NotesHelper#note_editable? and ProjectTeam#human_max_access currently
take about 16% of the load time of an issue page. This MR preloads
the maximum access level of users for all notes in issues and merge
requests with several queries instead of one per user and caches
the result in RequestStore.
There are several changes to this module:
1. The use of an explicit stack in Participable#participants
2. Proc behaviour has been changed
3. Batch permissions checking
== Explicit Stack
Participable#participants no longer uses recursion to process "self" and
all child objects, instead it uses an Array and processes objects in
breadth-first order. This allows us to for example create a single
Gitlab::ReferenceExtractor instance and pass this to any Procs. Re-using
a ReferenceExtractor removes the need for running potentially many SQL
queries every time a Proc is called on a new object.
== Proc Behaviour Changed
Previously a Proc in Participable was expected to return an Array of
User instances. This has been changed and instead it's now expected that
a Proc modifies the Gitlab::ReferenceExtractor passed to it. The return
value of the Proc is ignored.
== Permissions Checking
The method Participable#participants uses
Ability.users_that_can_read_project to check if the returned users have
access to the project of "self" _without_ running multiple SQL queries
for every user.
