Added support for POSIX character classes

compile.go

@@ -42,6 +42,38 @@ func priority(op rune) int {
 	return slices.Index(precedence, op)
 }
 
+// Returns the POSIX character class represented by the given string.
+// The given string must be of the form:
+//
+//	'blah1:]blah2'
+//
+// In order to be a _syntactically_ valid POSIX class.
+// Whether or not such a class actually exists is not relevant to this function, it just
+// parses and returns 'blah1'.
+// For example, if the regex was something like '[[:digit:]]', the caller must parse through the opening
+// brackets and the colon, and call this function with the remainder.
+//
+// If the given string represents a syntactically valid POSIX class, the second parameter is true.
+// Otherwise, it's false.
+func getPOSIXClass(str []rune) (bool, string) {
+	i := 0
+	rtv := ""
+	for i < len(str) && (str[i] != ':' && str[i] != RBRACKET) {
+		rtv += string(str[i])
+		i++
+	}
+	if i >= (len(str) - 1) { // We need to be atleast 1 character short, because the closing bracket must follow
+		return false, ""
+	}
+	if str[i] != ':' { // The POSIX class must end with a colon and a closing bracket. It cannot end with a closing bracket first.
+		return false, ""
+	}
+	if str[i+1] != RBRACKET {
+		return false, ""
+	}
+	return true, rtv
+}
+
 /*
 The Shunting-Yard algorithm is used to convert the given infix (regeular) expression to postfix.
 The primary benefit of this is getting rid of parentheses.
@@ -162,6 +194,21 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 					return nil, fmt.Errorf("Opening bracket without closing bracket.")
 				}
 
+				if re_runes[i] == LBRACKET && re_runes[i+1] == ':' { // POSIX character class
+					toAppend = append(toAppend, re_runes[i])
+					i++
+					toAppend = append(toAppend, re_runes[i])
+					i++
+					for i < len(re_runes)-1 && re_runes[i] != ':' && re_runes[i] != ']' {
+						toAppend = append(toAppend, re_runes[i])
+						i++
+					}
+					if i >= len(re_runes)-1 && re_runes[i] != ':' {
+						return nil, fmt.Errorf("Unable to parse what looks like a POSIX character class.")
+					}
+					toAppend = append(toAppend, re_runes[i])
+					i++
+				}
 				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
 				}
@@ -501,6 +548,64 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 						i++
 					}
 				} else {
+					if re_postfix[i] == LBRACKET && i < len(re_postfix)-8 { // Could be the start of a POSIX class - the smallest POSIX class by word-length [[:word:]] takes 8 more characters
+						temp_i := i
+						temp_i++
+						if re_postfix[temp_i] == ':' {
+							temp_i++
+							posixClassPresent, posixClass := getPOSIXClass(re_postfix[temp_i:])
+							// getPOSIXClass returns true if there is some set of characters that
+							// ends in a colon and then a closing bracket. If this is not the case, we
+							// just treat all the characters as literals.
+							// For example, [[:digit:a]] is _not_ a POSIX class, its just a regular
+							// character class contains the letters '[', ':', 'd', 'i', 'g', 'i', 't', ':', 'a'.
+							// The final 'closing bracket' has no special meaning, its just another character.
+							if posixClassPresent {
+								var nodeToAdd postfixNode
+								switch posixClass {
+								case "digit": // Equivalent to '\d'
+									nodeToAdd = newPostfixCharNode(genRangeInclusive('0', '9')...)
+								case "upper": // [A-Z]
+									nodeToAdd = newPostfixCharNode(genRangeInclusive('A', 'Z')...)
+								case "lower": // [a-z]
+									nodeToAdd = newPostfixCharNode(genRangeInclusive('a', 'z')...)
+								case "alpha": //[A-Za-z]
+									nodeToAdd = newPostfixCharNode(slices.Concat(genRangeInclusive('A', 'Z'), genRangeInclusive('a', 'z'))...)
+								case "xdigit": // [0-9A-Fa-f]
+									nodeToAdd = newPostfixCharNode(slices.Concat(genRangeInclusive('A', 'F'), genRangeInclusive('a', 'f'), genRangeInclusive('0', '9'))...)
+								case "alnum": // [A-Za-z0-9]
+									nodeToAdd = newPostfixCharNode(slices.Concat(genRangeInclusive('A', 'Z'), genRangeInclusive('a', 'z'), genRangeInclusive('0', '9'))...)
+								case "blank": // [ \t]
+									nodeToAdd = newPostfixCharNode(' ', '\t')
+								case "space": // [ \t\n\r\f\v]
+									nodeToAdd = newPostfixCharNode(' ', '\t', '\n', '\r', '\f', '\v')
+								case "cntrl": // Control characters
+									nodeToAdd = newPostfixCharNode(append(genRangeInclusive('\x00', '\x1F'), '\x7F')...)
+								case "punct": // Punctuation and symbols
+									nodeToAdd = newPostfixCharNode([]rune(`!"\#$%&'()*+,\-./:;<=>?@\[\\\]^_` + "`" + `{|}~`)...)
+								case "graph": // Graphic characters
+									nodeToAdd = newPostfixCharNode(genRangeInclusive('\x21', '\x7E')...)
+								case "print": // Graphic characters + space
+									nodeToAdd = newPostfixCharNode(genRangeInclusive('\x20', '\x7E')...)
+								case "ascii": // ASCII values
+									nodeToAdd = newPostfixCharNode(genRangeInclusive('\x00', '\x7F')...)
+								case "word": // Word characters
+									nodeToAdd, _ = newEscapedNode('w', true) // This isn't going to error, so I suppress it
+								default:
+									return nil, fmt.Errorf("Invalid POSIX character class.")
+								}
+								chars = append(chars, nodeToAdd)
+								i = temp_i + len(posixClass) + 2 // Skip over the class name, the closing colon and the closing bracket
+								firstCharAdded = true
+								continue
+							}
+						}
+					}
+
+					// This used to be an else statement - I removed it, because if the previous if-block fails
+					// (ie. if it didn't actually find a character class), then this block must still execute.
+					// However, the checks for character classes are nested, so placing this inside an 'else' block
+					// will prevent it from running, as the outer if-statement will have evaluated to true.
 					if !firstCharAdded && re_postfix[i] > 0xF0000 { // It's a metacharacter that I defined, I'll have to convert it back to the regular character before adding it back, because I haven't added any characters yet. For example, '[[]', the second LBRACKET should be treated like a literal bracket.
 						switch re_postfix[i] {
 						case LBRACKET: