Create a blacklist to disallow mutator methods to be delegated to `Array`.

This change was necessary because the whitelist wouldn't work.
It would be painful for users trying to update their applications.

This blacklist intent to prevent odd bugs and confusion in code that call mutator
methods directely on the `Relation`.

1 files changed, 14 insertions, 11 deletions

diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 246c5db5bd..21beed332f 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -1,3 +1,4 @@
+require 'set'
 require 'active_support/concern'
 require 'active_support/deprecation'
 
@@ -36,18 +37,13 @@ module ActiveRecord
     # may vary depending on the klass of a relation, so we create a subclass of Relation
     # for each different klass, and the delegations are compiled into that subclass only.
 
-    # TODO: This is not going to work. Brittle, painful. We'll switch to a blacklist
-    # to disallow mutator methods like map!, pop, and delete_if instead.
-    ARRAY_DELEGATES = [
-      :+, :-, :|, :&, :[],
-      :all?, :collect, :detect, :each, :each_cons, :each_with_index,
-      :exclude?, :find_all, :flat_map, :group_by, :include?, :length,
-      :map, :none?, :one?, :partition, :reject, :reverse,
-      :sample, :second, :sort, :sort_by, :third,
-      :to_ary, :to_set, :to_xml, :to_yaml
-    ]
+    BLACKLISTED_ARRAY_METHODS = [
+      :compact!, :flatten!, :reject!, :reverse!, :rotate!, :map!,
+      :shuffle!, :slice!, :sort!, :sort_by!, :delete_if,
+      :keep_if, :pop, :shift, :delete_at, :compact
+    ].to_set # :nodoc:
 
-    delegate(*ARRAY_DELEGATES, to: :to_a)
+    delegate :to_xml, :to_yaml, :length, :collect, :map, :each, :all?, :include?, :to_ary, to: :to_a
 
     delegate :table_name, :quoted_table_name, :primary_key, :quoted_primary_key,
              :connection, :columns_hash, :to => :klass
@@ -119,14 +115,21 @@ module ActiveRecord
 
     def respond_to?(method, include_private = false)
       super || @klass.respond_to?(method, include_private) ||
+        array_delegable?(method) ||
         arel.respond_to?(method, include_private)
     end
 
     protected
 
+    def array_delegable?(method)
+      Array.method_defined?(method) && BLACKLISTED_ARRAY_METHODS.exclude?(method)
+    end
+
     def method_missing(method, *args, &block)
       if @klass.respond_to?(method)
         scoping { @klass.public_send(method, *args, &block) }
+      elsif array_delegable?(method)
+        to_a.public_send(method, *args, &block)
       elsif arel.respond_to?(method)
         arel.public_send(method, *args, &block)
       else