cgen: fix for_in array of fixed_array (fix #9098) (#9099)

vlib/v/gen/c/cgen.v

@@ -1385,6 +1385,10 @@ fn (mut g Gen) for_in_stmt(node ast.ForInStmt) {
 				g.write('\t')
 				g.write_fn_ptr_decl(val_sym.info as table.FnType, c_name(node.val_var))
 				g.writeln(' = ((voidptr*)$tmp${op_field}data)[$i];')
+			} else if val_sym.kind == .array_fixed && !node.val_is_mut {
+				right := '(($styp*)$tmp${op_field}data)[$i]'
+				g.writeln('\t$styp ${c_name(node.val_var)};')
+				g.writeln('\tmemcpy(*($styp*)${c_name(node.val_var)}, (byte*)$right, sizeof($styp));')
 			} else {
 				// If val is mutable (pointer behind the scenes), we need to generate
 				// `int* val = ((int*)arr.data) + i;`

vlib/v/tests/for_in_containers_of_fixed_array_test.v

@@ -0,0 +1,25 @@
+fn test_for_in_containers_of_fixed_array() {
+	mut rets := []string{}
+	arr := [][2]int{len: 3}
+
+	for pair in arr {
+		println(pair)
+		rets << '$pair'
+	}
+	assert rets[0] == '[0, 0]'
+	assert rets[1] == '[0, 0]'
+	assert rets[2] == '[0, 0]'
+}
+
+fn test_for_mut_in_containers_of_fixed_array() {
+	mut rets := []string{}
+	mut arr := [][2]int{len: 3}
+
+	for mut pair in arr {
+		println(pair)
+		rets << '$pair'
+	}
+	assert rets[0] == '[0, 0]'
+	assert rets[1] == '[0, 0]'
+	assert rets[2] == '[0, 0]'
+}