From cbd6ea136b02088b0c10eac723aa9a74707028ce Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Wed, 27 Nov 2024 11:46:38 -0500
Subject: [PATCH] If the NFA starts with an assertion, make sure it's true
 before doing anything else. Also, check for last-state _lookaround_ rather
 than just last state, before breaking (instead of aborting) when the
 assertion fails

---
 matching.go | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/matching.go b/matching.go
index cc47d50..62e7131 100644
--- a/matching.go
+++ b/matching.go
@@ -133,6 +133,14 @@ func findAllMatchesHelper(start *State, str []rune, offset int) (bool, MatchInde
 	i := offset                     // Index in string
 	startingFrom := i               // Store starting index
 
+	// If the first state is an assertion, makes sure the assertion
+	// is true before we do _anything_ else.
+	if start.assert != NONE {
+		if start.checkAssertion(str, offset) == false {
+			i++
+			return false, MatchIndex{}, i
+		}
+	}
 	// Increment until we hit a character matching the start state (assuming not 0-state)
 	if start.isEmpty == false {
 		for i < len(str) && !start.contentContains(str, i) {
@@ -171,10 +179,10 @@ func findAllMatchesHelper(start *State, str []rune, offset int) (bool, MatchInde
 		tempStates = nil
 
 		// Take any transitions corresponding to current character
-		numStatesMatched := 0    // The number of states which had at least 1 match for this round
-		assertionFailed := false // Whether or not an assertion failed for this round
-		lastStateInList := false // Whether or not a last state was in our list of states
-		//	lastStateLookaround := false // Whether or not a last state (that is also a lookaround) matched
+		numStatesMatched := 0         // The number of states which had at least 1 match for this round
+		assertionFailed := false      // Whether or not an assertion failed for this round
+		lastStateInList := false      // Whether or not a last state was in our list of states
+		lastLookaroundInList := false // Whether or not a last state (that is a lookaround) was in our list of states
 		for _, state := range currentStates {
 			matches, numMatches := state.matchesFor(str, i)
 			if numMatches > 0 {
@@ -186,17 +194,24 @@ func findAllMatchesHelper(start *State, str []rune, offset int) (bool, MatchInde
 				assertionFailed = true
 			}
 			if state.isLast {
+				if state.isLookaround() {
+					lastLookaroundInList = true
+				}
 				lastStateInList = true
 			}
 		}
 
 		if assertionFailed && numStatesMatched == 0 { // Nothing has matched and an assertion has failed
-			// One of the states in our list was a last state. In this case, we
-			// don't abort upon the failure of an assertion, because we have found
+			// If I'm being completely honest, I'm not sure why I have to check specifically for a _lookaround_
+			// state. The explanation below is my attempt to explain this behavior.
+			// If you replace 'lastLookaroundInList' with 'lastStateInList', one of the test cases fails.
+			//
+			// One of the states in our list was a last state and a lookaround. In this case, we
+			// don't abort upon failure of the assertion, because we have found
 			// another path to a final state.
 			// Even if the last state _was_ an assertion, we can use the previously
 			// saved indices to find a match.
-			if lastStateInList {
+			if lastLookaroundInList {
 				break
 			} else {
 				if i == startingFrom {