Support attribute restrictions (such as fixed/default values) on complex types derived by restriction

[mamift]

Fixed Value Handling in LinqToXsd

LinqToXsd does have special code generation logic for fixed values on attributes and elements, but there is a nuance in how it interacts with complex type derivation by restriction (as seen in metalex_mcontainerTypeBug.xsd).

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1. General Handling of Fixed Values for Attributes

When an attribute has fixed="value" in an XSD schema:

1. Extraction (XsdToTypesConverter.cs):

   • In SetFixedDefaultValue(XmlSchemaAttribute, ClrPropertyInfo), attribute.FixedValue is read and stored on ClrPropertyInfo.FixedValue.

2. Constant Field Emission (ClrPropertyInfo.CreateFixedDefaultValue):

   • LinqToXsd generates a static [DebuggerBrowsable(Never)] field holding the fixed value (e.g., <propertyName>FixedValue).

3. Getter Behavior (ClrPropertyInfo.AddGetStatements / ReturnFixedValue):

   • For attributes with a fixed value, the getter skips reading from the underlying XML attribute and directly returns the fixed value constant (return <propertyName>FixedValue;), adhering to XSD semantics where fixed attributes always evaluate to that fixed value.

4. Setter Validation (ClrPropertyInfo.AddFixedValueChecking):

   • The setter generates an equality check against the fixed constant. If the assigned value does not match the fixed value, it throws a LinqToXsdFixedValueException:

     if (typeFixedValue.Equals(value)) {
         // set attribute
     } else {
         throw new LinqToXsdFixedValueException(value, typeFixedValue);
     }

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2. Why It Is Not Applied in metalex_mcontainerTypeBug.xsd

In metalex_mcontainerTypeBug.xsd:

1. urType definition:

   • urType defines type through the typeopt attribute group without a fixed value (<xsd:attribute name="type" type="e:CMtype"/>).
   • LinqToXsd generates a normal, read/write type property on the C# urType class.

2. absMcontainerType restriction:

   • absMcontainerType derives from urType using <xsd:restriction base="e:urType"> and includes typemcontainer, which sets fixed="mcontainer" on the type attribute.
   • However, in XsdToTypesConverter.cs (lines 306–310):

     if (ct.IsDerivedByRestriction())
     {
         //Do not handle restrictions on complex content?
         return;
     }

   • LinqToXsd deliberately skips generating child particle and attribute properties for complex types derived by restriction from another complex type. Instead, the generated C# class (absMcontainerType) simply inherits from urType (public partial class absMcontainerType : global::MetalEx_mcontainerBug.urType).
   • As a result, absMcontainerType inherits the unconstrained type property from urType rather than generating a specialized or overridden type property with the fixed value logic.