ActionView: Layouts can access local variables

Local variable access was originally broken, reportedly, in Rails 5.1
in d6bac04 which dropped the `locals` keys from some of the layout
lookup methods to optimize the template resolver cache.

In the meantime, the template resolver cache was discarded in Rails
7.0 in 4db7ae5, and was replaced by a FileSystemResolver cache that
does not use the locals in the lookup key (because it's storing
unbound templates).

So this fix is, essentially, to once again pass the local variable
names through the many layers of the layout resolver/renderer stack to
make sure that when the unbound template is found and `#bind_locals`
is called on it, it's bound with the proper set of local variable
names.

Fixes rails#31680

Author: flavorjones

actionview/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Layouts have access to local variables passed to `render`.
+
+    This fixes #31680 which was a regression in Rails 5.1.
+
+    *Mike Dalessio*
+
 *   Argument errors related to strict locals in templates now raise an
     `ActionView::StrictLocalsError`, and all other argument errors are reraised as-is.
 

actionview/lib/action_view/layouts.rb

@@ -284,7 +284,7 @@ def _write_layout_method # :nodoc:
         silence_redefinition_of_method(:_layout)
 
         prefixes = /\blayouts/.match?(_implied_layout_name) ? [] : ["layouts"]
-        default_behavior = "lookup_context.find_all('#{_implied_layout_name}', #{prefixes.inspect}, false, [], { formats: formats }).first || super"
+        default_behavior = "lookup_context.find_all('#{_implied_layout_name}', #{prefixes.inspect}, false, keys, { formats: formats }).first || super"
         name_clause = if name
           default_behavior
         else
@@ -325,7 +325,7 @@ def _write_layout_method # :nodoc:
 
         class_eval <<-RUBY, __FILE__, __LINE__ + 1
           # frozen_string_literal: true
-          def _layout(lookup_context, formats)
+          def _layout(lookup_context, formats, keys)
             if _conditional_layout?
               #{layout_definition}
             else
@@ -389,8 +389,8 @@ def _layout_for_option(name)
       case name
       when String     then _normalize_layout(name)
       when Proc       then name
-      when true       then Proc.new { |lookup_context, formats| _default_layout(lookup_context, formats, true)  }
-      when :default   then Proc.new { |lookup_context, formats| _default_layout(lookup_context, formats, false) }
+      when true       then Proc.new { |lookup_context, formats, keys| _default_layout(lookup_context, formats, keys, true)  }
+      when :default   then Proc.new { |lookup_context, formats, keys| _default_layout(lookup_context, formats, keys, false) }
       when false, nil then nil
       else
         raise ArgumentError,
@@ -412,9 +412,9 @@ def _normalize_layout(value)
     #
     # ==== Returns
     # * <tt>template</tt> - The template object for the default layout (or +nil+)
-    def _default_layout(lookup_context, formats, require_layout = false)
+    def _default_layout(lookup_context, formats, keys, require_layout = false)
       begin
-        value = _layout(lookup_context, formats) if action_has_layout?
+        value = _layout(lookup_context, formats, keys) if action_has_layout?
       rescue NameError => e
         raise e, "Could not render layout: #{e.message}"
       end

actionview/lib/action_view/renderer/template_renderer.rb

@@ -99,14 +99,14 @@ def resolve_layout(layout, keys, formats)
             if layout.start_with?("/")
               raise ArgumentError, "Rendering layouts from an absolute path is not supported."
             else
-              @lookup_context.find_template(layout, nil, false, [], details)
+              @lookup_context.find_template(layout, nil, false, keys, details)
             end
           rescue ActionView::MissingTemplate
             all_details = @details.merge(formats: @lookup_context.default_formats)
-            raise unless template_exists?(layout, nil, false, [], **all_details)
+            raise unless template_exists?(layout, nil, false, keys, **all_details)
           end
         when Proc
-          resolve_layout(layout.call(@lookup_context, formats), keys, formats)
+          resolve_layout(layout.call(@lookup_context, formats, keys), keys, formats)
         else
           layout
         end

actionview/test/actionpack/abstract/layouts_test.rb

@@ -15,7 +15,7 @@ class Base < AbstractController::Base
       self.view_paths = [ActionView::FixtureResolver.new(
         "some/template.erb"             => "hello <%= foo %> bar",
         "layouts/hello.erb"             => "With String <%= yield %>",
-        "layouts/hello_locals.erb"      => "With String <%= yield %>",
+        "layouts/hello_locals.erb"      => "With String <%= foo %> <%= yield %>",
         "layouts/hello_override.erb"    => "With Override <%= yield %>",
         "layouts/overwrite.erb"         => "Overwrite <%= yield %>",
         "layouts/with_false_layout.erb" => "False Layout <%= yield %>",
@@ -41,6 +41,10 @@ class WithStringLocals < Base
       def index
         render template: "some/template", locals: { foo: "less than 3" }
       end
+
+      def overwrite_with_default
+        render layout: :default, template: "some/template", locals: { foo: "less than 3" }
+      end
     end
 
     class WithString < Base
@@ -279,10 +283,16 @@ class TestBase < ActiveSupport::TestCase
         assert_equal "Hello blank!", controller.response_body
       end
 
-      test "with locals" do
+      test "when layout is specified as a string, render with locals" do
         controller = WithStringLocals.new
         controller.process(:index)
-        assert_equal "With String hello less than 3 bar", controller.response_body
+        assert_equal "With String less than 3 hello less than 3 bar", controller.response_body
+      end
+
+      test "when layout is specified as a string, overwriting with :default, render with locals" do
+        controller = WithStringLocals.new
+        controller.process(:overwrite_with_default)
+        assert_equal "With String less than 3 hello less than 3 bar", controller.response_body
       end
 
       test "when layout is specified as a string, render with that layout" do