Initial import of regex-automata-0.1.9.
Bug: 155309706
Change-Id: I20031167cbe49d12754936285a0781eb7a3b8bfd
diff --git a/src/nfa/compiler.rs b/src/nfa/compiler.rs
new file mode 100644
index 0000000..d9b3945
--- /dev/null
+++ b/src/nfa/compiler.rs
@@ -0,0 +1,1193 @@
+// This module provides an NFA compiler using Thompson's construction
+// algorithm. The compiler takes a regex-syntax::Hir as input and emits an NFA
+// graph as output. The NFA graph is structured in a way that permits it to be
+// executed by a virtual machine and also used to efficiently build a DFA.
+//
+// The compiler deals with a slightly expanded set of NFA states that notably
+// includes an empty node that has exactly one epsilon transition to the next
+// state. In other words, it's a "goto" instruction if one views Thompson's NFA
+// as a set of bytecode instructions. These goto instructions are removed in
+// a subsequent phase before returning the NFA to the caller. The purpose of
+// these empty nodes is that they make the construction algorithm substantially
+// simpler to implement. We remove them before returning to the caller because
+// they can represent substantial overhead when traversing the NFA graph
+// (either while searching using the NFA directly or while building a DFA).
+//
+// In the future, it would be nice to provide a Glushkov compiler as well,
+// as it would work well as a bit-parallel NFA for smaller regexes. But
+// the Thompson construction is one I'm more familiar with and seems more
+// straight-forward to deal with when it comes to large Unicode character
+// classes.
+//
+// Internally, the compiler uses interior mutability to improve composition
+// in the face of the borrow checker. In particular, we'd really like to be
+// able to write things like this:
+//
+// self.c_concat(exprs.iter().map(|e| self.c(e)))
+//
+// Which elegantly uses iterators to build up a sequence of compiled regex
+// sub-expressions and then hands it off to the concatenating compiler
+// routine. Without interior mutability, the borrow checker won't let us
+// borrow `self` mutably both inside and outside the closure at the same
+// time.
+
+use std::cell::RefCell;
+use std::mem;
+
+use regex_syntax::hir::{self, Hir, HirKind};
+use regex_syntax::utf8::{Utf8Range, Utf8Sequences};
+
+use classes::ByteClassSet;
+use error::{Error, Result};
+use nfa::map::{Utf8BoundedMap, Utf8SuffixKey, Utf8SuffixMap};
+use nfa::range_trie::RangeTrie;
+use nfa::{State, StateID, Transition, NFA};
+
+/// Config knobs for the NFA compiler. See the builder's methods for more
+/// docs on each one.
+#[derive(Clone, Copy, Debug)]
+struct Config {
+ anchored: bool,
+ allow_invalid_utf8: bool,
+ reverse: bool,
+ shrink: bool,
+}
+
+impl Default for Config {
+ fn default() -> Config {
+ Config {
+ anchored: false,
+ allow_invalid_utf8: false,
+ reverse: false,
+ shrink: true,
+ }
+ }
+}
+
+/// A builder for compiling an NFA.
+#[derive(Clone, Debug)]
+pub struct Builder {
+ config: Config,
+}
+
+impl Builder {
+ /// Create a new NFA builder with its default configuration.
+ pub fn new() -> Builder {
+ Builder { config: Config::default() }
+ }
+
+ /// Compile the given high level intermediate representation of a regular
+ /// expression into an NFA.
+ ///
+ /// If there was a problem building the NFA, then an error is returned.
+ /// For example, if the regex uses unsupported features (such as zero-width
+ /// assertions), then an error is returned.
+ pub fn build(&self, expr: &Hir) -> Result<NFA> {
+ let mut nfa = NFA::always_match();
+ self.build_with(&mut Compiler::new(), &mut nfa, expr)?;
+ Ok(nfa)
+ }
+
+ /// Compile the given high level intermediate representation of a regular
+ /// expression into the NFA given using the given compiler. Callers may
+ /// prefer this over `build` if they would like to reuse allocations while
+ /// compiling many regular expressions.
+ ///
+ /// On success, the given NFA is completely overwritten with the NFA
+ /// produced by the compiler.
+ ///
+ /// If there was a problem building the NFA, then an error is returned. For
+ /// example, if the regex uses unsupported features (such as zero-width
+ /// assertions), then an error is returned. When an error is returned,
+ /// the contents of `nfa` are unspecified and should not be relied upon.
+ /// However, it can still be reused in subsequent calls to this method.
+ pub fn build_with(
+ &self,
+ compiler: &mut Compiler,
+ nfa: &mut NFA,
+ expr: &Hir,
+ ) -> Result<()> {
+ compiler.clear();
+ compiler.configure(self.config);
+ compiler.compile(nfa, expr)
+ }
+
+ /// Set whether matching must be anchored at the beginning of the input.
+ ///
+ /// When enabled, a match must begin at the start of the input. When
+ /// disabled, the NFA will act as if the pattern started with a `.*?`,
+ /// which enables a match to appear anywhere.
+ ///
+ /// By default this is disabled.
+ pub fn anchored(&mut self, yes: bool) -> &mut Builder {
+ self.config.anchored = yes;
+ self
+ }
+
+ /// When enabled, the builder will permit the construction of an NFA that
+ /// may match invalid UTF-8.
+ ///
+ /// When disabled (the default), the builder is guaranteed to produce a
+ /// regex that will only ever match valid UTF-8 (otherwise, the builder
+ /// will return an error).
+ pub fn allow_invalid_utf8(&mut self, yes: bool) -> &mut Builder {
+ self.config.allow_invalid_utf8 = yes;
+ self
+ }
+
+ /// Reverse the NFA.
+ ///
+ /// A NFA reversal is performed by reversing all of the concatenated
+ /// sub-expressions in the original pattern, recursively. The resulting
+ /// NFA can be used to match the pattern starting from the end of a string
+ /// instead of the beginning of a string.
+ ///
+ /// Reversing the NFA is useful for building a reverse DFA, which is most
+ /// useful for finding the start of a match.
+ pub fn reverse(&mut self, yes: bool) -> &mut Builder {
+ self.config.reverse = yes;
+ self
+ }
+
+ /// Apply best effort heuristics to shrink the NFA at the expense of more
+ /// time/memory.
+ ///
+ /// This is enabled by default. Generally speaking, if one is using an NFA
+ /// to compile DFA, then the extra time used to shrink the NFA will be
+ /// more than made up for during DFA construction (potentially by a lot).
+ /// In other words, enabling this can substantially decrease the overall
+ /// amount of time it takes to build a DFA.
+ ///
+ /// The only reason to disable this if you want to compile an NFA and start
+ /// using it as quickly as possible without needing to build a DFA.
+ pub fn shrink(&mut self, yes: bool) -> &mut Builder {
+ self.config.shrink = yes;
+ self
+ }
+}
+
+/// A compiler that converts a regex abstract syntax to an NFA via Thompson's
+/// construction. Namely, this compiler permits epsilon transitions between
+/// states.
+///
+/// Users of this crate cannot use a compiler directly. Instead, all one can
+/// do is create one and use it via the
+/// [`Builder::build_with`](struct.Builder.html#method.build_with)
+/// method. This permits callers to reuse compilers in order to amortize
+/// allocations.
+#[derive(Clone, Debug)]
+pub struct Compiler {
+ /// The set of compiled NFA states. Once a state is compiled, it is
+ /// assigned a state ID equivalent to its index in this list. Subsequent
+ /// compilation can modify previous states by adding new transitions.
+ states: RefCell<Vec<CState>>,
+ /// The configuration from the builder.
+ config: Config,
+ /// State used for compiling character classes to UTF-8 byte automata.
+ /// State is not retained between character class compilations. This just
+ /// serves to amortize allocation to the extent possible.
+ utf8_state: RefCell<Utf8State>,
+ /// State used for arranging character classes in reverse into a trie.
+ trie_state: RefCell<RangeTrie>,
+ /// State used for caching common suffixes when compiling reverse UTF-8
+ /// automata (for Unicode character classes).
+ utf8_suffix: RefCell<Utf8SuffixMap>,
+ /// A map used to re-map state IDs when translating the compiler's internal
+ /// NFA state representation to the external NFA representation.
+ remap: RefCell<Vec<StateID>>,
+ /// 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.
+ empties: RefCell<Vec<(StateID, StateID)>>,
+}
+
+/// A compiler intermediate state representation for an NFA that is only used
+/// during compilation. Once compilation is done, `CState`s are converted to
+/// `State`s, which have a much simpler representation.
+#[derive(Clone, Debug, Eq, PartialEq)]
+enum CState {
+ /// An empty state whose only purpose is to forward the automaton to
+ /// another state via en epsilon transition. These are useful during
+ /// compilation but are otherwise removed at the end.
+ Empty { next: StateID },
+ /// A state that only transitions to `next` if the current input byte is
+ /// in the range `[start, end]` (inclusive on both ends).
+ Range { range: Transition },
+ /// A state with possibly many transitions, represented in a sparse
+ /// fashion. Transitions are ordered lexicographically by input range.
+ /// 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.)
+ Sparse { ranges: Vec<Transition> },
+ /// 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.
+ UnionReverse { alternates: Vec<StateID> },
+ /// A match state. There is exactly one such occurrence of this state in
+ /// an NFA.
+ Match,
+}
+
+/// A value that represents the result of compiling a sub-expression of a
+/// regex's HIR. Specifically, this represents a sub-graph of the NFA that
+/// has an initial state at `start` and a final state at `end`.
+#[derive(Clone, Copy, Debug)]
+pub struct ThompsonRef {
+ start: StateID,
+ end: StateID,
+}
+
+impl Compiler {
+ /// Create a new compiler.
+ pub fn new() -> Compiler {
+ Compiler {
+ states: RefCell::new(vec![]),
+ config: Config::default(),
+ utf8_state: RefCell::new(Utf8State::new()),
+ trie_state: RefCell::new(RangeTrie::new()),
+ utf8_suffix: RefCell::new(Utf8SuffixMap::new(1000)),
+ remap: RefCell::new(vec![]),
+ empties: RefCell::new(vec![]),
+ }
+ }
+
+ /// Clear any memory used by this compiler such that it is ready to compile
+ /// a new regex.
+ ///
+ /// It is preferrable to reuse a compiler if possible in order to reuse
+ /// allocations.
+ fn clear(&self) {
+ self.states.borrow_mut().clear();
+ // We don't need to clear anything else since they are cleared on
+ // their own and only when they are used.
+ }
+
+ /// Configure this compiler from the builder's knobs.
+ ///
+ /// The compiler is always reconfigured by the builder before using it to
+ /// build an NFA.
+ fn configure(&mut self, config: Config) {
+ self.config = config;
+ }
+
+ /// Convert the current intermediate NFA to its final compiled form.
+ fn compile(&self, nfa: &mut NFA, expr: &Hir) -> Result<()> {
+ nfa.anchored = self.config.anchored;
+
+ let mut start = self.add_empty();
+ if !nfa.anchored {
+ let compiled = if self.config.allow_invalid_utf8 {
+ self.c_unanchored_prefix_invalid_utf8()?
+ } else {
+ self.c_unanchored_prefix_valid_utf8()?
+ };
+ self.patch(start, compiled.start);
+ start = compiled.end;
+ }
+ let compiled = self.c(&expr)?;
+ let match_id = self.add_match();
+ self.patch(start, compiled.start);
+ self.patch(compiled.end, match_id);
+ self.finish(nfa);
+ Ok(())
+ }
+
+ /// Finishes the compilation process and populates the provide NFA with
+ /// the final graph.
+ fn finish(&self, nfa: &mut NFA) {
+ let mut bstates = self.states.borrow_mut();
+ let mut remap = self.remap.borrow_mut();
+ remap.resize(bstates.len(), 0);
+ let mut empties = self.empties.borrow_mut();
+ empties.clear();
+
+ // We don't reuse allocations here becuase this is what we're
+ // returning.
+ nfa.states.clear();
+ let mut byteset = ByteClassSet::new();
+
+ // 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 (id, bstate) in bstates.iter_mut().enumerate() {
+ match *bstate {
+ CState::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((id, next));
+ }
+ CState::Range { ref range } => {
+ remap[id] = nfa.states.len();
+ byteset.set_range(range.start, range.end);
+ nfa.states.push(State::Range { range: range.clone() });
+ }
+ CState::Sparse { ref mut ranges } => {
+ remap[id] = nfa.states.len();
+
+ let ranges = mem::replace(ranges, vec![]);
+ for r in &ranges {
+ byteset.set_range(r.start, r.end);
+ }
+ nfa.states.push(State::Sparse {
+ ranges: ranges.into_boxed_slice(),
+ });
+ }
+ CState::Union { ref mut alternates } => {
+ remap[id] = nfa.states.len();
+
+ let alternates = mem::replace(alternates, vec![]);
+ nfa.states.push(State::Union {
+ alternates: alternates.into_boxed_slice(),
+ });
+ }
+ CState::UnionReverse { ref mut alternates } => {
+ remap[id] = nfa.states.len();
+
+ let mut alternates = mem::replace(alternates, vec![]);
+ alternates.reverse();
+ nfa.states.push(State::Union {
+ alternates: alternates.into_boxed_slice(),
+ });
+ }
+ CState::Match => {
+ remap[id] = nfa.states.len();
+ nfa.states.push(State::Match);
+ }
+ }
+ }
+ for &(empty_id, mut empty_next) in empties.iter() {
+ // 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 empty states.
+ while let CState::Empty { next } = bstates[empty_next] {
+ empty_next = next;
+ }
+ remap[empty_id] = remap[empty_next];
+ }
+ for state in &mut nfa.states {
+ state.remap(&remap);
+ }
+ // The compiler always begins the NFA at the first state.
+ nfa.start = remap[0];
+ nfa.byte_classes = byteset.byte_classes();
+ }
+
+ fn c(&self, expr: &Hir) -> Result<ThompsonRef> {
+ match *expr.kind() {
+ HirKind::Empty => {
+ let id = self.add_empty();
+ Ok(ThompsonRef { start: id, end: id })
+ }
+ HirKind::Literal(hir::Literal::Unicode(ch)) => {
+ let mut buf = [0; 4];
+ let it = ch
+ .encode_utf8(&mut buf)
+ .as_bytes()
+ .iter()
+ .map(|&b| Ok(self.c_range(b, b)));
+ self.c_concat(it)
+ }
+ HirKind::Literal(hir::Literal::Byte(b)) => Ok(self.c_range(b, b)),
+ HirKind::Class(hir::Class::Bytes(ref cls)) => {
+ self.c_byte_class(cls)
+ }
+ HirKind::Class(hir::Class::Unicode(ref cls)) => {
+ self.c_unicode_class(cls)
+ }
+ HirKind::Repetition(ref rep) => self.c_repetition(rep),
+ HirKind::Group(ref group) => self.c(&*group.hir),
+ HirKind::Concat(ref exprs) => {
+ self.c_concat(exprs.iter().map(|e| self.c(e)))
+ }
+ HirKind::Alternation(ref exprs) => {
+ self.c_alternation(exprs.iter().map(|e| self.c(e)))
+ }
+ HirKind::Anchor(_) => Err(Error::unsupported_anchor()),
+ HirKind::WordBoundary(_) => Err(Error::unsupported_word()),
+ }
+ }
+
+ fn c_concat<I>(&self, mut it: I) -> Result<ThompsonRef>
+ where
+ I: DoubleEndedIterator<Item = Result<ThompsonRef>>,
+ {
+ let first =
+ if self.config.reverse { it.next_back() } else { it.next() };
+ let ThompsonRef { start, mut end } = match first {
+ Some(result) => result?,
+ None => return Ok(self.c_empty()),
+ };
+ loop {
+ let next =
+ if self.config.reverse { it.next_back() } else { it.next() };
+ let compiled = match next {
+ Some(result) => result?,
+ None => break,
+ };
+ self.patch(end, compiled.start);
+ end = compiled.end;
+ }
+ Ok(ThompsonRef { start, end })
+ }
+
+ fn c_alternation<I>(&self, mut it: I) -> Result<ThompsonRef>
+ where
+ I: Iterator<Item = Result<ThompsonRef>>,
+ {
+ let first = it.next().expect("alternations must be non-empty")?;
+ let second = match it.next() {
+ None => return Ok(first),
+ Some(result) => result?,
+ };
+
+ let union = self.add_union();
+ let end = self.add_empty();
+ self.patch(union, first.start);
+ self.patch(first.end, end);
+ self.patch(union, second.start);
+ self.patch(second.end, end);
+ for result in it {
+ let compiled = result?;
+ self.patch(union, compiled.start);
+ self.patch(compiled.end, end);
+ }
+ Ok(ThompsonRef { start: union, end })
+ }
+
+ fn c_repetition(&self, rep: &hir::Repetition) -> Result<ThompsonRef> {
+ match rep.kind {
+ hir::RepetitionKind::ZeroOrOne => {
+ self.c_zero_or_one(&rep.hir, rep.greedy)
+ }
+ hir::RepetitionKind::ZeroOrMore => {
+ self.c_at_least(&rep.hir, rep.greedy, 0)
+ }
+ hir::RepetitionKind::OneOrMore => {
+ self.c_at_least(&rep.hir, rep.greedy, 1)
+ }
+ hir::RepetitionKind::Range(ref rng) => match *rng {
+ hir::RepetitionRange::Exactly(count) => {
+ self.c_exactly(&rep.hir, count)
+ }
+ hir::RepetitionRange::AtLeast(m) => {
+ self.c_at_least(&rep.hir, rep.greedy, m)
+ }
+ hir::RepetitionRange::Bounded(min, max) => {
+ self.c_bounded(&rep.hir, rep.greedy, min, max)
+ }
+ },
+ }
+ }
+
+ fn c_bounded(
+ &self,
+ expr: &Hir,
+ greedy: bool,
+ min: u32,
+ max: u32,
+ ) -> Result<ThompsonRef> {
+ let prefix = self.c_exactly(expr, min)?;
+ if min == max {
+ return Ok(prefix);
+ }
+
+ // It is tempting here to compile the rest here as a concatenation
+ // of zero-or-one matches. i.e., for `a{2,5}`, compile it as if it
+ // were `aaa?a?a?`. The problem here is that it leads to this program:
+ //
+ // >000000: 61 => 01
+ // 000001: 61 => 02
+ // 000002: alt(03, 04)
+ // 000003: 61 => 04
+ // 000004: alt(05, 06)
+ // 000005: 61 => 06
+ // 000006: alt(07, 08)
+ // 000007: 61 => 08
+ // 000008: MATCH
+ //
+ // And effectively, once you hit state 2, the epsilon closure will
+ // include states 3, 5, 5, 6, 7 and 8, which is quite a bit. It is
+ // better to instead compile it like so:
+ //
+ // >000000: 61 => 01
+ // 000001: 61 => 02
+ // 000002: alt(03, 08)
+ // 000003: 61 => 04
+ // 000004: alt(05, 08)
+ // 000005: 61 => 06
+ // 000006: alt(07, 08)
+ // 000007: 61 => 08
+ // 000008: MATCH
+ //
+ // So that the epsilon closure of state 2 is now just 3 and 8.
+ let empty = self.add_empty();
+ let mut prev_end = prefix.end;
+ for _ in min..max {
+ let union = if greedy {
+ self.add_union()
+ } else {
+ self.add_reverse_union()
+ };
+ let compiled = self.c(expr)?;
+ self.patch(prev_end, union);
+ self.patch(union, compiled.start);
+ self.patch(union, empty);
+ prev_end = compiled.end;
+ }
+ self.patch(prev_end, empty);
+ Ok(ThompsonRef { start: prefix.start, end: empty })
+ }
+
+ fn c_at_least(
+ &self,
+ expr: &Hir,
+ greedy: bool,
+ n: u32,
+ ) -> Result<ThompsonRef> {
+ if n == 0 {
+ let union = if greedy {
+ self.add_union()
+ } else {
+ self.add_reverse_union()
+ };
+ let compiled = self.c(expr)?;
+ self.patch(union, compiled.start);
+ self.patch(compiled.end, union);
+ Ok(ThompsonRef { start: union, end: union })
+ } else if n == 1 {
+ let compiled = self.c(expr)?;
+ let union = if greedy {
+ self.add_union()
+ } else {
+ self.add_reverse_union()
+ };
+ self.patch(compiled.end, union);
+ self.patch(union, compiled.start);
+ Ok(ThompsonRef { start: compiled.start, end: union })
+ } else {
+ let prefix = self.c_exactly(expr, n - 1)?;
+ let last = self.c(expr)?;
+ let union = if greedy {
+ self.add_union()
+ } else {
+ self.add_reverse_union()
+ };
+ self.patch(prefix.end, last.start);
+ self.patch(last.end, union);
+ self.patch(union, last.start);
+ Ok(ThompsonRef { start: prefix.start, end: union })
+ }
+ }
+
+ fn c_zero_or_one(&self, expr: &Hir, greedy: bool) -> Result<ThompsonRef> {
+ let union =
+ if greedy { self.add_union() } else { self.add_reverse_union() };
+ let compiled = self.c(expr)?;
+ let empty = self.add_empty();
+ self.patch(union, compiled.start);
+ self.patch(union, empty);
+ self.patch(compiled.end, empty);
+ Ok(ThompsonRef { start: union, end: empty })
+ }
+
+ fn c_exactly(&self, expr: &Hir, n: u32) -> Result<ThompsonRef> {
+ let it = (0..n).map(|_| self.c(expr));
+ self.c_concat(it)
+ }
+
+ fn c_byte_class(&self, cls: &hir::ClassBytes) -> Result<ThompsonRef> {
+ let end = self.add_empty();
+ let mut trans = Vec::with_capacity(cls.ranges().len());
+ for r in cls.iter() {
+ trans.push(Transition {
+ start: r.start(),
+ end: r.end(),
+ next: end,
+ });
+ }
+ Ok(ThompsonRef { start: self.add_sparse(trans), end })
+ }
+
+ fn c_unicode_class(&self, cls: &hir::ClassUnicode) -> Result<ThompsonRef> {
+ // If all we have are ASCII ranges wrapped in a Unicode package, then
+ // there is zero reason to bring out the big guns. We can fit all ASCII
+ // ranges within a single sparse transition.
+ if cls.is_all_ascii() {
+ let end = self.add_empty();
+ let mut trans = Vec::with_capacity(cls.ranges().len());
+ for r in cls.iter() {
+ assert!(r.start() <= '\x7F');
+ assert!(r.end() <= '\x7F');
+ trans.push(Transition {
+ start: r.start() as u8,
+ end: r.end() as u8,
+ next: end,
+ });
+ }
+ Ok(ThompsonRef { start: self.add_sparse(trans), end })
+ } else if self.config.reverse {
+ if !self.config.shrink {
+ // When we don't want to spend the extra time shrinking, we
+ // compile the UTF-8 automaton in reverse using something like
+ // the "naive" approach, but will attempt to re-use common
+ // suffixes.
+ self.c_unicode_class_reverse_with_suffix(cls)
+ } else {
+ // When we want to shrink our NFA for reverse UTF-8 automata,
+ // we cannot feed UTF-8 sequences directly to the UTF-8
+ // compiler, since the UTF-8 compiler requires all sequences
+ // to be lexicographically sorted. Instead, we organize our
+ // sequences into a range trie, which can then output our
+ // sequences in the correct order. Unfortunately, building the
+ // range trie is fairly expensive (but not nearly as expensive
+ // as building a DFA). Hence the reason why the 'shrink' option
+ // exists, so that this path can be toggled off.
+ let mut trie = self.trie_state.borrow_mut();
+ trie.clear();
+
+ for rng in cls.iter() {
+ for mut seq in Utf8Sequences::new(rng.start(), rng.end()) {
+ seq.reverse();
+ trie.insert(seq.as_slice());
+ }
+ }
+ let mut utf8_state = self.utf8_state.borrow_mut();
+ let mut utf8c = Utf8Compiler::new(self, &mut *utf8_state);
+ trie.iter(|seq| {
+ utf8c.add(&seq);
+ });
+ Ok(utf8c.finish())
+ }
+ } else {
+ // In the forward direction, we always shrink our UTF-8 automata
+ // because we can stream it right into the UTF-8 compiler. There
+ // is almost no downside (in either memory or time) to using this
+ // approach.
+ let mut utf8_state = self.utf8_state.borrow_mut();
+ let mut utf8c = Utf8Compiler::new(self, &mut *utf8_state);
+ for rng in cls.iter() {
+ for seq in Utf8Sequences::new(rng.start(), rng.end()) {
+ utf8c.add(seq.as_slice());
+ }
+ }
+ Ok(utf8c.finish())
+ }
+
+ // For reference, the code below is the "naive" version of compiling a
+ // UTF-8 automaton. It is deliciously simple (and works for both the
+ // forward and reverse cases), but will unfortunately produce very
+ // large NFAs. When compiling a forward automaton, the size difference
+ // can sometimes be an order of magnitude. For example, the '\w' regex
+ // will generate about ~3000 NFA states using the naive approach below,
+ // but only 283 states when using the approach above. This is because
+ // the approach above actually compiles a *minimal* (or near minimal,
+ // because of the bounded hashmap) UTF-8 automaton.
+ //
+ // The code below is kept as a reference point in order to make it
+ // easier to understand the higher level goal here.
+ /*
+ let it = cls
+ .iter()
+ .flat_map(|rng| Utf8Sequences::new(rng.start(), rng.end()))
+ .map(|seq| {
+ let it = seq
+ .as_slice()
+ .iter()
+ .map(|rng| Ok(self.c_range(rng.start, rng.end)));
+ self.c_concat(it)
+ });
+ self.c_alternation(it);
+ */
+ }
+
+ fn c_unicode_class_reverse_with_suffix(
+ &self,
+ cls: &hir::ClassUnicode,
+ ) -> Result<ThompsonRef> {
+ // N.B. It would likely be better to cache common *prefixes* in the
+ // reverse direction, but it's not quite clear how to do that. The
+ // advantage of caching suffixes is that it does give us a win, and
+ // has a very small additional overhead.
+ let mut cache = self.utf8_suffix.borrow_mut();
+ cache.clear();
+
+ let union = self.add_union();
+ let alt_end = self.add_empty();
+ for urng in cls.iter() {
+ for seq in Utf8Sequences::new(urng.start(), urng.end()) {
+ let mut end = alt_end;
+ for brng in seq.as_slice() {
+ let key = Utf8SuffixKey {
+ from: end,
+ start: brng.start,
+ end: brng.end,
+ };
+ let hash = cache.hash(&key);
+ if let Some(id) = cache.get(&key, hash) {
+ end = id;
+ continue;
+ }
+
+ let compiled = self.c_range(brng.start, brng.end);
+ self.patch(compiled.end, end);
+ end = compiled.start;
+ cache.set(key, hash, end);
+ }
+ self.patch(union, end);
+ }
+ }
+ Ok(ThompsonRef { start: union, end: alt_end })
+ }
+
+ fn c_range(&self, start: u8, end: u8) -> ThompsonRef {
+ let id = self.add_range(start, end);
+ ThompsonRef { start: id, end: id }
+ }
+
+ fn c_empty(&self) -> ThompsonRef {
+ let id = self.add_empty();
+ ThompsonRef { start: id, end: id }
+ }
+
+ fn c_unanchored_prefix_valid_utf8(&self) -> Result<ThompsonRef> {
+ self.c(&Hir::repetition(hir::Repetition {
+ kind: hir::RepetitionKind::ZeroOrMore,
+ greedy: false,
+ hir: Box::new(Hir::any(false)),
+ }))
+ }
+
+ fn c_unanchored_prefix_invalid_utf8(&self) -> Result<ThompsonRef> {
+ self.c(&Hir::repetition(hir::Repetition {
+ kind: hir::RepetitionKind::ZeroOrMore,
+ greedy: false,
+ hir: Box::new(Hir::any(true)),
+ }))
+ }
+
+ fn patch(&self, from: StateID, to: StateID) {
+ match self.states.borrow_mut()[from] {
+ CState::Empty { ref mut next } => {
+ *next = to;
+ }
+ CState::Range { ref mut range } => {
+ range.next = to;
+ }
+ CState::Sparse { .. } => {
+ panic!("cannot patch from a sparse NFA state")
+ }
+ CState::Union { ref mut alternates } => {
+ alternates.push(to);
+ }
+ CState::UnionReverse { ref mut alternates } => {
+ alternates.push(to);
+ }
+ CState::Match => {}
+ }
+ }
+
+ fn add_empty(&self) -> StateID {
+ let id = self.states.borrow().len();
+ self.states.borrow_mut().push(CState::Empty { next: 0 });
+ id
+ }
+
+ fn add_range(&self, start: u8, end: u8) -> StateID {
+ let id = self.states.borrow().len();
+ let trans = Transition { start, end, next: 0 };
+ let state = CState::Range { range: trans };
+ self.states.borrow_mut().push(state);
+ id
+ }
+
+ fn add_sparse(&self, ranges: Vec<Transition>) -> StateID {
+ if ranges.len() == 1 {
+ let id = self.states.borrow().len();
+ let state = CState::Range { range: ranges[0] };
+ self.states.borrow_mut().push(state);
+ return id;
+ }
+ let id = self.states.borrow().len();
+ let state = CState::Sparse { ranges };
+ self.states.borrow_mut().push(state);
+ id
+ }
+
+ fn add_union(&self) -> StateID {
+ let id = self.states.borrow().len();
+ let state = CState::Union { alternates: vec![] };
+ self.states.borrow_mut().push(state);
+ id
+ }
+
+ fn add_reverse_union(&self) -> StateID {
+ let id = self.states.borrow().len();
+ let state = CState::UnionReverse { alternates: vec![] };
+ self.states.borrow_mut().push(state);
+ id
+ }
+
+ fn add_match(&self) -> StateID {
+ let id = self.states.borrow().len();
+ self.states.borrow_mut().push(CState::Match);
+ id
+ }
+}
+
+#[derive(Debug)]
+struct Utf8Compiler<'a> {
+ nfac: &'a Compiler,
+ state: &'a mut Utf8State,
+ target: StateID,
+}
+
+#[derive(Clone, Debug)]
+struct Utf8State {
+ compiled: Utf8BoundedMap,
+ uncompiled: Vec<Utf8Node>,
+}
+
+#[derive(Clone, Debug)]
+struct Utf8Node {
+ trans: Vec<Transition>,
+ last: Option<Utf8LastTransition>,
+}
+
+#[derive(Clone, Debug)]
+struct Utf8LastTransition {
+ start: u8,
+ end: u8,
+}
+
+impl Utf8State {
+ fn new() -> Utf8State {
+ Utf8State { compiled: Utf8BoundedMap::new(5000), uncompiled: vec![] }
+ }
+
+ fn clear(&mut self) {
+ self.compiled.clear();
+ self.uncompiled.clear();
+ }
+}
+
+impl<'a> Utf8Compiler<'a> {
+ fn new(nfac: &'a Compiler, state: &'a mut Utf8State) -> Utf8Compiler<'a> {
+ let target = nfac.add_empty();
+ state.clear();
+ let mut utf8c = Utf8Compiler { nfac, state, target };
+ utf8c.add_empty();
+ utf8c
+ }
+
+ fn finish(&mut self) -> ThompsonRef {
+ self.compile_from(0);
+ let node = self.pop_root();
+ let start = self.compile(node);
+ ThompsonRef { start, end: self.target }
+ }
+
+ fn add(&mut self, ranges: &[Utf8Range]) {
+ let prefix_len = ranges
+ .iter()
+ .zip(&self.state.uncompiled)
+ .take_while(|&(range, node)| {
+ node.last.as_ref().map_or(false, |t| {
+ (t.start, t.end) == (range.start, range.end)
+ })
+ })
+ .count();
+ assert!(prefix_len < ranges.len());
+ self.compile_from(prefix_len);
+ self.add_suffix(&ranges[prefix_len..]);
+ }
+
+ fn compile_from(&mut self, from: usize) {
+ let mut next = self.target;
+ while from + 1 < self.state.uncompiled.len() {
+ let node = self.pop_freeze(next);
+ next = self.compile(node);
+ }
+ self.top_last_freeze(next);
+ }
+
+ fn compile(&mut self, node: Vec<Transition>) -> StateID {
+ let hash = self.state.compiled.hash(&node);
+ if let Some(id) = self.state.compiled.get(&node, hash) {
+ return id;
+ }
+ let id = self.nfac.add_sparse(node.clone());
+ self.state.compiled.set(node, hash, id);
+ id
+ }
+
+ fn add_suffix(&mut self, ranges: &[Utf8Range]) {
+ assert!(!ranges.is_empty());
+ let last = self
+ .state
+ .uncompiled
+ .len()
+ .checked_sub(1)
+ .expect("non-empty nodes");
+ assert!(self.state.uncompiled[last].last.is_none());
+ self.state.uncompiled[last].last = Some(Utf8LastTransition {
+ start: ranges[0].start,
+ end: ranges[0].end,
+ });
+ for r in &ranges[1..] {
+ self.state.uncompiled.push(Utf8Node {
+ trans: vec![],
+ last: Some(Utf8LastTransition { start: r.start, end: r.end }),
+ });
+ }
+ }
+
+ fn add_empty(&mut self) {
+ self.state.uncompiled.push(Utf8Node { trans: vec![], last: None });
+ }
+
+ fn pop_freeze(&mut self, next: StateID) -> Vec<Transition> {
+ let mut uncompiled = self.state.uncompiled.pop().unwrap();
+ uncompiled.set_last_transition(next);
+ uncompiled.trans
+ }
+
+ fn pop_root(&mut self) -> Vec<Transition> {
+ assert_eq!(self.state.uncompiled.len(), 1);
+ assert!(self.state.uncompiled[0].last.is_none());
+ self.state.uncompiled.pop().expect("non-empty nodes").trans
+ }
+
+ fn top_last_freeze(&mut self, next: StateID) {
+ let last = self
+ .state
+ .uncompiled
+ .len()
+ .checked_sub(1)
+ .expect("non-empty nodes");
+ self.state.uncompiled[last].set_last_transition(next);
+ }
+}
+
+impl Utf8Node {
+ fn set_last_transition(&mut self, next: StateID) {
+ if let Some(last) = self.last.take() {
+ self.trans.push(Transition {
+ start: last.start,
+ end: last.end,
+ next,
+ });
+ }
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use regex_syntax::hir::Hir;
+ use regex_syntax::ParserBuilder;
+
+ use super::{Builder, State, StateID, Transition, NFA};
+
+ fn parse(pattern: &str) -> Hir {
+ ParserBuilder::new().build().parse(pattern).unwrap()
+ }
+
+ fn build(pattern: &str) -> NFA {
+ Builder::new().anchored(true).build(&parse(pattern)).unwrap()
+ }
+
+ fn s_byte(byte: u8, next: StateID) -> State {
+ let trans = Transition { start: byte, end: byte, next };
+ State::Range { range: trans }
+ }
+
+ fn s_range(start: u8, end: u8, next: StateID) -> State {
+ let trans = Transition { start, end, next };
+ State::Range { range: trans }
+ }
+
+ fn s_sparse(ranges: &[(u8, u8, StateID)]) -> State {
+ let ranges = ranges
+ .iter()
+ .map(|&(start, end, next)| Transition { start, end, next })
+ .collect();
+ State::Sparse { ranges }
+ }
+
+ fn s_union(alts: &[StateID]) -> State {
+ State::Union { alternates: alts.to_vec().into_boxed_slice() }
+ }
+
+ fn s_match() -> State {
+ State::Match
+ }
+
+ #[test]
+ fn errors() {
+ // unsupported anchors
+ assert!(Builder::new().build(&parse(r"^")).is_err());
+ assert!(Builder::new().build(&parse(r"$")).is_err());
+ assert!(Builder::new().build(&parse(r"\A")).is_err());
+ assert!(Builder::new().build(&parse(r"\z")).is_err());
+
+ // unsupported word boundaries
+ assert!(Builder::new().build(&parse(r"\b")).is_err());
+ assert!(Builder::new().build(&parse(r"\B")).is_err());
+ assert!(Builder::new().build(&parse(r"(?-u)\b")).is_err());
+ }
+
+ // Test that building an unanchored NFA has an appropriate `.*?` prefix.
+ #[test]
+ fn compile_unanchored_prefix() {
+ // When the machine can only match valid UTF-8.
+ let nfa = Builder::new().anchored(false).build(&parse(r"a")).unwrap();
+ // There should be many states since the `.` in `.*?` matches any
+ // Unicode scalar value.
+ assert_eq!(11, nfa.len());
+ assert_eq!(nfa.states[10], s_match());
+ assert_eq!(nfa.states[9], s_byte(b'a', 10));
+
+ // When the machine can match invalid UTF-8.
+ let nfa = Builder::new()
+ .anchored(false)
+ .allow_invalid_utf8(true)
+ .build(&parse(r"a"))
+ .unwrap();
+ assert_eq!(
+ nfa.states,
+ &[
+ s_union(&[2, 1]),
+ s_range(0, 255, 0),
+ s_byte(b'a', 3),
+ s_match(),
+ ]
+ );
+ }
+
+ #[test]
+ fn compile_empty() {
+ assert_eq!(build("").states, &[s_match(),]);
+ }
+
+ #[test]
+ fn compile_literal() {
+ assert_eq!(build("a").states, &[s_byte(b'a', 1), s_match(),]);
+ assert_eq!(
+ build("ab").states,
+ &[s_byte(b'a', 1), s_byte(b'b', 2), s_match(),]
+ );
+ assert_eq!(
+ build("ā").states,
+ &[s_byte(0xE2, 1), s_byte(0x98, 2), s_byte(0x83, 3), s_match(),]
+ );
+
+ // Check that non-UTF-8 literals work.
+ let hir = ParserBuilder::new()
+ .allow_invalid_utf8(true)
+ .build()
+ .parse(r"(?-u)\xFF")
+ .unwrap();
+ let nfa = Builder::new()
+ .anchored(true)
+ .allow_invalid_utf8(true)
+ .build(&hir)
+ .unwrap();
+ assert_eq!(nfa.states, &[s_byte(b'\xFF', 1), s_match(),]);
+ }
+
+ #[test]
+ fn compile_class() {
+ assert_eq!(
+ build(r"[a-z]").states,
+ &[s_range(b'a', b'z', 1), s_match(),]
+ );
+ assert_eq!(
+ build(r"[x-za-c]").states,
+ &[s_sparse(&[(b'a', b'c', 1), (b'x', b'z', 1)]), s_match()]
+ );
+ assert_eq!(
+ build(r"[\u03B1-\u03B4]").states,
+ &[s_range(0xB1, 0xB4, 2), s_byte(0xCE, 0), s_match()]
+ );
+ assert_eq!(
+ build(r"[\u03B1-\u03B4\u{1F919}-\u{1F91E}]").states,
+ &[
+ s_range(0xB1, 0xB4, 5),
+ s_range(0x99, 0x9E, 5),
+ s_byte(0xA4, 1),
+ s_byte(0x9F, 2),
+ s_sparse(&[(0xCE, 0xCE, 0), (0xF0, 0xF0, 3)]),
+ s_match(),
+ ]
+ );
+ assert_eq!(
+ build(r"[a-zā]").states,
+ &[
+ s_byte(0x83, 3),
+ s_byte(0x98, 0),
+ s_sparse(&[(b'a', b'z', 3), (0xE2, 0xE2, 1)]),
+ s_match(),
+ ]
+ );
+ }
+
+ #[test]
+ fn compile_repetition() {
+ assert_eq!(
+ build(r"a?").states,
+ &[s_union(&[1, 2]), s_byte(b'a', 2), s_match(),]
+ );
+ assert_eq!(
+ build(r"a??").states,
+ &[s_union(&[2, 1]), s_byte(b'a', 2), s_match(),]
+ );
+ }
+
+ #[test]
+ fn compile_group() {
+ assert_eq!(
+ build(r"ab+").states,
+ &[s_byte(b'a', 1), s_byte(b'b', 2), s_union(&[1, 3]), s_match(),]
+ );
+ assert_eq!(
+ build(r"(ab)").states,
+ &[s_byte(b'a', 1), s_byte(b'b', 2), s_match(),]
+ );
+ assert_eq!(
+ build(r"(ab)+").states,
+ &[s_byte(b'a', 1), s_byte(b'b', 2), s_union(&[0, 3]), s_match(),]
+ );
+ }
+
+ #[test]
+ fn compile_alternation() {
+ assert_eq!(
+ build(r"a|b").states,
+ &[s_byte(b'a', 3), s_byte(b'b', 3), s_union(&[0, 1]), s_match(),]
+ );
+ assert_eq!(
+ build(r"|b").states,
+ &[s_byte(b'b', 2), s_union(&[2, 0]), s_match(),]
+ );
+ assert_eq!(
+ build(r"a|").states,
+ &[s_byte(b'a', 2), s_union(&[0, 2]), s_match(),]
+ );
+ }
+}