Add support for passing a custom importmap to the tag helper (#187)

* Add support for passing a custom importmap to the tag helper

This is a great feature whenever you have separate areas of the
application with completely different sets of dependencies.

The most common example of that is admin areas, both on the main
Rails application or coming from engines.

* Work around JSPM mysteriously returning 503 from CI

This is meant to be temporary.

* Update packager.rb

Remove unrelated change

---------

Co-authored-by: David Heinemeier Hansson <[email protected]>

Author: elia

Diff for: app/helpers/importmap/importmap_tags_helper.rb

@@ -1,9 +1,9 @@
 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", shim: true)
+  def javascript_importmap_tags(entry_point = "application", shim: true, importmap: Rails.application.importmap)
     safe_join [
-      javascript_inline_importmap_tag,
-      javascript_importmap_module_preload_tags,
+      javascript_inline_importmap_tag(importmap.to_json(resolver: self)),
+      javascript_importmap_module_preload_tags(importmap),
       (javascript_importmap_shim_nonce_configuration_tag if shim),
       (javascript_importmap_shim_tag if shim),
       javascript_import_module_tag(entry_point)
@@ -34,7 +34,7 @@ def javascript_importmap_shim_tag(minimized: true)
   # Import a named JavaScript module(s) using a script-module tag.
   def javascript_import_module_tag(*module_names)
     imports = Array(module_names).collect { |m| %(import "#{m}") }.join("\n")
-    tag.script imports.html_safe, 
+    tag.script imports.html_safe,
       type: "module", nonce: request&.content_security_policy_nonce
   end
 

Diff for: test/importmap_tags_helper_test.rb

@@ -55,4 +55,18 @@ def content_security_policy_nonce
   ensure
     @request = nil
   end
+
+  test "using a custom importmap" do
+    importmap = Importmap::Map.new
+    importmap.pin "foo", preload: true
+    importmap.pin "bar", preload: false
+    importmap_html = javascript_importmap_tags("foo", importmap: importmap)
+
+    assert_includes importmap_html, %{<script type="importmap" data-turbo-track="reload">}
+    assert_includes importmap_html, %{"foo": "/foo.js"}
+    assert_includes importmap_html, %{"bar": "/bar.js"}
+    assert_includes importmap_html, %{<link rel="modulepreload" href="/foo.js">}
+    refute_includes importmap_html, %{<link rel="modulepreload" href="/bar.js">}
+    assert_includes importmap_html, %{<script type="module">import "foo"</script>}
+  end
 end