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:

  https://github.com/rails/rails/blob/94d54fa4ab641a0ddeb173409cb41cc5becc02a9/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.

14 files changed, 61 insertions, 26 deletions

diff --git a/actionpack/lib/action_controller/metal/helpers.rb b/actionpack/lib/action_controller/metal/helpers.rb
index 0faaac1ce4..f1fb7ab0f7 100644
--- a/actionpack/lib/action_controller/metal/helpers.rb
+++ b/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
diff --git a/actionpack/lib/action_dispatch/middleware/debug_view.rb b/actionpack/lib/action_dispatch/middleware/debug_view.rb
index ac12dc13a1..5a7010a1c2 100644
--- a/actionpack/lib/action_dispatch/middleware/debug_view.rb
+++ b/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)
diff --git a/actionview/lib/action_view/base.rb b/actionview/lib/action_view/base.rb
index 6cb342a0a9..fe9f3f9503 100644
--- a/actionview/lib/action_view/base.rb
+++ b/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 = {}
diff --git a/actionview/lib/action_view/template/handlers/erb/erubi.rb b/actionview/lib/action_view/template/handlers/erb/erubi.rb
index e155bae89d..15ca202024 100644
--- a/actionview/lib/action_view/template/handlers/erb/erubi.rb
+++ b/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
 
diff --git a/actionview/test/abstract_unit.rb b/actionview/test/abstract_unit.rb
index d71944e938..56d617309c 100644
--- a/actionview/test/abstract_unit.rb
+++ b/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
 
diff --git a/actionview/test/actionpack/controller/view_paths_test.rb b/actionview/test/actionpack/controller/view_paths_test.rb
index 7f3fe0fa08..c5238dd746 100644
--- a/actionview/test/actionpack/controller/view_paths_test.rb
+++ b/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"
diff --git a/actionview/test/activerecord/multifetch_cache_test.rb b/actionview/test/activerecord/multifetch_cache_test.rb
index 12be069e69..229b4e56d0 100644
--- a/actionview/test/activerecord/multifetch_cache_test.rb
+++ b/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
diff --git a/actionview/test/template/capture_helper_test.rb b/actionview/test/template/capture_helper_test.rb
index e172497c88..45070674ad 100644
--- a/actionview/test/template/capture_helper_test.rb
+++ b/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
 
diff --git a/actionview/test/template/compiled_templates_test.rb b/actionview/test/template/compiled_templates_test.rb
index 3cd6448e38..ded4786e62 100644
--- a/actionview/test/template/compiled_templates_test.rb
+++ b/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)
diff --git a/actionview/test/template/render_test.rb b/actionview/test/template/render_test.rb
index afe68b7ff0..ab67423ea1 100644
--- a/actionview/test/template/render_test.rb
+++ b/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
 
diff --git a/actionview/test/template/streaming_render_test.rb b/actionview/test/template/streaming_render_test.rb
index f196c42c4f..dda2095013 100644
--- a/actionview/test/template/streaming_render_test.rb
+++ b/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
 
diff --git a/actionview/test/template/test_case_test.rb b/actionview/test/template/test_case_test.rb
index 976b6bc77e..ab3ababba4 100644
--- a/actionview/test/template/test_case_test.rb
+++ b/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
diff --git a/actionview/test/template/translation_helper_test.rb b/actionview/test/template/translation_helper_test.rb
index e756348938..d04e68e182 100644
--- a/actionview/test/template/translation_helper_test.rb
+++ b/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
diff --git a/guides/rails_guides/generator.rb b/guides/rails_guides/generator.rb
index fd33c3f8a7..b0ddb0e7e0 100644
--- a/guides/rails_guides/generator.rb
+++ b/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}",