Refactor GroupProjectsFinder#init_collection

This optimises how GroupProjectsFinder builds it collection, producing
simpler and faster queries in the process. It also cleans up the code a
bit to make it easier to understand.

app/finders/events_finder.rb

@@ -33,7 +33,8 @@ class EventsFinder
   private
 
   def by_current_user_access(events)
-    events.merge(ProjectsFinder.new(current_user: current_user).execute).references(:project)
+    events.merge(ProjectsFinder.new(current_user: current_user).execute).
+      joins(:project)
   end
 
   def by_action(events)

app/finders/group_projects_finder.rb

@@ -29,35 +29,69 @@ class GroupProjectsFinder < ProjectsFinder
   private
 
   def init_collection
-    only_owned  = options.fetch(:only_owned, false)
-    only_shared = options.fetch(:only_shared, false)
+    projects = if current_user
+                 collection_with_user
+               else
+                 collection_without_user
+               end
 
-    projects = []
+    union(projects)
+  end
 
-    if current_user
-      if group.users.include?(current_user)
-        projects << group.projects unless only_shared
-        projects << group.shared_projects unless only_owned
+  def collection_with_user
+    if group.users.include?(current_user)
+      if only_shared?
+        [shared_projects]
+      elsif only_owned?
+        [owned_projects]
       else
-        unless only_shared
-          projects << group.projects.visible_to_user(current_user)
-          projects << group.projects.public_to_user(current_user)
-        end
-
-        unless only_owned
-          projects << group.shared_projects.visible_to_user(current_user)
-          projects << group.shared_projects.public_to_user(current_user)
-        end
+        [shared_projects, owned_projects]
       end
     else
-      projects << group.projects.public_only unless only_shared
-      projects << group.shared_projects.public_only unless only_owned
+      if only_shared?
+        [shared_projects.public_or_visible_to_user(current_user)]
+      elsif only_owned?
+        [owned_projects.public_or_visible_to_user(current_user)]
+      else
+        [
+          owned_projects.public_or_visible_to_user(current_user),
+          shared_projects.public_or_visible_to_user(current_user)
+        ]
+      end
     end
+  end
 
-    projects
+  def collection_without_user
+    if only_shared?
+      [shared_projects.public_only]
+    elsif only_owned?
+      [owned_projects.public_only]
+    else
+      [shared_projects.public_only, owned_projects.public_only]
+    end
   end
 
   def union(items)
-    find_union(items, Project)
+    if items.one?
+      items.first
+    else
+      find_union(items, Project)
+    end
+  end
+
+  def only_owned?
+    options.fetch(:only_owned, false)
+  end
+
+  def only_shared?
+    options.fetch(:only_shared, false)
+  end
+
+  def owned_projects
+    group.projects
+  end
+
+  def shared_projects
+    group.shared_projects
   end
 end

app/finders/projects_finder.rb

@@ -58,27 +58,11 @@ class ProjectsFinder < UnionFinder
       if private_only?
         current_user.authorized_projects
       else
-        collection_with_user_and_public_projects
+        Project.public_or_visible_to_user(current_user)
       end
     end
   end
 
-  # Builds a collection for a signed in user that includes additional projects
-  # such as public and internal ones.
-  #
-  # This method manually constructs some WHERE conditions in order to ensure the
-  # produced query is as efficient as possible.
-  def collection_with_user_and_public_projects
-    levels = Gitlab::VisibilityLevel.levels_for_user(current_user)
-    authorized = current_user.project_authorizations.
-      select(1).
-      where('project_id = projects.id')
-
-    Project.where('EXISTS (?) OR projects.visibility_level IN (?)',
-                  authorized,
-                  levels)
-  end
-
   # Builds a collection for an anonymous user.
   def collection_without_user
     if private_only? || owned_projects?

app/models/project.rb

@@ -266,6 +266,23 @@ class Project < ActiveRecord::Base
 
   enum auto_cancel_pending_pipelines: { disabled: 0, enabled: 1 }
 
+  # Returns a collection of projects that is either public or visible to the
+  # logged in user.
+  def self.public_or_visible_to_user(user = nil)
+    if user
+      authorized = user.
+        project_authorizations.
+        select(1).
+        where('project_authorizations.project_id = projects.id')
+
+      levels = Gitlab::VisibilityLevel.levels_for_user(user)
+
+      where('EXISTS (?) OR projects.visibility_level IN (?)', authorized, levels)
+    else
+      public_to_user
+    end
+  end
+
   # project features may be "disabled", "internal" or "enabled". If "internal",
   # they are only available to team members. This scope returns projects where
   # the feature is either enabled, or internal with permission for the user.

spec/models/project_spec.rb

@@ -2060,4 +2060,36 @@ describe Project, models: true do
       expect(project.last_repository_updated_at.to_i).to eq(project.created_at.to_i)
     end
   end
+
+  describe '.public_or_visible_to_user' do
+    let!(:user) { create(:user) }
+
+    let!(:private_project) do
+      create(:empty_project, :private, creator: user, namespace: user.namespace)
+    end
+
+    let!(:public_project) { create(:empty_project, :public) }
+
+    context 'with a user' do
+      let(:projects) do
+        Project.all.public_or_visible_to_user(user)
+      end
+
+      it 'includes projects the user has access to' do
+        expect(projects).to include(private_project)
+      end
+
+      it 'includes projects the user can see' do
+        expect(projects).to include(public_project)
+      end
+    end
+
+    context 'without a user' do
+      it 'only includes public projects' do
+        projects = Project.all.public_or_visible_to_user
+
+        expect(projects).to eq([public_project])
+      end
+    end
+  end
 end