Fix expression quantification in NFA compilation

Expression quantification is now implemented with a quantification
"guard" state. This decides whether or not to (re)parse the expression
and/or continue to the next expresssion.

src/fsm/nfa/model.rs

@@ -52,6 +52,13 @@ impl Nfa {
  NfaBuilder::new(start_state_final)
  }
 
+ pub(super) fn get_state(&self, id: StateId) -> &State {
+ self.states
+ .iter()
+ .find(|s| s.id == id)
+ .expect("requested state does not exist")
+ }
+
  fn get_final_states(&self) -> impl Iterator<Item = &State> + '_ {
  self.states.iter().filter(|s| s.fin)
  }
@@ -309,6 +316,22 @@ impl Compiler {
  self.nfa.build()
  }
 
+ fn insert_quantifier_state(
+ &mut self,
+ quantifier: QuantifierKind,
+ start_state: StateId,
+ end_state: StateId,
+ ) -> StateId {
+ let quantifier_state = self
+ .nfa
+ .add_state_with_quantifier(false, (quantifier, end_state));
+
+ self.nfa
+ .add_transition(start_state, quantifier_state, Input::Eps);
+
+ quantifier_state
+ }
+
  #[allow(clippy::only_used_in_recursion)]
  fn expr(&mut self, expr: &ExprKind, start: StateId, end: StateId) {
  match expr {
@@ -346,15 +369,13 @@ impl Compiler {
  //
  // Quantification can be implemented using an extra gateway state and a
 
- let start = match quantifier {
+ let (start, end) = match quantifier {
  Some(quantifier) => {
- let new_start = self
- .nfa
- .add_state_with_quantifier(false, (*quantifier, end));
- self.nfa.add_transition(start, new_start, Input::Eps);
- new_start
+ let quantifier_state =
+ self.insert_quantifier_state(*quantifier, start, end);
+ (quantifier_state, quantifier_state)
  }
- None => start,
+ None => (start, end),
  };
 
  self.nfa
@@ -367,16 +388,13 @@ impl Compiler {
  // wrapper and redo the expression when the quantification is still or not yet
  // valid.
 
- let start = match quantifier {
+ let (start, end) = match quantifier {
  Some(quantifier) => {
- let new_start = self
- .nfa
- .add_state_with_quantifier(false, (*quantifier, end));
- // Transition from the expression start state to the quantifier state
- self.nfa.add_transition(start, new_start, Input::Eps);
- new_start
+ let quantifier_state =
+ self.insert_quantifier_state(*quantifier, start, end);
+ (quantifier_state, quantifier_state)
  }
- None => start,
+ None => (start, end),
  };
 
  self.expr(expr, start, end);

src/fsm/nfa/sim.rs

@@ -67,13 +67,7 @@ impl Simulateable for NfaSimulator<'_> {
  .iter()
  .filter_map(|(expected, states)| {
  if expected.can_take(input) {
- Some(states.iter().map(|state_id| {
- self.nfa
- .states
- .iter()
- .find(|state| state.id == *state_id)
- .expect("state should always exist, otherwise the NFA is invalid")
- }))
+ Some(states.iter().map(|state_id| self.nfa.get_state(*state_id)))
  } else {
  None
  }