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egliegli
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Add recursive traversal of the nfa
so that we can handle offsets into the search string which is needed for lookbehind. The liblouis match pre-patterns are a form of lookbehind
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‎src/translator/nfa.rs‎

Lines changed: 208 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -34,11 +34,17 @@ enum Boundary {
3434
/// An transition between two [States](State) in the [NFA]
3535
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
3636
enum Transition {
37+
/// A transition that accepts a character
3738
Character(char),
39+
/// A transition that accepts any character
3840
Any,
3941
Start(Boundary),
4042
End(Boundary),
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/// An epsilon transition that accepts the empty string
4144
Epsilon,
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/// An Offset transition is essentially an epsilon transition that marks the end of a
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/// non-capturing group. It is used to mark the end of the pre pattern in match rules
47+
Offset,
4248
}
4349

4450
/// An NFA consisting of a set of states and transitions between them
@@ -273,6 +279,78 @@ impl NFA {
273279
.iter()
274280
.any(|s| self.states[*s].translation.is_some())
275281
}
282+
283+
fn find_translations_from_state(
284+
&self,
285+
state: StateId,
286+
input: &str,
287+
match_length: usize,
288+
offset: usize,
289+
) -> Vec<Translation> {
290+
dbg!(&state);
291+
let mut matching_rules = Vec::new();
292+
let mut next_states = self.epsilon_closure(&HashSet::from([state]));
293+
294+
// if any of the states in the epsilon closure (reachable via epsilon transition)
295+
// has a translation add it to the list of matching rules
296+
matching_rules.extend(
297+
next_states
298+
.iter()
299+
.flat_map(|state| &self.states[*state].translation)
300+
.map(|translation| {
301+
translation
302+
.clone()
303+
.with_offset(offset)
304+
// if there is an offset (typically in a match opcode), the weight needs
305+
// to be calculated at run-time. The weight is the actual length of match.
306+
.with_weight_if_offset(match_length, offset)
307+
}),
308+
);
309+
310+
// traverse all states that are reachable via an offset transition (essentially an
311+
// epsilon transition that marks the end of a non-capture group)
312+
let reachable_via_offset = self.move_state(&next_states, Transition::Offset);
313+
let next_states_with_offset = self.epsilon_closure(&reachable_via_offset);
314+
for state in next_states_with_offset {
315+
matching_rules.extend(self.find_translations_from_state(
316+
state,
317+
input,
318+
match_length + 1,
319+
offset + match_length,
320+
));
321+
}
322+
323+
match input.chars().next() {
324+
Some(c) => {
325+
let reachable_via_character =
326+
self.move_state(&next_states, Transition::Character(c));
327+
let reachable_via_any = self.move_state(&next_states, Transition::Any);
328+
next_states = reachable_via_character
329+
.union(&reachable_via_any)
330+
.cloned()
331+
.collect();
332+
next_states = self.epsilon_closure(&next_states);
333+
for state in next_states {
334+
let bytes = c.len_utf8();
335+
matching_rules.extend(self.find_translations_from_state(
336+
state,
337+
&input[bytes..],
338+
match_length + 1,
339+
offset,
340+
));
341+
}
342+
matching_rules
343+
}
344+
None => matching_rules,
345+
}
346+
}
347+
348+
pub fn find_translations(&self, input: &str) -> Vec<Translation> {
349+
let mut matching_rules = Vec::new();
350+
351+
matching_rules.extend(self.find_translations_from_state(self.start, input, 0, 0));
352+
matching_rules
353+
}
276354
}
277355

278356
/**
@@ -297,6 +375,9 @@ pub fn nfa_dot(nfa: &NFA) -> String {
297375
Transition::Any => {
298376
dot.push_str(&format!("\t{} -> {} [label=\"{}\"]\n", from, to, "Any"))
299377
}
378+
Transition::Offset => {
379+
dot.push_str(&format!("\t{} -> {} [label=\"{}\"]\n", from, to, "Offset"))
380+
}
300381
Transition::Start(boundary) => dot.push_str(&format!(
301382
"\t{} -> {} [label=\"{:?}\"]\n",
302383
from, to, boundary
@@ -329,6 +410,14 @@ mod tests {
329410
assert!(!nfa.accepts("b"));
330411
}
331412

413+
#[test]
414+
fn find_character() {
415+
let ast = AST::Character('a');
416+
let nfa = NFA::from(&ast);
417+
assert!(!nfa.find_translations("a").is_empty());
418+
assert!(nfa.find_translations("b").is_empty());
419+
}
420+
332421
#[test]
333422
fn alteration() {
334423
let ast = AST::Either(Box::new(AST::Character('a')), Box::new(AST::Character('b')));
@@ -339,6 +428,16 @@ mod tests {
339428
assert!(!nfa.accepts("c"));
340429
}
341430

431+
#[test]
432+
fn find_alteration() {
433+
let ast = AST::Either(Box::new(AST::Character('a')), Box::new(AST::Character('b')));
434+
let nfa = NFA::from(&ast);
435+
assert!(!nfa.find_translations("a").is_empty());
436+
assert!(!nfa.find_translations("b").is_empty());
437+
assert!(!nfa.find_translations("ab").is_empty());
438+
assert!(nfa.find_translations("c").is_empty());
439+
}
440+
342441
#[test]
343442
fn concatenation() {
344443
let ast = AST::Concat(Box::new(AST::Character('a')), Box::new(AST::Character('b')));
@@ -351,6 +450,18 @@ mod tests {
351450
assert!(!nfa.accepts("abc"));
352451
}
353452

453+
#[test]
454+
fn find_concatenation() {
455+
let ast = AST::Concat(Box::new(AST::Character('a')), Box::new(AST::Character('b')));
456+
let nfa = NFA::from(&ast);
457+
assert!(!nfa.find_translations("ab").is_empty());
458+
assert!(!nfa.find_translations("abc").is_empty());
459+
assert!(nfa.find_translations("a").is_empty());
460+
assert!(nfa.find_translations("b").is_empty());
461+
assert!(nfa.find_translations("ba").is_empty());
462+
assert!(nfa.find_translations("c").is_empty());
463+
}
464+
354465
#[test]
355466
fn kleene() {
356467
let ast = AST::ZeroOrMore(Box::new(AST::Character('a')));
@@ -366,6 +477,38 @@ mod tests {
366477
assert!(!nfa.accepts("abc"));
367478
}
368479

480+
#[test]
481+
fn find_kleene() {
482+
let ast = AST::ZeroOrMore(Box::new(AST::Character('a')));
483+
let nfa = dbg!(NFA::from(&ast));
484+
assert!(!nfa.find_translations("").is_empty());
485+
assert!(!nfa.find_translations("a").is_empty());
486+
assert!(!nfa.find_translations("aa").is_empty());
487+
assert!(!nfa.find_translations("aaaaa").is_empty());
488+
assert!(!nfa.find_translations("ab").is_empty());
489+
assert!(!nfa.find_translations("abc").is_empty());
490+
assert!(!nfa.find_translations("b").is_empty());
491+
assert!(!nfa.find_translations("ba").is_empty());
492+
assert!(!nfa.find_translations("c").is_empty());
493+
494+
let ast = AST::Concat(
495+
Box::new(AST::Character('a')),
496+
Box::new(AST::ZeroOrMore(Box::new(AST::Character('b')))),
497+
);
498+
let nfa = dbg!(NFA::from(&ast));
499+
assert!(!nfa.find_translations("a").is_empty());
500+
assert!(!nfa.find_translations("aa").is_empty());
501+
assert!(!nfa.find_translations("ab").is_empty());
502+
assert!(!nfa.find_translations("abbbb").is_empty());
503+
assert!(nfa.find_translations("").is_empty());
504+
assert!(nfa.find_translations("ccccc").is_empty());
505+
assert!(nfa.find_translations("cb").is_empty());
506+
assert!(nfa.find_translations("cba").is_empty());
507+
assert!(nfa.find_translations("b").is_empty());
508+
assert!(nfa.find_translations("ba").is_empty());
509+
assert!(nfa.find_translations("c").is_empty());
510+
}
511+
369512
#[test]
370513
fn one_or_more() {
371514
let ast = AST::OneOrMore(Box::new(AST::Character('a')));
@@ -381,6 +524,21 @@ mod tests {
381524
assert!(!nfa.accepts("abc"));
382525
}
383526

527+
#[test]
528+
fn find_one_or_more() {
529+
let ast = AST::OneOrMore(Box::new(AST::Character('a')));
530+
let nfa = NFA::from(&ast);
531+
assert!(nfa.find_translations("").is_empty());
532+
assert!(!nfa.find_translations("a").is_empty());
533+
assert!(!nfa.find_translations("aa").is_empty());
534+
assert!(!nfa.find_translations("aaaaa").is_empty());
535+
assert!(nfa.find_translations("b").is_empty());
536+
assert!(nfa.find_translations("ba").is_empty());
537+
assert!(!nfa.find_translations("ab").is_empty());
538+
assert!(nfa.find_translations("c").is_empty());
539+
assert!(!nfa.find_translations("abc").is_empty());
540+
}
541+
384542
#[test]
385543
fn any() {
386544
let ast = AST::Concat(
@@ -394,6 +552,19 @@ mod tests {
394552
assert!(nfa.accepts("abb"));
395553
}
396554

555+
#[test]
556+
fn find_any() {
557+
let ast = AST::Concat(
558+
Box::new(AST::Concat(
559+
Box::new(AST::Character('a')),
560+
Box::new(AST::Any),
561+
)),
562+
Box::new(AST::Character('b')),
563+
);
564+
let nfa = NFA::from(&ast);
565+
assert!(!nfa.find_translations("abb").is_empty());
566+
}
567+
397568
#[test]
398569
fn optional() {
399570
let ast = AST::Concat(
@@ -411,6 +582,24 @@ mod tests {
411582
assert!(!nfa.accepts("bbb"));
412583
}
413584

585+
#[test]
586+
fn find_optional() {
587+
let ast = AST::Concat(
588+
Box::new(AST::Optional(Box::new(AST::Concat(
589+
Box::new(AST::Character('a')),
590+
Box::new(AST::Any),
591+
)))),
592+
Box::new(AST::Character('b')),
593+
);
594+
let nfa = NFA::from(&ast);
595+
assert!(!nfa.find_translations("acb").is_empty());
596+
assert!(!nfa.find_translations("axb").is_empty());
597+
assert!(!nfa.find_translations("b").is_empty());
598+
assert!(!nfa.find_translations("bbb").is_empty());
599+
assert!(nfa.find_translations("c").is_empty());
600+
assert!(nfa.find_translations("").is_empty());
601+
}
602+
414603
#[test]
415604
fn string() {
416605
let ast = AST::Concat(
@@ -429,4 +618,23 @@ mod tests {
429618
assert!(!nfa.accepts("()"));
430619
assert!(!nfa.accepts("(helo)"));
431620
}
621+
622+
#[test]
623+
fn find_string() {
624+
let ast = AST::Concat(
625+
Box::new(AST::Concat(
626+
Box::new(AST::OneOrMore(Box::new(AST::Character('(')))),
627+
Box::new(AST::String("hello".to_string())),
628+
)),
629+
Box::new(AST::OneOrMore(Box::new(AST::Character(')')))),
630+
);
631+
let nfa = NFA::from(&ast);
632+
assert!(!nfa.find_translations("(hello)").is_empty());
633+
assert!(!nfa.find_translations("(((((hello)))").is_empty());
634+
assert!(nfa.find_translations("hello").is_empty());
635+
assert!(nfa.find_translations("(hello").is_empty());
636+
assert!(nfa.find_translations("hello)").is_empty());
637+
assert!(nfa.find_translations("()").is_empty());
638+
assert!(nfa.find_translations("(helo)").is_empty());
639+
}
432640
}

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