Disable send_preload_links_header outright

[stanhu]

Steps to reproduce

Suppose you have a partial like this:

= cache([ActionController::Base.asset_host], expires_in: 1.minute) do
    = preload_link_tag(path_to_stylesheet('application')

If the partial is not cached, then preload_link_tag will call send_preload_links_header, which modifies the Link HTTP header.

However, if the partial is cached, then the Link HTTP header is not sent.

This is a surprising side effect of caching preload_link_tag. I was surprised that send_preload_links_header is even called in the first place.

#48405 lowered the max header size from 8K to 1000 bytes, but I think Rails should go farther than that: provide an option to disable this sending altogether, perhaps as an argument to preload_link_tag. For example:

diff --git a/actionview/lib/action_view/helpers/asset_tag_helper.rb b/actionview/lib/action_view/helpers/asset_tag_helper.rb
index 11528eb33d..0dd3ff517a 100644
--- a/actionview/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionview/lib/action_view/helpers/asset_tag_helper.rb
@@ -325,6 +325,7 @@ def preload_link_tag(source, options = {})
         crossorigin = "anonymous" if crossorigin == true || (crossorigin.blank? && as_type == "font")
         integrity = options[:integrity]
         nopush = options.delete(:nopush) || false
+        send_link_header = options.key?(:preload_links_header) ? options.delete(:preload_links_header) : true
         rel = mime_type == "module" ? "modulepreload" : "preload"
 
         link_tag = tag.link(**{
@@ -341,7 +342,7 @@ def preload_link_tag(source, options = {})
         preload_link += "; integrity=#{integrity}" if integrity
         preload_link += "; nopush" if nopush
 
-        send_preload_links_header([preload_link])
+        send_preload_links_header([preload_link]) if send_link_header
 
         link_tag
       end
diff --git a/actionview/test/template/asset_tag_helper_test.rb b/actionview/test/template/asset_tag_helper_test.rb
index f0c8a10f57..cd6cdd8925 100644
--- a/actionview/test/template/asset_tag_helper_test.rb
+++ b/actionview/test/template/asset_tag_helper_test.rb
@@ -628,6 +628,13 @@ def test_should_set_preload_early_hints_with_rel_modulepreload
     end
   end
 
+  def test_should_not_set_preload_link_with_rel_modulepreload
+    with_preload_links_header do
+      preload_link_tag("http://example.com/all.js", type: "module", preload_links_header: false)
+      assert_nil @response.headers["Link"]
+    end
+  end
+
   def test_should_set_preload_links_with_integrity_hashes
     with_preload_links_header do
       stylesheet_link_tag("http://example.com/style.css", integrity: "sha256-AbpHGcgLb+kRsJGnwFEktk7uzpZOCcBY74+YBdrKVGs")

[stanhu]

I see there is also ActionView::Helpers::AssetTagHelper.preload_links_header defined. Perhaps we can just check that?