scanner: add check for `_` in num literals (#5849)

vlib/builtin/int_test.v

@@ -156,12 +156,12 @@ fn test_num_separator() {
 	assert 0b010_ == 2
 
 	// oct
-	assert 0o_173 == 123
+	assert 0o1_73 == 123
-	assert -0o_175 == -125
+	assert -0o17_5 == -125
 	assert -0o175_ == -125
 
 	// hex
-	assert 0x_FF == 255
+	assert 0xFF == 255
 	assert 0xFF_ == 255
 	assert 0xF_F == 255
 

vlib/v/scanner/scanner.v

@@ -324,6 +324,9 @@ fn (mut s Scanner) ident_bin_number() string {
 	mut first_wrong_digit := `\0`
 	start_pos := s.pos
 	s.pos += 2 // skip '0b'
+	if s.text[s.pos] == num_sep {
+		s.error('separator `_` is only valid between digits in a numeric literal')
+	}
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
 		if !c.is_bin_digit() && c != num_sep {
@@ -355,6 +358,9 @@ fn (mut s Scanner) ident_hex_number() string {
 	mut first_wrong_digit := `\0`
 	start_pos := s.pos
 	s.pos += 2 // skip '0x'
+	if s.text[s.pos] == num_sep {
+		s.error('separator `_` is only valid between digits in a numeric literal')
+	}
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
 		if !c.is_hex_digit() && c != num_sep {
@@ -386,6 +392,9 @@ fn (mut s Scanner) ident_oct_number() string {
 	mut first_wrong_digit := `\0`
 	start_pos := s.pos
 	s.pos += 2 // skip '0o'
+	if s.text[s.pos] == num_sep {
+		s.error('separator `_` is only valid between digits in a numeric literal')
+	}
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
 		if !c.is_oct_digit() && c != num_sep {