votes: make upvotes visible to everyone by default.

Make upvotes public the same way favorites are public:

* Rename the "Private favorites" account setting to "Private favorites and upvotes".
* Make upvotes public, unless the user has private upvotes enabled. Note
  that private upvotes are still visible to admins. Downvotes are still
  hidden to everyone except for admins.
* Make https://danbooru.donmai.us/post_votes visible to all users. This
  page shows all public upvotes. Private upvotes and downvotes are only
  visible on the page to admins and to the voter themselves.
* Make votes searchable with the `upvote:username` and `downvote:username`
  metatags. These already existed before, but they were only usable by
  admins and by people searching for their own votes.

Upvotes are public to discourage users from upvoting with multiple
accounts. Upvote abuse is obvious to everyone when upvotes are public.
The other reason is to make upvotes consistent with favorites, which are
already public.

app/models/post_vote.rb

@@ -10,13 +10,15 @@ class PostVote < ApplicationRecord
 
   scope :positive, -> { where("post_votes.score > 0") }
   scope :negative, -> { where("post_votes.score < 0") }
+  scope :public_votes, -> { positive.where(user: User.has_public_favorites) }
 
   def self.visible(user)
-    user.is_admin? ? all : where(user: user)
+    user.is_admin? ? all : where(user: user).or(public_votes)
   end
 
   def self.search(params)
     q = search_attributes(params, :id, :created_at, :updated_at, :score, :user, :post)
+
     q.apply_default_order(params)
   end
 

app/models/user.rb

@@ -152,6 +152,8 @@ class User < ApplicationRecord
   scope :admins, -> { where(level: Levels::ADMIN) }
 
   scope :has_blacklisted_tag, ->(name) { where_regex(:blacklisted_tags, "(^| )[~-]?#{Regexp.escape(name)}( |$)", flags: "ni") }
+  scope :has_private_favorites, -> { bit_prefs_match(:enable_private_favorites, true) }
+  scope :has_public_favorites,  -> { bit_prefs_match(:enable_private_favorites, false) }
 
   module BanMethods
     def unban!

app/policies/post_vote_policy.rb

@@ -8,6 +8,16 @@ class PostVotePolicy < ApplicationPolicy
   end
 
   def show?
-    user.is_admin? || record.user == user
+    user.is_admin? || record.user == user || (record.is_positive? && !record.user.enable_private_favorites?)
+  end
+
+  def can_see_voter?
+    show?
+  end
+
+  def api_attributes
+    attributes = super
+    attributes -= [:user_id] unless can_see_voter?
+    attributes
   end
 end

app/views/post_votes/index.html.erb

@@ -24,8 +24,12 @@
         <div><%= time_ago_in_words_tagged(vote.post.created_at) %></div>
       <% end %>
       <% t.column "Voter" do |vote| %>
-        <%= link_to_user vote.user %>
-        <%= link_to "»", post_votes_path(search: { user_name: vote.user.name }) %>
+        <% if policy(vote).can_see_voter? %>
+          <%= link_to_user vote.user %>
+          <%= link_to "»", post_votes_path(search: { user_name: vote.user.name }) %>
+        <% else %>
+          <i>hidden</i>
+        <% end %>
         <div><%= time_ago_in_words_tagged(vote.created_at) %></div>
       <% end %>
       <% t.column column: "control" do |vote| %>

app/views/users/edit.html.erb

@@ -63,7 +63,7 @@
         <%= f.input :hide_deleted_posts, :as => :select, :label => "Deleted post filter", :hint => "Remove deleted posts from search results", :include_blank => false, :collection => [["Yes", "true"], ["No", "false"]] %>
         <%= f.input :show_deleted_children, :as => :select, :label => "Show deleted children", :hint => "Show thumbnail borders on parent posts even if the children are deleted", :include_blank => false, :collection => [["Yes", "true"], ["No", "false"]] %>
         <%= f.input :disable_categorized_saved_searches, :hint => "Don't show dialog box when creating a new saved search", :as => :select, :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false %>
-        <%= f.input :enable_private_favorites, :as => :select, :hint => "Make your favorites private", :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false %>
+        <%= f.input :enable_private_favorites, :label => "Private favorites and votes", :as => :select, :hint => "Make your favorites and upvotes private", :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false %>
         <%= f.input :disable_tagged_filenames, :as => :select, :hint => "Don't include tags in image filenames", :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false %>
         <%= f.input :disable_mobile_gestures, :as => :select, :hint => "Disable swipe left / swipe right gestures on mobile", :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false %>
         <%= f.input :disable_post_tooltips, :as => :select, :hint => "Disable advanced tooltips when hovering over thumbnails", :collection => [["No", "false"], ["Yes", "true"]], :include_blank => false %>