Remove FallbackFileSystemResolver

This removes FallbackFileSystemResolver, LookupContext#with_fallbacks,
and LookupContext.fallbacks.

These used to exist to support `render file:`, and rendering templates
outside of the defined view paths. `render file:` has since been changed
to not use template resolution, and to only render absolute paths.

These were no longer callable through any public API.

Author: jhawthorn

actionview/lib/action_view/lookup_context.rb

@@ -15,8 +15,6 @@ module ActionView
   class LookupContext #:nodoc:
     attr_accessor :prefixes, :rendered_format
 
-    mattr_accessor :fallbacks, default: FallbackFileSystemResolver.instances
-
     mattr_accessor :registered_details, default: []
 
     def self.register_detail(name, &block)
@@ -75,7 +73,6 @@ def self.clear
         ActionView::ViewPaths.all_view_paths.each do |path_set|
           path_set.each(&:clear_cache)
         end
-        ActionView::LookupContext.fallbacks.each(&:clear_cache)
         @view_context_class = nil
         @details_keys.clear
         @digest_cache.clear
@@ -142,21 +139,6 @@ def any?(name, prefixes = [], partial = false)
       end
       alias :any_templates? :any?
 
-      # Adds fallbacks to the view paths. Useful in cases when you are rendering
-      # a :file.
-      def with_fallbacks
-        view_paths = build_view_paths((@view_paths.paths + self.class.fallbacks).uniq)
-
-        if block_given?
-          raise ArgumentError, <<~eowarn.squish
-          Calling `with_fallbacks` with a block is not supported. Call methods on
-          the lookup context returned by `with_fallbacks` instead.
-          eowarn
-        else
-          ActionView::LookupContext.new(view_paths, @details, @prefixes)
-        end
-      end
-
     private
       # Whenever setting view paths, makes a copy so that we can manipulate them in
       # instance objects as we wish.

actionview/lib/action_view/template/resolver.rb

@@ -411,22 +411,4 @@ def build_regex(path, details)
         %r{\A#{query}#{exts}\z}
       end
   end
-
-  # The same as FileSystemResolver but does not allow templates to store
-  # a virtual path since it is invalid for such resolvers.
-  class FallbackFileSystemResolver < FileSystemResolver #:nodoc:
-    private_class_method :new
-
-    def self.instances
-      [new(""), new("/")]
-    end
-
-    def build_unbound_template(template, _)
-      super(template, nil)
-    end
-
-    def reject_files_external_to_app(files)
-      files
-    end
-  end
 end

actionview/test/activerecord/multifetch_cache_test.rb

@@ -8,7 +8,6 @@ class MultifetchCacheTest < ActiveRecordTestCase
   def setup
     view_paths = ActionController::Base.view_paths
     view_paths.each(&:clear_cache)
-    ActionView::LookupContext.fallbacks.each(&:clear_cache)
 
     @view = Class.new(ActionView::Base.with_empty_template_cache) do
       def view_cache_dependencies

actionview/test/template/compiled_templates_test.rb

@@ -9,7 +9,6 @@ def setup
     super
     view_paths = ActionController::Base.view_paths
     view_paths.each(&:clear_cache)
-    ActionView::LookupContext.fallbacks.each(&:clear_cache)
     @view_class = ActionView::Base.with_empty_template_cache
   end
 

actionview/test/template/fallback_file_system_resolver_test.rb

@@ -127,22 +127,6 @@ def teardown
     end
   end
 
-  test "adds fallbacks to view paths when required" do
-    assert_equal 1, @lookup_context.view_paths.size
-
-    @lookup_context = @lookup_context.with_fallbacks
-
-    assert_equal 3, @lookup_context.view_paths.size
-    assert_includes @lookup_context.view_paths, ActionView::FallbackFileSystemResolver.instances[0]
-    assert_includes @lookup_context.view_paths, ActionView::FallbackFileSystemResolver.instances[1]
-  end
-
-  test "with_fallbacks with block raises an ArgumentError" do
-    assert_raises(ArgumentError) do
-      @lookup_context.with_fallbacks { }
-    end
-  end
-
   test "generates a new details key for each details hash" do
     keys = []
     keys << @lookup_context.details_key

actionview/test/template/lookup_context_test.rb

@@ -41,7 +41,6 @@ class TranslationHelperTest < ActiveSupport::TestCase
     )
     view_paths = ActionController::Base.view_paths
     view_paths.each(&:clear_cache)
-    ActionView::LookupContext.fallbacks.each(&:clear_cache)
     @view = ::ActionView::Base.with_empty_template_cache.with_view_paths(view_paths, {})
   end