Make AR::SpawnMethods#merge! to check an arg is a Proc

From Ruby ( 2.3.0dev trunk 52520), `Hash#to_proc` is defined
(ruby/ruby@fbe967e),
and many tests have been failed with
`ArgumentError: wrong number of arguments (given 0, expected 1)`.
Because we call `Hash#to_proc` with no args in `#merge!`.

This commit changes order of conditionals to not call `Hash#to_proc`.

(cherry picked from commit a98475c)

Author: yui-knk

activerecord/lib/active_record/relation/spawn_methods.rb

@@ -12,6 +12,7 @@ def spawn #:nodoc:
 
     # Merges in the conditions from <tt>other</tt>, if <tt>other</tt> is an <tt>ActiveRecord::Relation</tt>.
     # Returns an array representing the intersection of the resulting records with <tt>other</tt>, if <tt>other</tt> is an array.
+    #
     #   Post.where(published: true).joins(:comments).merge( Comment.where(spam: false) )
     #   # Performs a single join query with both where conditions.
     #
@@ -37,11 +38,14 @@ def merge(other)
     end
 
     def merge!(other) # :nodoc:
-      if !other.is_a?(Relation) && other.respond_to?(:to_proc)
+      if other.is_a?(Hash)
+        Relation::HashMerger.new(self, other).merge
+      elsif other.is_a?(Relation)
+        Relation::Merger.new(self, other).merge
+      elsif other.respond_to?(:to_proc)
         instance_exec(&other)
       else
-        klass = other.is_a?(Hash) ? Relation::HashMerger : Relation::Merger
-        klass.new(self, other).merge
+        raise ArgumentError, "#{other.inspect} is not an ActiveRecord::Relation"
       end
     end
 

activerecord/test/cases/relation_test.rb

@@ -235,5 +235,12 @@ def test_relation_merging_with_merged_joins_as_strings
       posts_with_special_comments_with_ratings = Post.group("posts.id").joins(:special_comments).merge(special_comments_with_ratings)
       assert_equal 3, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
     end
+
+    def test_merge_raises_with_invalid_argument
+      assert_raises ArgumentError do
+        relation = Relation.new(FakeKlass, :b)
+        relation.merge(true)
+      end
+    end
   end
 end