cgen: fix comptime for in field selector (#12457)

vlib/v/gen/c/fn.v

@@ -810,6 +810,16 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 		if rec_type.has_flag(.shared_f) {
 			rec_type = rec_type.clear_flag(.shared_f).set_nr_muls(0)
 		}
+		if node.left is ast.ComptimeSelector {
+			if node.left.field_expr is ast.SelectorExpr {
+				if node.left.field_expr.expr is ast.Ident {
+					key_str := '${node.left.field_expr.expr.name}.typ'
+					rec_type = g.comptime_var_type_map[key_str] or { rec_type }
+					g.gen_expr_to_string(node.left, rec_type)
+					return
+				}
+			}
+		}
 		g.get_str_fn(rec_type)
 	} else if node.name == 'free' {
 		mut rec_type := node.receiver_type
@@ -1113,6 +1123,14 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 				g.writeln('; ${c_name(print_method)}($tmp); string_free(&$tmp);')
 			} else {
 				g.write('${c_name(print_method)}(')
+				if expr is ast.ComptimeSelector {
+					if expr.field_expr is ast.SelectorExpr {
+						if expr.field_expr.expr is ast.Ident {
+							key_str := '${expr.field_expr.expr.name}.typ'
+							typ = g.comptime_var_type_map[key_str] or { typ }
+						}
+					}
+				}
 				g.gen_expr_to_string(expr, typ)
 				g.write(')')
 			}

vlib/v/tests/comptime_for_in_field_selector_test.v

@@ -0,0 +1,30 @@
+fn print_field_values<T>(s T) {
+	mut value_list := []string{}
+
+	$for field in T.fields {
+		println(s.$(field.name))
+		value_list << s.$(field.name).str()
+	}
+	assert value_list.len == 4
+	assert value_list[0] == 'Simon'
+	assert value_list[1] == 'simon1234'
+	assert value_list[2] == 'simon@gmail.com'
+	assert value_list[3] == '15'
+}
+
+struct Foo {
+	name     string
+	password string
+	email    string
+	age      int
+}
+
+fn test_comptime_for_in_field_selector() {
+	bar := Foo{
+		name: 'Simon'
+		password: 'simon1234'
+		email: 'simon@gmail.com'
+		age: 15
+	}
+	print_field_values<Foo>(bar)
+}