gen: fix autogeneration of .str() methods for sumtypes that have child types with custom .str() methods

vlib/v/gen/auto_str_methods.v

@@ -600,11 +600,13 @@ fn (mut g Gen) gen_str_for_union_sum_type(info table.SumType, styp string, str_f
 			g.gen_str_for_type(typ)
 		}
 		sym := g.table.get_type_symbol(typ)
-		if sym.kind == .struct_ {
+		sym_has_str_method, str_method_expects_ptr, _ := sym.str_method_info()
+		deref := if sym_has_str_method && str_method_expects_ptr { ' ' } else { '*' }
+		if sym.kind == .struct_ && !sym_has_str_method {
 			func_name = 'indent_$func_name'
 		}
-		g.auto_str_funcs.write('\t\tcase $typ: return _STR("${clean_sum_type_v_type_name}($value_fmt)", 2, ${func_name}(*($typ_str*)x._$sym.cname')
-		if sym.kind == .struct_ {
+		g.auto_str_funcs.write('\t\tcase $typ: return _STR("${clean_sum_type_v_type_name}($value_fmt)", 2, ${func_name}(${deref}($typ_str*)x._$sym.cname')
+		if sym.kind == .struct_ && !sym_has_str_method {
 			g.auto_str_funcs.write(', indent_count')
 		}
 		g.auto_str_funcs.writeln('));')

vlib/v/tests/sumtype_str_for_subtypes_with_str_test.v

@@ -0,0 +1,43 @@
+// Test whether a sumtype that has multiple subtypes,
+// some with custom .str() methods, can be converted to a string,
+// i.e. whether its own autogenerated .str() method will work.
+// NB: Dictionary.str() calls $v.str() in the string interpolation,
+// which in turn can call Dictionary.str(), i.e. they are mutually
+// recursive.
+type Object = Dictionary | Stream | bool | f32 | int | string
+
+struct Dictionary {
+	items map[string]Object
+}
+
+struct Stream {
+mut:
+	content string
+}
+
+fn (dict Dictionary) str() string {
+	mut temp := []string{}
+	for k, v in dict.items {
+		temp << '    << "$k": ' + v.str().replace('\n', ' ')
+	}
+	return '\n' + temp.join('\n') + '\n'
+}
+
+fn test_str_of_sumtype_works() {
+	o := Object(Dictionary{
+		items: {
+			'abc': Object(Stream{
+				content: 'xyz'
+			})
+			'aaa': Object(int(321))
+			'bbb': Object(f32(3.14))
+		}
+	})
+	so := o.str()
+	println(so)
+	assert so.starts_with('Object(')
+	assert so.contains('<< "abc": Object(Stream{')
+	assert so.contains('<< "aaa": Object(321)')
+	assert so.contains('<< "bbb": Object(3.14')
+	assert so.ends_with(')')
+}