Entity Query Alter

Drupal 8 is missing the D7 equivalent of hook_entity_query_alter() in D7, which is fine...until you need to alter the entity query. A use case would be for implementing access logic for custom entities at the query level. There is an open issue against Entity module (and hopefully, later, core) to do just that, however in the meantime it is painful to construct your own SQL queries based on Drupal's field API, akin to what an entity query does. Once you're at hook_entity_TAG_alter(), though, the entity query has been compiled into a standard SQL select.

This simple module aims to provide an alter event on the entity query, until the above API lands. Use at your own risk and do understand the impacts of hooking into the entity query build process. From a technical perspective, this module adds a ::alter() method which is called prior to preparing or compiling the entity query inside of ::execute(), and copies in the standard set of alter metadata and tags which would normally be used in identifying and altering the SQL select statement in the above core hook.