Add search_none/none scopes

When called directly on a model, the method is `search_none`:

    Article.search_none

But otherwise, it’s available as just `none`, either on ThinkingSphinx,
or through an existing Thinking Sphinx scope:

    ThinkingSphinx.none
    Article.search(“something”).none

lib/thinking_sphinx.rb

@@ -34,6 +34,10 @@ def self.search_for_ids(query = '', options = {})
     ThinkingSphinx::Search::Merger.new(search).merge! nil, :ids_only => true
   end
 
+  def self.none
+    ThinkingSphinx::Search.new nil, :none => true
+  end
+
   def self.before_index_hooks
     @before_index_hooks
   end

lib/thinking_sphinx/active_record/base.rb

@@ -58,6 +58,10 @@ def sphinx_search_for_ids(query = nil, options = {})
       ).merge! nil, :ids_only => true
     end
 
+    def sphinx_search_none
+      merge ThinkingSphinx.search, nil, none: true
+    end
+
     private
 
     def default_sphinx_scope?

lib/thinking_sphinx/masks/scopes_mask.rb

@@ -26,6 +26,12 @@ def search_for_ids(query = nil, options = {})
     search query, options.merge(:ids_only => true)
   end
 
+  def none
+    ThinkingSphinx::Search::Merger.new(@search).merge! nil, :none => true
+  end
+
+  alias_method :search_none, :none
+
   private
 
   def apply_scope(scope, *args)

lib/thinking_sphinx/search.rb

@@ -12,7 +12,7 @@ class ThinkingSphinx::Search < Array
     [
       :classes, :conditions, :excerpts, :geo, :group_by, :ids_only,
       :ignore_scopes, :indices, :limit, :masks, :max_matches, :middleware,
-      :offset, :order, :order_group_by, :page, :per_page, :populate,
+      :none, :offset, :order, :order_group_by, :page, :per_page, :populate,
       :retry_stale, :select, :skip_sti, :sql, :star, :with, :with_all, :without,
       :without_ids
     ] +
@@ -92,7 +92,7 @@ def per_page(value = nil)
   def populate
     return self if @populated
 
-    middleware.call [context]
+    middleware.call [context] unless options[:none]
     @populated = true
 
     self

lib/thinking_sphinx/search/context.rb

@@ -7,6 +7,7 @@ def initialize(search, configuration = nil)
     @search        = search
     @configuration = configuration || ThinkingSphinx::Configuration.instance
     @memory        = {
+      :raw     => [],
       :results => [],
       :panes   => ThinkingSphinx::Configuration::Defaults::PANES.clone
     }

spec/acceptance/searching_across_models_spec.rb

@@ -37,4 +37,11 @@
     expect(ThinkingSphinx.search(:classes => [User, Article]).to_a).
       to match_array([article, user])
   end
+
+  it "has a 'none' default scope" do
+    article = Article.create! :title => 'Pancakes'
+    index
+
+    expect(ThinkingSphinx.none).to be_empty
+  end
 end

spec/acceptance/searching_within_a_model_spec.rb

@@ -99,6 +99,13 @@
 
     expect(Article.sphinx_search.first).to eq(article)
   end
+
+  it "has a 'none' default scope" do
+    article = Article.create! :title => 'Pancakes'
+    index
+
+    expect(Article.search_none).to be_empty
+  end
 end
 
 describe 'Searching within a model with a realtime index', :live => true do

spec/acceptance/sphinx_scopes_spec.rb

@@ -77,4 +77,11 @@
       ThinkingSphinx::PopulatedResultsError
     )
   end
+
+  it "handles a chainable 'none' scope and returns nothing" do
+    Book.create! :title => 'Small Gods'
+    index
+
+    expect(Book.by_query('gods').none).to be_empty
+  end
 end