SourcePluginBase::next() calls Row constructor incorrectly

Problem/Motivation

SourcePluginBase has this line in its next() method:

$row = new Row($row_data, $this->migration->getSourcePlugin()->getIds(), $this->migration->getDestinationIds());

However, Row's constructor looks like this:

public function __construct(array $values = [], array $source_ids = [], $is_stub = FALSE)

$is_stub is supposed to be a boolean. SourcePluginBase is giving it an array.

The only reason this has ever worked is because Migration::getDestinationIds() returns the migration's $destinationIds property, which is an empty array -- that its default value, and nothing ever sets it differently; it's a vestigial property that should be removed from the Migration class. And the empty array evaluates to false (even PHPUnit's assertFalse() will not catch this).

So, entirely by accident, Row::isStub() does what it's supposed to do. If anything in Migrate did $row->isStub() === false, it would break.

Additionally, the call uses a roundabout $this->migration->getSourcePlugin()->getIds() call instead of simply calling $this->getIds()

Proposed resolution

SourcePluginBase::next() should neither call another copy of itself, nor pass a third argument when creating the row. It defaults to FALSE anyway.

Remaining tasks

Write a fail patch, write a passing patch, RTBC, and swiftly commit.

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

Fixed a bug where \Drupal\migrate\Row::isStub() could return an incorrect value, depending on how the object was instantiated.