post queries: show full error message on error page.

app/controllers/application_controller.rb

@@ -132,6 +132,8 @@ class ApplicationController < ActionController::Base
       render_error_page(410, exception, template: "static/pagination_error", message: "You cannot go beyond page #{CurrentUser.user.page_limit}.")
     when PostQuery::TagLimitError
       render_error_page(422, exception, template: "static/tag_limit_error", message: "You cannot search for more than #{CurrentUser.tag_query_limit} tags at a time.")
+    when PostQuery::Error
+      render_error_page(422, exception, message: exception.message)
     when RateLimiter::RateLimitError
       render_error_page(429, exception, message: "Rate limit exceeded. You're doing that too fast")
     when Rack::Timeout::RequestTimeoutException

app/logical/post_query.rb

@@ -275,13 +275,14 @@ class PostQuery
     def validate_metatags!
       return if metatags.empty?
 
-      raise Error, "Can't have multiple order metatags" if select_metatags(*ORDER_METATAGS).size > 1
+      order_metatags = select_metatags(*ORDER_METATAGS)
+      raise Error, "#{order_metatags.to_sentence} can't be used together." if order_metatags.size > 1
 
       SINGLETON_METATAGS.each do |name|
         metatag = select_metatags(name).first
-        raise Error, "'#{name}:' can't be used more than once" if select_metatags(name).size > 1
-        raise Error, "#{metatag} can't be negated" if metatag&.parents&.any?(&:not?)
-        raise Error, "#{metatag} can't be used in an 'or' clause" if metatag&.parents&.any?(&:or?)
+        raise Error, "'#{name}:' can't be used more than once." if select_metatags(name).size > 1
+        raise Error, "'#{metatag}' can't be negated." if metatag&.parents&.any?(&:not?)
+        raise Error, "'#{metatag}' can't be used with the 'or' operator." if metatag&.parents&.any?(&:or?)
       end
     end
 

app/views/static/error.html.erb

@@ -3,7 +3,7 @@
 <h1>Error</h1>
 
 <% if @message.present? %>
-  <p><%= @message %></p>
+  <p>Error: <%= @message %></p>
 <% else %>
   <p>Unexpected error: <%= @exception.class %>.</p>