favorites: remove is_favorited attribute from post API.

* Remove the data-is-favorited attribute from post thumbnails.
* Remove the is_favorited attribute from the /posts.json API.
* Remove the fav_string attribute from the /posts.json API (only visible
  to moderators).
* Change `Post#favorited_by?` to not use the fav_string.

Further addresses #4652 by eliminating the last places where fav_string
was used.

app/models/post.rb

@@ -762,12 +762,11 @@ class Post < ApplicationRecord
       update_column(:fav_count, fav_count)
     end
 
-    def favorited_by?(user_id = CurrentUser.id)
-      fav_string.match?(/(?:\A| )fav:#{user_id}(?:\Z| )/)
+    def favorited_by?(user)
+      return false if user.is_anonymous?
+      Favorite.exists?(post: self, user: user)
     end
 
-    alias is_favorited? favorited_by?
-
     def append_user_to_fav_string(user_id)
       update_column(:fav_string, (fav_string + " fav:#{user_id}").strip)
       clean_fav_string! if clean_fav_string?

app/policies/post_policy.rb

@@ -88,11 +88,11 @@ class PostPolicy < ApplicationPolicy
 
   def api_attributes
     attributes = super
-    attributes += [:has_large, :has_visible_children, :is_favorited?]
+    attributes += [:has_large, :has_visible_children]
     attributes += TagCategory.categories.map {|x| "tag_string_#{x}".to_sym}
     attributes += [:file_url, :large_file_url, :preview_file_url] if visible?
     attributes -= [:id, :md5, :file_ext] if !visible?
-    attributes -= [:fav_string] if !user.is_moderator?
+    attributes -= [:fav_string]
     attributes
   end
 

app/presenters/post_presenter.rb

@@ -131,7 +131,6 @@ class PostPresenter
       "data-source" => post.source,
       "data-uploader-id" => post.uploader_id,
       "data-normalized-source" => post.normalized_source,
-      "data-is-favorited" => post.favorited_by?(CurrentUser.user.id)
     }
 
     if post.visible?

app/views/posts/partials/index/_preview.html.erb

@@ -38,11 +38,7 @@
       <%= link_to recommended_posts_path(search: { post_id: post.id }), class: "more-recommended-posts", "data-post-id": post.id do %>
         <%= post.fav_count %>
 
-        <% if post.favorited_by?(CurrentUser.id) %>
-          <i class="fas fa-heart fa-xs"></i>
-        <% else %>
-          <i class="far fa-heart fa-xs"></i>
-        <% end %>
+        <i class="far fa-heart fa-xs"></i>
 
         <br>more »
       <% end %>

app/views/posts/partials/show/_options.html.erb

@@ -23,10 +23,10 @@
 
   <% if policy(Favorite).create? %>
     <li id="post-option-add-to-favorites">
-      <%= link_to "Favorite", favorites_path(post_id: post.id), remote: true, method: :post, id: "add-to-favorites", "data-shortcut": "f", style: ("display: none;" if @post.is_favorited?) %>
+      <%= link_to "Favorite", favorites_path(post_id: post.id), remote: true, method: :post, id: "add-to-favorites", "data-shortcut": "f", style: ("display: none;" if @post.favorited_by?(CurrentUser.user)) %>
     </li>
     <li id="post-option-remove-from-favorites">
-      <%= link_to "Unfavorite", favorite_path(post), remote: true, method: :delete, id: "remove-from-favorites", "data-shortcut": "shift+f", "data-shortcut-when": ":visible", style: ("display: none;" if !@post.is_favorited?) %>
+      <%= link_to "Unfavorite", favorite_path(post), remote: true, method: :delete, id: "remove-from-favorites", "data-shortcut": "shift+f", "data-shortcut-when": ":visible", style: ("display: none;" if !@post.favorited_by?(CurrentUser.user)) %>
     </li>
   <% end %>
   <% if policy(post).update? %>

app/views/posts/show.html.erb

@@ -50,7 +50,7 @@
   <% end -%>
 
   <% if policy(Favorite).create? %>
-    <%= content_tag(:div, class: "fav-buttons fav-buttons-#{@post.is_favorited?}") do %>
+    <%= content_tag(:div, class: "fav-buttons fav-buttons-#{@post.favorited_by?(CurrentUser.user)}") do %>
       <%= form_tag(favorites_path(post_id: @post.id), method: "post", id: "add-fav-button", "data-remote": true) do %>
         <%= button_tag tag.i(class: "far fa-heart"), class: "ui-button ui-widget ui-corner-all", "data-disable-with": tag.i(class: "fas fa-spinner fa-spin") %>
       <% end %>

test/functional/posts_controller_test.rb

@@ -633,7 +633,6 @@ class PostsControllerTest < ActionDispatch::IntegrationTest
           assert_response :success
           assert_nil(response.parsed_body["md5"])
           assert_nil(response.parsed_body["file_url"])
-          assert_nil(response.parsed_body["fav_string"])
         end
       end
     end