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.

2 files changed, 43 insertions, 10 deletions

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