Adding reactive forms

- Style user, placeholder user and group avatars
  depending on their class.
- Extend autocompleter options to communicate
  that an option is a placeholder or group.

app/cells/placeholder_user_filter_cell.rb

@@ -0,0 +1,69 @@
+class PlaceholderUserFilterCell < RailsCell
+  include UsersHelper
+  include ActionView::Helpers::FormOptionsHelper
+
+  options :groups, :roles, :clear_url, :project
+
+  class << self
+    def filter(params)
+      q = base_query.new
+
+      filter_project q, params[:project_id]
+      filter_name q, params[:name]
+      filter_group q, params[:group_id]
+      filter_role q, params[:role_id]
+
+      q.results
+    end
+
+    def filtered?(params)
+      %i(name group_id role_id).any? { |name| params[name].present? }
+    end
+
+    def filter_name(query, name)
+      if name.present?
+        query.where(:any_name_attribute, '~', name)
+      end
+    end
+
+    def filter_group(query, group_id)
+      if group_id.present?
+        query.where(:group, '=', group_id)
+      end
+    end
+
+    def filter_role(query, role_id)
+      if role_id.present?
+        query.where(:role_id, '=', role_id)
+      end
+    end
+
+    def filter_project(query, project_id)
+      if project_id.present?
+        query.where(:project_id, '=', project_id)
+      end
+    end
+
+    def base_query
+      Queries::PlaceholderUsers::PlaceholderUserQuery
+    end
+  end
+
+  # INSTANCE METHODS:
+
+  def filter_path
+    placeholder_users_path
+  end
+
+  def initially_visible?
+    true
+  end
+
+  def has_close_icon?
+    false
+  end
+
+  def params
+    model
+  end
+end

app/cells/placeholder_users/placeholder_user_filter_cell.rb

@@ -0,0 +1,11 @@
+module PlaceholderUsers
+  class PlaceholderUserFilterCell < ::PlaceholderUserFilterCell
+    def filter_role(query, role_id)
+      super.uniq
+    end
+
+    def clear_url
+      placeholder_users_path
+    end
+  end
+end

app/cells/placeholder_users/row_cell.rb

@@ -0,0 +1,28 @@
+module PlaceholderUsers
+  class RowCell < ::RowCell
+    include AvatarHelper
+    include UsersHelper
+
+    def placeholder_user
+      model
+    end
+
+    def lastname
+      link_to h(placeholder_user.name), edit_placeholder_user_path(placeholder_user)
+    end
+
+    def button_links
+      [delete_link].compact
+    end
+
+    def delete_link
+      return nil unless Users::DeleteService.deletion_allowed? placeholder_user, User.current
+
+      link_to '',
+              placeholder_user_path(placeholder_user),
+              data: { confirm: 'Are you sure?' },
+              class: 'icon icon-delete',
+              method: :delete
+    end
+  end
+end

app/cells/placeholder_users/table_cell.rb

@@ -0,0 +1,28 @@
+module PlaceholderUsers
+  class TableCell < ::TableCell
+    options :current_user # adds this option to those of the base class
+    columns :lastname, :created_at
+
+    def initial_sort
+      [:id, :asc]
+    end
+
+    def headers
+      columns.map do |name|
+        [name.to_s, header_options(name)]
+      end
+    end
+
+    def header_options(name)
+      options = { caption: name == :lastname ? User.human_attribute_name(:name) : User.human_attribute_name(name) }
+
+      options[:default_order] = 'desc' if desc_by_default.include? name
+
+      options
+    end
+
+    def desc_by_default
+      [:created_at]
+    end
+  end
+end

app/cells/views/placeholder_user_filter/show.erb

@@ -0,0 +1,85 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2013 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+
+<%= form_tag(filter_path, method: :get) do %>
+   <% collapsed_class =  initially_visible? ? '' : 'collapsed' %>
+  <fieldset class="simple-filters--container <%= collapsed_class %>">
+    <legend><%= t(:label_filter_plural) %></legend>
+    <% if has_close_icon? %>
+      <a title="<%= t('js.close_form_title') %>"
+         class="toggle-member-filter-link simple-filters--close icon-context icon-close">
+      </a>
+    <% end %>
+    <ul class="simple-filters--filters">
+      <% if groups.present? %>
+        <li class="simple-filters--filter">
+          <label class='simple-filters--filter-name' for='group_id'><%= Group.model_name.human %>:</label>
+          <%= collection_select :group,
+                              :id,
+                              groups,
+                              :id,
+                              :name,
+                              { include_blank: true,
+                                selected: params[:group_id].to_i },
+                              { name: "group_id",
+                                class: 'simple-filters--filter-value' } %>
+        </li>
+      <% end %>
+      <% if roles.present? %>
+        <li class="simple-filters--filter">
+          <label class='simple-filters--filter-name' for='role_id'><%= Role.model_name.human %>:</label>
+          <%=
+            collection_select(
+              :role,
+              :id,
+              roles,
+              :id,
+              :name,
+              {
+                include_blank: true,
+                selected: params[:role_id].to_i
+              },
+              {
+                name: "role_id",
+                class: 'simple-filters--filter-value'
+              })
+            %>
+        </li>
+      <% end %>
+      <li class="simple-filters--filter">
+        <label class='simple-filters--filter-name' for='name'><%= User.human_attribute_name :name %>:</label>
+        <%= text_field_tag 'name', params[:name], class: 'simple-filters--filter-value' %>
+      </li>
+      <li class="simple-filters--controls">
+        <%= submit_tag t(:button_apply), class: 'button -highlight -small', name: nil %>
+        <%= link_to t(:button_clear), clear_url, class: 'button -small -with-icon icon-undo' %>
+      </li>
+    </ul>
+  </fieldset>
+<% end %>

app/controllers/placeholder_users/memberships_controller.rb

@@ -0,0 +1,92 @@
+#-- encoding: UTF-8
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+class PlaceholderUsers::MembershipsController < ApplicationController
+  layout 'admin'
+
+  before_action :require_admin
+  before_action :find_placeholder_user
+
+  def update
+    update_or_create(request.patch?, :notice_successful_update)
+  end
+
+  def create
+    update_or_create(request.post?, :notice_successful_create)
+  end
+
+  def destroy
+    @membership = @placeholder_user.memberships.find(params[:id])
+    tab = redirected_to_tab(@membership)
+
+    if @membership.deletable? && request.delete?
+      @membership.destroy
+      @membership = nil
+
+      flash[:notice] = I18n.t(:notice_successful_delete)
+    end
+
+    redirect_to controller: '/placeholder_users', action: 'edit', id: @user, tab: tab
+  end
+
+  private
+
+  def update_or_create(save_record, message)
+    @membership = params[:id].present? ? Member.find(params[:id]) : Member.new(principal: @placeholder_user, project: nil)
+
+    result = ::Members::EditMembershipService
+             .new(@membership, save: save_record, current_user: current_user)
+             .call(attributes: permitted_params.membership)
+
+    if result.success?
+      flash[:notice] = I18n.t(message)
+    else
+      flash[:error] = result.errors.full_messages.join("\n")
+    end
+
+    redirect_to controller: '/placeholder_users',
+                action: 'edit',
+                id: @placeholder_user,
+                tab: redirected_to_tab(@membership)
+  end
+
+  def find_placeholder_user
+    @placeholder_user = PlaceholderUser.find(params[:placeholder_user_id])
+  rescue ActiveRecord::RecordNotFound
+    render_404
+  end
+
+  def redirected_to_tab(membership)
+    if membership.project
+      'memberships'
+    else
+      'global_roles'
+    end
+  end
+end

app/controllers/placeholder_users_controller.rb

@@ -0,0 +1,160 @@
+#-- encoding: UTF-8
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+class PlaceholderUsersController < ApplicationController
+  layout 'admin'
+
+  helper_method :gon
+
+  before_action :require_admin, except: [:show, :deletion_info, :destroy]
+  before_action :find_placeholder_user, only: [:show,
+                                               :edit,
+                                               :update,
+                                               :destroy,
+                                               :resend_invitation]
+  before_action :check_if_deletion_allowed, only: [:destroy]
+
+  def index
+    @groups = Group.all.sort
+    @placeholder_users = PlaceholderUsers::PlaceholderUserFilterCell.filter params
+
+    respond_to do |format|
+      format.html do
+        render layout: !request.xhr?
+      end
+    end
+  end
+
+  def show
+    # show projects based on current user visibility
+    @memberships = @user.memberships
+                        .visible(current_user)
+
+    events = Activities::Fetcher.new(User.current, author: @user).events(nil, nil, limit: 10)
+    @events_by_day = events.group_by { |e| e.event_datetime.to_date }
+
+    if !User.current.admin? &&
+       (!(@user.active? ||
+       @user.registered?) ||
+       (@user != User.current && @memberships.empty? && events.empty?))
+      render_404
+    else
+      respond_to do |format|
+        format.html { render layout: 'no_menu' }
+      end
+    end
+  end
+
+  def new
+    @placeholder_user = PlaceholderUser.new
+  end
+
+  def create
+    @placeholder_user = PlaceholderUser.new
+    @placeholder_user.attributes = permitted_params.placeholder_user
+
+    if @placeholder_user.save
+      respond_to do |format|
+        format.html do
+          flash[:notice] = I18n.t(:notice_successful_create)
+          redirect_to(params[:continue] ? new_placeholder_user_path : edit_placeholder_user_path(@placeholder_user))
+        end
+      end
+    else
+      respond_to do |format|
+        format.html do
+          render action: :new
+        end
+      end
+    end
+  end
+
+  def edit
+    @membership ||= Member.new
+  end
+
+  def update
+    @placeholder_user.attributes = permitted_params.placeholder_user
+
+    if @placeholder_user.save
+      respond_to do |format|
+        format.html do
+          flash[:notice] = I18n.t(:notice_successful_update)
+          redirect_back(fallback_location: edit_placeholder_user_path(@placeholder_user))
+        end
+      end
+    else
+      @membership ||= Member.new
+
+      respond_to do |format|
+        format.html do
+          render action: :edit
+        end
+      end
+    end
+  end
+
+  def destroy
+    Users::DeleteService.new(@placeholder_user, User.current).call
+
+    flash[:notice] = I18n.t('account.deleted')
+
+    respond_to do |format|
+      format.html do
+        redirect_to placeholder_users_path
+      end
+    end
+  end
+
+  private
+
+  def find_placeholder_user
+    @placeholder_user = PlaceholderUser.find(params[:id])
+  rescue ActiveRecord::RecordNotFound
+    render_404
+  end
+
+  def check_if_deletion_allowed
+    render_404 unless Users::DeleteService.deletion_allowed? @placeholder_user, User.current
+  end
+
+  protected
+
+  def default_breadcrumb
+    if action_name == 'index'
+      t('label_placeholder_user_plural')
+    else
+      ActionController::Base.helpers.link_to(t('label_placeholder_user_plural'), placeholder_users_path)
+    end
+  end
+
+  def show_local_breadcrumb
+    current_user.admin?
+  end
+end

app/models/anonymous_user.rb

@@ -1,3 +1,33 @@
+#-- encoding: UTF-8
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
 class AnonymousUser < User
   validate :validate_unique_anonymous_user, on: :create
 

app/models/group.rb

@@ -33,6 +33,10 @@ class Group < Principal
                           before_add: :fail_add,
                           after_remove: :user_removed
 
+  has_and_belongs_to_many :placeholder_users,
+                          join_table:   "#{table_name_prefix}group_users#{table_name_suffix}",
+                          before_add: :fail_add,
+                          after_remove: :user_removed
   acts_as_customizable
 
   before_destroy :remove_references_before_destroy

app/models/permitted_params.rb

@@ -188,6 +188,13 @@ class PermittedParams
     permitted_params
   end
 
+  def placeholder_user
+    permitted_params = params.require(:placeholder_user).permit(*self.class.permitted_attributes[:placeholder_user])
+    permitted_params = permitted_params.merge(custom_field_values(:placeholder_user))
+
+    permitted_params
+  end
+
   def user_register_via_omniauth
     permitted_params = params
                        .require(:user)
@@ -534,6 +541,10 @@ class PermittedParams
           :client_credentials_user_id,
           scopes: []
         ],
+        placeholder_user: %i(
+          lastname
+          custom_fields
+        ),
         project_type: [
           :name,
           type_ids: []],

app/models/placeholder_user.rb

@@ -0,0 +1,46 @@
+#-- encoding: UTF-8
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+class PlaceholderUser < Principal
+  validates_presence_of(:lastname)
+  validates_uniqueness_of(:lastname)
+
+  acts_as_customizable
+
+  has_and_belongs_to_many :groups,
+                          join_table:   "#{table_name_prefix}group_users#{table_name_suffix}",
+                          foreign_key: 'user_id',
+                          after_add:    ->(user, group) { group.user_added(user) },
+                          after_remove: ->(user, group) { group.user_removed(user) }
+
+  def to_s
+    lastname
+  end
+end

app/models/principal.rb

@@ -73,6 +73,13 @@ class Principal < ApplicationRecord
   }
 
   scope :not_builtin, -> {
+    # TODO: Remove PlaceholderUser from this list. This is a temporary hack.
+    where.not(type: [SystemUser.name, AnonymousUser.name, DeletedUser.name, PlaceholderUser.name])
+  }
+
+  scope :not_builtin_but_with_placeholder_users, -> {
+    # TODO: This is temporary precaution scope to circumvent the hack in the :not_builtin scope. Needs to be
+    # removed.
     where.not(type: [SystemUser.name, AnonymousUser.name, DeletedUser.name])
   }
 

app/models/project.rb

@@ -101,6 +101,7 @@ class Project < ApplicationRecord
              includes(:principal)
                .references(:principals)
                .where("#{Principal.table_name}.type='Group' OR " +
+               "(#{Principal.table_name}.type='PlaceholderUser' OR " +
                "(#{Principal.table_name}.type='User' AND " +
                "(#{Principal.table_name}.status=#{Principal::STATUSES[:active]} OR " +
                "#{Principal.table_name}.status=#{Principal::STATUSES[:registered]} OR " +
@@ -522,9 +523,9 @@ class Project < ApplicationRecord
 
   def self.possible_principles_condition
     condition = if Setting.work_package_group_assignment?
-                  ["(#{Principal.table_name}.type=? OR #{Principal.table_name}.type=?)", 'User', 'Group']
+                  ["(#{Principal.table_name}.type=? OR #{Principal.table_name}.type=?  OR #{Principal.table_name}.type=?)", 'User', 'Group', 'PlaceholderUser']
                 else
-                  ["(#{Principal.table_name}.type=?)", 'User']
+                  ["(#{Principal.table_name}.type=? OR #{Principal.table_name}.type=?)", 'User', 'PlaceholderUser']
                 end
 
     condition[0] += " AND (#{User.table_name}.status=? OR #{User.table_name}.status=?) AND roles.assignable = ?"

app/models/queries/placeholder_users.rb

@@ -0,0 +1,39 @@
+#-- encoding: UTF-8
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+module Queries::PlaceholderUsers
+  Queries::Register.filter Queries::PlaceholderUsers::PlaceholderUserQuery, Queries::Users::Filters::NameFilter
+  Queries::Register.filter Queries::PlaceholderUsers::PlaceholderUserQuery, Queries::Users::Filters::AnyNameAttributeFilter
+  Queries::Register.filter Queries::PlaceholderUsers::PlaceholderUserQuery, Queries::Users::Filters::GroupFilter
+
+  Queries::Register.order Queries::PlaceholderUsers::PlaceholderUserQuery, Queries::Users::Orders::DefaultOrder
+  Queries::Register.order Queries::PlaceholderUsers::PlaceholderUserQuery, Queries::Users::Orders::NameOrder
+  Queries::Register.order Queries::PlaceholderUsers::PlaceholderUserQuery, Queries::Users::Orders::GroupOrder
+end

app/models/queries/placeholder_users/placeholder_user_query.rb

@@ -0,0 +1,37 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+class Queries::PlaceholderUsers::PlaceholderUserQuery < Queries::BaseQuery
+  def self.model
+    PlaceholderUser
+  end
+
+  def default_scope
+    PlaceholderUser.not_builtin_but_with_placeholder_users
+  end
+end

app/models/user.rb

@@ -118,11 +118,15 @@ class User < Principal
   attr_accessor :password, :password_confirmation
   attr_accessor :last_before_login_on
 
-  validates_presence_of :login,
+  validates_presence_of(:login,
                         :firstname,
                         :lastname,
                         :mail,
-                        unless: Proc.new { |user| user.is_a?(AnonymousUser) || user.is_a?(DeletedUser) || user.is_a?(SystemUser) }
+                        unless: Proc.new do |user|
+                          user.is_a?(AnonymousUser) ||
+                          user.is_a?(DeletedUser) ||
+                          user.is_a?(SystemUser) ||
+                          user.is_a?(PlaceholderUser) end)
 
   validates_uniqueness_of :login, if: Proc.new { |user| !user.login.blank? }, case_sensitive: false
   validates_uniqueness_of :mail, allow_blank: true, case_sensitive: false

app/views/placeholder_users/_form.html.erb

@@ -0,0 +1,45 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+
+<%= error_messages_for 'placeholder_user' %>
+
+
+<!--[form:user]-->
+<section class="form--section">
+  <div class="form--field -required"><%= f.text_field :lastname, label: t('label_name'),  required: true, container_class: '-middle' %></div>
+
+  <h3 class="form--section-title"><%= t(:label_custom_field_plural) %></h3>
+  <%= render partial:     'customizable/field',
+             collection:  @placeholder_user.custom_field_values,
+             as:          :value,
+             locals:      { form: f } %>
+
+  <%= call_hook(:view_placeholder_users_form, placeholder_user: @placeholder_user, form: f) %>
+</section>
+<!--[eoform:user]-->

app/views/placeholder_users/_general.html.erb

@@ -0,0 +1,40 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+
+<%= labelled_tabular_form_for @user,
+                              url: { controller: '/placeholder_users',
+                                        action: "update",
+                                        tab: nil },
+                              html: { method: :put,
+                                         autocomplete: 'off' },
+                              as: :placeholder_user do |f| %>
+  <%= render partial: 'form', locals: { f: f } %>
+
+  <%= styled_button_tag t(:button_save), class: '-highlight -with-icon icon-checkmark' %>
+<% end %>

app/views/placeholder_users/_groups.html.erb

@@ -0,0 +1,49 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+<% groups = @placeholder_user.groups.pluck(:id, :lastname) %>
+
+<%= labelled_tabular_form_for(:placeholder_user, url: { action: 'update' }, html: { method: :put }) do %>
+  <section class="form--section">
+    <% if groups.empty? %>
+      <%= no_results_box action_url: groups_path,
+                         display_action: true,
+                         custom_title: t('placeholder_users.groups.no_results_title_text'),
+                         custom_action_text: t(:label_manage_groups)
+      %>
+    <% else %>
+      <p><%= t('placeholder_users.groups.member_in_these_groups') %></p>
+    <% end %>
+
+    <% groups.each do |id, name| %>
+      <ul>
+        <li><%= link_to name, edit_group_path(id) %></li>
+      </ul>
+    <% end %>
+  </section>
+<% end %>

app/views/placeholder_users/_memberships.html.erb

@@ -0,0 +1,148 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+<% roles = Role.givable %>
+<% projects = Project.active.order(Arel.sql('lft')) %>
+
+<div class="grid-block">
+  <div class="grid-content">
+  <% if @placeholder_user.memberships.any? %>
+    <div class="generic-table--container">
+      <div class="generic-table--results-container">
+        <table class="generic-table memberships">
+          <colgroup>
+            <col highlight-col>
+            <col highlight-col>
+            <%= call_hook(:view_placeholder_users_memberships_table_colgroup, placeholder_user: @placeholder_user )%>
+            <col>
+          </colgroup>
+          <thead>
+            <tr>
+              <th>
+                <div class="generic-table--sort-header-outer">
+                  <div class="generic-table--sort-header">
+                    <span>
+                      <%= Project.model_name.human %>
+                    </span>
+                  </div>
+                </div>
+              </th>
+              <th>
+                <div class="generic-table--sort-header-outer">
+                  <div class="generic-table--sort-header">
+                    <span>
+                      <%= t(:label_role_plural) %>
+                    </span>
+                  </div>
+                </div>
+              </th>
+              <%= call_hook(:view_users_memberships_table_header, placeholder_user: @placeholder_user )%>
+              <th><div class="generic-table--empty-header"></div></th>
+            </tr>
+          </thead>
+          <tbody>
+            <% @placeholder_user.memberships.where.not(project: nil).each do |membership| %>
+              <% next if membership.new_record? %>
+                <tr id="member-<%= membership.id %>" class="member">
+                  <td class="project">
+                    <%= link_to_project membership.project %>
+                  </td>
+                  <td class="roles">
+                    <span id="member-<%= membership.id %>-roles"
+                          class="member-<%= membership.id %>--edit-toggle-item">
+                      <%=h membership.roles.sort.collect(&:to_s).join(', ') %>
+                    </span>
+                    <%= labelled_tabular_form_for(:membership,
+                                                  url: placeholder_user_membership_path(placeholder_user_id: @placeholder_user, id: membership),
+                                                  html: { id: "member-#{membership.id}-roles-form",
+                                                          class: "member-#{membership.id}--edit-toggle-item",
+                                                          style: 'display:none;'},
+                                                  method: :patch) do |f| %>
+                      <div>
+                        <% roles.each do |role| %>
+                            <label class="form--label-with-check-box">
+                            <%= f.collection_check_box :role_ids,
+                                                       role.id,
+                                                       membership.roles.include?(role),
+                                                       role.name,
+                                                       disabled: membership.member_roles.detect {|mr| mr.role_id == role.id && !mr.inherited_from.nil?},
+                                                       no_label: true,
+                                                       id: nil
+                            %>
+                            <%= role %>
+                            </label>
+                        <% end %>
+                      </div>
+                      <p><%= submit_tag t(:button_change), class: 'user-memberships--edit-submit-button button -highlight -small' %>
+                        <%= link_to_function t(:button_cancel),
+                                             "jQuery('.member-#{membership.id}--edit-toggle-item').toggle();",
+                  class: 'button -small' %></p>
+                    <% end %>
+                  </td>
+                  <%= call_hook(:view_placheholder_users_memberships_table_row, placeholder_user: @placeholder_user, membership: membership, roles: roles, projects: projects )%>
+                  <td class="buttons">
+                    <%= link_to_function icon_wrapper('icon icon-edit', t(:button_edit)),
+                                         "jQuery('.member-#{membership.id}--edit-toggle-item').toggle();",
+                                         class: "member-#{membership.id}--edit-toggle-item user-memberships--edit-button",
+                                         title: t(:button_edit) %>
+                    <%= link_to(icon_wrapper('icon icon-remove', t(:button_remove)),
+                                placeholder_user_membership_path(placeholder_user_id: @placeholder_user, id: membership),
+                                method: :delete,
+                                title: t(:button_remove)) if membership.deletable? %>
+                  </td>
+                </tr>
+              <% end %>
+            </tbody>
+          </table>
+
+        </div>
+      </div>
+    <% else %>
+      <%= no_results_box %>
+    <% end %>
+  </div>
+  <div class="grid-content">
+    <% if projects.any? %>
+      <%= labelled_tabular_form_for(:membership,
+                                    url: placeholder_user_memberships_path(placeholder_user_id: @placeholder_user),
+                                    html: {id: "new_project_membership"}) do %>
+        <fieldset class="form--fieldset">
+          <legend class="form--fieldset-legend"><%=t(:label_project_new)%></legend>
+          <%= styled_select_tag 'membership[project_id]', options_for_membership_project_select(@placeholder_user, projects) %>
+          <div class="form--field -vertical">
+            <%= styled_label_tag nil, "#{t(:label_role_plural)}:" %>
+            <div class="form--field-container -vertical">
+              <%= labeled_check_box_tags 'membership[role_ids][]', roles %>
+            </div>
+          </div>
+          <div><%= styled_button_tag t(:button_add), class: '-highlight -with-icon icon-checkmark' %></div>
+        </fieldset>
+      <% end %>
+    <% end %>
+  </div>
+</div>

app/views/placeholder_users/edit.html.erb

@@ -0,0 +1,36 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+
+
+<% html_title(t(:label_administration), "#{t(:label_edit)} #{PlaceholderUser.model_name.human} #{h(@placeholder_user.name)}") -%>
+
+<% local_assigns[:additional_breadcrumb] = @placeholder_user.name %>
+<%= render partial: 'users/toolbar', locals: { new_user: false, :@user => @placeholder_user } %>
+
+<%= render_extensible_tabs :placeholder_user, placeholder_user: @placeholder_user %>

app/views/placeholder_users/index.html.erb

@@ -0,0 +1,46 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+<% html_title t(:label_administration), t(:label_placeholder_user_plural) -%>
+
+<%= toolbar title: t(:label_placeholder_user_plural), title_class: 'no-padding-bottom' do %>
+  <li class="toolbar-item">
+    <%= link_to new_placeholder_user_path,
+                { class: 'button -alt-highlight',
+                  aria: { label: t(:label_placeholder_user_new) },
+                  title: t(:label_placeholder_user_new) } do %>
+      <%= op_icon('button--icon icon-add') %>
+      <span class="button--text"><%= t('activerecord.models.placeholder_user') %></span>
+    <% end %>
+  </li>
+  <%= call_hook(:user_admin_action_menu) %>
+<% end %>
+
+<%= cell PlaceholderUsers::PlaceholderUserFilterCell, params, groups: @groups %>
+&nbsp;
+<%= cell PlaceholderUsers::TableCell, @placeholder_users, project: @project, current_user: current_user %>

app/views/placeholder_users/new.html.erb

@@ -0,0 +1,43 @@
+<%#-- copyright
+OpenProject is an open source project management software.
+Copyright (C) 2012-2020 the OpenProject GmbH
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License version 3.
+
+OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+Copyright (C) 2006-2017 Jean-Philippe Lang
+Copyright (C) 2010-2013 the ChiliProject Team
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+See docs/COPYRIGHT.rdoc for more details.
+
+++#%>
+
+<% html_title t(:label_administration), t("label_placeholder_user_new") %>
+<% local_assigns[:additional_breadcrumb] = t(:label_placeholder_user_new) %>
+<%= render partial: 'users/toolbar', locals: { new_user: true, :@user => @placeholder_user } %>
+<%= labelled_tabular_form_for @placeholder_user,
+                              url: { action: "create" },
+                              html: { class: nil, autocomplete: 'off' },
+                              as: :placeholder_user do |f| %>
+  <%= render partial: 'form', locals: { f: f, placeholder_user: @placeholder_user } %>
+
+  <p>
+    <%= styled_button_tag t(:button_create), class: '-highlight -with-icon icon-checkmark' %>
+    <%= styled_button_tag t(:button_create_and_continue), name: 'continue', class: '-highlight -with-icon icon-checkmark' %>
+  </p>
+<% end %>

app/views/users/_groups.html.erb

@@ -28,7 +28,7 @@ See docs/COPYRIGHT.rdoc for more details.
 ++#%>
 <% groups = @user.groups.pluck(:id, :lastname) %>
 
-<%= labelled_tabular_form_for(:user, url: { action: 'update' }, html: {method: :put}) do %>
+<%= labelled_tabular_form_for(:user, url: { action: 'update' }, html: { method: :put }) do %>
   <section class="form--section">
     <% if groups.empty? %>
       <%= no_results_box action_url: groups_path,

app/views/users/_toolbar.html.erb

@@ -26,9 +26,9 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 See docs/COPYRIGHT.rdoc for more details.
 
 ++#%>
-<%= breadcrumb_toolbar(@user.new_record? ? t(:label_user_new) : @user.name) do %>
+<%= breadcrumb_toolbar(@user.new_record? ? t("label_#{@user.class.name.underscore}_new".to_sym) : @user.name) do %>
   <% unless @user.new_record? %>
-    <% if current_user.admin? || current_user.id == @user.id %>
+    <% if (current_user.admin? || current_user.id == @user.id) && !@user.is_a?(PlaceholderUser) %>
       <li class="toolbar-item hidden-for-mobile">
         <%= form_for(@user, html: { class: 'toolbar-item'},
                             url: { action: :resend_invitation },
@@ -46,7 +46,7 @@ See docs/COPYRIGHT.rdoc for more details.
         <span class="button--text"><%= t(:label_profile) %></span>
       <% end %>
     </li>
-    <% unless current_user.id == @user.id %>
+    <% if current_user.id != @user.id && @user.is_a?(User) %>
       <%= form_for @user, html: { class: 'toolbar-item hidden-for-mobile' }, :url => {:action => :change_status},
                 :method => :post do %>
         <li>

app/views/users/index.html.erb

@@ -44,8 +44,8 @@ See docs/COPYRIGHT.rdoc for more details.
   <li class="toolbar-item">
     <%= link_to new_user_path,
         { class: 'button -alt-highlight',
-          aria: {label: t(:label_user_new)},
-          title: t(:label_user_new)} do %>
+          aria: { label: t(:label_user_new) },
+          title: t(:label_user_new) } do %>
       <%= op_icon('button--icon icon-add') %>
       <span class="button--text"><%= t('activerecord.models.user') %></span>
     <% end %>

config/initializers/menus.rb

@@ -144,6 +144,11 @@ Redmine::MenuManager.map :admin_menu do |menu|
             caption: :label_user_plural,
             parent: :users_and_permissions
 
+  menu.push :placeholder_users,
+            { controller: '/placeholder_users' },
+            caption: :label_placeholder_user_plural,
+            parent: :users_and_permissions
+
   menu.push :groups,
             { controller: '/groups' },
             caption: :label_group_plural,

config/locales/en.yml

@@ -268,6 +268,13 @@ en:
       no_results_title_text: There is currently no news to report.
       no_results_content_text: Add a news item
 
+  placeholder_users:
+    groups:
+      member_in_these_groups: 'This placeholder user is currently a member of the following groups:'
+      no_results_title_text: This placeholder user is currently not a member in any group.
+    memberships:
+      no_results_title_text: This placeholder user is currently not a member of a project.
+
   users:
     groups:
       member_in_these_groups: 'This user is currently a member of the following groups:'
@@ -773,6 +780,7 @@ en:
       status: "Work package status"
       member: "Member"
       news: "News"
+      placeholder_user: "Placeholder user"
       project: "Project"
       query: "Custom query"
       role:
@@ -1534,6 +1542,7 @@ en:
   label_my_account_data: "My account data"
   label_my_projects: "My projects"
   label_my_queries: "My custom queries"
+  label_name: "Name"
   label_never: "Never"
   label_new: "New"
   label_new_features: "New features"
@@ -1583,6 +1592,9 @@ en:
   label_permissions: "Permissions"
   label_permissions_report: "Permissions report"
   label_personalize_page: "Personalize this page"
+  label_placeholder_user: "Placeholder user"
+  label_placeholder_user_new: "New placeholder user"
+  label_placeholder_user_plural: "Placeholder users"
   label_planning: "Planning"
   label_please_login: "Please log in"
   label_plugins: "Plugins"

config/locales/js-en.yml

@@ -1037,3 +1037,6 @@ en:
       card: 'Cards'
       list: 'Table'
       timeline: 'Gantt'
+
+    invite_user_modal:
+      title: "Invite User"

config/routes.rb

@@ -1,4 +1,5 @@
 #-- encoding: UTF-8
+#-- encoding: UTF-8
 
 #-- copyright
 # OpenProject is an open source project management software.
@@ -465,6 +466,17 @@ OpenProject::Application.routes.draw do
     end
   end
 
+  resources :placeholder_users do
+    resources :memberships, controller: 'placeholder_users/memberships', only: %i[update create destroy]
+
+    member do
+      match '/edit/:tab' => 'placeholder_users#edit', via: :get, as: 'tab_edit'
+      match '/change_status/:change_action' => 'users#change_status_info', via: :get, as: 'change_status_info'
+      post :change_status
+      get :deletion_info
+    end
+  end
+
   scope controller: 'users_settings' do
     get 'users_settings' => 'users_settings#index'
     post 'users_settings' => 'users_settings#edit'

docker-compose.yml

@@ -32,25 +32,6 @@ x-op-frontend-build: &frontend-build
     DEV_GID: $DEV_GID
 
 services:
-  db:
-    image: postgres:10
-    <<: *restart_policy
-    stop_grace_period: "3s"
-    volumes:
-      - "pgdata:/var/lib/postgresql/data"
-    environment:
-      POSTGRES_USER: ${DB_USERNAME:-postgres}
-      POSTGRES_PASSWORD: ${DB_PASSWORD:-postgres}
-      POSTGRES_DB: ${DB_DATABASE:-openproject}
-    networks:
-      - network
-
-  cache:
-    image: memcached
-    <<: *restart_policy
-    networks:
-      - network
-
   backend:
     build:
       <<: *build
@@ -94,6 +75,25 @@ services:
     depends_on:
       - backend
 
+  db:
+    image: postgres:10
+    <<: *restart_policy
+    stop_grace_period: "3s"
+    volumes:
+      - "pgdata:/var/lib/postgresql/data"
+    environment:
+      POSTGRES_USER: ${DB_USERNAME:-postgres}
+      POSTGRES_PASSWORD: ${DB_PASSWORD:-postgres}
+      POSTGRES_DB: ${DB_DATABASE:-openproject}
+    networks:
+      - network
+
+  cache:
+    image: memcached
+    <<: *restart_policy
+    networks:
+      - network
+
 ######### Testing stuff below ############
 
   db-test:

frontend/src/app/angular4-modules.ts

@@ -76,6 +76,7 @@ import {globalDynamicComponents} from "core-app/global-dynamic-components.const"
 import {OpenprojectMembersModule} from "core-app/modules/members/members.module";
 import {OpenprojectEnterpriseModule} from "core-components/enterprise/openproject-enterprise.module";
 import {OpenprojectAugmentingModule} from "core-app/modules/augmenting/openproject-augmenting.module";
+import {OpenprojectInviteUserModalModule} from "core-app/modules/invite-user-modal/invite-user-modal.module";
 import {RevitAddInSettingsButtonService} from "core-app/modules/bim/revit_add_in/revit-add-in-settings-button.service";
 
 @NgModule({
@@ -138,6 +139,9 @@ import {RevitAddInSettingsButtonService} from "core-app/modules/bim/revit_add_in
 
     // Augmenting Module
     OpenprojectAugmentingModule,
+
+    // Invite user modal
+    OpenprojectInviteUserModalModule,
   ],
   providers: [
     { provide: States, useValue: new States() },

frontend/src/app/components/user/user-avatar/user-avatar-renderer.service.ts

@@ -6,6 +6,7 @@ import {APIV3Service} from "core-app/modules/apiv3/api-v3.service";
 export interface UserLike {
   name:string;
   id:string|number|null;
+  href:string|null;
 }
 
 @Injectable({ providedIn: 'root' })
@@ -49,14 +50,25 @@ export class UserAvatarRendererService {
          user:UserLike,
          renderName:boolean = true,
          classes:string = 'avatar-medium'):void {
-    const userInitials = this.getInitials(user.name);
     const colorCode = this.colors.toHsl(user.name);
 
     let fallback = document.createElement('div');
     fallback.className = classes;
+    fallback.textContent = this.getInitials(user.name)
     fallback.classList.add('avatar-default');
-    fallback.textContent = userInitials;
-    fallback.style.background = colorCode;
+    // Todo: move this matcher to HAL ressource
+    if (user.href && user.href.includes('/placeholder_users/')) {
+      fallback.classList.add("-placeholder-user");
+      fallback.style.color = colorCode;
+      fallback.style.borderColor = colorCode;
+      fallback.style.background = 'transparent';
+    } else if (user.href && user.href.includes('/groups/')) {
+      fallback.classList.add("-group");
+      fallback.style.background = colorCode;
+    } else {
+      fallback.classList.add("-user");
+      fallback.style.background = colorCode;
+    }
 
     container.appendChild(fallback);
 

frontend/src/app/components/user/user-avatar/user-avatar.component.ts

@@ -49,7 +49,7 @@ export class UserAvatarComponent implements AfterViewInit {
 
   public ngAfterViewInit() {
     const element = this.elementRef.nativeElement;
-    let user = this.user || { name: element.dataset.userName!, id: element.dataset.userId };
+    let user = this.user || { name: element.dataset.userName!, id: element.dataset.userId, href: null };
     this.avatarRenderer.render(element, user, false, element.dataset.classList);
   }
 }

frontend/src/app/modules/boards/openproject-boards.module.ts

@@ -29,6 +29,7 @@
 import {NgModule} from '@angular/core';
 import {OpenprojectCommonModule} from "core-app/modules/common/openproject-common.module";
 import {OpenprojectWorkPackagesModule} from "core-app/modules/work_packages/openproject-work-packages.module";
+import {OpenprojectInviteUserModalModule} from "core-app/modules/invite-user-modal/invite-user-modal.module";
 import {UIRouterModule} from "@uirouter/angular";
 import {BoardListComponent} from "core-app/modules/boards/board/board-list/board-list.component";
 import {BoardsRootComponent} from "core-app/modules/boards/boards-root/boards-root.component";

frontend/src/app/modules/common/openproject-common.module.ts

@@ -84,6 +84,7 @@ import {TimeEntryWorkPackageAutocompleterComponent} from "core-app/modules/commo
 import {DraggableAutocompleteComponent} from "core-app/modules/common/draggable-autocomplete/draggable-autocomplete.component";
 import {DragulaModule} from "ng2-dragula";
 import {SlideToggleComponent} from "core-app/modules/common/slide-toggle/slide-toggle.component";
+import {OpOptionListComponent} from "core-app/modules/common/option-list/option-list.component";
 
 export function bootstrapModule(injector:Injector) {
   // Ensure error reporter is run
@@ -149,6 +150,7 @@ export function bootstrapModule(injector:Injector) {
     OpDatePickerComponent,
     OpDateTimeComponent,
     OpIcon,
+    OpOptionListComponent,
     AutofocusDirective,
 
     FocusWithinDirective,
@@ -202,6 +204,7 @@ export function bootstrapModule(injector:Injector) {
     OpDatePickerComponent,
     OpDateTimeComponent,
     OpIcon,
+    OpOptionListComponent,
     AutofocusDirective,
 
     FocusWithinDirective,

frontend/src/app/modules/common/option-list/option-list.component.html

@@ -0,0 +1,22 @@
+<!-- This is an example structure -->
+<div class="op-option-list">
+  <label
+    *ngFor="let option of options"
+    class="op-option-list--item"
+    [ngClass]="option.value === selected ? 'op-option-list--item_selected' : ''"
+  >
+    <input
+      type="radio"
+      [attr.name]="name"
+      [value]="option.value"
+      [(ngModel)]="selectedInternal"
+    />
+    <div>
+      <p class="op-option-list--title">{{ option.title }}</p>
+      <p
+        *ngIf="option.description"
+        class="op-option-list--description"
+      >{{ option.description }}</p>
+    </div>
+  </label>
+</div>

frontend/src/app/modules/common/option-list/option-list.component.sass

@@ -0,0 +1,17 @@
+.op-option-list
+  display: flex
+  flex-direction: column
+  font-size: 1rem
+
+  &--item
+    padding: 1rem 0.75rem
+    display: flex
+    border: 1px solid #cbd5e0
+    background: #f7fafc
+
+    &:not(:last-child)
+      margin-bottom: 0.5rem
+
+    &_selected
+      border: 1px solid #90cdf4
+      background: #ebf8ff

frontend/src/app/modules/common/option-list/option-list.component.ts

@@ -0,0 +1,48 @@
+import {
+  Component,
+  Input,
+  Output,
+  EventEmitter,
+} from "@angular/core";
+import { ControlValueAccessor } from "@angular/forms";
+
+export interface IOpOptionListOption<T> {
+  value:T;
+  title:string;
+  description?:string;
+}
+
+export type IOpOptionListValue<T> = T|null;
+
+@Component({
+  // Style is imported globally
+  templateUrl: './option-list.component.html',
+  selector: 'op-option-list',
+})
+export class OpOptionListComponent<T> implements ControlValueAccessor {
+  @Input() options:IOpOptionListOption<T>[] = [];
+  @Input() name:string = `op-option-list-${+(new Date())}`;
+  @Output() selectedChange = new EventEmitter<T>();
+
+  private _selected:IOpOptionListValue<T> = null;
+  get selected() {
+    return this._selected;
+  }
+  set selected(data:IOpOptionListValue<T>) {
+    this.onChange(data);
+  }
+  onChange = (_:IOpOptionListValue<T>) => {};
+  onTouched = (_:IOpOptionListValue<T>) => {};
+
+  writeValue(value:IOpOptionListValue<T>) {
+    this._selected = value;
+  }
+
+  registerOnChange(fn:any) {
+    this.onChange = fn;
+  }
+
+  registerOnTouched(fn:any) {
+    this.onTouched = fn;
+  }
+}

frontend/src/app/modules/fields/edit/field-types/select-edit-field.component.ts

@@ -258,7 +258,13 @@ export class SelectEditFieldComponent extends EditFieldComponent implements OnIn
   }
 
   protected mapAllowedValue(value:HalResource):ValueOption {
-    return { name: value.name, $href: value.$href };
+    let option = { name: value.name, $href: value.$href };
+    if (value._type === "PlaceholderUser") {
+      option.name = `${value.name} - Placeholder`;
+    } else if (value._type === "Group") {
+      option.name = `${value.name} - Group`;
+    }
+    return option;
   }
 
   // Subclasses shall be able to override the filters with which the

frontend/src/app/modules/invite-user-modal/group.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-group',
+  templateUrl: './group.component.html',
+  styleUrls: ['./group.component.sass'],
+})
+export class InviteGroupComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/invite-user-modal/invite-user-modal.module.ts

@@ -0,0 +1,34 @@
+import {NgModule} from "@angular/core";
+import {ReactiveFormsModule} from "@angular/forms";
+import {InviteUserModalComponent} from "./invite-user.component";
+import {InviteProjectSelectionComponent} from "./project-selection.component";
+import {InviteUserComponent} from "./user.component";
+import {InviteGroupComponent} from "./group.component";
+import {InvitePlaceholderComponent} from "./placeholder.component";
+import {InviteRoleComponent} from "./role.component";
+import {InviteMessageComponent} from "./message.component";
+import {InviteSuccessComponent} from "./success.component";
+import {InviteSummaryComponent} from "./summary.component";
+import {NgSelectModule} from "@ng-select/ng-select";
+import {OpenprojectCommonModule} from "core-app/modules/common/openproject-common.module";
+
+@NgModule({
+  imports: [
+    OpenprojectCommonModule,
+    NgSelectModule,
+    ReactiveFormsModule,
+  ],
+  exports: [],
+  declarations: [
+    InviteUserModalComponent,
+    InviteProjectSelectionComponent,
+    InviteUserComponent,
+    InviteGroupComponent,
+    InvitePlaceholderComponent,
+    InviteRoleComponent,
+    InviteMessageComponent,
+    InviteSuccessComponent,
+    InviteSummaryComponent,
+  ]
+})
+export class OpenprojectInviteUserModalModule { }

frontend/src/app/modules/invite-user-modal/invite-user.component.html

@@ -0,0 +1,17 @@
+<div class="op-modal--portal">
+  <op-ium-project-selection
+    *ngIf="step === 'project-selection'"
+    class="op-modal--modal-container"
+    [project]="project"
+    [type]="type"
+    (save)="onProjectSelectionSave"
+    (close)="close"
+  ></op-ium-project-selection>
+  <op-ium-user
+    *ngIf="step === 'user' && type === 'user'"
+    class="op-modal--modal-container"
+    [user]="principal"
+    (save)="onUserSave"
+    (back)="back"
+  ></op-ium-user>
+</div>

frontend/src/app/modules/invite-user-modal/invite-user.component.ts

@@ -0,0 +1,60 @@
+import {ChangeDetectionStrategy, ChangeDetectorRef, Component, ElementRef, Inject, OnInit} from '@angular/core';
+import {OpModalLocalsMap} from 'core-components/op-modals/op-modal.types';
+import {OpModalComponent} from 'core-components/op-modals/op-modal.component';
+import {OpModalLocalsToken} from "core-components/op-modals/op-modal.service";
+import * as URI from 'urijs';
+import {HttpClient} from '@angular/common/http';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+import {Observable} from 'rxjs';
+
+@Component({
+  templateUrl: './invite-user.component.html',
+  styleUrls: ['./invite-user.component.sass'],
+  changeDetection: ChangeDetectionStrategy.OnPush,
+})
+export class InviteUserModalComponent extends OpModalComponent implements OnInit {
+  private steps = [
+    'project-selection',
+    'username',
+    'role',
+    'message',
+    'summary',
+    'success',
+  ];
+  private stepIndex = 0;
+
+  /* Close on escape? */
+  public closeOnEscape = true;
+
+  /* Close on outside click */
+  public closeOnOutsideClick = true;
+
+  public type:string|null = null;
+  public project = null;
+  public principal = null;
+  public role = null;
+  public message = '';
+
+  public get step() {
+    return this.steps[this.stepIndex];
+  }
+
+  constructor(@Inject(OpModalLocalsToken) public locals:OpModalLocalsMap,
+              readonly cdRef:ChangeDetectorRef,
+              readonly elementRef:ElementRef,
+              readonly httpClient:HttpClient) {
+    super(locals, cdRef, elementRef);
+  }
+
+  ngOnInit() {
+    super.ngOnInit();
+  }
+
+  onProjectSelectionSave() {
+    console.log('select project');
+  }
+
+  back() {
+    this.stepIndex = Math.max(this.stepIndex - 1, 0);
+  }
+}

frontend/src/app/modules/invite-user-modal/message.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-message',
+  templateUrl: './message.component.html',
+  styleUrls: ['./message.component.sass'],
+})
+export class InviteMessageComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/invite-user-modal/placeholder.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-placeholder',
+  templateUrl: './placeholder.component.html',
+  styleUrls: ['./placeholder.component.sass'],
+})
+export class InvitePlaceholderComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/invite-user-modal/project-selection.component.html

@@ -0,0 +1,33 @@
+<form
+  [formGroup]="projectAndTypeForm"
+  ngSubmit="onSubmit"
+>
+  <div class="op-modal--modal-container">
+    <div class="op-modal--modal-header">
+      <button
+        class="op-modal--modal-close-button"
+        type="button"
+        (click)="close"
+        [attr.aria-label]="text.closePopup"
+      >
+        <span class="icon-close"></span>
+      </button>
+      <h3 class="icon-context icon-attention" [textContent]="text.title"></h3>
+    </div>
+
+    <div class="op-modal--modal-body">
+      <op-option-list
+        [options]="typeOptions"
+        formControlName="type"
+      ></op-option-list> 
+    </div>
+
+    <div class="op-modal--modal-footer">
+      <button
+        type="button"
+        (click)="back"
+      >Back</button>
+      <button>Next</button>
+    </div>
+  </div>
+</form>

frontend/src/app/modules/invite-user-modal/project-selection.component.ts

@@ -0,0 +1,75 @@
+import {
+  Component,
+  Input,
+  EventEmitter,
+  Output,
+  ElementRef,
+} from '@angular/core';
+import { 
+  FormControl,
+  FormGroup,
+  Validators,
+} from '@angular/forms';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-project-selection',
+  templateUrl: './project-selection.component.html',
+  styleUrls: ['./project-selection.component.sass'],
+})
+export class InviteProjectSelectionComponent {
+  public text = {
+    title: this.I18n.t('js.invite_user_modal.title'),
+    closePopup: this.I18n.t('js.close_popup_title'),
+    exportPreparing: this.I18n.t('js.label_export_preparing')
+  };
+
+  public typeOptions = [
+    {
+      value: 'user',
+      title: 'User',
+      description: 'Permissions based on the assigned role in the selected project'
+    },
+    {
+      value: 'group',
+      title: 'Group',
+      description: 'Permissions based on the assigned role in the selected project'
+    },
+    {
+      value: 'placeholder',
+      title: 'Placeholder',
+      description: 'Has no access to the proejct and no emails are sent out'
+    },
+  ];
+
+  @Input('type') type:string;
+  @Input('project') project:null;
+
+  projectAndTypeForm = new FormGroup({
+    type: new FormControl('', [ Validators.required ]),
+    project: new FormControl(null, [ Validators.required ]),
+  });
+
+  @Output('close') closeModal = new EventEmitter<void>();
+  @Output() save = new EventEmitter<{project:any, type:string}>();
+
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  close() {
+    this.closeModal.emit();
+  }
+
+  onSubmit($e:Event) {
+    console.log(this.projectAndTypeForm);
+    debugger;
+
+    this.save.emit({
+      project: this.projectAndTypeForm.get('project'),
+      type: this.projectAndTypeForm.get('type'),
+    });
+  }
+
+  back() {
+  }
+}

frontend/src/app/modules/invite-user-modal/role.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-role',
+  templateUrl: './role.component.html',
+  styleUrls: ['./role.component.sass'],
+})
+export class InviteRoleComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/invite-user-modal/success.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-success',
+  templateUrl: './success.component.html',
+  styleUrls: ['./success.component.sass'],
+})
+export class InviteSuccessComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/invite-user-modal/summary.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-summary',
+  templateUrl: './summary.component.html',
+  styleUrls: ['./summary.component.sass'],
+})
+export class InviteSummaryComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/invite-user-modal/user.component.ts

@@ -0,0 +1,15 @@
+import {Component, ElementRef, OnInit} from '@angular/core';
+import {I18nService} from "core-app/modules/common/i18n/i18n.service";
+
+@Component({
+  selector: 'op-ium-user',
+  templateUrl: './user.component.html',
+  styleUrls: ['./user.component.sass'],
+})
+export class InviteUserComponent implements OnInit {
+  constructor(readonly I18n:I18nService,
+              readonly elementRef:ElementRef) {}
+
+  ngOnInit() {
+  }
+}

frontend/src/app/modules/work_packages/routing/partitioned-query-space-page/partitioned-query-space-page.component.html

@@ -17,6 +17,9 @@
 
       <ul class="toolbar-items hide-when-print"
           *ngIf="showToolbar">
+        <li>
+          <button (click)="openInviteUserModal()">Invite User</button>
+        </li>
 
         <ng-container *ngFor="let definition of toolbarButtonComponents">
           <li class="toolbar-item"

frontend/src/app/modules/work_packages/routing/partitioned-query-space-page/partitioned-query-space-page.component.ts

@@ -39,6 +39,8 @@ import {ComponentType} from "@angular/cdk/overlay";
 import {Ng2StateDeclaration} from "@uirouter/angular";
 import {I18nService} from "core-app/modules/common/i18n/i18n.service";
 import {WorkPackageFilterContainerComponent} from "core-components/filters/filter-container/filter-container.directive";
+import {OpModalService} from 'core-app/components/op-modals/op-modal.service';
+import {InviteUserModalComponent} from 'core-app/modules/invite-user-modal/invite-user.component';
 
 export interface DynamicComponentDefinition {
   component:ComponentType<any>;
@@ -68,6 +70,7 @@ export class PartitionedQuerySpacePageComponent extends WorkPackagesViewBase imp
   @InjectField() I18n!:I18nService;
   @InjectField() titleService:OpTitleService;
   @InjectField() queryParamListener:QueryParamListenerService;
+  @InjectField() opModalService:OpModalService;
 
   text:{ [key:string]:string } = {
     'jump_to_pagination': this.I18n.t('js.work_packages.jump_marks.pagination'),
@@ -257,6 +260,15 @@ export class PartitionedQuerySpacePageComponent extends WorkPackagesViewBase imp
     });
   }
 
+  protected inviteModal = InviteUserModalComponent;
+
+  openInviteUserModal() {
+    const inviteModal = this.opModalService.show(this.inviteModal, 'global');
+    inviteModal.closingEvent.subscribe((modal:any) => {
+      console.log('Modal closed!', modal);
+    });
+  }
+
   protected loadFirstPage():Promise<QueryResource> {
     if (this.currentQuery) {
       return this.wpListService.reloadQuery(this.currentQuery, this.projectIdentifier).toPromise();

frontend/src/global_styles/content/_user.sass

@@ -62,6 +62,14 @@
   cursor: inherit
   user-select: none
 
+  &.-placeholder-user
+    border: 1px dashed
+    background: none
+
+  &.-group
+    border: 1px solid white
+    box-shadow: 4px 0px 0px -1px #cccccc
+
 h1, h2, h3, h4
   user-avatar
     vertical-align: middle

frontend/src/global_styles/openproject.sass

@@ -2,4 +2,6 @@
 @import "openproject/_index.sass"
 @import "vendor/_index.sass"
 @import "layout/_index.sass"
-@import "content/_index.sass"
+@import "content/_index.sass"
+
+@import "../app/modules/common/option-list/option-list.component";

lib/api/v3/placeholder_users/placeholder_user_representer.rb

@@ -0,0 +1,144 @@
+#-- encoding: UTF-8
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2020 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2017 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See docs/COPYRIGHT.rdoc for more details.
+#++
+
+module API
+  module V3
+    module PlaceholderUsers
+      class PlaceholderUserRepresenter < ::API::V3::Principals::PrincipalRepresenter
+        include AvatarHelper
+
+        cached_representer dependencies: ->(*) { avatar_cache_dependencies }
+
+        def self.create(user, current_user:)
+          new(user, current_user: current_user)
+        end
+
+        def initialize(user, current_user:)
+          super(user, current_user: current_user)
+        end
+
+        self_link
+
+        link :updateImmediately,
+             cache_if: -> { current_user_is_admin } do
+          {
+            href: api_v3_paths.user(represented.id),
+            title: "Update #{represented.login}",
+            method: :patch
+          }
+        end
+
+        link :delete,
+             cache_if: -> { current_user_can_delete_represented? } do
+          {
+            href: api_v3_paths.user(represented.id),
+            title: "Delete #{represented.login}",
+            method: :delete
+          }
+        end
+
+        property :name,
+                 exec_context: :decorator,
+                 getter: ->(*) { represented.lastname },
+                 setter: ->(fragment:, represented:, **) { represented.lastname = fragment },
+                 render_nil: false,
+                 cache_if: -> { current_user_is_admin_or_self }
+
+        property :avatar,
+                 exec_context: :decorator,
+                 getter: ->(*) { avatar_url(represented) },
+                 render_nil: true
+
+        property :identity_url,
+                 exec_context: :decorator,
+                 as: 'identityUrl',
+                 getter: ->(*) { represented.identity_url },
+                 setter: ->(fragment:, represented:, **) { represented.identity_url = fragment },
+                 render_nil: true,
+                 cache_if: -> { current_user_is_admin_or_self }
+
+        ##
+        # Used while parsing JSON to initialize `auth_source_id` through the given link.
+        def initialize_embedded_links!(data)
+          auth_source_id = parse_auth_source_id data, "auth_source"
+
+          if auth_source_id
+            auth_source = AuthSource.find_by_unique auth_source_id
+            id = auth_source ? auth_source.id : 0
+
+            # set id to 0 (as opposed to nil) to produce an auth source not found
+            # error further down the line in the user's base contract
+            represented.auth_source_id = id
+          end
+        end
+
+        ##
+        # Overrides Roar::JSON::HAL::Resources#from_hash
+        def from_hash(hash, *)
+          if hash["_links"]
+            initialize_embedded_links! hash
+          end
+
+          super
+        end
+
+        def parse_auth_source_id(data, link_name)
+          value = data.dig("_links", link_name, "href")
+
+          if value
+            ::API::Utilities::ResourceLinkParser.parse_id(
+              value,
+              property: :auth_source,
+              expected_version: "3",
+              expected_namespace: "auth_sources"
+            )
+          end
+        end
+
+        def _type
+          'PlaceholderUser'
+        end
+
+        def current_user_can_delete_represented?
+          current_user && ::Users::DeleteService.deletion_allowed?(represented, current_user)
+        end
+
+        private
+
+        ##
+        # Dependencies required to cache users with avatars
+        # Extended by plugin
+        def avatar_cache_dependencies
+          []
+        end
+      end
+    end
+  end
+end

lib/api/v3/principals/associated_subclass_lambda.rb

@@ -43,6 +43,8 @@ module API
                         :user
                       when Group
                         :group
+                      when PlaceholderUser
+                        :placeholder_user
                       when NilClass
                         # Fall back to user for unknown principal
                         # since we do not have a principal route.
@@ -62,7 +64,6 @@ module API
         def self.getter(name)
           ->(*) {
             next unless embed_links
-
             instance = represented.send(name)
 
             case instance
@@ -70,6 +71,8 @@ module API
               ::API::V3::Users::UserRepresenter.new(represented.send(name), current_user: current_user)
             when Group
               ::API::V3::Groups::GroupRepresenter.new(represented.send(name), current_user: current_user)
+            when PlaceholderUser
+              ::API::V3::PlaceholderUsers::PlaceholderUserRepresenter.new(represented.send(name), current_user: current_user)
             when NilClass
               nil
             else
@@ -78,7 +81,7 @@ module API
           }
         end
 
-        def self.setter(name, property_name: name, namespaces: %i(groups users))
+        def self.setter(name, property_name: name, namespaces: %i(groups users placeholder_users))
           ->(fragment:, **) {
             link = ::API::Decorators::LinkObject.new(represented,
                                                      property_name: property_name,

lib/api/v3/principals/group_or_user_or_placeholder_user_elements.rb

@@ -31,7 +31,7 @@
 module API
   module V3
     module Principals
-      module GroupOrUserElements
+      module GroupOrUserOrPlaceholderUserElements
         extend ::ActiveSupport::Concern
 
         included do
@@ -41,6 +41,8 @@ module API
                          representer_class = case model
                                              when User
                                                ::API::V3::Users::UserRepresenter
+                                             when PlaceholderUser
+                                               ::API::V3::PlaceholderUsers::PlaceholderUserRepresenter
                                              when Group
                                                ::API::V3::Groups::GroupRepresenter
                                              else

lib/api/v3/users/paginated_user_collection_representer.rb

@@ -38,7 +38,7 @@ module API
   module V3
     module Users
       class PaginatedUserCollectionRepresenter < ::API::Decorators::OffsetPaginatedCollection
-        include API::V3::Principals::GroupOrUserElements
+        include API::V3::Principals::GroupOrUserOrPlaceholderUserElements
       end
     end
   end

lib/api/v3/users/user_collection_representer.rb

@@ -31,7 +31,7 @@ module API
   module V3
     module Users
       class UserCollectionRepresenter < ::API::Decorators::UnpaginatedCollection
-        include API::V3::Principals::GroupOrUserElements
+        include API::V3::Principals::GroupOrUserOrPlaceholderUserElements
       end
     end
   end

lib/api/v3/utilities/path_helper.rb

@@ -378,6 +378,10 @@ module API
             "#{root}/groups/#{id}"
           end
 
+          def self.placeholder_user(id)
+            "#{root}/placeholder_users/#{id}"
+          end
+
           resources :version
 
           def self.versions_available_projects

lib/api/v3/work_packages/principal_setter.rb

@@ -34,7 +34,7 @@ module API
       class PrincipalSetter
         def self.lambda(name, property_name = name)
           ->(args) {
-            expected_namespaces = Setting.work_package_group_assignment? ? %i(groups users) : %i(users)
+            expected_namespaces = Setting.work_package_group_assignment? ? %i(groups users placeholder_users) : %i(users)
 
             lambda = ::API::V3::Principals::AssociatedSubclassLambda
                      .setter(name,

lib/open_project/ui/extensible_tabs.rb

@@ -33,7 +33,8 @@ module OpenProject
       class << self
         def tabs
           @tabs ||= {
-            user: core_user_tabs
+            user: core_user_tabs,
+            placeholder_user: core_placeholder_user_tabs
           }
         end
 
@@ -82,6 +83,30 @@ module OpenProject
             }
           ]
         end
+
+        def core_placeholder_user_tabs
+          [
+              {
+                  name: 'general',
+                  partial: 'placeholder_users/general',
+                  path: ->(params) { tab_edit_placeholder_user_path(params[:placeholder_user], tab: :general) },
+                  label: :label_general
+              },
+              {
+                  name: 'memberships',
+                  partial: 'placeholder_users/memberships',
+                  path: ->(params) { tab_edit_placeholder_user_path(params[:placeholder_user], tab: :memberships) },
+                  label: :label_project_plural
+              },
+              {
+                  name: 'groups',
+                  partial: 'placeholder_users/groups',
+                  path: ->(params) { tab_edit_placeholder_user_path(params[:placeholder_user], tab: :groups) },
+                  label: :label_group_plural,
+                  if: ->(*) { Group.all.any? }
+              }
+          ]
+        end
       end
     end
   end