Add a finalizer to inline templates

This commit adds a finalizer just to inline templates.  We can't cache
compilation of inline templates because it's possible that people could
have render calls that look like this:

```ruby
loop do
  render inline: "#{rand}"
end
```

and we would cache every one of these different inline templates.  That
would cause a memory leak.  OTOH, we don't need finalizers on regular
templates because we can cache, control, and detect changes to the
template source.

Fixes: #35372

3 files changed, 24 insertions, 1 deletions

diff --git a/actionview/lib/action_view/renderer/template_renderer.rb b/actionview/lib/action_view/renderer/template_renderer.rb
index a129ef0e15..87f6cf3de3 100644
--- a/actionview/lib/action_view/renderer/template_renderer.rb
+++ b/actionview/lib/action_view/renderer/template_renderer.rb
@@ -34,7 +34,7 @@ module ActionView
           else
             @lookup_context.formats.first
           end
-          Template.new(options[:inline], "inline template", handler, locals: keys, format: format)
+          Template::Inline.new(options[:inline], "inline template", handler, locals: keys, format: format)
         elsif options.key?(:template)
           if options[:template].respond_to?(:render)
             options[:template]
diff --git a/actionview/lib/action_view/template.rb b/actionview/lib/action_view/template.rb
index 907b322c8a..133a316405 100644
--- a/actionview/lib/action_view/template.rb
+++ b/actionview/lib/action_view/template.rb
@@ -115,6 +115,7 @@ module ActionView
       autoload :Error
       autoload :Handlers
       autoload :HTML
+      autoload :Inline
       autoload :Text
       autoload :Types
     end
diff --git a/actionview/lib/action_view/template/inline.rb b/actionview/lib/action_view/template/inline.rb
new file mode 100644
index 0000000000..44658487ea
--- /dev/null
+++ b/actionview/lib/action_view/template/inline.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module ActionView #:nodoc:
+  class Template #:nodoc:
+    class Inline < Template #:nodoc:
+      # This finalizer is needed (and exactly with a proc inside another proc)
+      # otherwise templates leak in development.
+      Finalizer = proc do |method_name, mod| # :nodoc:
+        proc do
+          mod.module_eval do
+            remove_possible_method method_name
+          end
+        end
+      end
+
+      def compile(mod)
+        super
+        ObjectSpace.define_finalizer(self, Finalizer[method_name, mod])
+      end
+    end
+  end
+end