Allow ?edit[field_xyz] as query parameter in contextual filter

Problem/Motivation

The query parameter (query_parameter) plugin provides a Views default argument with a value taken from a query parameter from the current request. For instance, if the request has a query string such as ?foo=bar&baz=qux, by configuring the plugin to get the argument default value from the foo param, will return bar.

However, the request query string might look like ?foo[bar][baz]=qux. With the current code, setting the the param to foo[bar][baz] will return NULL instead of qux. The reason is that QueryParameter::getArgument() only checks for the 1st tier of query string parameters and is not able to process array structured values.

Steps to reproduce

See the tests.

Proposed resolution

• Convert the param name into an array: the foo[bar][baz] will become ['foo', 'bar', 'baz'].
• Use NestedArray::getValue() to vertically traverse the array and find the nested value.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

Site builders are able to store query param names having an array structure.

Release notes snippet

N/A

Original report

By providing a query parameter as contextual filter argument, we can already limit the referenceable entitities in an entity reference view, with #1699378: Allow tokens in entity reference views selection arguments being only an alternative approach.

In many cases we can use a simple ?key=value query parameter.

When creating a new entity in a dependent dropdown setting with two fields (the entity reference field_city depending on another field_country), we however might want to use the Prepopulate module to prepopulate both field_country and the (dependent) entity reference field_city. We could easily do so, setting both fields at the same time using a single query parameter for field_country that is also caught by the entity reference view and used to restrict the referenceable entities in field_city.

Prepopulate however expects all parameters in the ?edit[field_xyz] form in order to avoid name collisions, and our QueryParameter default argument doesn't support this kind of array structure. Or actually it does. The only problem is the

if ($current_request->query->has($this->options['query_param'])) {

clause, as the flattened edit[field_xyz] parameter is send to ParameterBag->has() which uses array_key_exists() to find the (string) needle in the (array) haystack. Which can't work.

I'm not sure if beyond Prepopulate module there is any use for this kind of array structure in query parameters, and clearly this could be solved by prepopulate module itself, by supplying an altered QueryParameter default argument plugin. On the other hand, why wouldn't we want to support this kind of array structure in Core views, plus the parse_str making this work isn't expensive at all.