cgen: fix auto str for map of reference struct (fix #11024) (#11028)

vlib/v/gen/c/auto_str_methods.v

@@ -679,7 +679,8 @@ fn (mut g Gen) gen_str_for_map(info ast.Map, styp string, str_fn_name string) {
 		tmp_str := str_intp_sq('*($val_styp*)DenseArray_value(&m.key_values, i)')
 		g.auto_str_funcs.writeln('\t\tstrings__Builder_write_string(&sb, $tmp_str);')
 	} else if should_use_indent_func(val_sym.kind) && !val_sym.has_method('str') {
-		g.auto_str_funcs.writeln('\t\tstrings__Builder_write_string(&sb, indent_${elem_str_fn_name}(*($val_styp*)DenseArray_value(&m.key_values, i), indent_count));')
+		ptr_str := '*'.repeat(val_typ.nr_muls())
+		g.auto_str_funcs.writeln('\t\tstrings__Builder_write_string(&sb, indent_${elem_str_fn_name}(*${ptr_str}($val_styp*)DenseArray_value(&m.key_values, i), indent_count));')
 	} else if val_sym.kind in [.f32, .f64] {
 		tmp_val := '*($val_styp*)DenseArray_value(&m.key_values, i)'
 		if val_sym.kind == .f32 {

vlib/v/tests/string_struct_interpolation_test.v

@@ -22,3 +22,18 @@ fn test_adding_to_mutable_string_field() {
 	eprintln(foo.str)
 	assert foo.str == 'hi!'
 }
+
+struct MyStruct {
+	a string
+	b int
+}
+
+fn test_map_of_ref_struct_string() {
+	mut ar := map[string]&MyStruct{}
+	ar['a'] = &MyStruct{}
+	println(ar)
+	assert '$ar'.contains('MyStruct')
+	assert ('b' in ar) == false
+	assert ('a' in ar) == true
+	assert 'a' in ar
+}