Refactor ProjectsFinder to not pluck IDs

This class now uses a UNION (when needed) instead of plucking tens of
thousands of project IDs into memory. The tests have also been
re-written to ensure all different use cases are tested properly
(assuming I didn't forget any cases).

The finder has also been broken up into 3 different finder classes:

* ContributedProjectsFinder: class for getting the projects a user
  contributed to.
* PersonalProjectsFinder: class for getting the personal projects of a
  user.
* ProjectsFinder: class for getting generic projects visible to a given
  user.

Previously a lot of the logic of these finders was handled directly in
the users controller.

3 files changed, 128 insertions, 67 deletions

diff --git a/app/finders/contributed_projects_finder.rb b/app/finders/contributed_projects_finder.rb
new file mode 100644
index 00000000000..0209649b017
--- /dev/null
+++ b/app/finders/contributed_projects_finder.rb
@@ -0,0 +1,37 @@
+class ContributedProjectsFinder
+  def initialize(user)
+    @user = user
+  end
+
+  # Finds the projects "@user" contributed to, limited to either public projects
+  # or projects visible to the given user.
+  #
+  # current_user - When given the list of the projects is limited to those only
+  #                visible by this user.
+  #
+  # Returns an ActiveRecord::Relation.
+  def execute(current_user = nil)
+    if current_user
+      relation = projects_visible_to_user(current_user)
+    else
+      relation = public_projects
+    end
+
+    relation.includes(:namespace).order_id_desc
+  end
+
+  private
+
+  def projects_visible_to_user(current_user)
+    authorized = @user.contributed_projects.visible_to_user(current_user)
+
+    union = Gitlab::SQL::Union.
+      new([authorized.select(:id), public_projects.select(:id)])
+
+    Project.where("projects.id IN (#{union.to_sql})")
+  end
+
+  def public_projects
+    @user.contributed_projects.public_only
+  end
+end
diff --git a/app/finders/personal_projects_finder.rb b/app/finders/personal_projects_finder.rb
new file mode 100644
index 00000000000..7c039573614
--- /dev/null
+++ b/app/finders/personal_projects_finder.rb
@@ -0,0 +1,37 @@
+class PersonalProjectsFinder
+  def initialize(user)
+    @user = user
+  end
+
+  # Finds the projects belonging to the user in "@user", limited to either
+  # public projects or projects visible to the given user.
+  #
+  # current_user - When given the list of projects is limited to those only
+  #                visible by this user.
+  #
+  # Returns an ActiveRecord::Relation.
+  def execute(current_user = nil)
+    if current_user
+      relation = projects_visible_to_user(current_user)
+    else
+      relation = public_projects
+    end
+
+    relation.includes(:namespace).order_id_desc
+  end
+
+  private
+
+  def projects_visible_to_user(current_user)
+    authorized = @user.personal_projects.visible_to_user(current_user)
+
+    union = Gitlab::SQL::Union.
+      new([authorized.select(:id), public_projects.select(:id)])
+
+    Project.where("projects.id IN (#{union.to_sql})")
+  end
+
+  def public_projects
+    @user.personal_projects.public_only
+  end
+end
diff --git a/app/finders/projects_finder.rb b/app/finders/projects_finder.rb
index c81bb51583a..dd35c215c50 100644
--- a/app/finders/projects_finder.rb
+++ b/app/finders/projects_finder.rb
@@ -1,11 +1,39 @@
 class ProjectsFinder
-  def execute(current_user, options = {})
+  # Returns all projects, optionally including group projects a user has access
+  # to.
+  #
+  # ## Examples
+  #
+  # Retrieving all public projects:
+  #
+  #     ProjectsFinder.new.execute
+  #
+  # Retrieving all public/internal projects and those the given user has access
+  # to:
+  #
+  #     ProjectsFinder.new.execute(some_user)
+  #
+  # Retrieving all public/internal projects as well as the group's projects the
+  # user has access to:
+  #
+  #     ProjectsFinder.new.execute(some_user, group: some_group)
+  #
+  # Returns an ActiveRecord::Relation.
+  def execute(current_user = nil, options = {})
     group = options[:group]
 
     if group
-      group_projects(current_user, group)
+      base, extra = group_projects(current_user, group)
     else
-      all_projects(current_user)
+      base, extra = all_projects(current_user)
+    end
+
+    if base and extra
+      union = Gitlab::SQL::Union.new([base.select(:id), extra.select(:id)])
+
+      Project.where("projects.id IN (#{union.to_sql})")
+    else
+      base
     end
   end
 
@@ -13,77 +41,36 @@ class ProjectsFinder
 
   def group_projects(current_user, group)
     if current_user
-      if group.users.include?(current_user)
-        # User is group member
-        #
-        # Return ALL group projects
-        group.projects
-      else
-        projects_members = ProjectMember.in_projects(group.projects).
-          with_user(current_user)
-
-        if projects_members.any?
-          # User is a project member
-          #
-          # Return only:
-          #   public projects
-          #   internal projects
-          #   joined projects
-          #
-          group.projects.where(
-            "projects.id IN (?) OR projects.visibility_level IN (?)",
-            projects_members.pluck(:source_id),
-            Project.public_and_internal_levels
-          )
-        else
-          # User has no access to group or group projects
-          #
-          # Return only:
-          #   public projects
-          #   internal projects
-          #
-          group.projects.public_and_internal_only
-        end
-      end
+      [
+        group_projects_for_user(current_user, group),
+        group.projects.public_and_internal_only
+      ]
     else
-      # Not authenticated
-      #
-      # Return only:
-      #   public projects
-      group.projects.public_only
+      [group.projects.public_only]
     end
   end
 
   def all_projects(current_user)
     if current_user
-      if current_user.authorized_projects.any?
-        # User has access to private projects
-        #
-        # Return only:
-        #   public projects
-        #   internal projects
-        #   joined projects
-        #
-        Project.where(
-          "projects.id IN (?) OR projects.visibility_level IN (?)",
-          current_user.authorized_projects.pluck(:id),
-          Project.public_and_internal_levels
-        )
-      else
-        # User has no access to private projects
-        #
-        # Return only:
-        #   public projects
-        #   internal projects
-        #
-        Project.public_and_internal_only
-      end
+      [current_user.authorized_projects, public_and_internal_projects]
     else
-      # Not authenticated
-      #
-      # Return only:
-      #   public projects
-      Project.public_only
+      [Project.public_only]
     end
   end
+
+  def group_projects_for_user(current_user, group)
+    if group.users.include?(current_user)
+      group.projects
+    else
+      group.projects.visible_to_user(current_user)
+    end
+  end
+
+  def public_projects
+    Project.unscoped.public_only
+  end
+
+  def public_and_internal_projects
+    Project.unscoped.public_and_internal_only
+  end
 end