Use UserSerializer instead of `User.to_json`

app/controllers/autocomplete_controller.rb

@@ -8,7 +8,7 @@ class AutocompleteController < ApplicationController
   def users
     @users = AutocompleteUsersFinder.new(params: params, current_user: current_user, project: @project, group: @group).execute
 
-    render json: @users, only: [:name, :username, :id], methods: [:avatar_url]
+    render json: UserSerializer.new.represent(@users)
   end
 
   def project_groups
@@ -17,7 +17,7 @@ class AutocompleteController < ApplicationController
 
   def user
     @user = User.find(params[:id])
-    render json: @user, only: [:name, :username, :id], methods: [:avatar_url]
+    render json: UserSerializer.new.represent(@user)
   end
 
   def projects

app/helpers/form_helper.rb

@@ -37,7 +37,7 @@ module FormHelper
         multi_select: true,
         'input-meta': 'name',
         'always-show-selectbox': true,
-        current_user_info: current_user.to_json(only: [:id, :name])
+        current_user_info: UserSerializer.new.represent(current_user)
       }
     }
   end

app/helpers/issuables_helper.rb

@@ -365,7 +365,7 @@ module IssuablesHelper
       moveIssueEndpoint: move_namespace_project_issue_path(namespace_id: issuable.project.namespace.to_param, project_id: issuable.project, id: issuable),
       projectsAutocompleteEndpoint: autocomplete_projects_path(project_id: @project.id),
       editable: can_edit_issuable,
-      currentUser: current_user.as_json(only: [:username, :id, :name], methods: :avatar_url),
+      currentUser: UserSerializer.new.represent(current_user),
       rootPath: root_path,
       fullPath: @project.full_path,
       weightOptions: Issue.weight_options,

app/helpers/search_helper.rb

@@ -149,7 +149,7 @@ module SearchHelper
         id: "filtered-search-#{type}",
         placeholder: 'Search or filter results...',
         data: {
-          'username-params' => @users.to_json(only: [:id, :username])
+          'username-params' => UserSerializer.new.represent(@users)
         },
         autocomplete: 'off'
       }

app/views/shared/boards/components/_sidebar.html.haml

-%board-sidebar{ "inline-template" => true,
-  ":current-user" => "#{current_user ? current_user.to_json(only: [:username, :id, :name], methods: [:avatar_url]) : {}}" }
+%board-sidebar{ "inline-template" => true,  ":current-user" => (UserSerializer.new.represent(current_user) || {}).to_json }
   %transition{ name: "boards-sidebar-slide" }
     %aside.right-sidebar.right-sidebar-expanded.issue-boards-sidebar{ "v-show" => "showSidebar" }
       .issuable-sidebar