Serve script tags from Vite's development server

CHANGELOG.md

@@ -1,3 +1,13 @@
+Unreleased
+------
+
+* Serve the `include_ember_script_tags` startup tags from Vite's development
+  server when ember-cli-rails serves the application from it, rewriting
+  root-relative URLs to absolute URLs on the server
+* Leave protocol-relative (`//`) URLs alone when remapping startup tags
+* Raise the Vite guidance from `include_ember_stylesheet_tags` for
+  applications served by the development server, whose `dist` may not exist
+
 0.8.1
 ------
 

Gemfile

@@ -14,7 +14,7 @@ gem "rails", rails_constraint
 gem "webrick"
 
 group :development, :test do
-  gem "ember-cli-rails", github: "tricknotes/ember-cli-rails"
+  gem "ember-cli-rails"
 end
 
 group :test do

README.md

@@ -67,6 +67,12 @@ extracted from the generated `index.html`:
 <%= include_ember_script_tags :frontend %>
 ```
 
+When ember-cli-rails serves the application from Vite's development server in
+`development`, `include_ember_script_tags` reads `index.html` from the server
+instead of a build directory, and emits the startup tags with absolute URLs
+pointing at the server. Nothing is built, so changes to the application are
+picked up by reloading the page.
+
 `include_ember_stylesheet_tags` only supports classic applications, and raises
 an error when called for a Vite-based application.
 

app/helpers/ember_cli_rails_assets_helper.rb

@@ -7,12 +7,16 @@ def include_ember_script_tags(name, prepend: "")
     app = EmberCli[name]
     app.build
 
-    paths = EmberCli::Assets::Paths.new(app)
-
-    if paths.vite?
-      vite_ember_script_tags(paths, prepend)
+    if dev_server?(app)
+      dev_server_ember_script_tags(app)
     else
-      classic_ember_script_tags(app, prepend)
+      paths = EmberCli::Assets::Paths.new(app)
+
+      if paths.vite?
+        vite_ember_script_tags(paths, prepend)
+      else
+        classic_ember_script_tags(app, prepend)
+      end
     end
   end
 
@@ -22,7 +26,7 @@ def include_ember_stylesheet_tags(name, prepend: "")
 
     paths = EmberCli::Assets::Paths.new(app)
 
-    if paths.vite?
+    if dev_server?(app) || paths.vite?
       raise EmberCli::Assets::NotSupportedError, <<~MSG
         `include_ember_stylesheet_tags` does not support Vite-based
         applications (`ember-cli >= 6.8`).
@@ -42,6 +46,22 @@ def include_ember_stylesheet_tags(name, prepend: "")
 
   private
 
+  # Whether ember-cli-rails serves the application from Vite's development
+  # server. Older ember-cli-rails releases have no development server, so
+  # feature-detect the reader.
+  def dev_server?(app)
+    app.respond_to?(:dev_server?) && app.dev_server?
+  end
+
+  # The application is served by Vite's development server, so read
+  # `index.html` from the server instead of a build directory, and rewrite
+  # its root-relative URLs to absolute URLs on the server — the same way
+  # ember-cli-rails serves the document itself. `app.build` has already
+  # booted the server.
+  def dev_server_ember_script_tags(app)
+    vite_startup_tags(app.dev_server.index_html, prefix: app.dev_server.origin)
+  end
+
   # Classic builds ship a fixed set of scripts (vendor and app) resolved
   # through the asset map, so emit a plain script tag per JavaScript asset
   # with `prepend` joined onto each path.
@@ -58,15 +78,24 @@ def classic_ember_script_tags(app, prepend)
   # the tags required for startup (including the config meta tag and
   # stylesheets) and remap root-absolute paths onto the mount point.
   def vite_ember_script_tags(paths, prepend)
-    document = Nokogiri::HTML5(paths.index_html.read)
-    prefix = prepend.to_s.chomp("/")
+    vite_startup_tags(paths.index_html.read, prefix: prepend.to_s.chomp("/"))
+  end
+
+  # Extracts the tags a Vite-based application needs to boot from an
+  # `index.html` document, with `prefix` joined onto every root-relative
+  # URL. Protocol-relative URLs (`//`) are left alone.
+  def vite_startup_tags(html, prefix:)
+    document = Nokogiri::HTML5(html)
 
     tags = document.css(
       'meta[name$="/config/environment"], link[rel="stylesheet"], link[rel="modulepreload"], script'
     ).map do |tag|
       %w(href src).each do |attribute|
         value = tag[attribute]
-        tag[attribute] = "#{prefix}#{value}" if value&.start_with?("/")
+
+        if value&.start_with?("/") && !value.start_with?("//")
+          tag[attribute] = "#{prefix}#{value}"
+        end
       end
       tag.to_html.html_safe
     end

spec/helpers/ember_cli_rails_assets_helper_spec.rb

@@ -1,10 +1,72 @@
 require "rails_helper"
 
 describe EmberCliRailsAssetsHelper do
+  describe "#include_ember_script_tags" do
+    context "when the application is served by Vite's development server" do
+      # The development server API ships with the ember-cli-rails release
+      # that serves Vite-based applications from the development server, so
+      # plain doubles stand in for `EmberCli::App` and `EmberCli::DevServer`
+      # here until the Gemfile can be pointed at a release carrying it.
+      it "emits the startup tags with root-relative URLs rewritten onto the server" do
+        index_html = <<~HTML
+          <html>
+            <head>
+              <script type="module" src="/@vite/client"></script>
+              <meta name="my-app/config/environment" content="%7B%7D">
+              <link rel="stylesheet" href="/@embroider/virtual/app.css">
+              <script type="module" src="https://cdn.example.com/analytics.js"></script>
+              <script type="module" src="//cdn.example.com/protocol-relative.js"></script>
+            </head>
+            <body>
+              <script src="/@embroider/virtual/vendor.js"></script>
+            </body>
+          </html>
+        HTML
+        dev_server = double(
+          "EmberCli::DevServer",
+          index_html: index_html,
+          origin: "http://127.0.0.1:4200",
+        )
+        app = double(
+          "EmberCli::App",
+          build: true,
+          dev_server?: true,
+          dev_server: dev_server,
+        )
+        allow(EmberCli).to receive(:[]).with(:frontend).and_return(app)
+
+        tags = helper.include_ember_script_tags(:frontend)
+
+        expect(app).to have_received(:build)
+        expect(tags).to include(%{src="http://127.0.0.1:4200/@vite/client"})
+        expect(tags).to include(%{src="http://127.0.0.1:4200/@embroider/virtual/vendor.js"})
+        expect(tags).to include(%{href="http://127.0.0.1:4200/@embroider/virtual/app.css"})
+        expect(tags).to include(%{name="my-app/config/environment"})
+        expect(tags).to include(%{src="https://cdn.example.com/analytics.js"})
+        expect(tags).to include(%{src="//cdn.example.com/protocol-relative.js"})
+      end
+    end
+  end
+
   describe "#include_ember_stylesheet_tags" do
+    context "when the application is served by Vite's development server" do
+      it "raises an error pointing at `include_ember_script_tags`" do
+        app = double("EmberCli::App", build: true, dev_server?: true)
+        paths = instance_double(EmberCli::Assets::Paths)
+        allow(EmberCli).to receive(:[]).with(:frontend).and_return(app)
+        allow(EmberCli::Assets::Paths).
+          to receive(:new).with(app).and_return(paths)
+
+        expect { helper.include_ember_stylesheet_tags(:frontend) }.to raise_error(
+          EmberCli::Assets::NotSupportedError,
+          /include_ember_script_tags/,
+        )
+      end
+    end
+
     context "when the application is built with Vite" do
       it "raises an error pointing at `include_ember_script_tags`" do
-        app = instance_double(EmberCli::App, build: true)
+        app = double("EmberCli::App", build: true, dev_server?: false)
         paths = instance_double(EmberCli::Assets::Paths, vite?: true)
         allow(EmberCli).to receive(:[]).with(:frontend).and_return(app)
         allow(EmberCli::Assets::Paths).