Ruby SDK support rails render_in interface (starfederation#617)

* Support Rails' #render_in(view_context) interface

So render arbitrary objects, including component libs like ViewComponent and Phlex Rails.

* Render anything that supports #to_s, including Rails' safe buffers

* Make sure Rails view_context is an ActionView::Base

* Document

sdk/ruby/README.md

@@ -24,9 +24,11 @@ In your Rack handler or Rails controller:
 
 ```ruby
 # Rails controllers, as well as Sinatra and others, 
-# already have request and response objects
+# already have request and response objects.
+# `view_context` is optional and is used to render Rails templates.
+# Or view components that need access to helpers, routes, or any other context.
 
-datastar = Datastar.new(request:, response:, view_context: self)
+datastar = Datastar.new(request:, response:, view_context:)
 
 # In a Rack handler, you can instantiate from the Rack env
 datastar = Datastar.from_rack_env(env)
@@ -130,7 +132,7 @@ See https://data-star.dev/reference/sse_events#datastar-execute-script
 
 ```ruby
 sse.execute_scriprt(%(alert('Hello World!'))
- ```
+```
 
 #### `signals`
 See https://data-star.dev/guide/getting_started#data-signals
@@ -139,14 +141,14 @@ Returns signals sent by the browser.
 
 ```ruby
 sse.signals # => { user: { name: 'John' } }
- ```
+```
 
 #### `redirect`
 This is just a helper to send a script to update the browser's location.
 
 ```ruby
 sse.redirect('/new_location')
- ```
+```
 
 ### Lifecycle callbacks
 
@@ -198,11 +200,14 @@ Datastar.configure do |config|
 end
 ```
 
-### Rails
+### Rendering Rails templates
 
-#### Rendering Rails templates
+In Rails, make sure to initialize Datastar with the `view_context` in a controller.
+This is so that rendered templates, components or views have access to helpers, routes, etc.
 
 ```ruby
+datastar = Datastar.new(request:, response:, view_context:)
+
 datastar.stream do |sse|
   10.times do |i|
     sleep 1
@@ -212,14 +217,44 @@ datastar.stream do |sse|
 end
 ```
 
-#### Rendering Phlex components
+### Rendering Phlex components
 
 `#merge_fragments` supports [Phlex](https://www.phlex.fun) component instances.
 
 ```ruby
 sse.merge_fragments(UserComponent.new(user: User.first))
 ```
 
+### Rendering ViewComponent instances
+
+`#merge_fragments` also works with [ViewComponent](https://viewcomponent.org) instances.
+
+```ruby
+sse.merge_fragments(UserViewComponent.new(user: User.first))
+```
+
+### Rendering `#render_in(view_context)` interfaces
+
+Any object that supports the `#render_in(view_context) => String` API can be used as a fragment.
+
+```ruby
+class MyComponent
+  def initialize(name)
+    @name = name
+  end
+
+  def render_in(view_context)
+    "<div>Hello #{@name}</div>""
+  end
+end
+```
+
+```ruby
+sse.merge_fragments MyComponent.new('Joe')
+```
+
+
+
 ### Tests
 
 ```ruby

sdk/ruby/lib/datastar/railtie.rb

@@ -3,7 +3,12 @@
 module Datastar
   class Railtie < ::Rails::Railtie
     FINALIZE = proc do |view_context, response|
-      view_context.response = response
+      case view_context
+      when ActionView::Base
+        view_context.controller.response = response
+      else
+        raise ArgumentError, 'view_context must be an ActionView::Base'
+      end
     end
 
     initializer 'datastar' do |_app|

sdk/ruby/lib/datastar/server_sent_event_generator.rb

@@ -41,7 +41,15 @@ def initialize(stream, signals:, view_context: nil)
 
     def merge_fragments(fragments, options = BLANK_OPTIONS)
       # Support Phlex components
-      fragments = fragments.call(view_context:) if fragments.respond_to?(:call)
+      # And Rails' #render_in interface
+      fragments = if fragments.respond_to?(:render_in)
+        fragments.render_in(view_context)
+      elsif fragments.respond_to?(:call)
+        fragments.call(view_context:)
+      else
+        fragments.to_s
+      end
+
       fragment_lines = fragments.to_s.split("\n")
 
       buffer = +"event: datastar-merge-fragments\n"

sdk/ruby/spec/dispatcher_spec.rb

@@ -112,6 +112,22 @@ def self.call(view_context:) = %(<div id="foo">\n<span>#{view_context}</span>\n<
       dispatcher.response.body.call(socket)
       expect(socket.lines).to eq([%(event: datastar-merge-fragments\nid: 72\nretry: 2000\ndata: settleDuration 1000\ndata: fragments <div id="foo">\ndata: fragments <span>#{view_context}</span>\ndata: fragments </div>\n\n\n)])
     end
+
+    it 'works with #render_in(view_context, &) interfaces' do
+      template_class = Class.new do
+        def self.render_in(view_context) = %(<div id="foo">\n<span>#{view_context}</span>\n</div>\n)
+      end
+
+      dispatcher.merge_fragments(
+        template_class,
+        id: 72,
+        retry_duration: 2000,
+        settle_duration: 1000
+      )
+      socket = TestSocket.new
+      dispatcher.response.body.call(socket)
+      expect(socket.lines).to eq([%(event: datastar-merge-fragments\nid: 72\nretry: 2000\ndata: settleDuration 1000\ndata: fragments <div id="foo">\ndata: fragments <span>#{view_context}</span>\ndata: fragments </div>\n\n\n)])
+    end
   end
 
   describe '#remove_fragments' do