artists: prevent Google from indexing banned artists.

Prevent search engines from indexing artist pages, wiki pages, and tag
searches for banned artists.

app/helpers/application_helper.rb

@@ -362,6 +362,10 @@ module ApplicationHelper
     end
   end
 
+  def noindex
+    content_for(:html_header, tag.meta(name: "robots", content: "noindex"))
+  end
+
   def atom_feed_tag(title, url = {})
     content_for(:html_header, auto_discovery_link_tag(:atom, url, title: title))
   end

app/logical/post_sets/post.rb

@@ -122,6 +122,7 @@ module PostSets
 
     def hide_from_crawler?
       return true if current_page > 50
+      return true if artist.present? && artist.is_banned?
       return false if query.is_empty_search? || query.is_simple_tag? || query.is_metatag?(:order, :rank)
       true
     end

app/views/artists/show.html.erb

@@ -1,3 +1,5 @@
+<% noindex if @artist.is_banned? %>
+
 <%= render layout: "show" do %>
   <div>
     <%= render "summary", artist: @artist %>

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

@@ -14,9 +14,7 @@
   <% canonical_url root_url(host: Danbooru.config.hostname) %>
 <% end %>
 
-<% if @post_set.hide_from_crawler? %>
-  <meta name="robots" content="nofollow,noindex">
-<% end %>
+<% noindex if @post_set.hide_from_crawler? %>
 
 <% if @post_set.has_explicit? %>
   <meta name="rating" content="adult">

app/views/wiki_pages/show.html.erb

@@ -1,6 +1,10 @@
 <% page_title "#{@wiki_page.pretty_title.titleize} Wiki" %>
 <% meta_description DText.excerpt(@wiki_page.body) %>
 
+<% if @wiki_page.artist.present? && @wiki_page.artist.is_banned? %>
+  <% noindex %>
+<% end %>
+
 <%= render "secondary_links" %>
 <%= render "sidebar" %>