Restore fallback to Blacklight::Solr::SearchBuilder, which will be re…

…moved in Blacklight 6

lib/blacklight/configuration.rb

@@ -226,6 +226,14 @@ def search_builder_class
 
     def locate_search_builder_class
       ::SearchBuilder
+    rescue NameError => e
+      # If the NameError is a result of the SearchBuilder having a
+      # NameError (e.g. NoMethodError) within it then raise the error.
+      raise e if Object.const_defined? "::SearchBuilder"
+
+      # Otherwise the NameError was a result of not being able to find SearchBuilder
+      Deprecation.warn(Configuration, "Your application is missing the SearchBuilder. Have you run `rails generate blacklight:search_builder`? Falling back to Blacklight::Solr::SearchBuilder")
+      Blacklight::Solr::SearchBuilder
     end
 
     def facet_paginator_class

lib/blacklight/solr.rb

@@ -6,6 +6,7 @@ module Solr
     autoload :Repository, 'blacklight/solr/repository'
     autoload :Request, 'blacklight/solr/request'
     autoload :Response, 'blacklight/solr/response'
+    autoload :SearchBuilder, 'blacklight/solr/search_builder'
     autoload :SearchBuilderBehavior, 'blacklight/solr/search_builder_behavior'
   end
 end

lib/blacklight/solr/search_builder.rb

@@ -0,0 +1,7 @@
+module Blacklight::Solr
+  # @deprecated In 6.0 you should have this class generated into your application and Blacklight will
+  #             no longer need to provide it.
+  class SearchBuilder < Blacklight::SearchBuilder
+    include Blacklight::Solr::SearchBuilderBehavior
+  end
+end