From 53b8121d829af7708ae833e9fdb00afa093abb95 Mon Sep 17 00:00:00 2001
From: Thomas Hutterer <5372947+thutterer@users.noreply.github.com>
Date: Tue, 5 Jul 2022 13:51:11 +0200
Subject: [PATCH] Prevent adding existing autoload_paths (#1383)

* Prevent adding duplicates to autoload_paths

* Add thutterer to contributors list
---
 docs/CHANGELOG.md                             |  4 ++++
 docs/index.md                                 |  1 +
 lib/view_component/engine.rb                  |  3 ++-
 test/sandbox/config/application.rb            |  4 ++++
 test/sandbox/test/initializers/engine_test.rb | 10 ++++++++++
 5 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 test/sandbox/test/initializers/engine_test.rb

diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 4261518d8..a92c45826 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -9,6 +9,10 @@ title: Changelog
 
 ## main
 
+* Prevent adding duplicates to `autoload_paths`.
+
+    *Thomas Hutterer*
+
 * Add FreeAgent to list of companies using ViewComponent.
 
     *Simon Fish*
diff --git a/docs/index.md b/docs/index.md
index e058c5d5d..3323cc908 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -188,6 +188,7 @@ ViewComponent is built by over a hundred members of the community, including:
 <img src="https://avatars.githubusercontent.com/tbroad-ramsey?s=64" alt="tbroad-ramsey" width="32" />
 <img src="https://avatars.githubusercontent.com/tclem?s=64" alt="tclem" width="32" />
 <img src="https://avatars.githubusercontent.com/tenderlove?s=64" alt="tenderlove" width="32" />
+<img src="https://avatars.githubusercontent.com/thutterer?s=64" alt="thutterer" width="32" />
 <img src="https://avatars.githubusercontent.com/tonkpils?s=64" alt="tonkpils" width="32" />
 <img src="https://avatars.githubusercontent.com/traels?s=64" alt="traels" width="32" />
 <img src="https://avatars.githubusercontent.com/vinistock?s=64" alt="vinistock" width="32" />
diff --git a/lib/view_component/engine.rb b/lib/view_component/engine.rb
index 6aab1132f..af3952496 100644
--- a/lib/view_component/engine.rb
+++ b/lib/view_component/engine.rb
@@ -77,7 +77,8 @@ class Engine < Rails::Engine # :nodoc:
       options = app.config.view_component
 
       if options.show_previews && !options.preview_paths.empty?
-        ActiveSupport::Dependencies.autoload_paths.concat(options.preview_paths)
+        paths_to_add = options.preview_paths - ActiveSupport::Dependencies.autoload_paths
+        ActiveSupport::Dependencies.autoload_paths.concat(paths_to_add) if paths_to_add.any?
       end
     end
 
diff --git a/test/sandbox/config/application.rb b/test/sandbox/config/application.rb
index cfcb0e99f..84ae7620c 100644
--- a/test/sandbox/config/application.rb
+++ b/test/sandbox/config/application.rb
@@ -17,6 +17,10 @@
 module Sandbox
   class Application < Rails::Application
     config.action_controller.asset_host = "http://assets.example.com"
+
+    # Prepare test_set_no_duplicate_autoload_paths
+    config.autoload_paths.push("#{config.root}/my/components/previews")
+    config.view_component.preview_paths << "#{config.root}/my/components/previews"
   end
 end
 
diff --git a/test/sandbox/test/initializers/engine_test.rb b/test/sandbox/test/initializers/engine_test.rb
new file mode 100644
index 000000000..ce030c3f7
--- /dev/null
+++ b/test/sandbox/test/initializers/engine_test.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class EngineTest < Minitest::Test
+  def test_set_no_duplicate_autoload_paths
+    test_path = "#{Rails.root}/my/components/previews" # set in sandbox/config/application.rb
+    assert_equal 1, ActiveSupport::Dependencies.autoload_paths.count(test_path)
+  end
+end