eclipse-aascw / aas-core-codegen / 35403500086

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Test optional in the common tuples meta-model (#733)

``Something`` of the ``tuples`` fixture carried three tuple properties,
every one of them required, so the combination of ``Optional`` and
``Tuple`` was never put in front of any generator. It gets one:

    #: Test an optional tuple, mixing a primitive with a polymorphic class
    optional_pair: Optional[Tuple[str, Abstract_item]]

The item types are picked so that the optional exercises both ends of
a tuple, a bare primitive and a model-typed class, which the XML side
writes in a ``<v1>`` and by dispatch on the element name respectively:

    "optionalPair": ["sixth", {"modelType": "AnotherItem", "serialNumber": 7}]

    <optionalPair><v1>sixth</v1><anotherItem>
      <serialNumber>7</serialNumber></anotherItem></optionalPair>

C++, Go, Java, Python, TypeScript, JSON Schema and XSD took the property
as it comes. C# did not, and failed to compile with nine errors:

    copying.cs(118,43): error CS1061: '(string, IAbstractItem)?' does not
    contain a definition for 'Item1'

A C# tuple is a ``System.ValueTuple`` and hence a value type, so an
optional of one is a ``System.Nullable`` and not the tuple itself: it is
probed with ``HasValue`` and unwrapped with ``Value`` before an item can
be reached. Every optional the generator had met so far -- a class,
a named union, a list -- is a reference type which is simply compared
against ``null``.

One bug is fixed along the way, in code which the optional tuple only
led us to read. The deep-equaliser of the generated ``TestCopying``
emitted a bare conditional for an optional property and joined the
properties with ``&&``, and the conditional operator binds weaker than
the conjunction, so everything in front of the first optional property
was swallowed into its condition:

    return (
        (that.EmbeddedDataSpecifications != null && ...)
            ? that.EmbeddedDataSpecifications.Count == ... && ...
            : that.EmbeddedDataSpecifications == nu... (continued)

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