Add preload_link_tag helper.

This helper creates a link tag with preload keyword that allows to
browser to initiate early fetch of resources. Additionally this send
Early Hints if supported.

See https://github.com/rails/rails/pull/30744/commits/59a02fb7bcbe68f26e1e7fdcec45c00c66e4a065
for more details about Early Hints.

Preload spec: https://w3c.github.io/preload/

1 files changed, 15 insertions, 0 deletions

diff --git a/actionview/test/template/asset_tag_helper_test.rb b/actionview/test/template/asset_tag_helper_test.rb
index a8b66191bc..284dacf2d4 100644
--- a/actionview/test/template/asset_tag_helper_test.rb
+++ b/actionview/test/template/asset_tag_helper_test.rb
@@ -214,6 +214,17 @@ class AssetTagHelperTest < ActionView::TestCase
     %(favicon_link_tag 'mb-icon.png', :rel => 'apple-touch-icon', :type => 'image/png') => %(<link href="/images/mb-icon.png" rel="apple-touch-icon" type="image/png" />)
   }
 
+  PreloadLinkToTag = {
+    %(preload_link_tag '/styles/custom_theme.css') => %(<link rel="preload" href="/styles/custom_theme.css" as="style" type="text/css" />),
+    %(preload_link_tag '/videos/video.webm') => %(<link rel="preload" href="/videos/video.webm" as="video" type="video/webm" />),
+    %(preload_link_tag '/posts.json', as: 'fetch') => %(<link rel="preload" href="/posts.json" as="fetch" type="application/json" />),
+    %(preload_link_tag '/users', as: 'fetch', type: 'application/json') => %(<link rel="preload" href="/users" as="fetch" type="application/json" />),
+    %(preload_link_tag '//example.com/map?callback=initMap', as: 'fetch', type: 'application/javascript') => %(<link rel="preload" href="//example.com/map?callback=initMap" as="fetch" type="application/javascript" />),
+    %(preload_link_tag '//example.com/font.woff2') => %(<link rel="preload" href="//example.com/font.woff2" as="font" type="font/woff2" crossorigin="anonymous"/>),
+    %(preload_link_tag '//example.com/font.woff2', crossorigin: 'use-credentials') => %(<link rel="preload" href="//example.com/font.woff2" as="font" type="font/woff2" crossorigin="use-credentials" />),
+    %(preload_link_tag '/media/audio.ogg', nopush: true) => %(<link rel="preload" href="/media/audio.ogg" as="audio" type="audio/ogg" />)
+  }
+
   VideoPathToTag = {
     %(video_path("xml"))          => %(/videos/xml),
     %(video_path("xml.ogg"))      => %(/videos/xml.ogg),
@@ -535,6 +546,10 @@ class AssetTagHelperTest < ActionView::TestCase
     FaviconLinkToTag.each { |method, tag| assert_dom_equal(tag, eval(method)) }
   end
 
+  def test_preload_link_tag
+    PreloadLinkToTag.each { |method, tag| assert_dom_equal(tag, eval(method)) }
+  end
+
   def test_video_path
     VideoPathToTag.each { |method, tag| assert_dom_equal(tag, eval(method)) }
   end