cgen: fix for loop with array fixed returned from fn (vlang#22069)

vlib/v/gen/c/cgen.v

@@ -5784,7 +5784,13 @@ fn (mut g Gen) return_stmt(node ast.Return) {
 						} else {
 							node.types[0]
 						}
-						g.write('memcpy(${tmpvar}.ret_arr, ${g.expr_string(node.exprs[0])}, sizeof(${g.typ(typ)}))')
+						typ_sym := g.table.final_sym(typ)
+						if typ_sym.kind == .array_fixed
+							&& (typ_sym.info as ast.ArrayFixed).is_fn_ret {
+							g.write('memcpy(${tmpvar}.ret_arr, ${g.expr_string(node.exprs[0])}.ret_arr, sizeof(${g.typ(typ)}))')
+						} else {
+							g.write('memcpy(${tmpvar}.ret_arr, ${g.expr_string(node.exprs[0])}, sizeof(${g.typ(typ)}))')
+						}
 					} else if node.exprs[0] in [ast.ArrayInit, ast.StructInit] {
 						if node.exprs[0] is ast.ArrayInit && node.exprs[0].is_fixed
 							&& node.exprs[0].has_init {

vlib/v/gen/c/for.v

@@ -333,6 +333,9 @@ fn (mut g Gen) for_in_stmt(node_ ast.ForInStmt) {
 				} else {
 					g.write(' = ${addr}')
 					g.expr(node.cond)
+					if info.is_fn_ret {
+						g.write('.ret_arr')
+					}
 					g.writeln('[${idx}];')
 				}
 			}

vlib/v/tests/array_fixed_for_loop_test.v

@@ -0,0 +1,16 @@
+fn double() (bool, [4]i16) {
+	return true, [4]i16{}
+}
+
+fn foo() [4]i16 {
+	_, b := double()
+	for i in b {
+		println(i)
+	}
+	return b
+}
+
+fn test_main() {
+	arr := foo()
+	assert arr == [4]i16{}
+}