Inconsistent use of ContextDefinitionInterface in Drupal\Component\Plugin\Context\Context::getConstraints()

Problem/Motivation

In writing unit tests for various parts of Component\Plugin for #2052109: [meta] Expand phpunit tests for \Drupal\Component\Plugin classes → , I discovered that Drupal\Component\Plugin\Context\Context::getConstraints() tries to access an array property of an object.

  /**
   * Implements \Drupal\Component\Plugin\Context\ContextInterface::getConstraints().
   */
  public function getConstraints() {
    if (empty($this->contextDefinition['class'])) {
      throw new ContextException("An error was encountered while trying to validate the context.");
    }
    return array(new Type($this->contextDefinition['class']));
  }

$contextDefinition is defined as a \Drupal\Component\Plugin\Context\ContextDefinitionInterface.

After talking about it with @EclipseGC in IRC it seems that this is a bug.

It also seems that most of the Component aspect of Context is overridden by Core, which is why this bug hadn't been found yet.

Proposed resolution

Analyze a proper solution.

Remaining tasks

Analyze the requirements for Context::getConstraints().
Possibly modify ContextDefinitionInterface.
Modify Context::getConstraints() to conform with ContextDefinitionInterface.
Add PHPUnit test for the function Context::getConstraints()

User interface changes

API changes

Beta phase evaluation