implement multiple importmaps

Author: manuelmeurer

app/helpers/importmap/importmap_tags_helper.rb

@@ -1,6 +1,14 @@
 module Importmap::ImportmapTagsHelper
   # Setup all script tags needed to use an importmap-powered entrypoint (which defaults to application.js)
-  def javascript_importmap_tags(entry_point = "application", importmap: Rails.application.importmap)
+  def javascript_importmap_tags(entry_point = "application")
+    entry_point = entry_point.to_s
+
+    importmap_identifier =
+      entry_point != "application" && Rails.application.importmaps.key?(entry_point) ?
+      entry_point :
+      "application"
+    importmap = Rails.application.importmaps.fetch(entry_point)
+
     safe_join [
       javascript_inline_importmap_tag(importmap.to_json(resolver: self)),
       javascript_importmap_module_preload_tags(importmap),
@@ -10,7 +18,7 @@ def javascript_importmap_tags(entry_point = "application", importmap: Rails.appl
 
   # Generate an inline importmap tag using the passed `importmap_json` JSON string.
   # By default, `Rails.application.importmap.to_json(resolver: self)` is used.
-  def javascript_inline_importmap_tag(importmap_json = Rails.application.importmap.to_json(resolver: self))
+  def javascript_inline_importmap_tag(importmap_json)
     tag.script importmap_json.html_safe,
       type: "importmap", "data-turbo-track": "reload", nonce: request&.content_security_policy_nonce
   end
@@ -24,7 +32,7 @@ def javascript_import_module_tag(*module_names)
   # Link tags for preloading all modules marked as preload: true in the `importmap`
   # (defaults to Rails.application.importmap), such that they'll be fetched
   # in advance by browsers supporting this link type (https://caniuse.com/?search=modulepreload).
-  def javascript_importmap_module_preload_tags(importmap = Rails.application.importmap)
+  def javascript_importmap_module_preload_tags(importmap)
     javascript_module_preload_tag(*importmap.preloaded_module_paths(resolver: self))
   end
 

lib/importmap/engine.rb

@@ -1,7 +1,7 @@
 require "importmap/map"
 
-# Use Rails.application.importmap to access the map
-Rails::Application.send(:attr_accessor, :importmap)
+# Use Rails.application.importmaps to access the maps
+Rails::Application.send(:attr_accessor, :importmaps)
 
 module Importmap
   class Engine < ::Rails::Engine
@@ -14,9 +14,20 @@ class Engine < ::Rails::Engine
     config.autoload_once_paths = %W( #{root}/app/helpers )
 
     initializer "importmap" do |app|
-      app.importmap = Importmap::Map.new
+      importmap = Importmap::Map.new
+      app.importmaps = {
+        "application" => importmap
+      }
       app.config.importmap.paths << app.root.join("config/importmap.rb")
-      app.config.importmap.paths.each { |path| app.importmap.draw(path) }
+      app.config.importmap.paths.each { |path| importmap.draw(path) }
+
+      Dir[app.root.join("config/importmaps/*.rb")].each do |path|
+        namespace = File.basename(path).delete_suffix(".rb")
+        importmap = Importmap::Map.new
+        app.config.importmap.paths.each { |path| importmap.draw(path) }
+        importmap.draw(path)
+        app.importmaps[namespace] = importmap
+      end
     end
 
     initializer "importmap.reloader" do |app|
@@ -33,10 +44,17 @@ class Engine < ::Rails::Engine
       if app.config.importmap.sweep_cache && !app.config.cache_classes
         app.config.importmap.cache_sweepers << app.root.join("app/javascript")
         app.config.importmap.cache_sweepers << app.root.join("vendor/javascript")
-        app.importmap.cache_sweeper(watches: app.config.importmap.cache_sweepers)
+
+        app.importmaps.values.each do |importmap|
+          importmap.cache_sweeper(watches: app.config.importmap.cache_sweepers)
+        end
 
         ActiveSupport.on_load(:action_controller_base) do
-          before_action { Rails.application.importmap.cache_sweeper.execute_if_updated }
+          before_action do
+            Rails.application.importmaps.values.each do |importmap|
+              importmap.cache_sweeper.execute_if_updated
+            end
+          end
         end
       end
     end

lib/importmap/reloader.rb

@@ -5,7 +5,9 @@ class Importmap::Reloader
   delegate :execute_if_updated, :execute, :updated?, to: :updater
 
   def reload!
-    import_map_paths.each { |path| Rails.application.importmap.draw(path) }
+    Rails.application.importmaps.values.each do |importmap|
+      import_map_paths.each { |path| importmap.draw(path) }
+    end
   end
 
   private