eclipse-aascw / aas-core-codegen / 37140921914

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Support nested collections (#833)

We allow the lists, the tuples and the sets to nest at any depth, *e.g.*,
``List[List[Tuple[Positive_int, Set[str]]]]``, and generate the code for
them in all the targets and schemas.

``Optional`` is allowed only at the top of a type annotation, since
the nested optionals can not be de/serialized in JSON and XML on many
targets. The items of the sets stay scalar. The mutability of
an argument is deep, so every level must be spelled alike:
``Sequence[Sequence[int]]`` or ``List[List[int]]``.

The type inference refuses ``==``, ``!=`` and ``in`` on lists, tuples
and sets, as the targets disagree on comparing them, and refuses deep
copies of lists and sets for now.

We copy the lists with ``list(...)`` instead of ``[:]``, since mypy
refuses to store the slice of a read-only ``Sequence`` as a ``List``.
For the same reason, we refuse to initialize a variable declared with
``List[...]`` with a read-only value:

    maybe_texts: Optional[List[str]] = optional_texts  # refused

The de/serializers are composed recursively, one function per container
type. In XML, the classes stay unwrapped, while the other items of
the lists and the sets are wrapped in ``<v>`` and the items of
the tuples in ``<v1>``, ``<v2>`` etc. at every level:

    <rowsOfPairs><v><v><v1>1</v1><v2><v>known</v></v2></v></v></rowsOfPairs>

We add the common meta-model ``nested_collections`` together with its
live test data, which check the round-trips and the paths of the errors
at every depth, *e.g.*, ``rowsOfPairs[0][1][0]``.

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