Fixed bug in character class implementation

compile.go

@@ -123,9 +123,12 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 		} else if c == '\\' && i < len(re_runes_orig)-1 && re_runes_orig[i+1] == '\\' { // Escaped backslash
 			re_runes = append(re_runes, ESC_BACKSLASH)
 			i++
-		} else if c == '[' && (i == 0 || re_runes_orig[i-1] != '\\')
-
-
+		} else if c == '[' && (i == 0 || re_runes[len(re_runes)-1] != '\\') {
+			re_runes = append(re_runes, LBRACKET)
+			continue
+		} else if c == ']' && (i == 0 || re_runes[len(re_runes)-1] != '\\') {
+			re_runes = append(re_runes, RBRACKET)
+			continue
 		} else {
 			re_runes = append(re_runes, c)
 		}
@@ -145,31 +148,28 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 	i := 0
 	for i < len(re_runes) {
 		re_postfix = append(re_postfix, re_runes[i])
-		if re_runes[i] == '[' && (i == 0 || re_runes[i-1] != '\\') { // We do not touch things inside brackets, unless they are escaped. Inside this block, the only task is to expand character ranges into their constituent characters.
-			re_postfix[len(re_postfix)-1] = LBRACKET         // Replace the '[' character with LBRACKET. This allows for easier parsing of all characters (including opening and closing brackets) within the character class
-			toAppend := make([]rune, 0)                      // Holds all the runes in the current character class
-			if i < len(re_runes)-1 && re_runes[i+1] == '^' { // Inverting class - match everything NOT in brackets
-				re_postfix = append(re_postfix, '^')
-				i++ // Skip opening bracket and caret
-			}
-			if i < len(re_runes)-1 && re_runes[i+1] == ']' { // Nothing inside brackets - panic.
-				return nil, fmt.Errorf("Empty character class.")
-			}
-			for re_runes[i] != ']' || i == 0 || re_runes[i-1] == '\\' {
-				i++ // Skip all characters inside _unescaped_ brackets (we are _not_ at a closing bracket, or if we are, the previous character is a backslash)
+		if re_runes[i] == LBRACKET && (i == 0 || re_runes[i-1] != '\\') { // We do not touch things inside brackets, unless they are escaped.
+			toAppend := make([]rune, 0) // Holds all the runes in the current character class
+
+			i++                     // Skip past LBRACKET, because it was already added
+			if i >= len(re_runes) { // Sanity check before we start
+				return nil, fmt.Errorf("Opening bracket without closing bracket.")
+			}
+
+			for re_runes[i] != RBRACKET || i == 0 || re_runes[i-1] == '\\' { // Skip all characters inside _unescaped_ brackets (we are _not_ at a closing bracket, or if we are, the previous character is a backslash)
 				// Make sure we haven't exceeded the length of the string. If we did, then the regex doesn't actually have a closing bracket and we should throw an error.
 				if i >= len(re_runes) {
 					return nil, fmt.Errorf("Opening bracket without closing bracket.")
 				}
 
-				if re_runes[i] == '-' && (i > 0 && re_runes[i-1] != '\\') && (i < len(re_runes)-1 && re_runes[i+1] != ']') { // Unescaped hyphen, that has some character (not a RBRACKET) after it - This represents a character range, so we replace with CHAR_RANGE. This metacharacter will be used later on to construct the range
+				if re_runes[i] == '-' && (i > 0 && re_runes[i-1] != '\\') && (i < len(re_runes)-1 && re_runes[i+1] != RBRACKET) { // Unescaped hyphen, that has some character (not a RBRACKET) after it - This represents a character range, so we replace with CHAR_RANGE. This metacharacter will be used later on to construct the range
 					re_runes[i] = CHAR_RANGE
 				}
-
 				toAppend = append(toAppend, re_runes[i])
+				i++
 			}
-			// Replace the last character (which should have been ']', with RBRACKET
-			toAppend[len(toAppend)-1] = RBRACKET
+			// Add in the RBRACKET
+			toAppend = append(toAppend, RBRACKET)
 			re_postfix = append(re_postfix, toAppend...)
 		}
 		if i < len(re_runes) && re_runes[i] == '{' && (i > 0 && re_runes[i-1] != '\\') { // We don't touch things inside braces, either
@@ -284,6 +284,17 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			}
 			continue
 		}
+		// Since every unescaped bracket is replaced by a LBRACKET / RBRACKET, there may
+		// have been false positives. For example, the regex ']' has a closing bracket, but it
+		// isn't denoting a character class; it's just a regular character. Since it's not escaped,
+		// though, I would have converted this into an RBRACKET.
+		// To deal with this, I make the following assertion:
+		// 	If at any point I see an RBRACKET 'in the wild' (not in a character class), then it must be
+		// 	a regular character, with no special significance.
+		if c == RBRACKET {
+			outQueue = append(outQueue, newPostfixCharNode(']'))
+			continue
+		}
 
 		if c == '\\' { // Escape character - invert special and non-special characters eg. \( is treated as a literal parentheses, \b is treated as word boundary
 			if i == len(re_postfix)-1 { // End of string - panic, because backslash is an escape character (something needs to come after it)
@@ -419,6 +430,10 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			firstCharAdded := false // A character class must have at least 1 character. This flag checks if the first character has been added.
 			endOfRange := false     // Set to 'true' when we encounter a CHAR_RANGE metacharacter
 			i++                     // Step forward so we can look at the character class
+			//  Oops, there's nothing there to look at
+			if i >= len(re_postfix) {
+				return nil, fmt.Errorf("Opening bracket with no closing bracket.")
+			}
 			var invertMatch bool
 			if re_postfix[i] == '^' {
 				invertMatch = true