Show different controls on project member page depending on if the membership lock is in place.

app/helpers/projects_helper.rb

@@ -279,4 +279,12 @@ module ProjectsHelper
     result.password = '*****' if result.password.present?
     result
   end
+
+  def membership_locked?
+    if @project.group && @project.group.membership_lock
+      true
+    else
+      false
+    end
+  end
 end

app/views/projects/team_members/_team_member.html.haml

 - user = member.user
 %li{id: dom_id(user), class: "team_member_row access-#{member.human_access.downcase}"}
+  - unless membership_locked?
     .pull-right
       - if current_user_can_admin_project
         - unless @project.personal? && user == current_user

app/views/projects/team_members/index.html.haml

 %h3.page-title
   Users with access to this project
 
-  - if can? current_user, :admin_team_member, @project
+  - unless membership_locked?
+    - if can?(current_user, :admin_team_member, @project)
       %span.pull-right
         = link_to new_project_team_member_path(@project), class: "btn btn-new btn-grouped", title: "New project member" do
           New project member
         = link_to import_project_team_members_path(@project), class: "btn btn-grouped", title: "Import members from another project" do
           Import members
 
+
 %p.light
   Read more about project permissions
   %strong= link_to "here", help_page_path("permissions", "permissions"), class: "vlink"
+  - if membership_locked?
+    %span.pull-right
+      Adding new user to membership is disabled by a group setting
+
 = render "team", members: @project_members
 - if @group
   = render "group_members"

app/views/shared/_group_form.html.haml

@@ -10,3 +10,10 @@
   .col-sm-10
     = f.text_area :description, maxlength: 250,
         class: 'form-control js-gfm-input', rows: 4
+.form-group
+  = f.label :name, class: 'control-label' do
+    Member lock
+  .col-sm-10
+    .checkbox
+      = f.check_box :membership_lock
+      %span.descr Prevent adding new members to project membership within this group