v.util: make util.smart_quote use its output string builder directly

vlib/strings/builder.v

@@ -45,7 +45,7 @@ pub fn (b &Builder) byte_at(n int) byte {
 // write appends the string `s` to the buffer
 [inline]
 pub fn (mut b Builder) write_string(s string) {
-	if s == '' {
+	if s.len == 0 {
 		return
 	}
 	unsafe { b.push_many(s.str, s.len) }

vlib/v/util/quote.v

@@ -2,93 +2,119 @@ module util
 
 import strings
 
-const (
-	invalid_escapes = ['(', '{', '$', '`', '.']
-)
+const invalid_escapes = r'({$`.'.bytes()
 
-[direct_array_access]
+const backslash = 92
+
+const backslash_r = 13
+
+const backslash_n = 10
+
+const double_quote = 34
+
+const double_escape = '\\\\'
+
+//[direct_array_access]
 pub fn smart_quote(str string, raw bool) string {
 	len := str.len
 	if len == 0 {
-		return str
+		return ''
 	}
 	mut result := strings.new_builder(len)
 	mut pos := -1
-	mut last := ''
-	// TODO: This should be a single char?
-	mut next := ''
+	mut last := byte(0)
+	mut current := byte(0)
+	mut next := byte(0)
 	mut skip_next := false
 	for {
-		pos = pos + 1
+		pos++
 		if skip_next {
 			skip_next = false
-			pos = pos + 1
+			pos++
 		}
 		if pos >= len {
 			break
 		}
 		if pos + 1 < len {
-			next = str[pos + 1].ascii_str()
-		}
-		mut current := str
-		mut toadd := str
-		if len > 1 {
-			current = str[pos].ascii_str()
-			toadd = current
+			next = str[pos + 1]
 		}
+		current = str[pos]
 		// double quote
-		if current == '"' {
-			toadd = '\\"'
-			current = ''
+		if current == util.double_quote {
+			current = 0
+			last = current
+			result.write_b(util.backslash)
+			result.write_b(util.double_quote)
+			continue
 		}
-		if current == '\\' {
+		if current == util.backslash {
 			if raw {
-				toadd = '\\\\'
+				last = current
+				result.write_string(util.double_escape)
+				continue
 			} else {
 				// escaped backslash - keep as is
-				if next == '\\' {
-					toadd = '\\\\'
+				if next == util.backslash {
 					skip_next = true
-				} else if next != '' {
+					last = current
+					result.write_string(util.double_escape)
+					continue
+				} else if next != 0 {
 					if raw {
-						toadd = '\\\\' + next
 						skip_next = true
-					}
-					// keep all valid escape sequences
-					else if next !in util.invalid_escapes {
-						toadd = '\\' + next
+						last = current
+						result.write_string(util.double_escape)
+						continue
+					} else if next in util.invalid_escapes {
 						skip_next = true
+						last = current
+						result.write_b(next)
+						continue
 					} else {
-						toadd = next
+						// keep all valid escape sequences
 						skip_next = true
+						last = current
+						result.write_b(current)
+						result.write_b(next)
+						continue
 					}
 				}
 			}
 		}
 		// keep newlines in string
-		if current == '\n' {
-			toadd = '\\n'
-			current = ''
-		} else if current == '\r' && next == '\n' {
-			toadd = '\r\n'
-			current = ''
+		if current == util.backslash_n {
+			current = 0
+			last = current
+			result.write_b(util.backslash)
+			result.write_b(`n`)
+			continue
+		} else if current == util.backslash_r && next == util.backslash_n {
+			result.write_b(current)
+			result.write_b(next)
+			current = 0
 			skip_next = true
+			last = current
+			continue
 		}
 		// Dolar sign
-		if !raw && current == '$' {
-			if last == '\\' {
-				toadd = r'\$'
+		if !raw && current == `$` {
+			if last == util.backslash {
+				result.write_b(last)
+				result.write_b(current)
+				last = current
+				continue
 			}
 		}
 		// Windows style new line \r\n
-		if !raw && current == '\r' {
-			if next == '\n' {
-				skip_next = true
-				toadd = '\\n'
-			}
+		if !raw && current == util.backslash_r && next == util.backslash_n {
+			skip_next = true
+			result.write_b(util.backslash)
+			result.write_b(`n`)
+			last = current
+			continue
 		}
-		result.write_string(toadd)
 		last = current
+		result.write_b(current)
 	}
 	return result.str()
 }