Prevent scope named same as a ActiveRecord::Relation instance method.

Due to inconsistent behavior when chaining scopes and one scope named after a Relation method

Validation code added in 2 places:

- scope, to prevent problematic scope names.
- enum, cause it tries to auto define scope.

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Don't allow scopes to be defined which conflict with instance methods on `Relation`.
+
+    Fixes #31120.
+    
+    *kinnrot*
+
 ## Rails 5.2.0.beta1 (November 27, 2017) ##
 
 *   Add new error class `QueryCanceled` which will be raised

activerecord/lib/active_record/enum.rb

@@ -221,6 +221,8 @@ module ActiveRecord
       def detect_enum_conflict!(enum_name, method_name, klass_method = false)
         if klass_method && dangerous_class_method?(method_name)
           raise_conflict_error(enum_name, method_name, type: "class")
+        elsif klass_method && method_defined_within?(method_name, Relation)
+          raise_conflict_error(enum_name, method_name, type: "class", source: Relation.name)
         elsif !klass_method && dangerous_attribute_method?(method_name)
           raise_conflict_error(enum_name, method_name)
         elsif !klass_method && method_defined_within?(method_name, _enum_methods_module, Module)

activerecord/lib/active_record/scoping/named.rb

@@ -171,6 +171,12 @@ module ActiveRecord
               "a class method with the same name."
           end
 
+          if method_defined_within?(name, Relation)
+            raise ArgumentError, "You tried to define a scope named \"#{name}\" " \
+              "on the model \"#{self.name}\", but ActiveRecord::Relation already defined " \
+              "an instance method with the same name."
+          end
+
           valid_scope_name?(name)
           extension = Module.new(&block) if block
 

activerecord/test/cases/enum_test.rb

@@ -308,6 +308,24 @@ class EnumTest < ActiveRecord::TestCase
     end
   end
 
+  test "reserved enum values for relation" do
+    relation_method_samples = [
+      :records,
+      :to_ary,
+      :scope_for_create
+    ]
+
+    relation_method_samples.each do |value|
+      e = assert_raises(ArgumentError, "enum value `#{value}` should not be allowed") do
+        Class.new(ActiveRecord::Base) do
+          self.table_name = "books"
+          enum category: [:other, value]
+        end
+      end
+      assert_match(/You tried to define an enum named .* on the model/, e.message)
+    end
+  end
+
   test "overriding enum method should not raise" do
     assert_nothing_raised do
       Class.new(ActiveRecord::Base) do

activerecord/test/cases/scoping/named_scoping_test.rb

@@ -151,6 +151,22 @@ class NamedScopingTest < ActiveRecord::TestCase
     assert_equal "The scope body needs to be callable.", e.message
   end
 
+  def test_scopes_name_is_relation_method
+    conflicts = [
+      :records,
+      :to_ary,
+      :to_sql,
+      :explain
+    ]
+
+    conflicts.each do |name|
+      e = assert_raises ArgumentError do
+        Class.new(Post).class_eval { scope name, -> { where(approved: true) } }
+      end
+      assert_match(/You tried to define a scope named \"#{name}\" on the model/, e.message)
+    end
+  end
+
   def test_active_records_have_scope_named__all__
     assert !Topic.all.empty?