Support combining scopes when loading records, use Arel instead of SQL

Appraisals

@@ -1,55 +1,3 @@
-appraise 'activerecord_4.2.0' do
-  gem 'activerecord', '~> 4.2.0', require: 'active_record'
-  gem 'activesupport', '~> 4.2.0', require: 'active_support/all'
-  gem 'actionpack', '~> 4.2.0', require: 'action_pack'
-  gem 'nokogiri', '~> 1.6.8', require: 'nokogiri' # TODO: fix for ruby 2.0.0
-
-  gemfile.platforms :jruby do
-    gem 'activerecord-jdbcsqlite3-adapter', '~> 1.3.24'
-    gem 'jdbc-sqlite3'
-    gem 'jdbc-postgres'
-  end
-
-  gemfile.platforms :ruby, :mswin, :mingw do
-    gem 'sqlite3', '~> 1.3.0'
-    gem 'pg', '~> 0.21'
-  end
-end
-
-appraise 'activerecord_5.0.2' do
-  gem 'activerecord', '~> 5.0.2', require: 'active_record'
-  gem 'activesupport', '~> 5.0.2', require: 'active_support/all'
-  gem 'actionpack', '~> 5.0.2', require: 'action_pack'
-
-  gemfile.platforms :jruby do
-    gem 'activerecord-jdbcsqlite3-adapter'
-    gem 'jdbc-sqlite3'
-    gem 'jdbc-postgres'
-  end
-
-  gemfile.platforms :ruby, :mswin, :mingw do
-    gem 'sqlite3', '~> 1.3.0'
-    gem 'pg', '~> 0.21'
-  end
-end
-
-appraise 'activerecord_5.1.0' do
-  gem 'activerecord', '~> 5.1.0', require: 'active_record'
-  gem 'activesupport', '~> 5.1.0', require: 'active_support/all'
-  gem 'actionpack', '~> 5.1.0', require: 'action_pack'
-
-  gemfile.platforms :jruby do
-    gem 'activerecord-jdbcsqlite3-adapter'
-    gem 'jdbc-sqlite3'
-    gem 'jdbc-postgres'
-  end
-
-  gemfile.platforms :ruby, :mswin, :mingw do
-    gem 'sqlite3', '~> 1.3.0'
-    gem 'pg', '~> 0.21'
-  end
-end
-
 appraise 'activerecord_5.2.2' do
   gem 'activerecord', '~> 5.2.2', require: 'active_record'
   gem 'activesupport', '~> 5.2.2', require: 'active_support/all'

docs/Fetching-Records.md

@@ -8,7 +8,7 @@ Sometimes you need to restrict which records are returned from the database base
 You can change the action by passing it as the second argument. Here we find only the records the user has permission to update.
 
 ```ruby
-@articles = Article.accessible_by(current_ability, :update) 
+@articles = Article.accessible_by(current_ability, :update)
 ```
 
 If you want to use the current controller's action, make sure to call `to_sym` on it:
@@ -17,7 +17,7 @@ If you want to use the current controller's action, make sure to call `to_sym` o
 @articles = Article.accessible_by(current_ability, params[:action].to_sym)
 ```
 
-This is an Active Record scope so other scopes and pagination can be chained onto it.
+This is an Active Record scope so other scopes and pagination can be chained onto it. It can also be chained onto existing scopes.
 
 This works with multiple `can` definitions, which allows you to define complex permission logic and have it translated properly to SQL.
 
@@ -29,19 +29,19 @@ class Ability
   can :manage, User, id: user.id
 end
 ```
-a call to User.accessible_by(current_ability) generates the following SQL
+a call to User.accessible_by(current_ability) generates the following or equivalent SQL, depending on your version of ActiveRecord.
 
 ```sql
 SELECT *
 FROM users
 WHERE (id = 1) OR (not (self_managed = 't') AND (manager_id = 1))
 ```
 
-It will raise an exception if any requested model's ability definition is defined using just block. 
+It will raise an exception if any requested model's ability definition is defined using just block.
 You can define SQL fragment in addition to block (look for more examples in [[Defining Abilities with Blocks]]).
 
 If you are using something other than Active Record you can fetch the conditions hash directly from the current ability.
 
 ```ruby
 current_ability.model_adapter(TargetClass, :read).conditions
-```
+```

lib/cancan.rb

@@ -19,6 +19,4 @@
   require 'cancan/model_adapters/conditions_normalizer'
   require 'cancan/model_adapters/sti_normalizer'
   require 'cancan/model_adapters/active_record_adapter'
-  require 'cancan/model_adapters/active_record_4_adapter'
-  require 'cancan/model_adapters/active_record_5_adapter'
 end

lib/cancan/ability.rb

@@ -167,9 +167,10 @@ def validate_target(target)
       raise Error, error_message if aliased_actions.values.flatten.include? target
     end
 
-    def model_adapter(model_class, action)
+    def model_adapter(relation_or_class, action)
+      model_class = relation_or_class.respond_to?(:klass) ? relation_or_class.klass : relation_or_class
       adapter_class = ModelAdapters::AbstractAdapter.adapter_class(model_class)
-      adapter_class.new(model_class, relevant_rules_for_query(action, model_class))
+      adapter_class.new(relation_or_class, relevant_rules_for_query(action, model_class))
     end
 
     # See ControllerAdditions#authorize! for documentation.

lib/cancan/config.rb

@@ -2,9 +2,7 @@
 
 module CanCan
   def self.valid_accessible_by_strategies
-    strategies = [:left_join]
-    strategies << :subquery unless does_not_support_subquery_strategy?
-    strategies
+    %i[left_join subquery]
   end
 
   # Determines how CanCan should build queries when calling accessible_by,
@@ -27,31 +25,18 @@ def self.accessible_by_strategy
   end
 
   def self.default_accessible_by_strategy
-    if does_not_support_subquery_strategy?
-      # see https://github.com/CanCanCommunity/cancancan/pull/655 for where this was added
-      # the `subquery` strategy (from https://github.com/CanCanCommunity/cancancan/pull/619
-      # only works in Rails 5 and higher
-      :left_join
-    else
-      :subquery
-    end
+    # see https://github.com/CanCanCommunity/cancancan/pull/655 for where this was added
+    # the `subquery` strategy (from https://github.com/CanCanCommunity/cancancan/pull/619
+    :left_join
   end
 
   def self.accessible_by_strategy=(value)
-    validate_accessible_by_strategy!(value)
-
-    if value == :subquery && does_not_support_subquery_strategy?
-      raise ArgumentError, 'accessible_by_strategy = :subquery requires ActiveRecord 5 or newer'
-    end
-
     @accessible_by_strategy = value
   end
 
   def self.with_accessible_by_strategy(value)
     return yield if value == accessible_by_strategy
 
-    validate_accessible_by_strategy!(value)
-
     begin
       strategy_was = accessible_by_strategy
       @accessible_by_strategy = value
@@ -60,15 +45,4 @@ def self.with_accessible_by_strategy(value)
       @accessible_by_strategy = strategy_was
     end
   end
-
-  def self.validate_accessible_by_strategy!(value)
-    return if valid_accessible_by_strategies.include?(value)
-
-    raise ArgumentError, "accessible_by_strategy must be one of #{valid_accessible_by_strategies.join(', ')}"
-  end
-
-  def self.does_not_support_subquery_strategy?
-    !defined?(CanCan::ModelAdapters::ActiveRecordAdapter) ||
-      CanCan::ModelAdapters::ActiveRecordAdapter.version_lower?('5.0.0')
-  end
 end