Tighten up the AV::Base constructor

The AV::Base constructor was too complicated, and this commit tightens
up the parameters it will take.  At runtime, AV::Base is most commonly
constructed here:

  94d54fa4ab/actionview/lib/action_view/rendering.rb (L72-L74)

This provides an AV::Renderer instance, a hash of assignments, and a
controller instance.  Since this is the common case for construction, we
should remove logic from the constructor that handles other cases.  This
commit introduces special constructors for those other cases.
Interestingly, most code paths that construct AV::Base "strangely" are
tests.

actionpack/lib/action_controller/metal/helpers.rb

@@ -75,7 +75,7 @@ module ActionController
       # Provides a proxy to access helper methods from outside the view.
       def helpers
         @helper_proxy ||= begin
-          proxy = ActionView::Base.new
+          proxy = ActionView::Base.empty
           proxy.config = config.inheritable_copy
           proxy.extend(_helpers)
         end

actionpack/lib/action_dispatch/middleware/debug_view.rb

@@ -10,7 +10,9 @@ module ActionDispatch
     RESCUES_TEMPLATE_PATH = File.expand_path("templates", __dir__)
 
     def initialize(assigns)
-      super([RESCUES_TEMPLATE_PATH], assigns)
+      paths = [RESCUES_TEMPLATE_PATH]
+      renderer = ActionView::Renderer.new ActionView::LookupContext.new(paths)
+      super(renderer, assigns)
     end
 
     def debug_params(params)

actionview/lib/action_view/base.rb

@@ -3,6 +3,7 @@
 require "active_support/core_ext/module/attr_internal"
 require "active_support/core_ext/module/attribute_accessors"
 require "active_support/ordered_options"
+require "active_support/deprecation"
 require "action_view/log_subscriber"
 require "action_view/helpers"
 require "action_view/context"
@@ -187,7 +188,7 @@ module ActionView #:nodoc:
       end
     end
 
-    attr_accessor :view_renderer
+    attr_reader :view_renderer
     attr_internal :config, :assigns
 
     delegate :lookup_context, to: :view_renderer
@@ -197,17 +198,49 @@ module ActionView #:nodoc:
       @_assigns = new_assigns.each { |key, value| instance_variable_set("@#{key}", value) }
     end
 
-    def initialize(context = nil, assigns = {}, controller = nil, formats = nil) #:nodoc:
+    # :stopdoc:
+
+    def self.build_renderer(context, controller, formats)
+      lookup_context = context.is_a?(ActionView::LookupContext) ?
+        context : ActionView::LookupContext.new(context)
+      lookup_context.formats  = formats if formats
+      lookup_context.prefixes = controller._prefixes if controller
+      ActionView::Renderer.new(lookup_context)
+    end
+
+    def self.empty
+      with_view_paths([])
+    end
+
+    def self.with_view_paths(view_paths, assigns = {}, controller = nil)
+      with_context ActionView::LookupContext.new(view_paths), assigns, controller
+    end
+
+    def self.with_context(context, assigns = {}, controller = nil)
+      new ActionView::Renderer.new(context), assigns, controller
+    end
+
+    NULL = Object.new
+
+    # :startdoc:
+
+    def initialize(renderer, assigns = {}, controller = nil, formats = NULL) #:nodoc:
       @_config = ActiveSupport::InheritableOptions.new
 
-      if context.is_a?(ActionView::Renderer)
-        @view_renderer = context
+      unless formats == NULL
+        ActiveSupport::Deprecation.warn <<~eowarn
+        Passing formats to ActionView::Base.new is deprecated
+        eowarn
+      end
+
+      if renderer.is_a?(ActionView::Renderer)
+        @view_renderer = renderer
       else
-        lookup_context = context.is_a?(ActionView::LookupContext) ?
-          context : ActionView::LookupContext.new(context)
-        lookup_context.formats  = formats if formats
-        lookup_context.prefixes = controller._prefixes if controller
-        @view_renderer = ActionView::Renderer.new(lookup_context)
+        ActiveSupport::Deprecation.warn <<~eowarn
+        ActionView::Base instances should be constructed with a view renderer,
+        assigments, and a controller.
+        eowarn
+        @view_renderer = self.class.build_renderer(renderer, controller, formats)
       end
 
       @cache_hit = {}

actionview/lib/action_view/template/handlers/erb/erubi.rb

@@ -26,7 +26,7 @@ module ActionView
             view = Class.new(ActionView::Base) {
               include action_view_erb_handler_context._routes.url_helpers
               class_eval("define_method(:_template) { |local_assigns, output_buffer| #{src} }", @filename || "(erubi)", 0)
-            }.new(action_view_erb_handler_context)
+            }.with_context(action_view_erb_handler_context)
             view.run(:_template, {}, ActionView::OutputBuffer.new)
           end
 

actionview/test/abstract_unit.rb

@@ -48,7 +48,7 @@ module RenderERBUtils
     @view ||= begin
       path = ActionView::FileSystemResolver.new(FIXTURE_LOAD_PATH)
       view_paths = ActionView::PathSet.new([path])
-      ActionView::Base.new(view_paths)
+      ActionView::Base.with_view_paths(view_paths)
     end
   end
 
@@ -61,7 +61,7 @@ module RenderERBUtils
       ActionView::Template::Handlers::ERB,
       {})
 
-    template.render(ActionView::Base.new, {}).strip
+    template.render(ActionView::Base.empty, {}).strip
   end
 end
 

actionview/test/actionpack/controller/view_paths_test.rb

@@ -77,7 +77,7 @@ class ViewLoadPathsTest < ActionController::TestCase
   end
 
   def test_template_appends_view_path_correctly
-    @controller.instance_variable_set :@template, ActionView::Base.new(TestController.view_paths, {}, @controller)
+    @controller.instance_variable_set :@template, ActionView::Base.with_view_paths(TestController.view_paths, {}, @controller)
     class_view_paths = TestController.view_paths
 
     @controller.append_view_path "foo"
@@ -89,7 +89,7 @@ class ViewLoadPathsTest < ActionController::TestCase
   end
 
   def test_template_prepends_view_path_correctly
-    @controller.instance_variable_set :@template, ActionView::Base.new(TestController.view_paths, {}, @controller)
+    @controller.instance_variable_set :@template, ActionView::Base.with_view_paths(TestController.view_paths, {}, @controller)
     class_view_paths = TestController.view_paths
 
     @controller.prepend_view_path "baz"

actionview/test/activerecord/multifetch_cache_test.rb

@@ -19,7 +19,7 @@ class MultifetchCacheTest < ActiveRecordTestCase
       def combined_fragment_cache_key(key)
         [ :views, key ]
       end
-    end.new(view_paths, {})
+    end.with_view_paths(view_paths, {})
   end
 
   def test_only_preloading_for_records_that_miss_the_cache

actionview/test/template/capture_helper_test.rb

@@ -5,7 +5,7 @@ require "abstract_unit"
 class CaptureHelperTest < ActionView::TestCase
   def setup
     super
-    @av = ActionView::Base.new
+    @av = ActionView::Base.empty
     @view_flow = ActionView::OutputFlow.new
   end
 

actionview/test/template/compiled_templates_test.rb

@@ -72,13 +72,13 @@ class CompiledTemplatesTest < ActiveSupport::TestCase
 
     def render_with_cache(*args)
       view_paths = ActionController::Base.view_paths
-      ActionView::Base.new(view_paths, {}).render(*args)
+      ActionView::Base.with_view_paths(view_paths, {}).render(*args)
     end
 
     def render_without_cache(*args)
       path = ActionView::FileSystemResolver.new(FIXTURE_LOAD_PATH)
       view_paths = ActionView::PathSet.new([path])
-      ActionView::Base.new(view_paths, {}).render(*args)
+      ActionView::Base.with_view_paths(view_paths, {}).render(*args)
     end
 
     def modify_template(template, content)

actionview/test/template/render_test.rb

@@ -15,7 +15,7 @@ module RenderTestCases
       def combined_fragment_cache_key(key)
         [ :views, key ]
       end
-    end.new(paths, @assigns)
+    end.with_view_paths(paths, @assigns)
 
     @controller_view = TestController.new.view_context
 

actionview/test/template/streaming_render_test.rb

@@ -9,7 +9,7 @@ class SetupFiberedBase < ActiveSupport::TestCase
   def setup
     view_paths = ActionController::Base.view_paths
     @assigns = { secret: "in the sauce", name: nil }
-    @view = ActionView::Base.new(view_paths, @assigns)
+    @view = ActionView::Base.with_view_paths(view_paths, @assigns)
     @controller_view = TestController.new.view_context
   end
 

actionview/test/template/test_case_test.rb

@@ -52,7 +52,7 @@ module ActionView
     end
 
     test "retrieve non existing config values" do
-      assert_nil ActionView::Base.new.config.something_odd
+      assert_nil ActionView::Base.empty.config.something_odd
     end
 
     test "works without testing a helper module" do

actionview/test/template/translation_helper_test.rb

@@ -36,7 +36,7 @@ class TranslationHelperTest < ActiveSupport::TestCase
         }
       }
     )
-    @view = ::ActionView::Base.new(ActionController::Base.view_paths, {})
+    @view = ::ActionView::Base.with_view_paths(ActionController::Base.view_paths, {})
   end
 
   teardown do

guides/rails_guides/generator.rb

@@ -150,8 +150,8 @@ module RailsGuides
         puts "Generating #{guide} as #{output_file}"
         layout = @kindle ? "kindle/layout" : "layout"
 
-        view = ActionView::Base.new(
-          @source_dir,
+        view = ActionView::Base.with_view_paths(
+          [@source_dir],
           edge:     @edge,
           version:  @version,
           mobi:     "kindle/#{mobi}",