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 }, /// 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 }, /// 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 }, /// 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 { 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::() } State::Union { ref alternates } => { alternates.len() * mem::size_of::() } State::UnionReverse { ref alternates } => { alternates.len() * mem::size_of::() } } } } /// 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>(()) /// ``` #[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, /// 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, /// 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, /// 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>>>, /// 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::() * 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, } 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 { 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 { 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 { 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 { 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, ) -> Result { 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, ) -> Result { 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 { 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, ) -> Result { 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 { 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>(()) /// ``` /// /// 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[a-z])' and '(?P[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[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[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 = /// 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>(()) /// ``` pub fn add_capture_start( &mut self, next: StateID, group_index: u32, name: Option>, ) -> Result { 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 { 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 { 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 { 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 { 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::(); } State::UnionReverse { ref mut alternates } => { alternates.push(to); self.memory_states += mem::size_of::(); } 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, ) -> 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 { 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`.) pub fn memory_usage(&self) -> usize { self.states.len() * mem::size_of::() + 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 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::()); #[cfg(target_pointer_width = "32")] assert_eq!(16, core::mem::size_of::()); } }