Double inclusion of config.asset_host in CSS url() used with .erb asset path helpers

[jrochkind]

I believe this began with release 3.3.0, and is a regression caused by #476

Let's say we have an application.css.erb with this in it:

@font-face {
  src: url('<%= font_path('example.eot') %>');
}

And we have config.asset_host = '//example.org'. (The // protocol-agnostic asset_host is a common setting for CDNs, often recommended in docs).

With sprockets-rails 3.3.0+, if you ./bin/rails assets:precompile, the output at ./public/assets/application-[fingerprint].css looks like:

@font-face {
  src: url(//example.com/example.com/fonts/example.eot);
}

Note that //example.com/example.com is there twice. This reproduces with sprockets rails 3.3.0 and 3.4.1. (both with sprockets 4.0.2).

If you downgrade to sprockets 3.2.2, the output is as expected:

@font-face {
  src: url('//example.com/fonts/example.eot');
}

I believe this is a regression beginning with sprockets-rails 3.3.0.

I actually ran into this using font-awesome-rails on an app that deploys to heroku, with a CDN config.asset_host. font-awesome-rails uses the font_path helper in a .css.erb here. While that font-awesome-rails gem may be no longer supported, we ought not to get a regression in a minor sprockets-rails release. But also, I then isolated the reproduction as above, which also seems to be a general problem. It may be possible to isolate/generalize further, may also occur with sass-rails helpers not just the erb ones? May occur with other helpers, not just font_path?

[jrochkind]

Verified problem still reproduces (problem is still there) on sprockets-rails main branch at 4e0f168

[jrochkind]

(Sorry, I keep making comments and then deleting them about whether different forms of absolute/relative url in config.assets_host exhibit or not, because I keep getting confused about what i'm observing. I am also not currently sure if it exhibits on main branch, sorry!).

[jrochkind]

OK, now I think maybe the problem IS fixed at main branch at 4e0f168.

Could someone else verify this though? I don't trust myself, I keep seeing different things!

If it is fixed on main, could we get a patch release soon, to spare others this trouble?

[dhh]

Fixed in https://github.com/rails/sprockets-rails/releases/tag/v3.4.2.

[mattbrictson]

I ran into this as well, and can confirm it is fixed in 3.4.2.

FWIW, for some reason I had to bump my config.assets.version in order to see the fix.

[jrochkind]

Confirmed fixed for me too in 3.4.2, with config.asset_host = "//example.com", and also config.asset_host = "example.com".

I think the second one (hostname-only) triggered bug previously as well, and is recommended in some Rails docs.

Both seem fixed to me in 3.4.2.