Refactor Participable

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.

1 files changed, 23 insertions, 0 deletions

diff --git a/spec/models/commit_range_spec.rb b/spec/models/commit_range_spec.rb
index 1cf51d8bab3..6bc496414a3 100644
--- a/spec/models/commit_range_spec.rb
+++ b/spec/models/commit_range_spec.rb
@@ -145,4 +145,27 @@ describe CommitRange, models: true do
       end
     end
   end
+
+  describe '#has_been_reverted?' do
+    it 'returns true if the commit has been reverted' do
+      issue = create(:issue)
+
+      create(:note_on_issue,
+             noteable_id: issue.id,
+             system: true,
+             note: commit1.revert_description)
+
+      expect_any_instance_of(Commit).to receive(:reverts_commit?).
+        with(commit1).
+        and_return(true)
+
+      expect(commit1.has_been_reverted?(nil, issue)).to eq(true)
+    end
+
+    it 'returns false a commit has not been reverted' do
+      issue = create(:issue)
+
+      expect(commit1.has_been_reverted?(nil, issue)).to eq(false)
+    end
+  end
 end