xs:union is interpreted wrongly

[mpkondrashin]

Description
If XSD contains xs:union in type definition, it produces struct that contains both values. As result, XML fails to be parsed
Steps to reproduce the issue:

1. Example XSD:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:simpleType name="integer-or-empty">
    <xs:union memberTypes="xs:integer empty-string" />
  </xs:simpleType>
  <xs:simpleType name="empty-string">
    <xs:restriction base="xs:string">
      <xs:enumeration value="" />
    </xs:restriction>
  </xs:simpleType>
  <xs:element name="NETWORK_ACCESS_URL">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="DomainCensus" maxOccurs="1" minOccurs="0">
          <xs:complexType>
            <xs:simpleContent>
              <xs:extension base="xs:string">
                <xs:attribute type="integer-or-empty" name="AccessCount"/>
              </xs:extension>
            </xs:simpleContent>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

2. Run following command

xgen -i filename.xsd -o report.go -l Go -p report

3. Following Go code is generated:

// Code generated by xgen. DO NOT EDIT.

package report

import (
	"encoding/xml"
)

// Integerorempty ...
type Integerorempty struct {
	XMLName     xml.Name `xml:"integer-or-empty"`
	Emptystring *Emptystring
	Integer     int
}

// Emptystring ...
type Emptystring string

// DomainCensus ...
type DomainCensus struct {
	AccessCountAttr *Integerorempty `xml:"AccessCount,attr,omitempty"`
	Value           string          `xml:",chardata"`
}

// NETWORKACCESSURL ...
type NETWORKACCESSURL struct {
	XMLName      xml.Name      `xml:"NETWORK_ACCESS_URL"`
	DomainCensus *DomainCensus `xml:"DomainCensus"`
}

4. Here is sample XML to parse (report.xml):

<?xml version="1.0" encoding="UTF-8"?>
<NETWORK_ACCESS_URL>
  <DomainCensus AccessCount="149511825">84786</DomainCensus>
</NETWORK_ACCESS_URL>

5. Test code (file report_test.go):

package report

import (
	"encoding/xml"
	"os"
	"testing"
)

func TestReport(t *testing.T) {
	data, err := os.ReadFile("report.xml")
	if err != nil {
		t.Fatal(err)
	}
	var report NETWORKACCESSURL
	if err := xml.Unmarshal(data, &report); err != nil {
		t.Fatal(err)
	}
}

Describe the results you received:
go test produces the following:

--- FAIL: TestReport (0.00s)
    report_test.go:16: cannot unmarshal into report.Integerorempty
FAIL
exit status 1
FAIL	github.com/mpkondrashin/ddan/report/t	0.251s

Describe the results you expected:
I have expected to parse file successfully
Output of go version:

go version go1.18.3 darwin/amd64

xgen version or commit ID:

xgen version: 0.1.0

Environment details (OS, physical, etc.):
MacOS Monterey

Possible solution
I have no clue, how to solve it as unions of types are not supported by Golang (not sure about other languages).

What worked for me: Changing Integerorempty to int through whole report.go file (using Search & Replace) fixes this issue

I assume some option to force some types to be substituted as other types would be the solution. See #10 issue. This option would solve this issue too (interpret xsd "integer" as int, int64 or big.Int as user whats it to)