tags/index: don't show aliases when search matches primary tag.

When searching e.g. "*mask*", don't show "surgical_mask <- medical_mask"
because "*mask*" already matches the primary tag.

app/helpers/tags_helper.rb

@@ -3,4 +3,12 @@ module TagsHelper
     return nil if tag.blank?
     "tag-type-#{tag.category}"
   end
+
+  def tag_alias_for_pattern(tag, pattern)
+    return nil if pattern.blank?
+
+    tag.consequent_aliases.find do |tag_alias|
+      !tag.name.ilike?(pattern) && tag_alias.antecedent_name.ilike?(pattern)
+    end
+  end
 end

app/views/tags/index.html.erb

@@ -10,9 +10,7 @@
         <%= link_to_wiki "?", tag.name, class: tag_class(tag) %>
         <%= link_to tag.name, posts_path(tags: tag.name), class: tag_class(tag) %>
 
-        <% pattern = params.dig(:search, :name_or_alias_matches).to_s %>
-        <% tag_alias = tag.consequent_aliases.find { |tag_alias| tag_alias.antecedent_name.ilike?(pattern) } %>
-
+        <% tag_alias = tag_alias_for_pattern(tag, params[:search][:name_or_alias_matches]) %>
         <% if tag_alias.present? %>
           ← <%= link_to tag_alias.antecedent_name, tag_alias, class: "fineprint" %>
         <% end %>