What can cause Rails 3.1 "= require jquery" to stop working?

I'm porting a Rails 3.0.9 app to Rails 3.1.rc5. My application.js is exactly the same as one generated by Rails 3.1 itself:

// This is a manifest file ...
//
//= require jquery
//= require jquery_ujs
//= require_tree .

But when I run my app and look at the application.js in Firebug or Chrome Developer Tools, all I see is:

// This is a manifest file ...
//

The directives are gone, so it would seem that the file has been processed by Sprockets, but the directives have not been replaced by the contents of jquery et al. There are no errors appearing on the server console or in the logs.

Curiously, when I run a blog app (you know, the canonical tutorial app) it works fine (that is, when I examine application.js in Firebug, it contains the text of jQuery.) This would seem to indicate that something in my app is somehow interfering with Sprockets. Has anyone out there heard of such an issue (and hopefully a workaround)?

Here's my setup:

$ gem list jquery

*** LOCAL GEMS ***

jquery-rails (1.0.12)
$ ruby -v
ruby 1.9.2p290 (2011-07-09) [i386-mingw32]
$ rails -v
Rails 3.1.0.rc5

I'm at a loss as开发者_如何学JAVA to what might be wrong. I've triple checked my Gemfile; I've run and re-run bundle install and bundle update; I've tried rc3, rc4 and now rc5; I'm running Ruby 1.9.2p290. Any ideas?

---

One workaround: include JavaScript files with the old-skool tag. For example, in my (Haml) layout:

= javascript_include_tag '/assets/jquery.js'
= javascript_include_tag '/assets/jquery_ujs.js'
= javascript_tag 'jQuery.noConflict();'

The /assets/ prefix tells Rails 3.1.x to look on the asset path, which includes gems, so you'll get the same files as with Sprockets directives. But you won't get concatenation or any other Sprockets preprocessing.

Still looking for better solutions.