checker: allow \uxxxxx in raw strings (vlang#21724)

vlib/v/checker/checker.v

@@ -3013,6 +3013,10 @@ pub fn (mut c Checker) expr(mut node ast.Expr) ast.Type {
 				// string literal starts with "c": `C.printf(c'hello')`
 				return ast.u8_type.set_nr_muls(1)
 			}
+			if node.is_raw {
+				// raw strings don't need any sort of checking related to unicode
+				return ast.string_type
+			}
 			return c.string_lit(mut node)
 		}
 		ast.StringInterLiteral {

vlib/v/tests/raw_string_test.v

@@ -17,6 +17,11 @@ fn test_raw_string_not_escaped_by_transformer() {
 	assert 'a\nb' + r'a\nb' == 'a\nba\\nb'
 }
 
+fn test_raw_string_backslash_u() {
+	assert r'\u0000004B' == r'\u0000004B'
+	println(r'\u0000004B')
+}
+
 // this test will cause test failure (see #12604)
 // fn test_many_pluses() {
 // 	a := r'x\n'