#117 - MappingTransformer: deprecate nested path target properties on an array destination

[njoubert-cleverage]

Description

Refs #117.

On an array destination, a target property that is not writable by the PropertyAccessor is added as a literal key. This fallback is needed for simple names (name gives the name key, the most common usage), but a nested path such as address.city (or address[city], [address].city) silently creates an address.city literal key instead of a nested array or an error.

This PR deprecates this case: the literal key is still set, with a deprecation explaining the alternatives, and it will throw an \UnexpectedValueException in v6.0 (consistent with \stdClass destinations since #244).

• [address.city]: literal key, no deprecation
• [address][city]: nested array, no deprecation
• name: name key, no deprecation

The other point of #117 (a missing source index returns null) depends on framework.property_access.throw_exception_on_invalid_index, already documented in the MappingTransformer reference; changing that default would break configurations relying on null for optional keys, so it is left for v6.0.

Checked end-to-end in process-bundle-demo with a demo.mapping_array_target_path process (the deprecation is logged for address.city only).

Requirements

• Documentation updates
  • Reference
  • Cookbooks
  • Changelog
• Unit tests

Breaking changes

None: deprecation only.

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