dependencies no longer trigger Kernel#autoload in remove_const [fixes #8213]

activesupport/CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Dependencies no longer trigger Kernel#autoload in remove_const [fixes #8213]. *Xavier Noria*
+
 *   Simplify mocha integration and remove monkey-patches, bumping mocha to 0.13.0. *James Mead*
 
 *   `#as_json` isolates options when encoding a hash.

activesupport/lib/active_support/dependencies.rb

@@ -572,7 +572,6 @@ module ActiveSupport #:nodoc:
 
     # Determine if the given constant has been automatically loaded.
     def autoloaded?(desc)
-      # No name => anonymous module.
       return false if desc.is_a?(Module) && desc.anonymous?
       name = to_constant_name desc
       return false unless qualified_const_defined? name
@@ -641,19 +640,38 @@ module ActiveSupport #:nodoc:
     end
 
     def remove_constant(const) #:nodoc:
-      return false unless qualified_const_defined? const
+      # Normalize ::Foo, ::Object::Foo, Object::Foo, Object::Object::Foo, etc. as Foo.
+      normalized = const.to_s.sub(/\A::/, '')
+      normalized.sub!(/\A(Object::)+/, '')
 
-      # Normalize ::Foo, Foo, Object::Foo, and ::Object::Foo to Object::Foo
-      names = const.to_s.sub(/^::(Object)?/, 'Object::').split("::")
-      to_remove = names.pop
-      parent = Inflector.constantize(names * '::')
+      constants   = normalized.split('::')
+      to_remove   = constants.pop
+      parent_name = constants.empty? ? 'Object' : constants.join('::')
 
-      log "removing constant #{const}"
-      constantized = constantize(const)
-      constantized.before_remove_const if constantized.respond_to?(:before_remove_const)
-      parent.instance_eval { remove_const to_remove }
+      if parent = safe_constantize(parent_name)
+        # In an autoloaded user.rb like this
+        #
+        #   autoload :Foo, 'foo'
+        #
+        #   class User < ActiveRecord::Base
+        #   end
+        #
+        # we correctly register "Foo" as being autoloaded. But if the app
+        # does not use the "Foo" constant we need to be careful not to
+        # trigger loading "foo". If the autoload has not been triggered
+        # we already know there is nothing to remove so just return.
+        return if parent.autoload?(to_remove)
 
-      true
+        begin
+          log "removing constant #{const}"
+          constantized = parent.const_get(to_remove, false)
+        rescue NameError
+          log "the constant #{const} is not reachable anymore, skipping"
+        else
+          constantized.before_remove_const if constantized.respond_to?(:before_remove_const)
+          parent.instance_eval { remove_const to_remove }
+        end
+      end
     end
 
     protected

activesupport/test/autoloading_fixtures/should_not_be_required.rb

@@ -0,0 +1 @@
+ShouldNotBeAutoloaded = 0

activesupport/test/dependencies_test.rb

@@ -928,6 +928,16 @@ class DependenciesTest < ActiveSupport::TestCase
     assert ! defined?(DeleteMe)
   end
 
+  def test_remove_constant_does_not_trigger_loading_autoloads
+    constant = 'ShouldNotBeAutoloaded'
+    Object.class_eval do
+      autoload constant, File.expand_path('../autoloading_fixtures/should_not_be_required', __FILE__)
+    end
+    ActiveSupport::Dependencies.remove_constant(constant)
+
+    assert Object.autoload?(constant), "Kernel#autoload of #{constant} has been triggered by remove_const"
+  end
+
   def test_load_once_constants_should_not_be_unloaded
     with_autoloading_fixtures do
       ActiveSupport::Dependencies.autoload_once_paths = ActiveSupport::Dependencies.autoload_paths