Allow secondary usage on m/r with inline output. [ fix #2584 ]

CHANGELOG.md

@@ -7,6 +7,12 @@ For instructions on upgrading to newer versions, visit
 
 ### Resolved Issues
 
+* \#2584 Allow map/reduce to operate on secondaries if output is set to `inline`.
+
+## 3.0.14
+
+### Resolved Issues
+
 * \#2575 Prevent end of month times from rounding up since floats are not
   precise enough to handle usec. (Steve Valaitis)
 

lib/mongoid/contextual/map_reduce.rb

@@ -286,7 +286,27 @@ def output_collection
       # @since 3.0.0
       def results
         raise Errors::NoMapReduceOutput.new(command) unless command[:out]
-        @results ||= session.with(consistency: :strong).command(command)
+        @results ||= __session__.command(command)
+      end
+
+      # Get the session with the proper consistency.
+      #
+      # @api private
+      #
+      # @note We can use eventual if the output is set to inline.
+      #
+      # @example Get the session.
+      #   map_reduce.__session__
+      #
+      # @return [ Session ] The session with consistency set.
+      #
+      # @since 3.0.15
+      def __session__
+        if command[:out][:inline] != 1
+          session.with(consistency: :strong)
+        else
+          session
+        end
       end
     end
   end