See dfa/special.rs for more details. + pub(crate) fn shuffle( + &mut self, + mut matches: BTreeMap<StateID, Vec<PatternID>>, + ) -> Result<(), BuildError> { + // The determinizer always adds a quit state and it is always second. + self.special.quit_id = self.to_state_id(1); + // If all we have are the dead and quit states, then we're done and + // the DFA will never produce a match. + if self.state_len() <= 2 { + self.special.set_max(); + return Ok(()); + } + + // Collect all our non-DEAD start states into a convenient set and + // confirm there is no overlap with match states. In the classicl DFA + // construction, start states can be match states. But because of + // look-around, we delay all matches by a byte, which prevents start + // states from being match states. + let mut is_start: BTreeSet<StateID> = BTreeSet::new(); + for (start_id, _, _) in self.starts() { + // If a starting configuration points to a DEAD state, then we + // don't want to shuffle it. The DEAD state is always the first + // state with ID=0. So we can just leave it be. + if start_id == DEAD { + continue; + } + assert!( + !matches.contains_key(&start_id), + "{:?} is both a start and a match state, which is not allowed", + start_id, + ); + is_start.insert(start_id); + } + + // We implement shuffling by a sequence of pairwise swaps of states. + // Since we have a number of things referencing states via their + // IDs and swapping them changes their IDs, we need to record every + // swap we make so that we can remap IDs. The remapper handles this + // book-keeping for us. + let mut remapper = Remapper::new(self); + + // Shuffle matching states. + if matches.is_empty() { + self.special.min_match = DEAD; + self.special.max_match = DEAD; + } else { + // The determinizer guarantees that the first two states are the + // dead and quit states, respectively. We want our match states to + // come right after quit. + let mut next_id = self.to_state_id(2); + let mut new_matches = BTreeMap::new(); + self.special.min_match = next_id; + for (id, pids) in matches { + remapper.swap(self, next_id, id); + new_matches.insert(next_id, pids); + // If we swapped a start state, then update our set. + if is_start.contains(&next_id) { + is_start.remove(&next_id); + is_start.insert(id); + } + next_id = self.tt.next_state_id(next_id); + } + matches = new_matches; + self.special.max_match = cmp::max( + self.special.min_match, + self.tt.prev_state_id(next_id), + ); + } + + // Shuffle starting states. + { + let mut next_id = self.to_state_id(2); + if self.special.matches() { + next_id = self.tt.next_state_id(self.special.max_match); + } + self.special.min_start = next_id; + for id in is_start { + remapper.swap(self, next_id, id); + next_id = self.tt.next_state_id(next_id); + } + self.special.max_start = cmp::max( + self.special.min_start, + self.tt.prev_state_id(next_id), + ); + } + + // Finally remap all transitions in our DFA. + remapper.remap(self); + self.set_pattern_map(&matches)?; + self.special.set_max(); + self.special.validate().expect("special state ranges should validate"); + self.special + .validate_state_len(self.state_len(), self.stride2()) + .expect( + "special state ranges should be consistent with state length", + ); + Ok(()) + } + + /// Checks whether there are universal start states (both anchored and + /// unanchored), and if so, sets the relevant fields to the start state + /// IDs. + /// + /// Universal start states occur precisely when the all patterns in the + /// DFA have no look-around assertions in their prefix. + fn set_universal_starts(&mut self) { + assert_eq!(6, Start::len(), "expected 6 start configurations"); + + let start_id = |dfa: &mut OwnedDFA, inp: &Input<'_>, start: Start| { + // This OK because we only call 'start' under conditions + // in which we know it will succeed. + dfa.st.start(inp, start).expect("valid Input configuration") + }; + if self.start_kind().has_unanchored() { + let inp = Input::new("").anchored(Anchored::No); + let sid = start_id(self, &inp, Start::NonWordByte); + if sid == start_id(self, &inp, Start::WordByte) + && sid == start_id(self, &inp, Start::Text) + && sid == start_id(self, &inp, Start::LineLF) + && sid == start_id(self, &inp, Start::LineCR) + && sid == start_id(self, &inp, Start::CustomLineTerminator) + { + self.st.universal_start_unanchored = Some(sid); + } + } + if self.start_kind().has_anchored() { + let inp = Input::new("").anchored(Anchored::Yes); + let sid = start_id(self, &inp, Start::NonWordByte); + if sid == start_id(self, &inp, Start::WordByte) + && sid == start_id(self, &inp, Start::Text) + && sid == start_id(self, &inp, Start::LineLF) + && sid == start_id(self, &inp, Start::LineCR) + && sid == start_id(self, &inp, Start::CustomLineTerminator) + { + self.st.universal_start_anchored = Some(sid); + } + } + } +} + +// A variety of generic internal methods for accessing DFA internals. +impl<T: AsRef<[u32]>> DFA<T> { + /// Return the info about special states. + pub(crate) fn special(&self) -> &Special { + &self.special + } + + /// Return the info about special states as a mutable borrow. + #[cfg(feature = "dfa-build")] + pub(crate) fn special_mut(&mut self) -> &mut Special { + &mut self.special + } + + /// Returns the quit set (may be empty) used by this DFA. + pub(crate) fn quitset(&self) -> &ByteSet { + &self.quitset + } + + /// Returns the flags for this DFA. + pub(crate) fn flags(&self) -> &Flags { + &self.flags + } + + /// Returns an iterator over all states in this DFA. + /// + /// This iterator yields a tuple for each state. The first element of the + /// tuple corresponds to a state's identifier, and the second element + /// corresponds to the state itself (comprised of its transitions). + pub(crate) fn states(&self) -> StateIter<'_, T> { + self.tt.states() + } + + /// Return the total number of states in this DFA. Every DFA has at least + /// 1 state, even the empty DFA. + pub(crate) fn state_len(&self) -> usize { + self.tt.len() + } + + /// Return an iterator over all pattern IDs for the given match state. + /// + /// If the given state is not a match state, then this panics. + #[cfg(feature = "dfa-build")] + pub(crate) fn pattern_id_slice(&self, id: StateID) -> &[PatternID] { + assert!(self.is_match_state(id)); + self.ms.pattern_id_slice(self.match_state_index(id)) + } + + /// Return the total number of pattern IDs for the given match state. + /// + /// If the given state is not a match state, then this panics. + pub(crate) fn match_pattern_len(&self, id: StateID) -> usize { + assert!(self.is_match_state(id)); + self.ms.pattern_len(self.match_state_index(id)) + } + + /// Returns the total number of patterns matched by this DFA. + pub(crate) fn pattern_len(&self) -> usize { + self.ms.pattern_len + } + + /// Returns a map from match state ID to a list of pattern IDs that match + /// in that state. + #[cfg(feature = "dfa-build")] + pub(crate) fn pattern_map(&self) -> BTreeMap<StateID, Vec<PatternID>> { + self.ms.to_map(self) + } + + /// Returns the ID of the quit state for this DFA. + #[cfg(feature = "dfa-build")] + pub(crate) fn quit_id(&self) -> StateID { + self.to_state_id(1) + } + + /// Convert the given state identifier to the state's index. The state's + /// index corresponds to the position in which it appears in the transition + /// table. When a DFA is NOT premultiplied, then a state's identifier is + /// also its index. When a DFA is premultiplied, then a state's identifier + /// is equal to `index * alphabet_len`. This routine reverses that. + pub(crate) fn to_index(&self, id: StateID) -> usize { + self.tt.to_index(id) + } + + /// Convert an index to a state (in the range 0..self.state_len()) to an + /// actual state identifier. + /// + /// This is useful when using a `Vec<T>` as an efficient map keyed by state + /// to some other information (such as a remapped state ID). + #[cfg(feature = "dfa-build")] + pub(crate) fn to_state_id(&self, index: usize) -> StateID { + self.tt.to_state_id(index) + } + + /// Return the table of state IDs for this DFA's start states. + pub(crate) fn starts(&self) -> StartStateIter<'_> { + self.st.iter() + } + + /// Returns the index of the match state for the given ID. If the + /// given ID does not correspond to a match state, then this may + /// panic or produce an incorrect result. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn match_state_index(&self, id: StateID) -> usize { + debug_assert!(self.is_match_state(id)); + // This is one of the places where we rely on the fact that match + // states are contiguous in the transition table. Namely, that the + // first match state ID always corresponds to dfa.special.min_match. + // From there, since we know the stride, we can compute the overall + // index of any match state given the match state's ID. + let min = self.special().min_match.as_usize(); + // CORRECTNESS: We're allowed to produce an incorrect result or panic, + // so both the subtraction and the unchecked StateID construction is + // OK. + self.to_index(StateID::new_unchecked(id.as_usize() - min)) + } + + /// Returns the index of the accelerator state for the given ID. If the + /// given ID does not correspond to an accelerator state, then this may + /// panic or produce an incorrect result. + fn accelerator_index(&self, id: StateID) -> usize { + let min = self.special().min_accel.as_usize(); + // CORRECTNESS: We're allowed to produce an incorrect result or panic, + // so both the subtraction and the unchecked StateID construction is + // OK. + self.to_index(StateID::new_unchecked(id.as_usize() - min)) + } + + /// Return the accelerators for this DFA. + fn accels(&self) -> Accels<&[u32]> { + self.accels.as_ref() + } + + /// Return this DFA's transition table as a slice. + fn trans(&self) -> &[StateID] { + self.tt.table() + } +} + +impl<T: AsRef<[u32]>> fmt::Debug for DFA<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + writeln!(f, "dense::DFA(")?; + for state in self.states() { + fmt_state_indicator(f, self, state.id())?; + let id = if f.alternate() { + state.id().as_usize() + } else { + self.to_index(state.id()) + }; + write!(f, "{:06?}: ", id)?; + state.fmt(f)?; + write!(f, "\n")?; + } + writeln!(f, "")?; + for (i, (start_id, anchored, sty)) in self.starts().enumerate() { + let id = if f.alternate() { + start_id.as_usize() + } else { + self.to_index(start_id) + }; + if i % self.st.stride == 0 { + match anchored { + Anchored::No => writeln!(f, "START-GROUP(unanchored)")?, + Anchored::Yes => writeln!(f, "START-GROUP(anchored)")?, + Anchored::Pattern(pid) => { + writeln!(f, "START_GROUP(pattern: {:?})", pid)? + } + } + } + writeln!(f, " {:?} => {:06?}", sty, id)?; + } + if self.pattern_len() > 1 { + writeln!(f, "")?; + for i in 0..self.ms.len() { + let id = self.ms.match_state_id(self, i); + let id = if f.alternate() { + id.as_usize() + } else { + self.to_index(id) + }; + write!(f, "MATCH({:06?}): ", id)?; + for (i, &pid) in self.ms.pattern_id_slice(i).iter().enumerate() + { + if i > 0 { + write!(f, ", ")?; + } + write!(f, "{:?}", pid)?; + } + writeln!(f, "")?; + } + } + writeln!(f, "state length: {:?}", self.state_len())?; + writeln!(f, "pattern length: {:?}", self.pattern_len())?; + writeln!(f, "flags: {:?}", self.flags)?; + writeln!(f, ")")?; + Ok(()) + } +} + +// SAFETY: We assert that our implementation of each method is correct. +unsafe impl<T: AsRef<[u32]>> Automaton for DFA<T> { + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_special_state(&self, id: StateID) -> bool { + self.special.is_special_state(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_dead_state(&self, id: StateID) -> bool { + self.special.is_dead_state(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_quit_state(&self, id: StateID) -> bool { + self.special.is_quit_state(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_match_state(&self, id: StateID) -> bool { + self.special.is_match_state(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_start_state(&self, id: StateID) -> bool { + self.special.is_start_state(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_accel_state(&self, id: StateID) -> bool { + self.special.is_accel_state(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn next_state(&self, current: StateID, input: u8) -> StateID { + let input = self.byte_classes().get(input); + let o = current.as_usize() + usize::from(input); + self.trans()[o] + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + unsafe fn next_state_unchecked( + &self, + current: StateID, + byte: u8, + ) -> StateID { + // We don't (or shouldn't) need an unchecked variant for the byte + // class mapping, since bound checks should be omitted automatically + // by virtue of its representation. If this ends up not being true as + // confirmed by codegen, please file an issue. ---AG + let class = self.byte_classes().get(byte); + let o = current.as_usize() + usize::from(class); + let next = *self.trans().get_unchecked(o); + next + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn next_eoi_state(&self, current: StateID) -> StateID { + let eoi = self.byte_classes().eoi().as_usize(); + let o = current.as_usize() + eoi; + self.trans()[o] + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn pattern_len(&self) -> usize { + self.ms.pattern_len + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn match_len(&self, id: StateID) -> usize { + self.match_pattern_len(id) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn match_pattern(&self, id: StateID, 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 state machine, which requires + // a bit of slicing/pointer-chasing. This optimization tends to only + // matter when matches are frequent. + if self.ms.pattern_len == 1 { + return PatternID::ZERO; + } + let state_index = self.match_state_index(id); + self.ms.pattern_id(state_index, match_index) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn has_empty(&self) -> bool { + self.flags.has_empty + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_utf8(&self) -> bool { + self.flags.is_utf8 + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn is_always_start_anchored(&self) -> bool { + self.flags.is_always_start_anchored + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn start_state_forward( + &self, + input: &Input<'_>, + ) -> Result<StateID, 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 = self.st.start_map.fwd(&input); + self.st.start(input, start) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn start_state_reverse( + &self, + input: &Input<'_>, + ) -> Result<StateID, 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 = self.st.start_map.rev(&input); + self.st.start(input, start) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn universal_start_state(&self, mode: Anchored) -> Option<StateID> { + match mode { + Anchored::No => self.st.universal_start_unanchored, + Anchored::Yes => self.st.universal_start_anchored, + Anchored::Pattern(_) => None, + } + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn accelerator(&self, id: StateID) -> &[u8] { + if !self.is_accel_state(id) { + return &[]; + } + self.accels.needles(self.accelerator_index(id)) + } + + #[cfg_attr(feature = "perf-inline", inline(always))] + fn get_prefilter(&self) -> Option<&Prefilter> { + self.pre.as_ref() + } +} + +/// The transition table portion of a dense DFA. +/// +/// The transition table is the core part of the DFA in that it describes how +/// to move from one state to another based on the input sequence observed. +#[derive(Clone)] +pub(crate) struct TransitionTable<T> { + /// A contiguous region of memory representing the transition table in + /// row-major order. The representation is dense. That is, every state + /// has precisely the same number of transitions. The maximum number of + /// transitions per state is 257 (256 for each possible byte value, plus 1 + /// for the special EOI transition). If a DFA has been instructed to use + /// byte classes (the default), then the number of transitions is usually + /// substantially fewer. + /// + /// In practice, T is either `Vec<u32>` or `&[u32]`. + table: T, + /// A set of equivalence classes, where a single equivalence class + /// represents a set of bytes that never discriminate between a match + /// and a non-match in the DFA. Each equivalence class corresponds to a + /// single character in this DFA's alphabet, where the maximum number of + /// characters is 257 (each possible value of a byte plus the special + /// EOI transition). Consequently, the number of equivalence classes + /// corresponds to the number of transitions for each DFA state. Note + /// though that the *space* used by each DFA state in the transition table + /// may be larger. The total space used by each DFA state is known as the + /// stride. + /// + /// The only time the number of equivalence classes is fewer than 257 is if + /// the DFA's kind uses byte classes (which is the default). Equivalence + /// classes should generally only be disabled when debugging, so that + /// the transitions themselves aren't obscured. Disabling them has no + /// other benefit, since the equivalence class map is always used while + /// searching. In the vast majority of cases, the number of equivalence + /// classes is substantially smaller than 257, particularly when large + /// Unicode classes aren't used. + classes: ByteClasses, + /// The stride of each DFA state, expressed as a power-of-two exponent. + /// + /// The stride of a DFA corresponds to the total amount of space used by + /// each DFA state in the transition table. This may be bigger than the + /// size of a DFA's alphabet, since the stride is always the smallest + /// power of two greater than or equal to the alphabet size. + /// + /// While this wastes space, this avoids the need for integer division + /// to convert between premultiplied state IDs and their corresponding + /// indices. Instead, we can use simple bit-shifts. + /// + /// See the docs for the `stride2` method for more details. + /// + /// The minimum `stride2` value is `1` (corresponding to a stride of `2`) + /// while the maximum `stride2` value is `9` (corresponding to a stride of + /// `512`). The maximum is not `8` since the maximum alphabet size is `257` + /// when accounting for the special EOI transition. However, an alphabet + /// length of that size is exceptionally rare since the alphabet is shrunk + /// into equivalence classes. + stride2: usize, +} + +impl<'a> TransitionTable<&'a [u32]> { + /// Deserialize a transition table starting at the beginning of `slice`. + /// Upon success, return the total number of bytes read along with the + /// transition table. + /// + /// If there was a problem deserializing any part of the transition table, + /// then this returns an error. Notably, if the given slice does not have + /// the same alignment as `StateID`, then this will return an error (among + /// other possible errors). + /// + /// This is guaranteed to execute in constant time. + /// + /// # Safety + /// + /// This routine is not safe because it does not check the validity of the + /// transition table itself. In particular, the transition table can be + /// quite large, so checking its validity can be somewhat expensive. An + /// invalid transition table is not safe because other code may rely on the + /// transition table being correct (such as explicit bounds check elision). + /// Therefore, an invalid transition table can lead to undefined behavior. + /// + /// Callers that use this function must either pass on the safety invariant + /// or guarantee that the bytes given contain a valid transition table. + /// This guarantee is upheld by the bytes written by `write_to`. + unsafe fn from_bytes_unchecked( + mut slice: &'a [u8], + ) -> Result<(TransitionTable<&'a [u32]>, usize), DeserializeError> { + let slice_start = slice.as_ptr().as_usize(); + + let (state_len, nr) = + wire::try_read_u32_as_usize(slice, "state length")?; + slice = &slice[nr..]; + + let (stride2, nr) = wire::try_read_u32_as_usize(slice, "stride2")?; + slice = &slice[nr..]; + + let (classes, nr) = ByteClasses::from_bytes(slice)?; + slice = &slice[nr..]; + + // The alphabet length (determined by the byte class map) cannot be + // bigger than the stride (total space used by each DFA state). + if stride2 > 9 { + return Err(DeserializeError::generic( + "dense DFA has invalid stride2 (too big)", + )); + } + // It also cannot be zero, since even a DFA that never matches anything + // has a non-zero number of states with at least two equivalence + // classes: one for all 256 byte values and another for the EOI + // sentinel. + if stride2 < 1 { + return Err(DeserializeError::generic( + "dense DFA has invalid stride2 (too small)", + )); + } + // This is OK since 1 <= stride2 <= 9. + let stride = + 1usize.checked_shl(u32::try_from(stride2).unwrap()).unwrap(); + if classes.alphabet_len() > stride { + return Err(DeserializeError::generic( + "alphabet size cannot be bigger than transition table stride", + )); + } + + let trans_len = + wire::shl(state_len, stride2, "dense table transition length")?; + let table_bytes_len = wire::mul( + trans_len, + StateID::SIZE, + "dense table state byte length", + )?; + wire::check_slice_len(slice, table_bytes_len, "transition table")?; + wire::check_alignment::<StateID>(slice)?; + let table_bytes = &slice[..table_bytes_len]; + slice = &slice[table_bytes_len..]; + // SAFETY: Since StateID is always representable as a u32, all we need + // to do is ensure that we have the proper length and alignment. We've + // checked both above, so the cast below is safe. + // + // N.B. This is the only not-safe code in this function. + let table = core::slice::from_raw_parts( + table_bytes.as_ptr().cast::<u32>(), + trans_len, + ); + let tt = TransitionTable { table, classes, stride2 }; + Ok((tt, slice.as_ptr().as_usize() - slice_start)) + } +} + +#[cfg(feature = "dfa-build")] +impl TransitionTable<Vec<u32>> { + /// Create a minimal transition table with just two states: a dead state + /// and a quit state. The alphabet length and stride of the transition + /// table is determined by the given set of equivalence classes. + fn minimal(classes: ByteClasses) -> TransitionTable<Vec<u32>> { + let mut tt = TransitionTable { + table: vec![], + classes, + stride2: classes.stride2(), + }; + // Two states, regardless of alphabet size, can always fit into u32. + tt.add_empty_state().unwrap(); // dead state + tt.add_empty_state().unwrap(); // quit state + tt + } + + /// Set a transition in this table. Both the `from` and `to` states must + /// already exist, otherwise this panics. `unit` should correspond to the + /// transition out of `from` to set to `to`. + fn set(&mut self, from: StateID, unit: alphabet::Unit, to: StateID) { + assert!(self.is_valid(from), "invalid 'from' state"); + assert!(self.is_valid(to), "invalid 'to' state"); + self.table[from.as_usize() + self.classes.get_by_unit(unit)] = + to.as_u32(); + } + + /// Add an empty state (a state where all transitions lead to a dead state) + /// and return its identifier. The identifier returned is guaranteed to + /// not point to any other existing state. + /// + /// If adding a state would exhaust the state identifier space, then this + /// returns an error. + fn add_empty_state(&mut self) -> Result<StateID, BuildError> { + // Normally, to get a fresh state identifier, we would just + // take the index of the next state added to the transition + // table. However, we actually perform an optimization here + // that premultiplies state IDs by the stride, such that they + // point immediately at the beginning of their transitions in + // the transition table. This avoids an extra multiplication + // instruction for state lookup at search time. + // + // Premultiplied identifiers means that instead of your matching + // loop looking something like this: + // + // state = dfa.start + // for byte in haystack: + // next = dfa.transitions[state * stride + byte] + // if dfa.is_match(next): + // return true + // return false + // + // it can instead look like this: + // + // state = dfa.start + // for byte in haystack: + // next = dfa.transitions[state + byte] + // if dfa.is_match(next): + // return true + // return false + // + // In other words, we save a multiplication instruction in the + // critical path. This turns out to be a decent performance win. + // The cost of using premultiplied state ids is that they can + // require a bigger state id representation. (And they also make + // the code a bit more complex, especially during minimization and + // when reshuffling states, as one needs to convert back and forth + // between state IDs and state indices.) + // + // To do this, we simply take the index of the state into the + // entire transition table, rather than the index of the state + // itself. e.g., If the stride is 64, then the ID of the 3rd state + // is 192, not 2. + let next = self.table.len(); + let id = + StateID::new(next).map_err(|_| BuildError::too_many_states())?; + self.table.extend(iter::repeat(0).take(self.stride())); + Ok(id) + } + + /// Swap the two states given in this transition table. + /// + /// This routine does not do anything to check the correctness of this + /// swap. Callers must ensure that other states pointing to id1 and id2 are + /// updated appropriately. + /// + /// Both id1 and id2 must point to valid states, otherwise this panics. + fn swap(&mut self, id1: StateID, id2: StateID) { + assert!(self.is_valid(id1), "invalid 'id1' state: {:?}", id1); + assert!(self.is_valid(id2), "invalid 'id2' state: {:?}", id2); + // We only need to swap the parts of the state that are used. So if the + // stride is 64, but the alphabet length is only 33, then we save a lot + // of work. + for b in 0..self.classes.alphabet_len() { + self.table.swap(id1.as_usize() + b, id2.as_usize() + b); + } + } + + /// Remap the transitions for the state given according to the function + /// given. This applies the given map function to every transition in the + /// given state and changes the transition in place to the result of the + /// map function for that transition. + fn remap(&mut self, id: StateID, map: impl Fn(StateID) -> StateID) { + for byte in 0..self.alphabet_len() { + let i = id.as_usize() + byte; + let next = self.table()[i]; + self.table_mut()[id.as_usize() + byte] = map(next); + } + } + + /// Truncate the states in this transition table to the given length. + /// + /// This routine does not do anything to check the correctness of this + /// truncation. Callers must ensure that other states pointing to truncated + /// states are updated appropriately. + fn truncate(&mut self, len: usize) { + self.table.truncate(len << self.stride2); + } +} + +impl<T: AsRef<[u32]>> TransitionTable<T> { + /// Writes a serialized form of this transition table to the buffer given. + /// If the buffer is too small, then an error is returned. To determine + /// how big the buffer must be, use `write_to_len`. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("transition table")); + } + dst = &mut dst[..nwrite]; + + // write state length + // Unwrap is OK since number of states is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.len()).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write state stride (as power of 2) + // Unwrap is OK since stride2 is guaranteed to be <= 9. + E::write_u32(u32::try_from(self.stride2).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write byte class map + let n = self.classes.write_to(dst)?; + dst = &mut dst[n..]; + + // write actual transitions + for &sid in self.table() { + let n = wire::write_state_id::<E>(sid, &mut dst); + dst = &mut dst[n..]; + } + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of this transition + /// table will use. + fn write_to_len(&self) -> usize { + size_of::<u32>() // state length + + size_of::<u32>() // stride2 + + self.classes.write_to_len() + + (self.table().len() * StateID::SIZE) + } + + /// Validates that every state ID in this transition table is valid. + /// + /// That is, every state ID can be used to correctly index a state in this + /// table. + fn validate(&self, sp: &Special) -> Result<(), DeserializeError> { + for state in self.states() { + // We check that the ID itself is well formed. That is, if it's + // a special state then it must actually be a quit, dead, accel, + // match or start state. + if sp.is_special_state(state.id()) { + let is_actually_special = sp.is_dead_state(state.id()) + || sp.is_quit_state(state.id()) + || sp.is_match_state(state.id()) + || sp.is_start_state(state.id()) + || sp.is_accel_state(state.id()); + if !is_actually_special { + // This is kind of a cryptic error message... + return Err(DeserializeError::generic( + "found dense state tagged as special but \ + wasn't actually special", + )); + } + } + for (_, to) in state.transitions() { + if !self.is_valid(to) { + return Err(DeserializeError::generic( + "found invalid state ID in transition table", + )); + } + } + } + Ok(()) + } + + /// Converts this transition table to a borrowed value. + fn as_ref(&self) -> TransitionTable<&'_ [u32]> { + TransitionTable { + table: self.table.as_ref(), + classes: self.classes.clone(), + stride2: self.stride2, + } + } + + /// Converts this transition table to an owned value. + #[cfg(feature = "alloc")] + fn to_owned(&self) -> TransitionTable<alloc::vec::Vec<u32>> { + TransitionTable { + table: self.table.as_ref().to_vec(), + classes: self.classes.clone(), + stride2: self.stride2, + } + } + + /// Return the state for the given ID. If the given ID is not valid, then + /// this panics. + fn state(&self, id: StateID) -> State<'_> { + assert!(self.is_valid(id)); + + let i = id.as_usize(); + State { + id, + stride2: self.stride2, + transitions: &self.table()[i..i + self.alphabet_len()], + } + } + + /// Returns an iterator over all states in this transition table. + /// + /// This iterator yields a tuple for each state. The first element of the + /// tuple corresponds to a state's identifier, and the second element + /// corresponds to the state itself (comprised of its transitions). + fn states(&self) -> StateIter<'_, T> { + StateIter { + tt: self, + it: self.table().chunks(self.stride()).enumerate(), + } + } + + /// Convert a state identifier to an index to a state (in the range + /// 0..self.len()). + /// + /// This is useful when using a `Vec<T>` as an efficient map keyed by state + /// to some other information (such as a remapped state ID). + /// + /// If the given ID is not valid, then this may panic or produce an + /// incorrect index. + fn to_index(&self, id: StateID) -> usize { + id.as_usize() >> self.stride2 + } + + /// Convert an index to a state (in the range 0..self.len()) to an actual + /// state identifier. + /// + /// This is useful when using a `Vec<T>` as an efficient map keyed by state + /// to some other information (such as a remapped state ID). + /// + /// If the given index is not in the specified range, then this may panic + /// or produce an incorrect state ID. + fn to_state_id(&self, index: usize) -> StateID { + // CORRECTNESS: If the given index is not valid, then it is not + // required for this to panic or return a valid state ID. + StateID::new_unchecked(index << self.stride2) + } + + /// Returns the state ID for the state immediately following the one given. + /// + /// This does not check whether the state ID returned is invalid. In fact, + /// if the state ID given is the last state in this DFA, then the state ID + /// returned is guaranteed to be invalid. + #[cfg(feature = "dfa-build")] + fn next_state_id(&self, id: StateID) -> StateID { + self.to_state_id(self.to_index(id).checked_add(1).unwrap()) + } + + /// Returns the state ID for the state immediately preceding the one given. + /// + /// If the dead ID given (which is zero), then this panics. + #[cfg(feature = "dfa-build")] + fn prev_state_id(&self, id: StateID) -> StateID { + self.to_state_id(self.to_index(id).checked_sub(1).unwrap()) + } + + /// Returns the table as a slice of state IDs. + fn table(&self) -> &[StateID] { + wire::u32s_to_state_ids(self.table.as_ref()) + } + + /// Returns the total number of states in this transition table. + /// + /// Note that a DFA always has at least two states: the dead and quit + /// states. In particular, the dead state always has ID 0 and is + /// correspondingly always the first state. The dead state is never a match + /// state. + fn len(&self) -> usize { + self.table().len() >> self.stride2 + } + + /// Returns the total stride for every state in this 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 total number of elements in the alphabet for this + /// transition table. This is always less than or equal to `self.stride()`. + /// It is only equal when the alphabet length is a power of 2. Otherwise, + /// it is always strictly less. + fn alphabet_len(&self) -> usize { + self.classes.alphabet_len() + } + + /// Returns true if and only if the given state ID is valid for this + /// transition table. Validity in this context means that the given ID can + /// be used as a valid offset with `self.stride()` to index this transition + /// table. + fn is_valid(&self, id: StateID) -> bool { + let id = id.as_usize(); + id < self.table().len() && id % self.stride() == 0 + } + + /// Return the memory usage, in bytes, of this transition table. + /// + /// This does not include the size of a `TransitionTable` value itself. + fn memory_usage(&self) -> usize { + self.table().len() * StateID::SIZE + } +} + +#[cfg(feature = "dfa-build")] +impl<T: AsMut<[u32]>> TransitionTable<T> { + /// Returns the table as a slice of state IDs. + fn table_mut(&mut self) -> &mut [StateID] { + wire::u32s_to_state_ids_mut(self.table.as_mut()) + } +} + +/// The set of all possible starting states in a DFA. +/// +/// The set of starting states corresponds to the possible choices one can make +/// in terms of starting a DFA. That is, before following the first transition, +/// you first need to select the state that you start in. +/// +/// Normally, a DFA converted from an NFA that has a single starting state +/// would itself just have one starting state. However, our support for look +/// around generally requires more starting states. The correct starting state +/// is chosen based on certain properties of the position at which we begin +/// our search. +/// +/// Before listing those properties, we first must define two terms: +/// +/// * `haystack` - The bytes to execute the search. The search always starts +/// at the beginning of `haystack` and ends before or at the end of +/// `haystack`. +/// * `context` - The (possibly empty) bytes surrounding `haystack`. `haystack` +/// must be contained within `context` such that `context` is at least as big +/// as `haystack`. +/// +/// This split is crucial for dealing with look-around. For example, consider +/// the context `foobarbaz`, the haystack `bar` and the regex `^bar$`. This +/// regex should _not_ match the haystack since `bar` does not appear at the +/// beginning of the input. Similarly, the regex `\Bbar\B` should match the +/// haystack because `bar` is not surrounded by word boundaries. But a search +/// that does not take context into account would not permit `\B` to match +/// since the beginning of any string matches a word boundary. Similarly, a +/// search that does not take context into account when searching `^bar$` in +/// the haystack `bar` would produce a match when it shouldn't. +/// +/// Thus, it follows that the starting state is chosen based on the following +/// criteria, derived from the position at which the search starts in the +/// `context` (corresponding to the start of `haystack`): +/// +/// 1. If the search starts at the beginning of `context`, then the `Text` +/// start state is used. (Since `^` corresponds to +/// `hir::Anchor::Start`.) +/// 2. If the search starts at a position immediately following a line +/// terminator, then the `Line` start state is used. (Since `(?m:^)` +/// corresponds to `hir::Anchor::StartLF`.) +/// 3. If the search starts at a position immediately following a byte +/// classified as a "word" character (`[_0-9a-zA-Z]`), then the `WordByte` +/// start state is used. (Since `(?-u:\b)` corresponds to a word boundary.) +/// 4. Otherwise, if the search starts at a position immediately following +/// a byte that is not classified as a "word" character (`[^_0-9a-zA-Z]`), +/// then the `NonWordByte` start state is used. (Since `(?-u:\B)` +/// corresponds to a not-word-boundary.) +/// +/// (N.B. Unicode word boundaries are not supported by the DFA because they +/// require multi-byte look-around and this is difficult to support in a DFA.) +/// +/// To further complicate things, we also support constructing individual +/// anchored start states for each pattern in the DFA. (Which is required to +/// implement overlapping regexes correctly, but is also generally useful.) +/// Thus, when individual start states for each pattern are enabled, then the +/// total number of start states represented is `4 + (4 * #patterns)`, where +/// the 4 comes from each of the 4 possibilities above. The first 4 represents +/// the starting states for the entire DFA, which support searching for +/// multiple patterns simultaneously (possibly unanchored). +/// +/// If individual start states are disabled, then this will only store 4 +/// start states. Typically, individual start states are only enabled when +/// constructing the reverse DFA for regex matching. But they are also useful +/// for building DFAs that can search for a specific pattern or even to support +/// both anchored and unanchored searches with the same DFA. +/// +/// Note though that while the start table always has either `4` or +/// `4 + (4 * #patterns)` starting state *ids*, the total number of states +/// might be considerably smaller. That is, many of the IDs may be duplicative. +/// (For example, if a regex doesn't have a `\b` sub-pattern, then there's no +/// reason to generate a unique starting state for handling word boundaries. +/// Similarly for start/end anchors.) +#[derive(Clone)] +pub(crate) struct StartTable<T> { + /// The initial start state IDs. + /// + /// In practice, T is either `Vec<u32>` or `&[u32]`. + /// + /// The first `2 * stride` (currently always 8) entries always correspond + /// to the starts states for the entire DFA, with the first 4 entries being + /// for unanchored searches and the second 4 entries being for anchored + /// searches. To keep things simple, we always use 8 entries even if the + /// `StartKind` is not both. + /// + /// After that, there are `stride * patterns` state IDs, where `patterns` + /// may be zero in the case of a DFA with no patterns or in the case where + /// the DFA was built without enabling starting states for each pattern. + table: T, + /// The starting state configuration supported. When 'both', both + /// unanchored and anchored searches work. When 'unanchored', anchored + /// searches panic. When 'anchored', unanchored searches panic. + kind: StartKind, + /// The start state configuration for every possible byte. + start_map: StartByteMap, + /// The number of starting state IDs per pattern. + stride: usize, + /// The total number of patterns for which starting states are encoded. + /// This is `None` for DFAs that were built without start states for each + /// pattern. Thus, one cannot use this field to say how many patterns + /// are in the DFA in all cases. It is specific to how many patterns are + /// represented in this start table. + pattern_len: Option<usize>, + /// The universal starting state for unanchored searches. This is only + /// present when the DFA supports unanchored searches and when all starting + /// state IDs for an unanchored search are equivalent. + universal_start_unanchored: Option<StateID>, + /// The universal starting state for anchored searches. This is only + /// present when the DFA supports anchored searches and when all starting + /// state IDs for an anchored search are equivalent. + universal_start_anchored: Option<StateID>, +} + +#[cfg(feature = "dfa-build")] +impl StartTable<Vec<u32>> { + /// Create a valid set of start states all pointing to the dead state. + /// + /// When the corresponding DFA is constructed with start states for each + /// pattern, then `patterns` should be the number of patterns. Otherwise, + /// it should be zero. + /// + /// If the total table size could exceed the allocatable limit, then this + /// returns an error. In practice, this is unlikely to be able to occur, + /// since it's likely that allocation would have failed long before it got + /// to this point. + fn dead( + kind: StartKind, + lookm: &LookMatcher, + pattern_len: Option<usize>, + ) -> Result<StartTable<Vec<u32>>, BuildError> { + if let Some(len) = pattern_len { + assert!(len <= PatternID::LIMIT); + } + let stride = Start::len(); + // OK because 2*4 is never going to overflow anything. + let starts_len = stride.checked_mul(2).unwrap(); + let pattern_starts_len = + match stride.checked_mul(pattern_len.unwrap_or(0)) { + Some(x) => x, + None => return Err(BuildError::too_many_start_states()), + }; + let table_len = match starts_len.checked_add(pattern_starts_len) { + Some(x) => x, + None => return Err(BuildError::too_many_start_states()), + }; + if let Err(_) = isize::try_from(table_len) { + return Err(BuildError::too_many_start_states()); + } + let table = vec![DEAD.as_u32(); table_len]; + let start_map = StartByteMap::new(lookm); + Ok(StartTable { + table, + kind, + start_map, + stride, + pattern_len, + universal_start_unanchored: None, + universal_start_anchored: None, + }) + } +} + +impl<'a> StartTable<&'a [u32]> { + /// Deserialize a table of start state IDs starting at the beginning of + /// `slice`. Upon success, return the total number of bytes read along with + /// the table of starting state IDs. + /// + /// If there was a problem deserializing any part of the starting IDs, + /// then this returns an error. Notably, if the given slice does not have + /// the same alignment as `StateID`, then this will return an error (among + /// other possible errors). + /// + /// This is guaranteed to execute in constant time. + /// + /// # Safety + /// + /// This routine is not safe because it does not check the validity of the + /// starting state IDs themselves. In particular, the number of starting + /// IDs can be of variable length, so it's possible that checking their + /// validity cannot be done in constant time. An invalid starting state + /// ID is not safe because other code may rely on the starting IDs being + /// correct (such as explicit bounds check elision). Therefore, an invalid + /// start ID can lead to undefined behavior. + /// + /// Callers that use this function must either pass on the safety invariant + /// or guarantee that the bytes given contain valid starting state IDs. + /// This guarantee is upheld by the bytes written by `write_to`. + unsafe fn from_bytes_unchecked( + mut slice: &'a [u8], + ) -> Result<(StartTable<&'a [u32]>, usize), DeserializeError> { + let slice_start = slice.as_ptr().as_usize(); + + let (kind, nr) = StartKind::from_bytes(slice)?; + slice = &slice[nr..]; + + let (start_map, nr) = StartByteMap::from_bytes(slice)?; + slice = &slice[nr..]; + + let (stride, nr) = + wire::try_read_u32_as_usize(slice, "start table stride")?; + slice = &slice[nr..]; + if stride != Start::len() { + return Err(DeserializeError::generic( + "invalid starting table stride", + )); + } + + let (maybe_pattern_len, nr) = + wire::try_read_u32_as_usize(slice, "start table patterns")?; + slice = &slice[nr..]; + let pattern_len = if maybe_pattern_len.as_u32() == u32::MAX { + None + } else { + Some(maybe_pattern_len) + }; + if pattern_len.map_or(false, |len| len > PatternID::LIMIT) { + return Err(DeserializeError::generic( + "invalid number of patterns", + )); + } + + let (universal_unanchored, nr) = + wire::try_read_u32(slice, "universal unanchored start")?; + slice = &slice[nr..]; + let universal_start_unanchored = if universal_unanchored == u32::MAX { + None + } else { + Some(StateID::try_from(universal_unanchored).map_err(|e| { + DeserializeError::state_id_error( + e, + "universal unanchored start", + ) + })?) + }; + + let (universal_anchored, nr) = + wire::try_read_u32(slice, "universal anchored start")?; + slice = &slice[nr..]; + let universal_start_anchored = if universal_anchored == u32::MAX { + None + } else { + Some(StateID::try_from(universal_anchored).map_err(|e| { + DeserializeError::state_id_error(e, "universal anchored start") + })?) + }; + + let pattern_table_size = wire::mul( + stride, + pattern_len.unwrap_or(0), + "invalid pattern length", + )?; + // Our start states always start with a two stride of start states for + // the entire automaton. The first stride is for unanchored starting + // states and the second stride is for anchored starting states. What + // follows it are an optional set of start states for each pattern. + let start_state_len = wire::add( + wire::mul(2, stride, "start state stride too big")?, + pattern_table_size, + "invalid 'any' pattern starts size", + )?; + let table_bytes_len = wire::mul( + start_state_len, + StateID::SIZE, + "pattern table bytes length", + )?; + wire::check_slice_len(slice, table_bytes_len, "start ID table")?; + wire::check_alignment::<StateID>(slice)?; + let table_bytes = &slice[..table_bytes_len]; + slice = &slice[table_bytes_len..]; + // SAFETY: Since StateID is always representable as a u32, all we need + // to do is ensure that we have the proper length and alignment. We've + // checked both above, so the cast below is safe. + // + // N.B. This is the only not-safe code in this function. + let table = core::slice::from_raw_parts( + table_bytes.as_ptr().cast::<u32>(), + start_state_len, + ); + let st = StartTable { + table, + kind, + start_map, + stride, + pattern_len, + universal_start_unanchored, + universal_start_anchored, + }; + Ok((st, slice.as_ptr().as_usize() - slice_start)) + } +} + +impl<T: AsRef<[u32]>> StartTable<T> { + /// Writes a serialized form of this start table to the buffer given. If + /// the buffer is too small, then an error is returned. To determine how + /// big the buffer must be, use `write_to_len`. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small( + "starting table ids", + )); + } + dst = &mut dst[..nwrite]; + + // write start kind + let nw = self.kind.write_to::<E>(dst)?; + dst = &mut dst[nw..]; + // write start byte map + let nw = self.start_map.write_to(dst)?; + dst = &mut dst[nw..]; + // write stride + // Unwrap is OK since the stride is always 4 (currently). + E::write_u32(u32::try_from(self.stride).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + // write pattern length + // Unwrap is OK since number of patterns is guaranteed to fit in a u32. + E::write_u32( + u32::try_from(self.pattern_len.unwrap_or(0xFFFF_FFFF)).unwrap(), + dst, + ); + dst = &mut dst[size_of::<u32>()..]; + // write universal start unanchored state id, u32::MAX if absent + E::write_u32( + self.universal_start_unanchored + .map_or(u32::MAX, |sid| sid.as_u32()), + dst, + ); + dst = &mut dst[size_of::<u32>()..]; + // write universal start anchored state id, u32::MAX if absent + E::write_u32( + self.universal_start_anchored.map_or(u32::MAX, |sid| sid.as_u32()), + dst, + ); + dst = &mut dst[size_of::<u32>()..]; + // write start IDs + for &sid in self.table() { + let n = wire::write_state_id::<E>(sid, &mut dst); + dst = &mut dst[n..]; + } + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of this start ID table + /// will use. + fn write_to_len(&self) -> usize { + self.kind.write_to_len() + + self.start_map.write_to_len() + + size_of::<u32>() // stride + + size_of::<u32>() // # patterns + + size_of::<u32>() // universal unanchored start + + size_of::<u32>() // universal anchored start + + (self.table().len() * StateID::SIZE) + } + + /// Validates that every state ID in this start table is valid by checking + /// it against the given transition table (which must be for the same DFA). + /// + /// That is, every state ID can be used to correctly index a state. + fn validate( + &self, + tt: &TransitionTable<T>, + ) -> Result<(), DeserializeError> { + if !self.universal_start_unanchored.map_or(true, |s| tt.is_valid(s)) { + return Err(DeserializeError::generic( + "found invalid universal unanchored starting state ID", + )); + } + if !self.universal_start_anchored.map_or(true, |s| tt.is_valid(s)) { + return Err(DeserializeError::generic( + "found invalid universal anchored starting state ID", + )); + } + for &id in self.table() { + if !tt.is_valid(id) { + return Err(DeserializeError::generic( + "found invalid starting state ID", + )); + } + } + Ok(()) + } + + /// Converts this start list to a borrowed value. + fn as_ref(&self) -> StartTable<&'_ [u32]> { + StartTable { + table: self.table.as_ref(), + kind: self.kind, + start_map: self.start_map.clone(), + stride: self.stride, + pattern_len: self.pattern_len, + universal_start_unanchored: self.universal_start_unanchored, + universal_start_anchored: self.universal_start_anchored, + } + } + + /// Converts this start list to an owned value. + #[cfg(feature = "alloc")] + fn to_owned(&self) -> StartTable<alloc::vec::Vec<u32>> { + StartTable { + table: self.table.as_ref().to_vec(), + kind: self.kind, + start_map: self.start_map.clone(), + stride: self.stride, + pattern_len: self.pattern_len, + universal_start_unanchored: self.universal_start_unanchored, + universal_start_anchored: self.universal_start_anchored, + } + } + + /// Return the start state for the given input and starting configuration. + /// This returns an error if the input configuration is not supported by + /// this DFA. For example, requesting an unanchored search when the DFA was + /// not built with unanchored starting states. Or asking for an anchored + /// pattern search with an invalid pattern ID or on a DFA that was not + /// built with start states for each pattern. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn start( + &self, + input: &Input<'_>, + start: Start, + ) -> Result<StateID, MatchError> { + let start_index = start.as_usize(); + let mode = input.get_anchored(); + let index = match mode { + Anchored::No => { + if !self.kind.has_unanchored() { + return Err(MatchError::unsupported_anchored(mode)); + } + start_index + } + Anchored::Yes => { + if !self.kind.has_anchored() { + return Err(MatchError::unsupported_anchored(mode)); + } + self.stride + start_index + } + Anchored::Pattern(pid) => { + let len = match self.pattern_len { + None => { + return Err(MatchError::unsupported_anchored(mode)) + } + Some(len) => len, + }; + if pid.as_usize() >= len { + return Ok(DEAD); + } + (2 * self.stride) + + (self.stride * pid.as_usize()) + + start_index + } + }; + Ok(self.table()[index]) + } + + /// Returns an iterator over all start state IDs in this table. + /// + /// Each item is a triple of: start state ID, the start state type and the + /// pattern ID (if any). + fn iter(&self) -> StartStateIter<'_> { + StartStateIter { st: self.as_ref(), i: 0 } + } + + /// Returns the table as a slice of state IDs. + fn table(&self) -> &[StateID] { + wire::u32s_to_state_ids(self.table.as_ref()) + } + + /// Return the memory usage, in bytes, of this start list. + /// + /// This does not include the size of a `StartList` value itself. + fn memory_usage(&self) -> usize { + self.table().len() * StateID::SIZE + } +} + +#[cfg(feature = "dfa-build")] +impl<T: AsMut<[u32]>> StartTable<T> { + /// Set the start state for the given index and pattern. + /// + /// If the pattern ID or state ID are not valid, then this will panic. + fn set_start(&mut self, anchored: Anchored, start: Start, id: StateID) { + let start_index = start.as_usize(); + let index = match anchored { + Anchored::No => start_index, + Anchored::Yes => self.stride + start_index, + Anchored::Pattern(pid) => { + let pid = pid.as_usize(); + let len = self + .pattern_len + .expect("start states for each pattern enabled"); + assert!(pid < len, "invalid pattern ID {:?}", pid); + self.stride + .checked_mul(pid) + .unwrap() + .checked_add(self.stride.checked_mul(2).unwrap()) + .unwrap() + .checked_add(start_index) + .unwrap() + } + }; + self.table_mut()[index] = id; + } + + /// Returns the table as a mutable slice of state IDs. + fn table_mut(&mut self) -> &mut [StateID] { + wire::u32s_to_state_ids_mut(self.table.as_mut()) + } +} + +/// An iterator over start state IDs. +/// +/// This iterator yields a triple of start state ID, the anchored mode and the +/// start state type. If a pattern ID is relevant, then the anchored mode will +/// contain it. Start states with an anchored mode containing a pattern ID will +/// only occur when the DFA was compiled with start states for each pattern +/// (which is disabled by default). +pub(crate) struct StartStateIter<'a> { + st: StartTable<&'a [u32]>, + i: usize, +} + +impl<'a> Iterator for StartStateIter<'a> { + type Item = (StateID, Anchored, Start); + + fn next(&mut self) -> Option<(StateID, Anchored, Start)> { + let i = self.i; + let table = self.st.table(); + if i >= table.len() { + return None; + } + self.i += 1; + + // This unwrap is okay since the stride of the starting state table + // must always match the number of start state types. + let start_type = Start::from_usize(i % self.st.stride).unwrap(); + let anchored = if i < self.st.stride { + Anchored::No + } else if i < (2 * self.st.stride) { + Anchored::Yes + } else { + let pid = (i - (2 * self.st.stride)) / self.st.stride; + Anchored::Pattern(PatternID::new(pid).unwrap()) + }; + Some((table[i], anchored, start_type)) + } +} + +/// This type represents that patterns that should be reported whenever a DFA +/// enters a match state. This structure exists to support DFAs that search for +/// matches for multiple regexes. +/// +/// This structure relies on the fact that all match states in a DFA occur +/// contiguously in the DFA's transition table. (See dfa/special.rs for a more +/// detailed breakdown of the representation.) Namely, when a match occurs, we +/// know its state ID. Since we know the start and end of the contiguous region +/// of match states, we can use that to compute the position at which the match +/// state occurs. That in turn is used as an offset into this structure. +#[derive(Clone, Debug)] +struct MatchStates<T> { + /// Slices is a flattened sequence of pairs, where each pair points to a + /// sub-slice of pattern_ids. The first element of the pair is an offset + /// into pattern_ids and the second element of the pair is the number + /// of 32-bit pattern IDs starting at that position. That is, each pair + /// corresponds to a single DFA match state and its corresponding match + /// IDs. The number of pairs always corresponds to the number of distinct + /// DFA match states. + /// + /// In practice, T is either Vec<u32> or &[u32]. + slices: T, + /// A flattened sequence of pattern IDs for each DFA match state. The only + /// way to correctly read this sequence is indirectly via `slices`. + /// + /// In practice, T is either Vec<u32> or &[u32]. + pattern_ids: T, + /// The total number of unique patterns represented by these match states. + pattern_len: usize, +} + +impl<'a> MatchStates<&'a [u32]> { + unsafe fn from_bytes_unchecked( + mut slice: &'a [u8], + ) -> Result<(MatchStates<&'a [u32]>, usize), DeserializeError> { + let slice_start = slice.as_ptr().as_usize(); + + // Read the total number of match states. + let (state_len, nr) = + wire::try_read_u32_as_usize(slice, "match state length")?; + slice = &slice[nr..]; + + // Read the slice start/length pairs. + let pair_len = wire::mul(2, state_len, "match state offset pairs")?; + let slices_bytes_len = wire::mul( + pair_len, + PatternID::SIZE, + "match state slice offset byte length", + )?; + wire::check_slice_len(slice, slices_bytes_len, "match state slices")?; + wire::check_alignment::<PatternID>(slice)?; + let slices_bytes = &slice[..slices_bytes_len]; + slice = &slice[slices_bytes_len..]; + // SAFETY: Since PatternID is always representable as a u32, all we + // need to do is ensure that we have the proper length and alignment. + // We've checked both above, so the cast below is safe. + // + // N.B. This is one of the few not-safe snippets in this function, + // so we mark it explicitly to call it out. + let slices = core::slice::from_raw_parts( + slices_bytes.as_ptr().cast::<u32>(), + pair_len, + ); + + // Read the total number of unique pattern IDs (which is always 1 more + // than the maximum pattern ID in this automaton, since pattern IDs are + // handed out contiguously starting at 0). + let (pattern_len, nr) = + wire::try_read_u32_as_usize(slice, "pattern length")?; + slice = &slice[nr..]; + + // Now read the pattern ID length. We don't need to store this + // explicitly, but we need it to know how many pattern IDs to read. + let (idlen, nr) = + wire::try_read_u32_as_usize(slice, "pattern ID length")?; + slice = &slice[nr..]; + + // Read the actual pattern IDs. + let pattern_ids_len = + wire::mul(idlen, PatternID::SIZE, "pattern ID byte length")?; + wire::check_slice_len(slice, pattern_ids_len, "match pattern IDs")?; + wire::check_alignment::<PatternID>(slice)?; + let pattern_ids_bytes = &slice[..pattern_ids_len]; + slice = &slice[pattern_ids_len..]; + // SAFETY: Since PatternID is always representable as a u32, all we + // need to do is ensure that we have the proper length and alignment. + // We've checked both above, so the cast below is safe. + // + // N.B. This is one of the few not-safe snippets in this function, + // so we mark it explicitly to call it out. + let pattern_ids = core::slice::from_raw_parts( + pattern_ids_bytes.as_ptr().cast::<u32>(), + idlen, + ); + + let ms = MatchStates { slices, pattern_ids, pattern_len }; + Ok((ms, slice.as_ptr().as_usize() - slice_start)) + } +} + +#[cfg(feature = "dfa-build")] +impl MatchStates<Vec<u32>> { + fn empty(pattern_len: usize) -> MatchStates<Vec<u32>> { + assert!(pattern_len <= PatternID::LIMIT); + MatchStates { slices: vec![], pattern_ids: vec![], pattern_len } + } + + fn new( + matches: &BTreeMap<StateID, Vec<PatternID>>, + pattern_len: usize, + ) -> Result<MatchStates<Vec<u32>>, BuildError> { + let mut m = MatchStates::empty(pattern_len); + for (_, pids) in matches.iter() { + let start = PatternID::new(m.pattern_ids.len()) + .map_err(|_| BuildError::too_many_match_pattern_ids())?; + m.slices.push(start.as_u32()); + // This is always correct since the number of patterns in a single + // match state can never exceed maximum number of allowable + // patterns. Why? Because a pattern can only appear once in a + // particular match state, by construction. (And since our pattern + // ID limit is one less than u32::MAX, we're guaranteed that the + // length fits in a u32.) + m.slices.push(u32::try_from(pids.len()).unwrap()); + for &pid in pids { + m.pattern_ids.push(pid.as_u32()); + } + } + m.pattern_len = pattern_len; + Ok(m) + } + + fn new_with_map( + &self, + matches: &BTreeMap<StateID, Vec<PatternID>>, + ) -> Result<MatchStates<Vec<u32>>, BuildError> { + MatchStates::new(matches, self.pattern_len) + } +} + +impl<T: AsRef<[u32]>> MatchStates<T> { + /// Writes a serialized form of these match states to the buffer given. If + /// the buffer is too small, then an error is returned. To determine how + /// big the buffer must be, use `write_to_len`. + fn write_to<E: Endian>( + &self, + mut dst: &mut [u8], + ) -> Result<usize, SerializeError> { + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("match states")); + } + dst = &mut dst[..nwrite]; + + // write state ID length + // Unwrap is OK since number of states is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.len()).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write slice offset pairs + for &pid in self.slices() { + let n = wire::write_pattern_id::<E>(pid, &mut dst); + dst = &mut dst[n..]; + } + + // write unique pattern ID length + // Unwrap is OK since number of patterns is guaranteed to fit in a u32. + E::write_u32(u32::try_from(self.pattern_len).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write pattern ID length + // Unwrap is OK since we check at construction (and deserialization) + // that the number of patterns is representable as a u32. + E::write_u32(u32::try_from(self.pattern_ids().len()).unwrap(), dst); + dst = &mut dst[size_of::<u32>()..]; + + // write pattern IDs + for &pid in self.pattern_ids() { + let n = wire::write_pattern_id::<E>(pid, &mut dst); + dst = &mut dst[n..]; + } + + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of these match states + /// will use. + fn write_to_len(&self) -> usize { + size_of::<u32>() // match state length + + (self.slices().len() * PatternID::SIZE) + + size_of::<u32>() // unique pattern ID length + + size_of::<u32>() // pattern ID length + + (self.pattern_ids().len() * PatternID::SIZE) + } + + /// Valides that the match state info is itself internally consistent and + /// consistent with the recorded match state region in the given DFA. + fn validate(&self, dfa: &DFA<T>) -> Result<(), DeserializeError> { + if self.len() != dfa.special.match_len(dfa.stride()) { + return Err(DeserializeError::generic( + "match state length mismatch", + )); + } + for si in 0..self.len() { + let start = self.slices()[si * 2].as_usize(); + let len = self.slices()[si * 2 + 1].as_usize(); + if start >= self.pattern_ids().len() { + return Err(DeserializeError::generic( + "invalid pattern ID start offset", + )); + } + if start + len > self.pattern_ids().len() { + return Err(DeserializeError::generic( + "invalid pattern ID length", + )); + } + for mi in 0..len { + let pid = self.pattern_id(si, mi); + if pid.as_usize() >= self.pattern_len { + return Err(DeserializeError::generic( + "invalid pattern ID", + )); + } + } + } + Ok(()) + } + + /// Converts these match states back into their map form. This is useful + /// when shuffling states, as the normal MatchStates representation is not + /// amenable to easy state swapping. But with this map, to swap id1 and + /// id2, all you need to do is: + /// + /// if let Some(pids) = map.remove(&id1) { + /// map.insert(id2, pids); + /// } + /// + /// Once shuffling is done, use MatchStates::new to convert back. + #[cfg(feature = "dfa-build")] + fn to_map(&self, dfa: &DFA<T>) -> BTreeMap<StateID, Vec<PatternID>> { + let mut map = BTreeMap::new(); + for i in 0..self.len() { + let mut pids = vec![]; + for j in 0..self.pattern_len(i) { + pids.push(self.pattern_id(i, j)); + } + map.insert(self.match_state_id(dfa, i), pids); + } + map + } + + /// Converts these match states to a borrowed value. + fn as_ref(&self) -> MatchStates<&'_ [u32]> { + MatchStates { + slices: self.slices.as_ref(), + pattern_ids: self.pattern_ids.as_ref(), + pattern_len: self.pattern_len, + } + } + + /// Converts these match states to an owned value. + #[cfg(feature = "alloc")] + fn to_owned(&self) -> MatchStates<alloc::vec::Vec<u32>> { + MatchStates { + slices: self.slices.as_ref().to_vec(), + pattern_ids: self.pattern_ids.as_ref().to_vec(), + pattern_len: self.pattern_len, + } + } + + /// Returns the match state ID given the match state index. (Where the + /// first match state corresponds to index 0.) + /// + /// This panics if there is no match state at the given index. + fn match_state_id(&self, dfa: &DFA<T>, index: usize) -> StateID { + assert!(dfa.special.matches(), "no match states to index"); + // This is one of the places where we rely on the fact that match + // states are contiguous in the transition table. Namely, that the + // first match state ID always corresponds to dfa.special.min_start. + // From there, since we know the stride, we can compute the ID of any + // match state given its index. + let stride2 = u32::try_from(dfa.stride2()).unwrap(); + let offset = index.checked_shl(stride2).unwrap(); + let id = dfa.special.min_match.as_usize().checked_add(offset).unwrap(); + let sid = StateID::new(id).unwrap(); + assert!(dfa.is_match_state(sid)); + sid + } + + /// Returns the pattern ID at the given match index for the given match + /// state. + /// + /// The match state index is the state index minus the state index of the + /// first match state in the DFA. + /// + /// The match index is the index of the pattern ID for the given state. + /// The index must be less than `self.pattern_len(state_index)`. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn pattern_id(&self, state_index: usize, match_index: usize) -> PatternID { + self.pattern_id_slice(state_index)[match_index] + } + + /// Returns the number of patterns in the given match state. + /// + /// The match state index is the state index minus the state index of the + /// first match state in the DFA. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn pattern_len(&self, state_index: usize) -> usize { + self.slices()[state_index * 2 + 1].as_usize() + } + + /// Returns all of the pattern IDs for the given match state index. + /// + /// The match state index is the state index minus the state index of the + /// first match state in the DFA. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn pattern_id_slice(&self, state_index: usize) -> &[PatternID] { + let start = self.slices()[state_index * 2].as_usize(); + let len = self.pattern_len(state_index); + &self.pattern_ids()[start..start + len] + } + + /// Returns the pattern ID offset slice of u32 as a slice of PatternID. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn slices(&self) -> &[PatternID] { + wire::u32s_to_pattern_ids(self.slices.as_ref()) + } + + /// Returns the total number of match states. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn len(&self) -> usize { + assert_eq!(0, self.slices().len() % 2); + self.slices().len() / 2 + } + + /// Returns the pattern ID slice of u32 as a slice of PatternID. + #[cfg_attr(feature = "perf-inline", inline(always))] + fn pattern_ids(&self) -> &[PatternID] { + wire::u32s_to_pattern_ids(self.pattern_ids.as_ref()) + } + + /// Return the memory usage, in bytes, of these match pairs. + fn memory_usage(&self) -> usize { + (self.slices().len() + self.pattern_ids().len()) * PatternID::SIZE + } +} + +/// A common set of flags for both dense and sparse DFAs. This primarily +/// centralizes the serialization format of these flags at a bitset. +#[derive(Clone, Copy, Debug)] +pub(crate) struct Flags { + /// Whether the DFA can match the empty string. When this is false, all + /// matches returned by this DFA are guaranteed to have non-zero length. + pub(crate) has_empty: bool, + /// Whether the DFA should only produce matches with spans that correspond + /// to valid UTF-8. This also includes omitting any zero-width matches that + /// split the UTF-8 encoding of a codepoint. + pub(crate) is_utf8: bool, + /// Whether the DFA is always anchored or not, regardless of `Input` + /// configuration. This is useful for avoiding a reverse scan even when + /// executing unanchored searches. + pub(crate) is_always_start_anchored: bool, +} + +impl Flags { + /// Creates a set of flags for a DFA from an NFA. + /// + /// N.B. This constructor was defined at the time of writing because all + /// of the flags are derived directly from the NFA. If this changes in the + /// future, we might be more thoughtful about how the `Flags` value is + /// itself built. + #[cfg(feature = "dfa-build")] + fn from_nfa(nfa: &thompson::NFA) -> Flags { + Flags { + has_empty: nfa.has_empty(), + is_utf8: nfa.is_utf8(), + is_always_start_anchored: nfa.is_always_start_anchored(), + } + } + + /// Deserializes the flags from the given slice. On success, this also + /// returns the number of bytes read from the slice. + pub(crate) fn from_bytes( + slice: &[u8], + ) -> Result<(Flags, usize), DeserializeError> { + let (bits, nread) = wire::try_read_u32(slice, "flag bitset")?; + let flags = Flags { + has_empty: bits & (1 << 0) != 0, + is_utf8: bits & (1 << 1) != 0, + is_always_start_anchored: bits & (1 << 2) != 0, + }; + Ok((flags, nread)) + } + + /// Writes these flags to the given byte slice. If the buffer is too small, + /// then an error is returned. To determine how big the buffer must be, + /// use `write_to_len`. + pub(crate) fn write_to<E: Endian>( + &self, + dst: &mut [u8], + ) -> Result<usize, SerializeError> { + fn bool_to_int(b: bool) -> u32 { + if b { + 1 + } else { + 0 + } + } + + let nwrite = self.write_to_len(); + if dst.len() < nwrite { + return Err(SerializeError::buffer_too_small("flag bitset")); + } + let bits = (bool_to_int(self.has_empty) << 0) + | (bool_to_int(self.is_utf8) << 1) + | (bool_to_int(self.is_always_start_anchored) << 2); + E::write_u32(bits, dst); + Ok(nwrite) + } + + /// Returns the number of bytes the serialized form of these flags + /// will use. + pub(crate) fn write_to_len(&self) -> usize { + size_of::<u32>() + } +} + +/// An iterator over all states in a DFA. +/// +/// This iterator yields a tuple for each state. The first element of the +/// tuple corresponds to a state's identifier, and the second element +/// corresponds to the state itself (comprised of its transitions). +/// +/// `'a` corresponding to the lifetime of original DFA, `T` corresponds to +/// the type of the transition table itself. +pub(crate) struct StateIter<'a, T> { + tt: &'a TransitionTable<T>, + it: iter::Enumerate<slice::Chunks<'a, StateID>>, +} + +impl<'a, T: AsRef<[u32]>> Iterator for StateIter<'a, T> { + type Item = State<'a>; + + fn next(&mut self) -> Option<State<'a>> { + self.it.next().map(|(index, _)| { + let id = self.tt.to_state_id(index); + self.tt.state(id) + }) + } +} + +/// An immutable representation of a single DFA state. +/// +/// `'a` correspondings to the lifetime of a DFA's transition table. +pub(crate) struct State<'a> { + id: StateID, + stride2: usize, + transitions: &'a [StateID], +} + +impl<'a> State<'a> { + /// Return an iterator over all transitions in this state. This yields + /// a number of transitions equivalent to the alphabet length of the + /// corresponding DFA. + /// + /// Each transition is represented by a tuple. The first element is + /// the input byte for that transition and the second element is the + /// transitions itself. + pub(crate) fn transitions(&self) -> StateTransitionIter<'_> { + StateTransitionIter { + len: self.transitions.len(), + it: self.transitions.iter().enumerate(), + } + } + + /// Return an iterator over a sparse representation of the transitions in + /// this state. Only non-dead transitions are returned. + /// + /// The "sparse" representation in this case corresponds to a sequence of + /// triples. The first two elements of the triple comprise an inclusive + /// byte range while the last element corresponds to the transition taken + /// for all bytes in the range. + /// + /// This is somewhat more condensed than the classical sparse + /// representation (where you have an element for every non-dead + /// transition), but in practice, checking if a byte is in a range is very + /// cheap and using ranges tends to conserve quite a bit more space. + pub(crate) fn sparse_transitions(&self) -> StateSparseTransitionIter<'_> { + StateSparseTransitionIter { dense: self.transitions(), cur: None } + } + + /// Returns the identifier for this state. + pub(crate) fn id(&self) -> StateID { + self.id + } + + /// Analyzes this state to determine whether it can be accelerated. If so, + /// it returns an accelerator that contains at least one byte. + #[cfg(feature = "dfa-build")] + fn accelerate(&self, classes: &ByteClasses) -> Option<Accel> { + // We just try to add bytes to our accelerator. Once adding fails + // (because we've added too many bytes), then give up. + let mut accel = Accel::new(); + for (class, id) in self.transitions() { + if id == self.id() { + continue; + } + for unit in classes.elements(class) { + if let Some(byte) = unit.as_u8() { + if !accel.add(byte) { + return None; + } + } + } + } + if accel.is_empty() { + None + } else { + Some(accel) + } + } +} + +impl<'a> fmt::Debug for State<'a> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + for (i, (start, end, sid)) in self.sparse_transitions().enumerate() { + let id = if f.alternate() { + sid.as_usize() + } else { + sid.as_usize() >> self.stride2 + }; + if i > 0 { + write!(f, ", ")?; + } + if start == end { + write!(f, "{:?} => {:?}", start, id)?; + } else { + write!(f, "{:?}-{:?} => {:?}", start, end, id)?; + } + } + Ok(()) + } +} + +/// An iterator over all transitions in a single DFA state. This yields +/// a number of transitions equivalent to the alphabet length of the +/// corresponding DFA. +/// +/// Each transition is represented by a tuple. The first element is the input +/// byte for that transition and the second element is the transition itself. +#[derive(Debug)] +pub(crate) struct StateTransitionIter<'a> { + len: usize, + it: iter::Enumerate<slice::Iter<'a, StateID>>, +} + +impl<'a> Iterator for StateTransitionIter<'a> { + type Item = (alphabet::Unit, StateID); + + fn next(&mut self) -> Option<(alphabet::Unit, StateID)> { + self.it.next().map(|(i, &id)| { + let unit = if i + 1 == self.len { + alphabet::Unit::eoi(i) + } else { + let b = u8::try_from(i) + .expect("raw byte alphabet is never exceeded"); + alphabet::Unit::u8(b) + }; + (unit, id) + }) + } +} + +/// An iterator over all non-DEAD transitions in a single DFA state using a +/// sparse representation. +/// +/// Each transition is represented by a triple. The first two elements of the +/// triple comprise an inclusive byte range while the last element corresponds +/// to the transition taken for all bytes in the range. +/// +/// As a convenience, this always returns `alphabet::Unit` values of the same +/// type. That is, you'll never get a (byte, EOI) or a (EOI, byte). Only (byte, +/// byte) and (EOI, EOI) values are yielded. +#[derive(Debug)] +pub(crate) struct StateSparseTransitionIter<'a> { + dense: StateTransitionIter<'a>, + cur: Option<(alphabet::Unit, alphabet::Unit, StateID)>, +} + +impl<'a> Iterator for StateSparseTransitionIter<'a> { + type Item = (alphabet::Unit, alphabet::Unit, StateID); + + fn next(&mut self) -> Option<(alphabet::Unit, alphabet::Unit, StateID)> { + while let Some((unit, next)) = self.dense.next() { + let (prev_start, prev_end, prev_next) = match self.cur { + Some(t) => t, + None => { + self.cur = Some((unit, unit, next)); + continue; + } + }; + if prev_next == next && !unit.is_eoi() { + self.cur = Some((prev_start, unit, prev_next)); + } else { + self.cur = Some((unit, unit, next)); + if prev_next != DEAD { + return Some((prev_start, prev_end, prev_next)); + } + } + } + if let Some((start, end, next)) = self.cur.take() { + if next != DEAD { + return Some((start, end, next)); + } + } + None + } +} + +/// An error that occurred during the construction of a DFA. +/// +/// This error does not provide many introspection capabilities. There are +/// generally only two things you can do with it: +/// +/// * Obtain a human readable message via its `std::fmt::Display` impl. +/// * Access an underlying [`nfa::thompson::BuildError`](thompson::BuildError) +/// type from its `source` method via the `std::error::Error` trait. This error +/// only occurs when using convenience routines for building a DFA directly +/// from a pattern string. +/// +/// When the `std` feature is enabled, this implements the `std::error::Error` +/// trait. +#[cfg(feature = "dfa-build")] +#[derive(Clone, Debug)] +pub struct BuildError { + kind: BuildErrorKind, +} + +/// The kind of error that occurred during the construction of a DFA. +/// +/// Note that this error is non-exhaustive. Adding new variants is not +/// considered a breaking change. +#[cfg(feature = "dfa-build")] +#[derive(Clone, Debug)] +enum BuildErrorKind { + /// An error that occurred while constructing an NFA as a precursor step + /// before a DFA is compiled. + NFA(thompson::BuildError), + /// An error that occurred because an unsupported regex feature was used. + /// The message string describes which unsupported feature was used. + /// + /// The primary regex feature that is unsupported by DFAs is the Unicode + /// word boundary look-around assertion (`\b`). This can be worked around + /// by either using an ASCII word boundary (`(?-u:\b)`) or by enabling + /// Unicode word boundaries when building a DFA. + Unsupported(&'static str), + /// An error that occurs if too many states are produced while building a + /// DFA. + TooManyStates, + /// An error that occurs if too many start states are needed while building + /// a DFA. + /// + /// This is a kind of oddball error that occurs when building a DFA with + /// start states enabled for each pattern and enough patterns to cause + /// the table of start states to overflow `usize`. + TooManyStartStates, + /// This is another oddball error that can occur if there are too many + /// patterns spread out across too many match states. + TooManyMatchPatternIDs, + /// An error that occurs if the DFA got too big during determinization. + DFAExceededSizeLimit { limit: usize }, + /// An error that occurs if auxiliary storage (not the DFA) used during + /// determinization got too big. + DeterminizeExceededSizeLimit { limit: usize }, +} + +#[cfg(feature = "dfa-build")] +impl BuildError { + /// Return the kind of this error. + fn kind(&self) -> &BuildErrorKind { + &self.kind + } + + pub(crate) fn nfa(err: thompson::BuildError) -> BuildError { + BuildError { kind: BuildErrorKind::NFA(err) } + } + + pub(crate) fn unsupported_dfa_word_boundary_unicode() -> BuildError { + let msg = "cannot build DFAs for regexes with Unicode word \ + boundaries; switch to ASCII word boundaries, or \ + heuristically enable Unicode word boundaries or use a \ + different regex engine"; + BuildError { kind: BuildErrorKind::Unsupported(msg) } + } + + pub(crate) fn too_many_states() -> BuildError { + BuildError { kind: BuildErrorKind::TooManyStates } + } + + pub(crate) fn too_many_start_states() -> BuildError { + BuildError { kind: BuildErrorKind::TooManyStartStates } + } + + pub(crate) fn too_many_match_pattern_ids() -> BuildError { + BuildError { kind: BuildErrorKind::TooManyMatchPatternIDs } + } + + pub(crate) fn dfa_exceeded_size_limit(limit: usize) -> BuildError { + BuildError { kind: BuildErrorKind::DFAExceededSizeLimit { limit } } + } + + pub(crate) fn determinize_exceeded_size_limit(limit: usize) -> BuildError { + BuildError { + kind: BuildErrorKind::DeterminizeExceededSizeLimit { limit }, + } + } +} + +#[cfg(all(feature = "std", feature = "dfa-build"))] +impl std::error::Error for BuildError { + fn source(&self) -> Option<&(dyn std::error::Error + 'static)> { + match self.kind() { + BuildErrorKind::NFA(ref err) => Some(err), + _ => None, + } + } +} + +#[cfg(feature = "dfa-build")] +impl core::fmt::Display for BuildError { + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { + match self.kind() { + BuildErrorKind::NFA(_) => write!(f, "error building NFA"), + BuildErrorKind::Unsupported(ref msg) => { + write!(f, "unsupported regex feature for DFAs: {}", msg) + } + BuildErrorKind::TooManyStates => write!( + f, + "number of DFA states exceeds limit of {}", + StateID::LIMIT, + ), + BuildErrorKind::TooManyStartStates => { + let stride = Start::len(); + // The start table has `stride` entries for starting states for + // the entire DFA, and then `stride` entries for each pattern + // if start states for each pattern are enabled (which is the + // only way this error can occur). Thus, the total number of + // patterns that can fit in the table is `stride` less than + // what we can allocate. + let max = usize::try_from(core::isize::MAX).unwrap(); + let limit = (max - stride) / stride; + write!( + f, + "compiling DFA with start states exceeds pattern \ + pattern limit of {}", + limit, + ) + } + BuildErrorKind::TooManyMatchPatternIDs => write!( + f, + "compiling DFA with total patterns in all match states \ + exceeds limit of {}", + PatternID::LIMIT, + ), + BuildErrorKind::DFAExceededSizeLimit { limit } => write!( + f, + "DFA exceeded size limit of {:?} during determinization", + limit, + ), + BuildErrorKind::DeterminizeExceededSizeLimit { limit } => { + write!(f, "determinization exceeded size limit of {:?}", limit) + } + } + } +} + +#[cfg(all(test, feature = "syntax", feature = "dfa-build"))] +mod tests { + use super::*; + + #[test] + fn errors_with_unicode_word_boundary() { + let pattern = r"\b"; + assert!(Builder::new().build(pattern).is_err()); + } + + #[test] + fn roundtrip_never_match() { + let dfa = DFA::never_match().unwrap(); + let (buf, _) = dfa.to_bytes_native_endian(); + let dfa: DFA<&[u32]> = DFA::from_bytes(&buf).unwrap().0; + + assert_eq!(None, dfa.try_search_fwd(&Input::new("foo12345")).unwrap()); + } + + #[test] + fn roundtrip_always_match() { + use crate::HalfMatch; + + let dfa = DFA::always_match().unwrap(); + let (buf, _) = dfa.to_bytes_native_endian(); + let dfa: DFA<&[u32]> = DFA::from_bytes(&buf).unwrap().0; + + assert_eq!( + Some(HalfMatch::must(0, 0)), + dfa.try_search_fwd(&Input::new("foo12345")).unwrap() + ); + } + + // See the analogous test in src/hybrid/dfa.rs. + #[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 input = Input::new("β123").range(2..); + let expected = MatchError::quit(0xB2, 1); + let got = dfa.try_search_rev(&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(&input); + assert_eq!(Err(expected), got); + } +} |