Sandbox::https://github.com/rails/rails/pull/50623

seanpdoyle · 2024-01-06T20:46:09Z

Motivation / Background

Support for objects that respond to #render_in was introduced in #36388 and #37919. Those implementations assume that the instance will all the context it needs to render itself. That assumption doesn't account for call-site arguments like locals: { ... } or a block.

Detail

This commit expands support for rendering with a :renderable option to incorporate locals and blocks. For example:

class Greeting
  def render_in(view_context, **options, &block)
    if block
      view_context.render html: block.call
    else
      view_context.render inline: <<~ERB.strip, **options
        Hello, <%= name %>
      ERB
    end
  end
end

render(Greeting.new)                    # => "Hello, World"
render(Greeting.new, name: "Local")     # => "Hello, Local"
render(Greeting.new) { "Hello, Block" } # => "Hello, Block"

Since existing tools depend on the #render_in(view_context) signature
without options, this commit deprecates that signature in favor of one
that accepts options and a block.

Checklist

Before submitting the PR make sure the following are checked:

This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
Tests are added or updated if you fix a bug or add a feature.
CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

seanpdoyle · 2024-01-06T20:50:32Z

The support for blocks was somewhat incidental here. My main goal was to support passing :locals provided at the call sites.

@joelhawksley (and @BlakeWilliams, since you've authored #45432) does this change support behavior that's desirable to ViewComponents?

BlakeWilliams · 2024-01-06T21:25:54Z

Thanks for adding block support! I lost that one in my TODO's a while back since I've been pretty busy lately.

I'm not positive the locals changes as-is would help us much since we expect all data to be passed in to components via the constructor, but also with the new API it's no longer clear to me when to pass something as a local vs constructor argument. e.g.

render(Greeting.new(name: "Fox Mulder"), name: "Dana Scully"))

I think the API changes make that valid code, but it's not obvious to me which argument would take precedence or how Greeting should respond to locals from a ViewComponent perspective (we use render_in as a hook into ActionView, but otherwise components are largely just Ruby including the constructor). I don't think this would be limited to ViewComponents, but all classes that implement render_in would have to reconcile constructor args with locals and provide guidance on when to use each.

Coming at this with a relatively heavy ViewComponent bias, I could see an API that delegates to the constructor making sense, maybe like:

render(Greeting.new(name: "local"))
render(Greeting, name: "local") # Equivalent to the above since Greeting has a `render_in` instance_method. `name:` is passed to the constructor

All of that has a heavy ViewComponent bias of course, but I'm curious if you had any particular use-cases for the locals changes in mind, ViewComponent or otherwise?

seanpdoyle · 2024-01-06T21:49:13Z

All of that has a heavy ViewComponent bias of course

I can relate to that! Since ViewComponent was the pilot tool for driving out render_in, that makes a lot of sense. In my understanding of where ViewComponent fits in, its constructor state is its render context. That's also reasonable, since it's aiming to serve as a View Model. In my mind, ViewComponent has an opportunity to take a stance on requiring constructor-time state and rejecting render-time locals.

I could see an API that delegates to the constructor making sense

With access to the options, that'd be possible as a class-method:

class ViewComponent::Base
  def self.render_in(view_context, locals: {}, **options, &block)
    view_context.render renderable: new(locals, &block), **options 
  end

  def render_in(view_context, **, &)
    # render without :locals or &block
  end
end

class Greeting < ViewComponent::Base
  # ...
end

render Greeting, name: "local" do 
  "from a block"
end

# the abbreviated form above is equivalent to the long-form below
render renderable: Greeting, locals: { name: "local" } do 
  "from a block"
end

Since render_in is meant to be flexible enough to hand-off all rendering responsibilities to the object, it has an opportunity to make as much information available at render-time. ViewComponent made the design decision to exclude the local_assigns in favor of attr_{accessor,reader}, and instance variables. I don't think imposing that design decision on other integrators is necessary. A separate integrator might envision a View Model as a different balance between View and Model. Instead of accepting :name as a :locals value, it might expect that to be available from the object whereas a :size or :variant might be expected as a :locals value.

I'm curious if you had any particular use-cases for the locals changes in mind, ViewComponent or otherwise?

At the moment, the main motivating use case is internal to Rails. I'm in the process of exploring an Action Text branch that adds support for editors other than Trix.

Incidentally, one part of the code I'm exploring re-structuring involves the ActionText::ContentHelper helper module, namely the render_action_text_attachment method:

rails/actiontext/app/helpers/action_text/content_helper.rb

Lines 43 to 55 in b294a25

    
           def render_action_text_attachment(attachment, locals: {}) # :nodoc: 
        
             options = { locals: locals, object: attachment, partial: attachment } 
        
             if attachment.respond_to?(:to_attachable_partial_path) 
        
               options[:partial] = attachment.to_attachable_partial_path 
        
             end 
        
             if attachment.respond_to?(:model_name) 
        
               options[:as] = attachment.model_name.element 
        
             end 
        
             render(**options).chomp 
        
           end

It's a :nodoc: method, and is only called within the module itself:

rails/actiontext/app/helpers/action_text/content_helper.rb

Line 30 in b294a25

    
           node.inner_html = render_action_text_attachment attachment, locals: { in_gallery: false }

rails/actiontext/app/helpers/action_text/content_helper.rb

Line 36 in b294a25

    
           attachment.node.inner_html = render_action_text_attachment attachment, locals: { in_gallery: true }

The implementation is fairly concerned with checking whether or not the attachment responds to various methods, all for the sake of building up the correct Hash or options to pass to render. One extra layer on top of that is that between the two call sites, the only difference is the :in_gallery local variable (true in one place, false in the other).

I'm imagining a world where each editor adapter (ckeditor5, tinymce, etc) have an opportunity to subclass ActionText::Attachment and want to override the default behavior. They wouldn't be able (or advised to) reach into the module-private :nodoc: method. However, if render_in accepted options, they'd be available to the subclasses at call time.

class ActionText::Attachment
  def to_attachable_partial_path
    # to be overridden
    to_partial_path
  end

  def render_in(view_context, **options)
    view_context.render options.with_defaults(
      partial: to_attachable_partial_path,
      object: self,
      as: model_name.element
    )
  end
end

That's a circumstance where the constructor arguments to the object and the values passed into the :locals wouldn't be similar enough to cause confusion. In this use case, it's more about the context with which they're rendered. The ActionText::Attachment objects are constructed in far-flung parts of Action Text very separate from the HTML rendering render_in calls. It would also provide the framework with an opportunity to maintain the consistency in the construction of the ActionText::Attachment instances while providing integrators with flexibility at render-time.

Outside of that use case, I'm imagining other scenarios where an application might want to build renderable objects (maybe even ViewComponents) prior to their render. I don't have a concrete example handy, but I'm imagining a component that yields itself into another component without knowledge of how the receiving component would want to treat it.

seanpdoyle · 2024-01-06T22:35:15Z

@BlakeWilliams if this change is accepted, I'm also exploring adding a default #render_in implementation to the ActiveModel::Conversion module:

seanpdoyle/rails@action-view-render-in-options...seanpdoyle:rails:active-model-conversion-render-in#diff-8ec888bfb07b8d4a67ffa913e3286d4ffcb052d1bf3b232d2874c7177cd96fbc

The idea there would be that any Active Model or Active Record instance would provide a seam for applications to take over control of rendering (for example, mapping a Person to a PersonComponent class).

rafaelfranca · 2024-01-08T21:37:06Z

-      def render(context, *args)
-        @renderable.render_in(context)
+      def render(context, locals)
+        @renderable.render_in(context, formats: @formats, locals: locals, &@block)


This is a breaking change for those objets. We probably need to deprecate the old signature and tell people to upgrade their objects

@rafaelfranca I could also see Rails checking the arity?

Regardless, it'd be a huge bummer to have a breaking change like this. I'd really hope we could avoid going down that route.

Yeah, I was thinking on doing the arity check to show the deprecation.

Why would it be a bummer if we deprecated the old signature? The old code would work, showing a deprecation, and if the library changed to the new one, as the arguments are optional, things would just work in old versions of Rails. In fact you can release a new version of a library right now with the new signature.

If this is a breaking change, would it need to be part of a major version like 7.2 to 8.0?

If not, is the deprecation in the current implementation sufficient enough for a future minor release (like 8.0 to 8.1)?

seanpdoyle · 2024-01-09T04:32:24Z

I think these examples could be improved, but I'm not entirely sure how.

In my mind, there's a few points worth highlighting:

#render_in and the :renderable key as an alternative to :partial is novel in its own right.

The object that defines #render_in can decide on its own how to mix and match its own internal state with the state provided at the render call site through the :locals options

The object that defines #render_in can also decide how to mix the block passed to render

The object can decide which format to render into

Prior to this commit, 1. is only point mentioned at all.

With the proposed changes, 2. poses an interesting opportunity. I consider it similar to React's split between State and Props. Maybe there's an Avatar object that manages its own internal state like the URL and alt text, but accepts overrides from :locals like :size:

class Avatar include ActiveModel::Model include ActiveModel::Attributes attribute :url, :string attribute :alt, :string attribute :size, :string, default: "medium" def render_in(view_context, **options) # ... end end avatar = Avatar.new(url: "https://example.com/avatar.jpg", alt: "A smiling person") render avatar # => <img src="https://example.com/avatar.jpg" alt="A smiling person" class="avatar avatar--medium"> render avatar, size: "small" # => <img src="https://example.com/avatar.jpg" alt="A smiling person" class="avatar avatar--small">

Block-centric rendering objects like ViewComponent::Base could benefit from 3. by forwarding the render call's block to its own constructor. Prior to this commit, calls like this wouldn't behave like you'd expect (as highlighted by #45432):

# ignores the block render MyComponent.new do "Content" end # ignores the block render(MyComponent.new) do "Content" end # captures the block render(MyComponent.new do "Content" end)

Support for determining the templating format (4.) is potentially desirable for objects that want to support multiple formats (like HTML, JSON, etc.). Unfortunately, that support might require more broad changes, and need to be incorporated in a subsequent PR. At the moment, it isn't clear the precedent between:

view_context.lookup_context.formats

the :formats option passed to render

the #format method defined by the same object as #render_in. At this point in time, the #format call would lack access to both the view_context and the render options

There's even potential for applications (or Rails itself) to extend models to know how to render themselves, if they want more control than what Action View provides out of the box:

class ApplicationRecord < ActiveRecord::Base # Renders the object into an Action View context. # # # app/models/person.rb # class Person < ApplicationRecord # end # # # app/views/people/_person.html.erb # <%= person.name %> # # person = Person.new name: "Ralph" # # render(person) # => "Ralph # render(renderable: person) # => "Ralph def render_in(view_context, **options, &block) view_context.render(partial: to_partial_path, object: self, **options, &block) end end class Person < ApplicationRecord end render Person.new(name: "Renders as a Partial") class Article < ApplicationRecord def render_in(view_context, ...) view_context.render ArticleComponent.new(name:) end end render Article.new(name: "Renders as a ViewComponent")

seanpdoyle · 2026-05-12T00:44:52Z

Thank you for the final review @rafaelfranca !

@joelhawksley @BlakeWilliams I've opened #57349 as a follow-up to this change to provide an opportunity to bridge from Active Model to other view layer integrations.

flavorjones · 2026-05-12T16:52:42Z

@seanpdoyle Just a note that libraries like Lexxy that call super in their render_in method like this:

  class Editor::LexxyEditor::Tag < Editor::Tag
    def render_in(view_context, ...)
      options[:value] = options[:value].to_str if options[:value].respond_to?(:to_str)
      super
    end
  end

will get an exception when super invokes Editor::Tag#render_in:

ArgumentError: wrong number of arguments (given 2, expected 1)

I've opened #57356 to fix it.

chaadow · 2026-05-12T21:54:27Z

-        @renderable.render_in(context)
-      rescue NoMethodError
+      def render(context, locals)
+        if @renderable.method(:render_in).arity == 1


@seanpdoyle @rafaelfranca Just FYI, i had an issue with a renderable having an attr_reader :method ( i'm using it as the HTTP method for my links)

and so was having wrong number of arguments (given 1, expected 0)

renaming my attr_reader from method to http_method fixed the issue, but thought I would tell you about it in case maybe you want to switch to an UnboundedMethod then bind the @renderable

Your call! 🫡

Can you open a pr? I don’t want people to have to change the code

@rafaelfranca Yes I will open a PR later, thanks for confirming.

Here is the PR: #57360 @rafaelfranca

Use Kernel#method explicitly when checking a renderable object's render_in arity, so objects that define their own method reader do not break rendering. Along with a regression test. More context: rails#50623 (comment)

Rails merged rails/rails#50623, which changes the `render_in` signature from `render_in(view_context, &block)` to `render_in(view_context, **options, &block)`. This enables objects implementing `render_in` to receive render-time options like locals. All tests pass. The changes maintain backward compatibility since `**options` is an optional parameter.

Related to rails#57781 As reported in rails#57781, new calls to `#render_in` emit `render_template.action_view` Active Support notifications, which themselves cause a spike in object allocations. This commit explores an alternative that preserves the behavior introduced in [rails#50623][] (support for passing `:locals` at the `#render_in` call-site) without also emitting `render_template.action_view` notifications. Rather than rely on the `ActionView::Renderer` instance returned by the `ActionView::Helpers::RenderingHelper#view_renderer` invocation, construct an instance of `Template::Renderable` and invoke `#render` on it directly. [rails#50623]: rails#50623

Guards against re-regressing rails#57781 by asserting that render(renderable) allocates <= 16 objects per call (currently ~10 on this branch, was ~19 post-rails#50623 and ~4 pre-rails#50623). Uses a fresh notifier so the measurement reflects the production case (no debug subscribers) that byroot flagged. Rails does not yet have any allocation-count assertions in its test suite, so this test is written in a small, self-contained style with GC.disable/enable around the sample and a warmup pass. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 3ec82d0c-59bb-4b6a-8ef2-8f6edb8967ea

Related to rails#57781 As reported in rails#57781, new calls to `#render_in` emit `render_template.action_view` Active Support notifications, which themselves cause a spike in object allocations. This commit explores an alternative that preserves the behavior introduced in [rails#50623][] (support for passing `:locals` at the `#render_in` call-site) without also emitting `render_template.action_view` notifications. Rather than rely on the `ActionView::Renderer` instance returned by the `ActionView::Helpers::RenderingHelper#view_renderer` invocation, construct an instance of `Template::Renderable` and invoke `#render` on it directly. [rails#50623]: rails#50623 Co-authored-by: Sean Doyle <sean.p.doyle24@gmail.com>

Related to rails#57781 As reported in rails#57781, routing calls to `#render_in` through the template renderer emits `render_template.action_view` notifications and significantly increases object allocations. Preserve the behavior introduced in rails#50623 by constructing `Template::Renderable` directly and invoking `#render`, passing locals and blocks without entering the instrumented template pipeline. Action View's structured event handlers are all debug-only, but were attached in every environment. Attach `ActionView::StructuredEventSubscriber` only when `Rails.event.debug_mode?` is true so non-debug applications do not allocate and dispatch notifications that will be discarded. Co-authored-by: Sean Doyle <sean.p.doyle24@gmail.com>

rails-bot Bot added actionpack actionview docs labels Jan 6, 2024

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PoC: AbstractController::Base#renderer_for #46202

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Document rendering :renderable and #render_in #50622

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Do not mask NoMethodError from within render_in #50699

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rafaelfranca merged commit f26f56e into rails:main May 11, 2026
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seanpdoyle mentioned this pull request May 12, 2026

Add default #render_in implementation to ActiveModel::Conversion #57349

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flavorjones mentioned this pull request May 12, 2026

Fix ActionText::Editor::Tag#render_in to accept kwargs #57356

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Fix renderable arity checks when method is overridden #57360

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joelhawksley mentioned this pull request May 15, 2026

Support Rails render_in options signature ViewComponent/view_component#2636

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issyl0 mentioned this pull request Jun 19, 2026

Strong increase in allocations in web UIs that use ViewComponents after d24d0b7187b6568d76972d61ce91eea698503797 #57781

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ayushn21 mentioned this pull request Jul 6, 2026

Block passed to a renderable object is ignored #58026

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seanpdoyle mentioned this pull request Aug 21, 2026

Adds locals when rendering ActionText attachments #58511

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Strong increase in allocations in web UIs that use ViewComponents after d24d0b7187b6568d76972d61ce91eea698503797 get-xor/rails-XOR-rails#9

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Block passed to a renderable object is ignored get-xor/rails-XOR-rails#22

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Reduce allocation overhead of #50623 joelhawksley/rails#1

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Reduce allocation overhead of #50623 #58621

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Reduce Action View renderable allocations #58700

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render_in: Skip emission of render_template.action_view joelhawksley/rails#3

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render_in: Skip emission of render_template.action_view #58805

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