Added field to denote all characters which an 'allChars' node _shouldn't_ match (useful for invertinc character classes

nfa.go

@@ -23,7 +23,8 @@ type State struct {
 	isKleene       bool             // Identifies whether current node is a 0-state representing Kleene star
 	assert         assertType       // Type of assertion of current node - NONE means that the node doesn't assert anything
 	zeroMatchFound bool             // Whether or not the state has been used for a zero-length match - only relevant for zero states
-	isDot          bool             // Whether or not the state represents a 'dot' metacharacter. A 'dot' node doesn't store any contents directly, as it would take up too much space
+	allChars       bool             // Whether or not the state represents all characters (eg. a 'dot' metacharacter). A 'dot' node doesn't store any contents directly, as it would take up too much space
+	except         []rune           // Only valid if allChars is true - match all characters _except_ the ones in this block. Useful for inverting character classes.
 }
 
 // Clones the NFA starting from the given state.
@@ -50,6 +51,8 @@ func cloneStateHelper(state *State, cloneMap map[*State]*State) *State {
 		isKleene:       state.isKleene,
 		assert:         state.assert,
 		zeroMatchFound: state.zeroMatchFound,
+		allChars:       state.allChars,
+		except:         append([]rune{}, state.except...),
 	}
 	cloneMap[state] = clone
 	for i, s := range state.output {
@@ -95,8 +98,8 @@ func (s State) contentContains(str []rune, idx int) bool {
 	if s.assert != NONE {
 		return s.checkAssertion(str, idx)
 	}
-	if s.isDot {
-		return !slices.Contains(notDotChars, str[idx])
+	if s.allChars {
+		return !slices.Contains(slices.Concat(notDotChars, s.except), str[idx]) // Return true only if the index isn't a 'notDotChar', or isn't one of the exception characters for the current node.
 	}
 	// Default - s.assert must be NONE
 	return slices.Contains(s.content, int(str[idx]))
@@ -122,7 +125,12 @@ func (s State) matchesFor(str []rune, idx int) ([]*State, int) {
 	}
 	listTransitions := s.transitions[int(str[idx])]
 	for _, dest := range s.transitions[int(ANY_CHAR)] {
-		listTransitions = append(listTransitions, dest)
+		if !slices.Contains(slices.Concat(notDotChars, dest.except), str[idx]) {
+			// Add an allChar state to the list of matches if:
+			// 		a. The current character isn't a 'notDotChars' character. In single line mode, this includes newline. In multiline mode, it doesn't.
+			// 		b. The current character isn't the state's exception list.
+			listTransitions = append(listTransitions, dest)
+		}
 	}
 	numTransitions := len(listTransitions)
 	return listTransitions, numTransitions