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Diffstat (limited to 'third_party/rust/regex-automata/src/nfa/thompson/builder.rs')
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diff --git a/third_party/rust/regex-automata/src/nfa/thompson/builder.rs b/third_party/rust/regex-automata/src/nfa/thompson/builder.rs new file mode 100644 index 0000000000..b57e5bc0f3 --- /dev/null +++ b/third_party/rust/regex-automata/src/nfa/thompson/builder.rs @@ -0,0 +1,1337 @@ +use core::mem; + +use alloc::{sync::Arc, vec, vec::Vec}; + +use crate::{ + nfa::thompson::{ + error::BuildError, + nfa::{self, SparseTransitions, Transition, NFA}, + }, + util::{ + look::{Look, LookMatcher}, + primitives::{IteratorIndexExt, PatternID, SmallIndex, StateID}, + }, +}; + +/// An intermediate NFA state used during construction. +/// +/// During construction of an NFA, it is often convenient to work with states +/// that are amenable to mutation and other carry more information than we +/// otherwise need once an NFA has been built. This type represents those +/// needs. +/// +/// Once construction is finished, the builder will convert these states to a +/// [`nfa::thompson::State`](crate::nfa::thompson::State). This conversion not +/// only results in a simpler representation, but in some cases, entire classes +/// of states are completely removed (such as [`State::Empty`]). +#[derive(Clone, Debug, Eq, PartialEq)] +enum State { + /// An empty state whose only purpose is to forward the automaton to + /// another state via an unconditional epsilon transition. + /// + /// Unconditional epsilon transitions are quite useful during the + /// construction of an NFA, as they permit the insertion of no-op + /// placeholders that make it easier to compose NFA sub-graphs. When + /// the Thompson NFA builder produces a final NFA, all unconditional + /// epsilon transitions are removed, and state identifiers are remapped + /// accordingly. + Empty { + /// The next state that this state should transition to. + next: StateID, + }, + /// A state that only transitions to another state if the current input + /// byte is in a particular range of bytes. + ByteRange { trans: Transition }, + /// A state with possibly many transitions, represented in a sparse + /// fashion. Transitions must be ordered lexicographically by input range + /// and be non-overlapping. As such, this may only be used when every + /// transition has equal priority. (In practice, this is only used for + /// encoding large UTF-8 automata.) In contrast, a `Union` state has each + /// alternate in order of priority. Priority is used to implement greedy + /// matching and also alternations themselves, e.g., `abc|a` where `abc` + /// has priority over `a`. + /// + /// To clarify, it is possible to remove `Sparse` and represent all things + /// that `Sparse` is used for via `Union`. But this creates a more bloated + /// NFA with more epsilon transitions than is necessary in the special case + /// of character classes. + Sparse { transitions: Vec<Transition> }, + /// A conditional epsilon transition satisfied via some sort of + /// look-around. + Look { look: Look, next: StateID }, + /// An empty state that records the start of a capture location. This is an + /// unconditional epsilon transition like `Empty`, except it can be used to + /// record position information for a captue group when using the NFA for + /// search. + CaptureStart { + /// The ID of the pattern that this capture was defined. + pattern_id: PatternID, + /// The capture group index that this capture state corresponds to. + /// The capture group index is always relative to its corresponding + /// pattern. Therefore, in the presence of multiple patterns, both the + /// pattern ID and the capture group index are required to uniquely + /// identify a capturing group. + group_index: SmallIndex, + /// The next state that this state should transition to. + next: StateID, + }, + /// An empty state that records the end of a capture location. This is an + /// unconditional epsilon transition like `Empty`, except it can be used to + /// record position information for a captue group when using the NFA for + /// search. + CaptureEnd { + /// The ID of the pattern that this capture was defined. + pattern_id: PatternID, + /// The capture group index that this capture state corresponds to. + /// The capture group index is always relative to its corresponding + /// pattern. Therefore, in the presence of multiple patterns, both the + /// pattern ID and the capture group index are required to uniquely + /// identify a capturing group. + group_index: SmallIndex, + /// The next state that this state should transition to. + next: StateID, + }, + /// An alternation such that there exists an epsilon transition to all + /// states in `alternates`, where matches found via earlier transitions + /// are preferred over later transitions. + Union { alternates: Vec<StateID> }, + /// An alternation such that there exists an epsilon transition to all + /// states in `alternates`, where matches found via later transitions are + /// preferred over earlier transitions. + /// + /// This "reverse" state exists for convenience during compilation that + /// permits easy construction of non-greedy combinations of NFA states. At + /// the end of compilation, Union and UnionReverse states are merged into + /// one Union type of state, where the latter has its epsilon transitions + /// reversed to reflect the priority inversion. + /// + /// The "convenience" here arises from the fact that as new states are + /// added to the list of `alternates`, we would like that add operation + /// to be amortized constant time. But if we used a `Union`, we'd need to + /// prepend the state, which takes O(n) time. There are other approaches we + /// could use to solve this, but this seems simple enough. + UnionReverse { alternates: Vec<StateID> }, + /// A state that cannot be transitioned out of. This is useful for cases + /// where you want to prevent matching from occurring. For example, if your + /// regex parser permits empty character classes, then one could choose a + /// `Fail` state to represent it. + Fail, + /// A match state. There is at most one such occurrence of this state in + /// an NFA for each pattern compiled into the NFA. At time of writing, a + /// match state is always produced for every pattern given, but in theory, + /// if a pattern can never lead to a match, then the match state could be + /// omitted. + /// + /// `pattern_id` refers to the ID of the pattern itself, which corresponds + /// to the pattern's index (starting at 0). + Match { pattern_id: PatternID }, +} + +impl State { + /// If this state is an unconditional espilon transition, then this returns + /// the target of the transition. + fn goto(&self) -> Option<StateID> { + match *self { + State::Empty { next } => Some(next), + State::Union { ref alternates } if alternates.len() == 1 => { + Some(alternates[0]) + } + State::UnionReverse { ref alternates } + if alternates.len() == 1 => + { + Some(alternates[0]) + } + _ => None, + } + } + + /// Returns the heap memory usage, in bytes, of this state. + fn memory_usage(&self) -> usize { + match *self { + State::Empty { .. } + | State::ByteRange { .. } + | State::Look { .. } + | State::CaptureStart { .. } + | State::CaptureEnd { .. } + | State::Fail + | State::Match { .. } => 0, + State::Sparse { ref transitions } => { + transitions.len() * mem::size_of::<Transition>() + } + State::Union { ref alternates } => { + alternates.len() * mem::size_of::<StateID>() + } + State::UnionReverse { ref alternates } => { + alternates.len() * mem::size_of::<StateID>() + } + } + } +} + +/// An abstraction for building Thompson NFAs by hand. +/// +/// A builder is what a [`thompson::Compiler`](crate::nfa::thompson::Compiler) +/// uses internally to translate a regex's high-level intermediate +/// representation into an [`NFA`]. +/// +/// The primary function of this builder is to abstract away the internal +/// representation of an NFA and make it difficult to produce NFAs are that +/// internally invalid or inconsistent. This builder also provides a way to +/// add "empty" states (which can be thought of as unconditional epsilon +/// transitions), despite the fact that [`thompson::State`](nfa::State) does +/// not have any "empty" representation. The advantage of "empty" states is +/// that they make the code for constructing a Thompson NFA logically simpler. +/// +/// Many of the routines on this builder may panic or return errors. Generally +/// speaking, panics occur when an invalid sequence of method calls were made, +/// where as an error occurs if things get too big. (Where "too big" might mean +/// exhausting identifier space or using up too much heap memory in accordance +/// with the configured [`size_limit`](Builder::set_size_limit).) +/// +/// # Overview +/// +/// ## Adding multiple patterns +/// +/// Each pattern you add to an NFA should correspond to a pair of +/// [`Builder::start_pattern`] and [`Builder::finish_pattern`] calls, with +/// calls inbetween that add NFA states for that pattern. NFA states may be +/// added without first calling `start_pattern`, with the exception of adding +/// capturing states. +/// +/// ## Adding NFA states +/// +/// Here is a very brief overview of each of the methods that add NFA states. +/// Every method adds a single state. +/// +/// * [`add_empty`](Builder::add_empty): Add a state with a single +/// unconditional epsilon transition to another state. +/// * [`add_union`](Builder::add_union): Adds a state with unconditional +/// epsilon transitions to two or more states, with earlier transitions +/// preferred over later ones. +/// * [`add_union_reverse`](Builder::add_union_reverse): Adds a state with +/// unconditional epsilon transitions to two or more states, with later +/// transitions preferred over earlier ones. +/// * [`add_range`](Builder::add_range): Adds a state with a single transition +/// to another state that can only be followed if the current input byte is +/// within the range given. +/// * [`add_sparse`](Builder::add_sparse): Adds a state with two or more +/// range transitions to other states, where a transition is only followed +/// if the current input byte is within one of the ranges. All transitions +/// in this state have equal priority, and the corresponding ranges must be +/// non-overlapping. +/// * [`add_look`](Builder::add_look): Adds a state with a single *conditional* +/// epsilon transition to another state, where the condition depends on a +/// limited look-around property. +/// * [`add_capture_start`](Builder::add_capture_start): Adds a state with +/// a single unconditional epsilon transition that also instructs an NFA +/// simulation to record the current input position to a specific location in +/// memory. This is intended to represent the starting location of a capturing +/// group. +/// * [`add_capture_end`](Builder::add_capture_end): Adds a state with +/// a single unconditional epsilon transition that also instructs an NFA +/// simulation to record the current input position to a specific location in +/// memory. This is intended to represent the ending location of a capturing +/// group. +/// * [`add_fail`](Builder::add_fail): Adds a state that never transitions to +/// another state. +/// * [`add_match`](Builder::add_match): Add a state that indicates a match has +/// been found for a particular pattern. A match state is a final state with +/// no outgoing transitions. +/// +/// ## Setting transitions between NFA states +/// +/// The [`Builder::patch`] method creates a transition from one state to the +/// next. If the `from` state corresponds to a state that supports multiple +/// outgoing transitions (such as "union"), then this adds the corresponding +/// transition. Otherwise, it sets the single transition. (This routine panics +/// if `from` corresponds to a state added by `add_sparse`, since sparse states +/// need more specialized handling.) +/// +/// # Example +/// +/// This annotated example shows how to hand construct the regex `[a-z]+` +/// (without an unanchored prefix). +/// +/// ``` +/// use regex_automata::{ +/// nfa::thompson::{pikevm::PikeVM, Builder, Transition}, +/// util::primitives::StateID, +/// Match, +/// }; +/// +/// let mut builder = Builder::new(); +/// // Before adding NFA states for our pattern, we need to tell the builder +/// // that we are starting the pattern. +/// builder.start_pattern()?; +/// // Since we use the Pike VM below for searching, we need to add capturing +/// // states. If you're just going to build a DFA from the NFA, then capturing +/// // states do not need to be added. +/// let start = builder.add_capture_start(StateID::ZERO, 0, None)?; +/// let range = builder.add_range(Transition { +/// // We don't know the state ID of the 'next' state yet, so we just fill +/// // in a dummy 'ZERO' value. +/// start: b'a', end: b'z', next: StateID::ZERO, +/// })?; +/// // This state will point back to 'range', but also enable us to move ahead. +/// // That is, this implements the '+' repetition operator. We add 'range' and +/// // then 'end' below to this alternation. +/// let alt = builder.add_union(vec![])?; +/// // The final state before the match state, which serves to capture the +/// // end location of the match. +/// let end = builder.add_capture_end(StateID::ZERO, 0)?; +/// // The match state for our pattern. +/// let mat = builder.add_match()?; +/// // Now we fill in the transitions between states. +/// builder.patch(start, range)?; +/// builder.patch(range, alt)?; +/// // If we added 'end' before 'range', then we'd implement non-greedy +/// // matching, i.e., '+?'. +/// builder.patch(alt, range)?; +/// builder.patch(alt, end)?; +/// builder.patch(end, mat)?; +/// // We must explicitly finish pattern and provide the starting state ID for +/// // this particular pattern. +/// builder.finish_pattern(start)?; +/// // Finally, when we build the NFA, we provide the anchored and unanchored +/// // starting state IDs. Since we didn't bother with an unanchored prefix +/// // here, we only support anchored searching. Thus, both starting states are +/// // the same. +/// let nfa = builder.build(start, start)?; +/// +/// // Now build a Pike VM from our NFA, and use it for searching. This shows +/// // how we can use a regex engine without ever worrying about syntax! +/// let re = PikeVM::new_from_nfa(nfa)?; +/// let mut cache = re.create_cache(); +/// let mut caps = re.create_captures(); +/// let expected = Some(Match::must(0, 0..3)); +/// re.captures(&mut cache, "foo0", &mut caps); +/// assert_eq!(expected, caps.get_match()); +/// +/// # Ok::<(), Box<dyn std::error::Error>>(()) +/// ``` +#[derive(Clone, Debug, Default)] +pub struct Builder { + /// The ID of the pattern that we're currently building. + /// + /// Callers are required to set (and unset) this by calling + /// {start,finish}_pattern. Otherwise, most methods will panic. + pattern_id: Option<PatternID>, + /// A sequence of intermediate NFA states. Once a state is added to this + /// sequence, it is assigned a state ID equivalent to its index. Once a + /// state is added, it is still expected to be mutated, e.g., to set its + /// transition to a state that didn't exist at the time it was added. + states: Vec<State>, + /// The starting states for each individual pattern. Starting at any + /// of these states will result in only an anchored search for the + /// corresponding pattern. The vec is indexed by pattern ID. When the NFA + /// contains a single regex, then `start_pattern[0]` and `start_anchored` + /// are always equivalent. + start_pattern: Vec<StateID>, + /// A map from pattern ID to capture group index to name. (If no name + /// exists, then a None entry is present. Thus, all capturing groups are + /// present in this mapping.) + /// + /// The outer vec is indexed by pattern ID, while the inner vec is indexed + /// by capture index offset for the corresponding pattern. + /// + /// The first capture group for each pattern is always unnamed and is thus + /// always None. + captures: Vec<Vec<Option<Arc<str>>>>, + /// The combined memory used by each of the 'State's in 'states'. This + /// only includes heap usage by each state, and not the size of the state + /// itself. In other words, this tracks heap memory used that isn't + /// captured via `size_of::<State>() * states.len()`. + memory_states: usize, + /// Whether this NFA only matches UTF-8 and whether regex engines using + /// this NFA for searching should report empty matches that split a + /// codepoint. + utf8: bool, + /// Whether this NFA should be matched in reverse or not. + reverse: bool, + /// The matcher to use for look-around assertions. + look_matcher: LookMatcher, + /// A size limit to respect when building an NFA. If the total heap memory + /// of the intermediate NFA states exceeds (or would exceed) this amount, + /// then an error is returned. + size_limit: Option<usize>, +} + +impl Builder { + /// Create a new builder for hand-assembling NFAs. + pub fn new() -> Builder { + Builder::default() + } + + /// Clear this builder. + /// + /// Clearing removes all state associated with building an NFA, but does + /// not reset configuration (such as size limits and whether the NFA + /// should only match UTF-8). After clearing, the builder can be reused to + /// assemble an entirely new NFA. + pub fn clear(&mut self) { + self.pattern_id = None; + self.states.clear(); + self.start_pattern.clear(); + self.captures.clear(); + self.memory_states = 0; + } + + /// Assemble a [`NFA`] from the states added so far. + /// + /// After building an NFA, more states may be added and `build` may be + /// called again. To reuse a builder to produce an entirely new NFA from + /// scratch, call the [`clear`](Builder::clear) method first. + /// + /// `start_anchored` refers to the ID of the starting state that anchored + /// searches should use. That is, searches who matches are limited to the + /// starting position of the search. + /// + /// `start_unanchored` refers to the ID of the starting state that + /// unanchored searches should use. This permits searches to report matches + /// that start after the beginning of the search. In cases where unanchored + /// searches are not supported, the unanchored starting state ID must be + /// the same as the anchored starting state ID. + /// + /// # Errors + /// + /// This returns an error if there was a problem producing the final NFA. + /// In particular, this might include an error if the capturing groups + /// added to this builder violate any of the invariants documented on + /// [`GroupInfo`](crate::util::captures::GroupInfo). + /// + /// # Panics + /// + /// If `start_pattern` was called, then `finish_pattern` must be called + /// before `build`, otherwise this panics. + /// + /// This may panic for other invalid uses of a builder. For example, if + /// a "start capture" state was added without a corresponding "end capture" + /// state. + pub fn build( + &self, + start_anchored: StateID, + start_unanchored: StateID, + ) -> Result<NFA, BuildError> { + assert!(self.pattern_id.is_none(), "must call 'finish_pattern' first"); + debug!( + "intermediate NFA compilation via builder is complete, \ + intermediate NFA size: {} states, {} bytes on heap", + self.states.len(), + self.memory_usage(), + ); + + let mut nfa = nfa::Inner::default(); + nfa.set_utf8(self.utf8); + nfa.set_reverse(self.reverse); + nfa.set_look_matcher(self.look_matcher.clone()); + // A set of compiler internal state IDs that correspond to states + // that are exclusively epsilon transitions, i.e., goto instructions, + // combined with the state that they point to. This is used to + // record said states while transforming the compiler's internal NFA + // representation to the external form. + let mut empties = vec![]; + // A map used to re-map state IDs when translating this builder's + // internal NFA state representation to the final NFA representation. + let mut remap = vec![]; + remap.resize(self.states.len(), StateID::ZERO); + + nfa.set_starts(start_anchored, start_unanchored, &self.start_pattern); + nfa.set_captures(&self.captures).map_err(BuildError::captures)?; + // The idea here is to convert our intermediate states to their final + // form. The only real complexity here is the process of converting + // transitions, which are expressed in terms of state IDs. The new + // set of states will be smaller because of partial epsilon removal, + // so the state IDs will not be the same. + for (sid, state) in self.states.iter().with_state_ids() { + match *state { + State::Empty { next } => { + // Since we're removing empty states, we need to handle + // them later since we don't yet know which new state this + // empty state will be mapped to. + empties.push((sid, next)); + } + State::ByteRange { trans } => { + remap[sid] = nfa.add(nfa::State::ByteRange { trans }); + } + State::Sparse { ref transitions } => { + remap[sid] = match transitions.len() { + 0 => nfa.add(nfa::State::Fail), + 1 => nfa.add(nfa::State::ByteRange { + trans: transitions[0], + }), + _ => { + let transitions = + transitions.to_vec().into_boxed_slice(); + let sparse = SparseTransitions { transitions }; + nfa.add(nfa::State::Sparse(sparse)) + } + } + } + State::Look { look, next } => { + remap[sid] = nfa.add(nfa::State::Look { look, next }); + } + State::CaptureStart { pattern_id, group_index, next } => { + // We can't remove this empty state because of the side + // effect of capturing an offset for this capture slot. + let slot = nfa + .group_info() + .slot(pattern_id, group_index.as_usize()) + .expect("invalid capture index"); + let slot = + SmallIndex::new(slot).expect("a small enough slot"); + remap[sid] = nfa.add(nfa::State::Capture { + next, + pattern_id, + group_index, + slot, + }); + } + State::CaptureEnd { pattern_id, group_index, next } => { + // We can't remove this empty state because of the side + // effect of capturing an offset for this capture slot. + // Also, this always succeeds because we check that all + // slot indices are valid for all capture indices when they + // are initially added. + let slot = nfa + .group_info() + .slot(pattern_id, group_index.as_usize()) + .expect("invalid capture index") + .checked_add(1) + .unwrap(); + let slot = + SmallIndex::new(slot).expect("a small enough slot"); + remap[sid] = nfa.add(nfa::State::Capture { + next, + pattern_id, + group_index, + slot, + }); + } + State::Union { ref alternates } => { + if alternates.is_empty() { + remap[sid] = nfa.add(nfa::State::Fail); + } else if alternates.len() == 1 { + empties.push((sid, alternates[0])); + remap[sid] = alternates[0]; + } else if alternates.len() == 2 { + remap[sid] = nfa.add(nfa::State::BinaryUnion { + alt1: alternates[0], + alt2: alternates[1], + }); + } else { + let alternates = + alternates.to_vec().into_boxed_slice(); + remap[sid] = nfa.add(nfa::State::Union { alternates }); + } + } + State::UnionReverse { ref alternates } => { + if alternates.is_empty() { + remap[sid] = nfa.add(nfa::State::Fail); + } else if alternates.len() == 1 { + empties.push((sid, alternates[0])); + remap[sid] = alternates[0]; + } else if alternates.len() == 2 { + remap[sid] = nfa.add(nfa::State::BinaryUnion { + alt1: alternates[1], + alt2: alternates[0], + }); + } else { + let mut alternates = + alternates.to_vec().into_boxed_slice(); + alternates.reverse(); + remap[sid] = nfa.add(nfa::State::Union { alternates }); + } + } + State::Fail => { + remap[sid] = nfa.add(nfa::State::Fail); + } + State::Match { pattern_id } => { + remap[sid] = nfa.add(nfa::State::Match { pattern_id }); + } + } + } + // Some of the new states still point to empty state IDs, so we need to + // follow each of them and remap the empty state IDs to their non-empty + // state IDs. + // + // We also keep track of which states we've already mapped. This helps + // avoid quadratic behavior in a long chain of empty states. For + // example, in 'a{0}{50000}'. + let mut remapped = vec![false; self.states.len()]; + for &(empty_id, empty_next) in empties.iter() { + if remapped[empty_id] { + continue; + } + // empty states can point to other empty states, forming a chain. + // So we must follow the chain until the end, which must end at + // a non-empty state, and therefore, a state that is correctly + // remapped. We are guaranteed to terminate because our compiler + // never builds a loop among only empty states. + let mut new_next = empty_next; + while let Some(next) = self.states[new_next].goto() { + new_next = next; + } + remap[empty_id] = remap[new_next]; + remapped[empty_id] = true; + + // Now that we've remapped the main 'empty_id' above, we re-follow + // the chain from above and remap every empty state we found along + // the way to our ultimate non-empty target. We are careful to set + // 'remapped' to true for each such state. We thus will not need + // to re-compute this chain for any subsequent empty states in + // 'empties' that are part of this chain. + let mut next2 = empty_next; + while let Some(next) = self.states[next2].goto() { + remap[next2] = remap[new_next]; + remapped[next2] = true; + next2 = next; + } + } + // Finally remap all of the state IDs. + nfa.remap(&remap); + let final_nfa = nfa.into_nfa(); + debug!( + "NFA compilation via builder complete, \ + final NFA size: {} states, {} bytes on heap, \ + has empty? {:?}, utf8? {:?}", + final_nfa.states().len(), + final_nfa.memory_usage(), + final_nfa.has_empty(), + final_nfa.is_utf8(), + ); + Ok(final_nfa) + } + + /// Start the assembly of a pattern in this NFA. + /// + /// Upon success, this returns the identifier for the new pattern. + /// Identifiers start at `0` and are incremented by 1 for each new pattern. + /// + /// It is necessary to call this routine before adding capturing states. + /// Otherwise, any other NFA state may be added before starting a pattern. + /// + /// # Errors + /// + /// If the pattern identifier space is exhausted, then this returns an + /// error. + /// + /// # Panics + /// + /// If this is called while assembling another pattern (i.e., before + /// `finish_pattern` is called), then this panics. + pub fn start_pattern(&mut self) -> Result<PatternID, BuildError> { + assert!(self.pattern_id.is_none(), "must call 'finish_pattern' first"); + + let proposed = self.start_pattern.len(); + let pid = PatternID::new(proposed) + .map_err(|_| BuildError::too_many_patterns(proposed))?; + self.pattern_id = Some(pid); + // This gets filled in when 'finish_pattern' is called. + self.start_pattern.push(StateID::ZERO); + Ok(pid) + } + + /// Finish the assembly of a pattern in this NFA. + /// + /// Upon success, this returns the identifier for the new pattern. + /// Identifiers start at `0` and are incremented by 1 for each new + /// pattern. This is the same identifier returned by the corresponding + /// `start_pattern` call. + /// + /// Note that `start_pattern` and `finish_pattern` pairs cannot be + /// interleaved or nested. A correct `finish_pattern` call _always_ + /// corresponds to the most recently called `start_pattern` routine. + /// + /// # Errors + /// + /// This currently never returns an error, but this is subject to change. + /// + /// # Panics + /// + /// If this is called without a corresponding `start_pattern` call, then + /// this panics. + pub fn finish_pattern( + &mut self, + start_id: StateID, + ) -> Result<PatternID, BuildError> { + let pid = self.current_pattern_id(); + self.start_pattern[pid] = start_id; + self.pattern_id = None; + Ok(pid) + } + + /// Returns the pattern identifier of the current pattern. + /// + /// # Panics + /// + /// If this doesn't occur after a `start_pattern` call and before the + /// corresponding `finish_pattern` call, then this panics. + pub fn current_pattern_id(&self) -> PatternID { + self.pattern_id.expect("must call 'start_pattern' first") + } + + /// Returns the number of patterns added to this builder so far. + /// + /// This only includes patterns that have had `finish_pattern` called + /// for them. + pub fn pattern_len(&self) -> usize { + self.start_pattern.len() + } + + /// Add an "empty" NFA state. + /// + /// An "empty" NFA state is a state with a single unconditional epsilon + /// transition to another NFA state. Such empty states are removed before + /// building the final [`NFA`] (which has no such "empty" states), but they + /// can be quite useful in the construction process of an NFA. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + pub fn add_empty(&mut self) -> Result<StateID, BuildError> { + self.add(State::Empty { next: StateID::ZERO }) + } + + /// Add a "union" NFA state. + /// + /// A "union" NFA state that contains zero or more unconditional epsilon + /// transitions to other NFA states. The order of these transitions + /// reflects a priority order where earlier transitions are preferred over + /// later transitions. + /// + /// Callers may provide an empty set of alternates to this method call, and + /// then later add transitions via `patch`. At final build time, a "union" + /// state with no alternates is converted to a "fail" state, and a "union" + /// state with exactly one alternate is treated as if it were an "empty" + /// state. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + pub fn add_union( + &mut self, + alternates: Vec<StateID>, + ) -> Result<StateID, BuildError> { + self.add(State::Union { alternates }) + } + + /// Add a "reverse union" NFA state. + /// + /// A "reverse union" NFA state contains zero or more unconditional epsilon + /// transitions to other NFA states. The order of these transitions + /// reflects a priority order where later transitions are preferred + /// over earlier transitions. This is an inverted priority order when + /// compared to `add_union`. This is useful, for example, for implementing + /// non-greedy repetition operators. + /// + /// Callers may provide an empty set of alternates to this method call, and + /// then later add transitions via `patch`. At final build time, a "reverse + /// union" state with no alternates is converted to a "fail" state, and a + /// "reverse union" state with exactly one alternate is treated as if it + /// were an "empty" state. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + pub fn add_union_reverse( + &mut self, + alternates: Vec<StateID>, + ) -> Result<StateID, BuildError> { + self.add(State::UnionReverse { alternates }) + } + + /// Add a "range" NFA state. + /// + /// A "range" NFA state is a state with one outgoing transition to another + /// state, where that transition may only be followed if the current input + /// byte falls between a range of bytes given. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + pub fn add_range( + &mut self, + trans: Transition, + ) -> Result<StateID, BuildError> { + self.add(State::ByteRange { trans }) + } + + /// Add a "sparse" NFA state. + /// + /// A "sparse" NFA state contains zero or more outgoing transitions, where + /// the transition to be followed (if any) is chosen based on whether the + /// current input byte falls in the range of one such transition. The + /// transitions given *must* be non-overlapping and in ascending order. (A + /// "sparse" state with no transitions is equivalent to a "fail" state.) + /// + /// A "sparse" state is like adding a "union" state and pointing it at a + /// bunch of "range" states, except that the different alternates have + /// equal priority. + /// + /// Note that a "sparse" state is the only state that cannot be patched. + /// This is because a "sparse" state has many transitions, each of which + /// may point to a different NFA state. Moreover, adding more such + /// transitions requires more than just an NFA state ID to point to. It + /// also requires a byte range. The `patch` routine does not support the + /// additional information required. Therefore, callers must ensure that + /// all outgoing transitions for this state are included when `add_sparse` + /// is called. There is no way to add more later. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + /// + /// # Panics + /// + /// This routine _may_ panic if the transitions given overlap or are not + /// in ascending order. + pub fn add_sparse( + &mut self, + transitions: Vec<Transition>, + ) -> Result<StateID, BuildError> { + self.add(State::Sparse { transitions }) + } + + /// Add a "look" NFA state. + /// + /// A "look" NFA state corresponds to a state with exactly one + /// *conditional* epsilon transition to another NFA state. Namely, it + /// represents one of a small set of simplistic look-around operators. + /// + /// Callers may provide a "dummy" state ID (typically [`StateID::ZERO`]), + /// and then change it later with [`patch`](Builder::patch). + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + pub fn add_look( + &mut self, + next: StateID, + look: Look, + ) -> Result<StateID, BuildError> { + self.add(State::Look { look, next }) + } + + /// Add a "start capture" NFA state. + /// + /// A "start capture" NFA state corresponds to a state with exactly one + /// outgoing unconditional epsilon transition to another state. Unlike + /// "empty" states, a "start capture" state also carries with it an + /// instruction for saving the current position of input to a particular + /// location in memory. NFA simulations, like the Pike VM, may use this + /// information to report the match locations of capturing groups in a + /// regex pattern. + /// + /// If the corresponding capturing group has a name, then callers should + /// include it here. + /// + /// Callers may provide a "dummy" state ID (typically [`StateID::ZERO`]), + /// and then change it later with [`patch`](Builder::patch). + /// + /// Note that unlike `start_pattern`/`finish_pattern`, capturing start and + /// end states may be interleaved. Indeed, it is typical for many "start + /// capture" NFA states to appear before the first "end capture" state. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded or if the given + /// capture index overflows `usize`. + /// + /// While the above are the only conditions in which this routine can + /// currently return an error, it is possible to call this method with an + /// inputs that results in the final `build()` step failing to produce an + /// NFA. For example, if one adds two distinct capturing groups with the + /// same name, then that will result in `build()` failing with an error. + /// + /// See the [`GroupInfo`](crate::util::captures::GroupInfo) type for + /// more information on what qualifies as valid capturing groups. + /// + /// # Example + /// + /// This example shows that an error occurs when one tries to add multiple + /// capturing groups with the same name to the same pattern. + /// + /// ``` + /// use regex_automata::{ + /// nfa::thompson::Builder, + /// util::primitives::StateID, + /// }; + /// + /// let name = Some(std::sync::Arc::from("foo")); + /// let mut builder = Builder::new(); + /// builder.start_pattern()?; + /// // 0th capture group should always be unnamed. + /// let start = builder.add_capture_start(StateID::ZERO, 0, None)?; + /// // OK + /// builder.add_capture_start(StateID::ZERO, 1, name.clone())?; + /// // This is not OK, but 'add_capture_start' still succeeds. We don't + /// // get an error until we call 'build' below. Without this call, the + /// // call to 'build' below would succeed. + /// builder.add_capture_start(StateID::ZERO, 2, name.clone())?; + /// // Finish our pattern so we can try to build the NFA. + /// builder.finish_pattern(start)?; + /// let result = builder.build(start, start); + /// assert!(result.is_err()); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + /// + /// However, adding multiple capturing groups with the same name to + /// distinct patterns is okay: + /// + /// ``` + /// use std::sync::Arc; + /// + /// use regex_automata::{ + /// nfa::thompson::{pikevm::PikeVM, Builder, Transition}, + /// util::{ + /// captures::Captures, + /// primitives::{PatternID, StateID}, + /// }, + /// Span, + /// }; + /// + /// // Hand-compile the patterns '(?P<foo>[a-z])' and '(?P<foo>[A-Z])'. + /// let mut builder = Builder::new(); + /// // We compile them to support an unanchored search, which requires + /// // adding an implicit '(?s-u:.)*?' prefix before adding either pattern. + /// let unanchored_prefix = builder.add_union_reverse(vec![])?; + /// let any = builder.add_range(Transition { + /// start: b'\x00', end: b'\xFF', next: StateID::ZERO, + /// })?; + /// builder.patch(unanchored_prefix, any)?; + /// builder.patch(any, unanchored_prefix)?; + /// + /// // Compile an alternation that permits matching multiple patterns. + /// let alt = builder.add_union(vec![])?; + /// builder.patch(unanchored_prefix, alt)?; + /// + /// // Compile '(?P<foo>[a-z]+)'. + /// builder.start_pattern()?; + /// let start0 = builder.add_capture_start(StateID::ZERO, 0, None)?; + /// // N.B. 0th capture group must always be unnamed. + /// let foo_start0 = builder.add_capture_start( + /// StateID::ZERO, 1, Some(Arc::from("foo")), + /// )?; + /// let lowercase = builder.add_range(Transition { + /// start: b'a', end: b'z', next: StateID::ZERO, + /// })?; + /// let foo_end0 = builder.add_capture_end(StateID::ZERO, 1)?; + /// let end0 = builder.add_capture_end(StateID::ZERO, 0)?; + /// let match0 = builder.add_match()?; + /// builder.patch(start0, foo_start0)?; + /// builder.patch(foo_start0, lowercase)?; + /// builder.patch(lowercase, foo_end0)?; + /// builder.patch(foo_end0, end0)?; + /// builder.patch(end0, match0)?; + /// builder.finish_pattern(start0)?; + /// + /// // Compile '(?P<foo>[A-Z]+)'. + /// builder.start_pattern()?; + /// let start1 = builder.add_capture_start(StateID::ZERO, 0, None)?; + /// // N.B. 0th capture group must always be unnamed. + /// let foo_start1 = builder.add_capture_start( + /// StateID::ZERO, 1, Some(Arc::from("foo")), + /// )?; + /// let uppercase = builder.add_range(Transition { + /// start: b'A', end: b'Z', next: StateID::ZERO, + /// })?; + /// let foo_end1 = builder.add_capture_end(StateID::ZERO, 1)?; + /// let end1 = builder.add_capture_end(StateID::ZERO, 0)?; + /// let match1 = builder.add_match()?; + /// builder.patch(start1, foo_start1)?; + /// builder.patch(foo_start1, uppercase)?; + /// builder.patch(uppercase, foo_end1)?; + /// builder.patch(foo_end1, end1)?; + /// builder.patch(end1, match1)?; + /// builder.finish_pattern(start1)?; + /// + /// // Now add the patterns to our alternation that we started above. + /// builder.patch(alt, start0)?; + /// builder.patch(alt, start1)?; + /// + /// // Finally build the NFA. The first argument is the anchored starting + /// // state (the pattern alternation) where as the second is the + /// // unanchored starting state (the unanchored prefix). + /// let nfa = builder.build(alt, unanchored_prefix)?; + /// + /// // Now build a Pike VM from our NFA and access the 'foo' capture + /// // group regardless of which pattern matched, since it is defined + /// // for both patterns. + /// let vm = PikeVM::new_from_nfa(nfa)?; + /// let mut cache = vm.create_cache(); + /// let caps: Vec<Captures> = + /// vm.captures_iter(&mut cache, "0123aAaAA").collect(); + /// assert_eq!(5, caps.len()); + /// + /// assert_eq!(Some(PatternID::must(0)), caps[0].pattern()); + /// assert_eq!(Some(Span::from(4..5)), caps[0].get_group_by_name("foo")); + /// + /// assert_eq!(Some(PatternID::must(1)), caps[1].pattern()); + /// assert_eq!(Some(Span::from(5..6)), caps[1].get_group_by_name("foo")); + /// + /// assert_eq!(Some(PatternID::must(0)), caps[2].pattern()); + /// assert_eq!(Some(Span::from(6..7)), caps[2].get_group_by_name("foo")); + /// + /// assert_eq!(Some(PatternID::must(1)), caps[3].pattern()); + /// assert_eq!(Some(Span::from(7..8)), caps[3].get_group_by_name("foo")); + /// + /// assert_eq!(Some(PatternID::must(1)), caps[4].pattern()); + /// assert_eq!(Some(Span::from(8..9)), caps[4].get_group_by_name("foo")); + /// + /// # Ok::<(), Box<dyn std::error::Error>>(()) + /// ``` + pub fn add_capture_start( + &mut self, + next: StateID, + group_index: u32, + name: Option<Arc<str>>, + ) -> Result<StateID, BuildError> { + let pid = self.current_pattern_id(); + let group_index = match SmallIndex::try_from(group_index) { + Err(_) => { + return Err(BuildError::invalid_capture_index(group_index)) + } + Ok(group_index) => group_index, + }; + // Make sure we have space to insert our (pid,index)|-->name mapping. + if pid.as_usize() >= self.captures.len() { + for _ in 0..=(pid.as_usize() - self.captures.len()) { + self.captures.push(vec![]); + } + } + // In the case where 'group_index < self.captures[pid].len()', it means + // that we are adding a duplicate capture group. This is somewhat + // weird, but permissible because the capture group itself can be + // repeated in the syntax. For example, '([a-z]){4}' will produce 4 + // capture groups. In practice, only the last will be set at search + // time when a match occurs. For duplicates, we don't need to push + // anything other than a CaptureStart NFA state. + if group_index.as_usize() >= self.captures[pid].len() { + // For discontiguous indices, push placeholders for earlier capture + // groups that weren't explicitly added. + for _ in 0..(group_index.as_usize() - self.captures[pid].len()) { + self.captures[pid].push(None); + } + self.captures[pid].push(name); + } + self.add(State::CaptureStart { pattern_id: pid, group_index, next }) + } + + /// Add a "end capture" NFA state. + /// + /// A "end capture" NFA state corresponds to a state with exactly one + /// outgoing unconditional epsilon transition to another state. Unlike + /// "empty" states, a "end capture" state also carries with it an + /// instruction for saving the current position of input to a particular + /// location in memory. NFA simulations, like the Pike VM, may use this + /// information to report the match locations of capturing groups in a + /// + /// Callers may provide a "dummy" state ID (typically [`StateID::ZERO`]), + /// and then change it later with [`patch`](Builder::patch). + /// + /// Note that unlike `start_pattern`/`finish_pattern`, capturing start and + /// end states may be interleaved. Indeed, it is typical for many "start + /// capture" NFA states to appear before the first "end capture" state. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded or if the given + /// capture index overflows `usize`. + /// + /// While the above are the only conditions in which this routine can + /// currently return an error, it is possible to call this method with an + /// inputs that results in the final `build()` step failing to produce an + /// NFA. For example, if one adds two distinct capturing groups with the + /// same name, then that will result in `build()` failing with an error. + /// + /// See the [`GroupInfo`](crate::util::captures::GroupInfo) type for + /// more information on what qualifies as valid capturing groups. + pub fn add_capture_end( + &mut self, + next: StateID, + group_index: u32, + ) -> Result<StateID, BuildError> { + let pid = self.current_pattern_id(); + let group_index = match SmallIndex::try_from(group_index) { + Err(_) => { + return Err(BuildError::invalid_capture_index(group_index)) + } + Ok(group_index) => group_index, + }; + self.add(State::CaptureEnd { pattern_id: pid, group_index, next }) + } + + /// Adds a "fail" NFA state. + /// + /// A "fail" state is simply a state that has no outgoing transitions. It + /// acts as a way to cause a search to stop without reporting a match. + /// For example, one way to represent an NFA with zero patterns is with a + /// single "fail" state. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + pub fn add_fail(&mut self) -> Result<StateID, BuildError> { + self.add(State::Fail) + } + + /// Adds a "match" NFA state. + /// + /// A "match" state has no outgoing transitions (just like a "fail" + /// state), but it has special significance in that if a search enters + /// this state, then a match has been found. The match state that is added + /// automatically has the current pattern ID associated with it. This is + /// used to report the matching pattern ID at search time. + /// + /// # Errors + /// + /// This returns an error if the state identifier space is exhausted, or if + /// the configured heap size limit has been exceeded. + /// + /// # Panics + /// + /// This must be called after a `start_pattern` call but before the + /// corresponding `finish_pattern` call. Otherwise, it panics. + pub fn add_match(&mut self) -> Result<StateID, BuildError> { + let pattern_id = self.current_pattern_id(); + let sid = self.add(State::Match { pattern_id })?; + Ok(sid) + } + + /// The common implementation of "add a state." It handles the common + /// error cases of state ID exhausting (by owning state ID allocation) and + /// whether the size limit has been exceeded. + fn add(&mut self, state: State) -> Result<StateID, BuildError> { + let id = StateID::new(self.states.len()) + .map_err(|_| BuildError::too_many_states(self.states.len()))?; + self.memory_states += state.memory_usage(); + self.states.push(state); + self.check_size_limit()?; + Ok(id) + } + + /// Add a transition from one state to another. + /// + /// This routine is called "patch" since it is very common to add the + /// states you want, typically with "dummy" state ID transitions, and then + /// "patch" in the real state IDs later. This is because you don't always + /// know all of the necessary state IDs to add because they might not + /// exist yet. + /// + /// # Errors + /// + /// This may error if patching leads to an increase in heap usage beyond + /// the configured size limit. Heap usage only grows when patching adds a + /// new transition (as in the case of a "union" state). + /// + /// # Panics + /// + /// This panics if `from` corresponds to a "sparse" state. When "sparse" + /// states are added, there is no way to patch them after-the-fact. (If you + /// have a use case where this would be helpful, please file an issue. It + /// will likely require a new API.) + pub fn patch( + &mut self, + from: StateID, + to: StateID, + ) -> Result<(), BuildError> { + let old_memory_states = self.memory_states; + match self.states[from] { + State::Empty { ref mut next } => { + *next = to; + } + State::ByteRange { ref mut trans } => { + trans.next = to; + } + State::Sparse { .. } => { + panic!("cannot patch from a sparse NFA state") + } + State::Look { ref mut next, .. } => { + *next = to; + } + State::Union { ref mut alternates } => { + alternates.push(to); + self.memory_states += mem::size_of::<StateID>(); + } + State::UnionReverse { ref mut alternates } => { + alternates.push(to); + self.memory_states += mem::size_of::<StateID>(); + } + State::CaptureStart { ref mut next, .. } => { + *next = to; + } + State::CaptureEnd { ref mut next, .. } => { + *next = to; + } + State::Fail => {} + State::Match { .. } => {} + } + if old_memory_states != self.memory_states { + self.check_size_limit()?; + } + Ok(()) + } + + /// Set whether the NFA produced by this builder should only match UTF-8. + /// + /// This should be set when both of the following are true: + /// + /// 1. The caller guarantees that the NFA created by this build will only + /// report non-empty matches with spans that are valid UTF-8. + /// 2. The caller desires regex engines using this NFA to avoid reporting + /// empty matches with a span that splits a valid UTF-8 encoded codepoint. + /// + /// Property (1) is not checked. Instead, this requires the caller to + /// promise that it is true. Property (2) corresponds to the behavior of + /// regex engines using the NFA created by this builder. Namely, there + /// is no way in the NFA's graph itself to say that empty matches found + /// by, for example, the regex `a*` will fall on valid UTF-8 boundaries. + /// Instead, this option is used to communicate the UTF-8 semantic to regex + /// engines that will typically implement it as a post-processing step by + /// filtering out empty matches that don't fall on UTF-8 boundaries. + /// + /// If you're building an NFA from an HIR (and not using a + /// [`thompson::Compiler`](crate::nfa::thompson::Compiler)), then you can + /// use the [`syntax::Config::utf8`](crate::util::syntax::Config::utf8) + /// option to guarantee that if the HIR detects a non-empty match, then it + /// is guaranteed to be valid UTF-8. + /// + /// Note that property (2) does *not* specify the behavior of executing + /// a search on a haystack that is not valid UTF-8. Therefore, if you're + /// *not* running this NFA on strings that are guaranteed to be valid + /// UTF-8, you almost certainly do not want to enable this option. + /// Similarly, if you are running the NFA on strings that *are* guaranteed + /// to be valid UTF-8, then you almost certainly want to enable this option + /// unless you can guarantee that your NFA will never produce a zero-width + /// match. + /// + /// It is disabled by default. + pub fn set_utf8(&mut self, yes: bool) { + self.utf8 = yes; + } + + /// Returns whether UTF-8 mode is enabled for this builder. + /// + /// See [`Builder::set_utf8`] for more details about what "UTF-8 mode" is. + pub fn get_utf8(&self) -> bool { + self.utf8 + } + + /// Sets whether the NFA produced by this builder should be matched in + /// reverse or not. Generally speaking, when enabled, the NFA produced + /// should be matched by moving backwards through a haystack, from a higher + /// memory address to a lower memory address. + /// + /// See also [`NFA::is_reverse`] for more details. + /// + /// This is disabled by default, which means NFAs are by default matched + /// in the forward direction. + pub fn set_reverse(&mut self, yes: bool) { + self.reverse = yes; + } + + /// Returns whether reverse mode is enabled for this builder. + /// + /// See [`Builder::set_reverse`] for more details about what "reverse mode" + /// is. + pub fn get_reverse(&self) -> bool { + self.reverse + } + + /// Sets the look-around matcher that should be used for the resulting NFA. + /// + /// A look-around matcher can be used to configure how look-around + /// assertions are matched. For example, a matcher might carry + /// configuration that changes the line terminator used for `(?m:^)` and + /// `(?m:$)` assertions. + pub fn set_look_matcher(&mut self, m: LookMatcher) { + self.look_matcher = m; + } + + /// Returns the look-around matcher used for this builder. + /// + /// If a matcher was not explicitly set, then `LookMatcher::default()` is + /// returned. + pub fn get_look_matcher(&self) -> &LookMatcher { + &self.look_matcher + } + + /// Set the size limit on this builder. + /// + /// Setting the size limit will also check whether the NFA built so far + /// fits within the given size limit. If it doesn't, then an error is + /// returned. + /// + /// By default, there is no configured size limit. + pub fn set_size_limit( + &mut self, + limit: Option<usize>, + ) -> Result<(), BuildError> { + self.size_limit = limit; + self.check_size_limit() + } + + /// Return the currently configured size limit. + /// + /// By default, this returns `None`, which corresponds to no configured + /// size limit. + pub fn get_size_limit(&self) -> Option<usize> { + self.size_limit + } + + /// Returns the heap memory usage, in bytes, used by the NFA states added + /// so far. + /// + /// Note that this is an approximation of how big the final NFA will be. + /// In practice, the final NFA will likely be a bit smaller because of + /// its simpler state representation. (For example, using things like + /// `Box<[StateID]>` instead of `Vec<StateID>`.) + pub fn memory_usage(&self) -> usize { + self.states.len() * mem::size_of::<State>() + self.memory_states + } + + fn check_size_limit(&self) -> Result<(), BuildError> { + if let Some(limit) = self.size_limit { + if self.memory_usage() > limit { + return Err(BuildError::exceeded_size_limit(limit)); + } + } + Ok(()) + } +} + +#[cfg(test)] +mod tests { + use super::*; + + // This asserts that a builder state doesn't have its size changed. It is + // *really* easy to accidentally increase the size, and thus potentially + // dramatically increase the memory usage of NFA builder. + // + // This assert doesn't mean we absolutely cannot increase the size of a + // builder state. We can. It's just here to make sure we do it knowingly + // and intentionally. + // + // A builder state is unfortunately a little bigger than an NFA state, + // since we really want to support adding things to a pre-existing state. + // i.e., We use Vec<thing> instead of Box<[thing]>. So we end up using an + // extra 8 bytes per state. Sad, but at least it gets freed once the NFA + // is built. + #[test] + fn state_has_small_size() { + #[cfg(target_pointer_width = "64")] + assert_eq!(32, core::mem::size_of::<State>()); + #[cfg(target_pointer_width = "32")] + assert_eq!(16, core::mem::size_of::<State>()); + } +} |