Return proper results for posts searches consisting only of word exclusions

app/helpers/search_helper.rb

@@ -28,10 +28,10 @@ def search_posts(user, params)
     posts = posts.paginate(page: params[:page], per_page: 25)
 
     posts = if search_string.present?
-              posts.search(search_data[:search]).user_sort({ term: params[:sort], default: :search_score },
-                                                           relevance: :search_score,
-                                                           score: :score, age: :created_at,
-                                                           activity: :updated_at)
+              posts.search(search_string).user_sort({ term: params[:sort], default: :search_score },
+                                                    relevance: :search_score,
+                                                    score: :score, age: :created_at,
+                                                    activity: :updated_at)
             else
               posts.user_sort({ term: params[:sort], default: :score },
                               score: :score, age: :created_at, activity: :updated_at)

app/models/application_record.rb

@@ -11,6 +11,11 @@ def self.match_search(term, **cols)
     select(Arel.sql("`#{table_name}`.*, #{sanitized} AS search_score")).where(sanitized)
   end
 
+  def self.exclusion_search(term, **cols)
+    matched = match_search(term[1..], **cols)
+    select(Arel.sql("`#{table_name}`.*, 1 AS search_score")).excluding(matched)
+  end
+
   def self.sanitize_name(name)
     name.to_s.delete('`').insert(0, '`').insert(-1, '`')
   end

app/models/post.rb

@@ -76,7 +76,11 @@
   # @param term [String] the search term
   # @return [ActiveRecord::Relation<Post>]
   def self.search(term)
-    match_search term, posts: [:body_markdown, :title]
+    if term.match(/^(?:\s*?-\S+?)+?$/)
+      exclusion_search term, posts: [:body_markdown, :title]
+    else
+      match_search term, posts: [:body_markdown, :title]
+    end
   end
 
   def self.by_slug(slug, user)