scanner: print multibyte char for invalid char error (#8804)

vlib/encoding/utf8/utf8_util.v

@@ -23,7 +23,7 @@ pub fn len(s string) int {
 	mut index := 0
 
 	for {
-		ch_len := utf8util_char_len(s[index])
+		ch_len := char_len(s[index])
 		index += ch_len
 		count++
 		if index >= s.len {
@@ -38,12 +38,17 @@ pub fn u_len(s ustring) int {
 	return len(s.s)
 }
 
+// char_len calculate the length in bytes of a utf8 char
+pub fn char_len(b byte) int {
+	return ((0xe5000000 >> ((b >> 3) & 0x1e)) & 3) + 1
+}
+
 // get_uchar convert a unicode glyph in string[index] into a int unicode char
 pub fn get_uchar(s string, index int) int {
 	mut res := 0
 	mut ch_len := 0
 	if s.len > 0 {
-		ch_len = utf8util_char_len(s[index])
+		ch_len = char_len(s[index])
 
 		if ch_len == 1 {
 			return u16(s[index])
@@ -153,10 +158,6 @@ pub fn is_uchar_global_punct( uchar int ) bool {
 Private functions
 
 */
-// utf8util_char_len calculate the length in bytes of a utf8 char
-fn utf8util_char_len(b byte) int {
-	return (( 0xe5000000 >> (( b >> 3 ) & 0x1e )) & 3 ) + 1
-}
 
 //
 // if upper_flag == true  then make low ==> upper conversion
@@ -168,7 +169,7 @@ fn up_low(s string, upper_flag bool) string {
 	mut str_res := unsafe {malloc(s.len + 1)}
 
 	for {
-		ch_len := utf8util_char_len(s[index])
+		ch_len := char_len(s[index])
 
 		if ch_len == 1 {
 			if upper_flag==true {

vlib/v/checker/tests/invalid_char_err.out

@@ -0,0 +1,3 @@
+vlib/v/checker/tests/invalid_char_err.vv:1:1: error: invalid character `🐈`
+    1 | 🐈println('')
+      | ^

vlib/v/checker/tests/invalid_char_err.vv

@@ -0,0 +1 @@
+🐈println('')

vlib/v/scanner/scanner.v

@@ -4,6 +4,7 @@
 module scanner
 
 import os
+import encoding.utf8
 import v.token
 import v.pref
 import v.util
@@ -1002,12 +1003,19 @@ fn (mut s Scanner) text_scan() token.Token {
 				return s.end_of_file()
 			}
 		}
-		s.error('invalid character `$c.ascii_str()`')
+		s.invalid_character()
 		break
 	}
 	return s.end_of_file()
 }
 
+fn (mut s Scanner) invalid_character() {
+	len := utf8.char_len(s.text[s.pos])
+	end := util.imin(s.pos + len, s.text.len)
+	c := s.text[s.pos..end]
+	s.error('invalid character `$c`')
+}
+
 fn (s &Scanner) current_column() int {
 	return s.pos - s.last_nl_pos
 }