Added function to reset threads

regex/nfa.go

@@ -104,6 +104,26 @@ func cloneStateHelper(stateToClone *nfaState, cloneMap map[*nfaState]*nfaState)
 	return clone
 }
 
+// Reset any thread-related fields of the NFA starting from the given state.
+func resetThreads(start *nfaState) {
+	visitedMap := make(map[*nfaState]bool) // The value type doesn't matter here
+	resetThreadsHelper(start, visitedMap)
+}
+
+func resetThreadsHelper(state *nfaState, visitedMap map[*nfaState]bool) {
+	if _, ok := visitedMap[state]; ok {
+		return
+	}
+	// Assuming it hasn't been visited
+	state.threadGroups = nil
+	visitedMap[state] = true
+	for _, v := range state.transitions {
+		for _, nextState := range v {
+			resetThreadsHelper(nextState, visitedMap)
+		}
+	}
+}
+
 // Checks if the given state's assertion is true. Returns true if the given
 // state doesn't have an assertion.
 func (s nfaState) checkAssertion(str []rune, idx int) bool {
@@ -274,7 +294,7 @@ func concatenate(s1 *nfaState, s2 *nfaState) *nfaState {
 	}
 	for i := range s1.output {
 		for _, c := range s2.content { // Create transitions for every element in s1's content to s2'
-			s1.output[i].transitions[c], _ = unique_append(s1.output[i].transitions[c], s2)
+			s1.output[i].transitions[c], _ = uniqueAppend(s1.output[i].transitions[c], s2)
 		}
 	}
 	s1.output = s2.output
@@ -294,11 +314,11 @@ func kleene(s1 nfaState) (*nfaState, error) {
 	toReturn.output = append(toReturn.output, toReturn)
 	for i := range s1.output {
 		for _, c := range toReturn.content {
-			s1.output[i].transitions[c], _ = unique_append(s1.output[i].transitions[c], toReturn)
+			s1.output[i].transitions[c], _ = uniqueAppend(s1.output[i].transitions[c], toReturn)
 		}
 	}
 	for _, c := range s1.content {
-		toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], &s1)
+		toReturn.transitions[c], _ = uniqueAppend(toReturn.transitions[c], &s1)
 	}
 	return toReturn, nil
 }
@@ -314,10 +334,10 @@ func alternate(s1 *nfaState, s2 *nfaState) *nfaState {
 	// This would lead to multiple instances of the same set of match indices, since both
 	// 's1' states would be considered to match.
 	for _, c := range s1.content {
-		toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], s1)
+		toReturn.transitions[c], _ = uniqueAppend(toReturn.transitions[c], s1)
 	}
 	for _, c := range s2.content {
-		toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], s2)
+		toReturn.transitions[c], _ = uniqueAppend(toReturn.transitions[c], s2)
 	}
 	toReturn.content = newContents(epsilon)
 	toReturn.isEmpty = true