Allow to add to Alchemy's importmap from Rails application

Rails applications are technically engines, but not really. For example
the `engine_name` is the `config/application.rb` modularized class
name. Which makes it not nice for this interface from an app developers
perspective.

Let's make the interface more explicit by using a options hash with readable keys.

    Rails.application.config.before_initialize do
      Alchemy.admin_importmaps.add({
        importmap_path: Rails.application.root.join("config/alchemy/importmap.rb"),
        source_paths: [
          Rails.application.root.join("app/javascript/components/product_select.js")
        ],
        name: "product_select"
      })
    end

app/views/layouts/alchemy/admin.html.erb

@@ -21,11 +21,9 @@
     <%= render 'alchemy/admin/partials/routes' %>
     <%= javascript_include_tag('alchemy/admin/all', 'data-turbo-track' => true) %>
     <%= javascript_importmap_tags("alchemy_admin", importmap: Alchemy.importmap) %>
-    <% if Alchemy.admin_js_imports.any? %>
+    <% Alchemy.admin_js_imports.each do |path| %>
       <script type="module">
-        <% Alchemy.admin_js_imports.each do |path| %>
-          import "<%= path %>"
-        <% end %>
+        import "<%= path %>"
       </script>
     <% end %>
     <%= yield :javascript_includes %>

config/alchemy/importmap.rb → config/importmap.rb

@@ -9,4 +9,4 @@
 pin "tinymce", to: "tinymce.min.js", preload: true
 
 pin "alchemy_admin", to: "alchemy_admin.js", preload: true
-pin_all_from File.expand_path("../../app/javascript/alchemy_admin", __dir__), under: "alchemy_admin", preload: true
+pin_all_from File.expand_path("../app/javascript/alchemy_admin", __dir__), under: "alchemy_admin", preload: true

lib/alchemy.rb

@@ -62,7 +62,7 @@ def self.admin_js_imports=(sources)
     @_admin_js_imports = Set[sources]
   end
 
-  # Additional importmaps from engines to be included in the Alchemy admin UI
+  # Additional importmaps to be included in the Alchemy admin UI
   #
   # Be sure to also pin modules with +Alchemy.importmap+.
   #
@@ -76,13 +76,26 @@ def self.admin_js_imports=(sources)
   #
   #    # lib/alchemy/solidus/engine.rb
   #    initializer "alchemy_solidus.assets", before: "alchemy.importmap" do |app|
-  #      Alchemy.engine_importmaps.add(Engine)
+  #      Alchemy.admin_importmaps.add({
+  #        importmap_path: root.join("config/importmap.rb"),
+  #        source_paths: [
+  #          root.join("app/javascript")
+  #        ],
+  #        name: "alchemy_solidus"
+  #      })
   #      app.config.assets.precompile << "alchemy_solidus/manifest.js"
   #    end
   #
-  # @return [Set<Rails::Engine>]
-  def self.engine_importmaps
-    @_engine_importmaps ||= Set.new([Alchemy::Engine])
+  # @return [Set<Hash>]
+  def self.admin_importmaps
+    @_admin_importmaps ||= Set.new([{
+      importmap_path: Engine.root.join("config/importmap.rb"),
+      source_paths: [
+        Engine.root.join("app/javascript"),
+        Engine.root.join("vendor/javascript")
+      ],
+      name: "alchemy_admin"
+    }])
   end
 
   # Define page publish targets

lib/alchemy/engine.rb

@@ -23,14 +23,12 @@ class Engine < Rails::Engine
     initializer "alchemy.importmap" do |app|
       watch_paths = []
 
-      Alchemy.engine_importmaps.each do |engine|
-        Alchemy.importmap.draw engine.root.join("config/alchemy", "importmap.rb")
-        package_path = engine.root.join("app/javascript")
-        watch_paths << package_path
-        vendor_packages_path = engine.root.join("vendor/javascript")
-        app.config.assets.paths += [package_path, vendor_packages_path]
-        if engine.engine_name != "alchemy"
-          Alchemy.admin_js_imports.add(engine.engine_name)
+      Alchemy.admin_importmaps.each do |admin_import|
+        Alchemy.importmap.draw admin_import[:importmap_path]
+        watch_paths += admin_import[:source_paths]
+        app.config.assets.paths += admin_import[:source_paths]
+        if admin_import[:name] != "alchemy_admin"
+          Alchemy.admin_js_imports.add(admin_import[:name])
         end
       end
 

spec/libraries/alchemy_spec.rb

@@ -0,0 +1,38 @@
+require "rails_helper"
+
+RSpec.describe Alchemy do
+  describe ".admin_importmaps" do
+    subject { Alchemy.admin_importmaps }
+
+    it "returns a Set of admin importmaps" do
+      is_expected.to be_a(Set)
+    end
+
+    it "includes alchemy_admin importmap" do
+      expect(subject.first).to eq({
+        importmap_path: Alchemy::Engine.root.join("config/importmap.rb"),
+        name: "alchemy_admin",
+        source_paths: [
+          Alchemy::Engine.root.join("app/javascript"),
+          Alchemy::Engine.root.join("vendor/javascript")
+        ]
+      })
+    end
+
+    context "with additional importmaps" do
+      before do
+        Alchemy.admin_importmaps.add({
+          importmap_path: Rails.root.join("config/importmap.rb"),
+          name: "additional_importmap",
+          source_paths: [Rails.root.join("app/javascript")]
+        })
+      end
+
+      it "adds additional importmap to admin imports" do
+        initializer = Alchemy::Engine.initializers.find { _1.name == "alchemy.importmap" }
+        expect(Alchemy.admin_js_imports).to receive(:add).with("additional_importmap")
+        initializer.run(Rails.application)
+      end
+    end
+  end
+end