xsd:group generates incorrect output in Go

[mark-edgeworth]

Description

When a complex type contains an xsd:group reference, the generated
code produces a new struct type for the group rather than expanding
the group content in the original type. Also, no xml:"..." mapping code is
generated, so the group is not parsed from the XML.

I'd prefer it that the group did not yield a new type (as it is just
syntactic sugar inside the schema rather than a real hierarchical
component).

Steps to reproduce the issue:
Using the following test schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="qualified" version="0.0.1">
    <!-- Device Properties Group -->
    <xs:group name="MyGroup">
        <xs:sequence>
            <!-- A couple of test elements -->
            <xs:element name="element_1"  type="xs:string"/>
            <xs:element name="element_2" type="xs:string"/>
        </xs:sequence>
    </xs:group>

    <xs:element name="parent_element">
        <xs:complexType>
            <xs:group ref="MyGroup" />
            <xs:attribute name="attr_1" type="xs:string" use="required" />
        </xs:complexType>
    </xs:element>

</xs:schema>

Describe the results you received:

Generated code is

// Code generated by xgen. DO NOT EDIT.

package schema

import (
	"encoding/xml"
)

// MyGroup ...
type MyGroup struct {
	Element1 string
	Element2 string
}

// Parentelement ...
type Parentelement struct {
	XMLName   xml.Name `xml:"parent_element"`
	Attr1Attr string   `xml:"attr_1,attr"`
	MyGroup   *MyGroup
}

Describe the results you expected:
Something like:

// Code generated by xgen. DO NOT EDIT.

package schema

import (
	"encoding/xml"
)

// Parentelement ...
type Parentelement struct {
	XMLName   xml.Name `xml:"parent_element"`
	Attr1Attr string   `xml:"attr_1,attr"`
	Element1 string `xml:"element_1"`
	Element2 string `xml:"element_2"`
}

Output of go version:

go version go1.16.6 darwin/amd64

xgen version or commit ID:

v0.1.0

Environment details (OS, physical, etc.):
MacOS 11.6 Big Sur on Mac Book Pro

[zadeck]

I think that the problem is more subtle than this and that the proper solution is not to inline the group.
Consider the following xsd schemata:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
<xs:element name="e">
xs:complexType
xs:sequence
<xs:group ref="foo1"/>
<xs:group ref="foo2"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:group name="foo1">
xs:sequence
<xs:element name="foo">
xs:complexType
<xs:attribute name="name" use="required" type="xs:string"/>
<xs:attribute name="value1" use="required" type="xs:double"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:group>
<xs:group name="foo2">
xs:sequence
<xs:element name="foo">
xs:complexType
<xs:attribute name="name" use="required" type="xs:string"/>
<xs:attribute name="value2" use="required" type="xs:integer"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:group>
</xs:schema>

xgen generated the following incorrect code:

// Code generated by xgen. DO NOT EDIT.

package test2

import (
"encoding/xml"
)

// E ...
type E struct {
XMLName xml.Name xml:"e"
Foo1 *Foo1
Foo2 *Foo2
}

// Foo ...
type Foo struct {
XMLName xml.Name xml:"foo"
NameAttr string xml:"name,attr"
Value1Attr float64 xml:"value1,attr"
}

What I think that it really should have done is to use the group name as the name of the structure but put the element name in the attribute for the XMLName.

// Code generated by xgen. DO NOT EDIT.

package test2

import (
"encoding/xml"
)

// E ...
type E struct {
XMLName xml.Name xml:"e"
Foo1 *Foo1
Foo2 *Foo2
}

// Foo1 ...
type Foo1 struct {
XMLName xml.Name xml:"foo"
NameAttr string xml:"name,attr"
Value1Attr float64 xml:"value1,attr"
}

// Foo2 ...
type Foo2 struct {
XMLName xml.Name xml:"foo"
NameAttr string xml:"name,attr"
Value1Attr int xml:"value1,attr"
}

The problem with inlining the group is that if it is referenced many times, you can get a big expansion.