scanner: fix single backslash in raw string (#10890)

cmd/tools/vcheck-md.v

@@ -292,7 +292,7 @@ fn (mut ad AnchorData) add_link_targets(line_number int, line string) {
 			}
 		}
 	} else {
-		query := r'<a\s*id=["\'](?P<link>[a-z0-9\-\_\x7f-\uffff]+)["\']\s*/>'
+		query := '<a\\s*id=["\'](?P<link>[a-z0-9\\-\\_\\x7f-\\uffff]+)["\']\\s*/>'
 		mut re := regex.regex_opt(query) or { panic(err) }
 		res := re.find_all_str(line)
 

vlib/v/scanner/scanner.v

@@ -1126,7 +1126,8 @@ fn (mut s Scanner) ident_string() string {
 		c := s.text[s.pos]
 		prevc := s.text[s.pos - 1]
 		// end of string
-		if c == s.quote && (prevc != slash || (prevc == slash && s.text[s.pos - 2] == slash)) {
+		if c == s.quote
+			&& (is_raw || prevc != slash || (prevc == slash && s.text[s.pos - 2] == slash)) {
 			// handle '123\\'  slash at the end
 			break
 		}

vlib/v/tests/raw_string_test.v

@@ -0,0 +1,3 @@
+fn test_raw_string_backslash() {
+	assert r'\' == r'\'
+}