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, 117 insertions, 0 deletions

diff --git a/spec/models/ability_spec.rb b/spec/models/ability_spec.rb
new file mode 100644
index 00000000000..1acb5846fcf
--- /dev/null
+++ b/spec/models/ability_spec.rb
@@ -0,0 +1,117 @@
+require 'spec_helper'
+
+describe Ability, lib: true do
+  describe '.users_that_can_read_project' do
+    context 'using a public project' do
+      it 'returns all the users' do
+        project = create(:project, :public)
+        user = build(:user)
+
+        expect(described_class.users_that_can_read_project([user], project)).
+          to eq([user])
+      end
+    end
+
+    context 'using an internal project' do
+      let(:project) { create(:project, :internal) }
+
+      it 'returns users that are administrators' do
+        user = build(:user, admin: true)
+
+        expect(described_class.users_that_can_read_project([user], project)).
+          to eq([user])
+      end
+
+      it 'returns internal users while skipping external users' do
+        user1 = build(:user)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([user1])
+      end
+
+      it 'returns external users if they are the project owner' do
+        user1 = build(:user, external: true)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(project).to receive(:owner).twice.and_return(user1)
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([user1])
+      end
+
+      it 'returns external users if they are project members' do
+        user1 = build(:user, external: true)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(project.team).to receive(:members).twice.and_return([user1])
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([user1])
+      end
+
+      it 'returns an empty Array if all users are external users without access' do
+        user1 = build(:user, external: true)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([])
+      end
+    end
+
+    context 'using a private project' do
+      let(:project) { create(:project, :private) }
+
+      it 'returns users that are administrators' do
+        user = build(:user, admin: true)
+
+        expect(described_class.users_that_can_read_project([user], project)).
+          to eq([user])
+      end
+
+      it 'returns external users if they are the project owner' do
+        user1 = build(:user, external: true)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(project).to receive(:owner).twice.and_return(user1)
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([user1])
+      end
+
+      it 'returns external users if they are project members' do
+        user1 = build(:user, external: true)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(project.team).to receive(:members).twice.and_return([user1])
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([user1])
+      end
+
+      it 'returns an empty Array if all users are internal users without access' do
+        user1 = build(:user)
+        user2 = build(:user)
+        users = [user1, user2]
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([])
+      end
+
+      it 'returns an empty Array if all users are external users without access' do
+        user1 = build(:user, external: true)
+        user2 = build(:user, external: true)
+        users = [user1, user2]
+
+        expect(described_class.users_that_can_read_project(users, project)).
+          to eq([])
+      end
+    end
+  end
+end