Refactor Participableseparate-banzai-references

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, 37 insertions, 1 deletions

diff --git a/spec/models/commit_spec.rb b/spec/models/commit_spec.rb
index ccb100cd96f..eda91ee0768 100644
--- a/spec/models/commit_spec.rb
+++ b/spec/models/commit_spec.rb
@@ -1,7 +1,7 @@
 require 'spec_helper'
 
 describe Commit, models: true do
-  let(:project) { create(:project) }
+  let(:project) { create(:project, :public) }
   let(:commit)  { project.commit }
 
   describe 'modules' do
@@ -171,4 +171,40 @@ eos
   describe '#status' do
     # TODO: kamil
   end
+
+  describe '#participants' do
+    let(:user1) { build(:user) }
+    let(:user2) { build(:user) }
+
+    let!(:note1) do
+      create(:note_on_commit,
+             commit_id: commit.id,
+             project: project,
+             note: 'foo')
+    end
+
+    let!(:note2) do
+      create(:note_on_commit,
+             commit_id: commit.id,
+             project: project,
+             note: 'bar')
+    end
+
+    before do
+      allow(commit).to receive(:author).and_return(user1)
+      allow(commit).to receive(:committer).and_return(user2)
+    end
+
+    it 'includes the commit author as the 1st participant' do
+      expect(commit.participants[0]).to eq(commit.author)
+    end
+
+    it 'includes the committer as the 2nd participant' do
+      expect(commit.participants[1]).to eq(commit.committer)
+    end
+
+    it 'includes the authors of the commit notes' do
+      expect(commit.participants).to include(note1.author, note2.author)
+    end
+  end
 end