Dependency Tracker finds dependencies in HTML tags and incorrectly in render calls

[romaimperator]

I'm not sure that this is technically a bug but it does list extra dependencies for templates that are not actually dependencies. This occurs because of how the dependency tracker looks for render calls in templates.

I ran into this bug when I was using a decorator object that defined to_partial_path. I had in my view a render call like this <%= render MyDecorator.new(model_object) %> and I also had calls to the cache helper in the same template. When the cache helper was getting the dependencies to use for digesting, I saw in the log Couldn't find template for digesting: news/new. I was able to track this down to how the dependency tracker finds render calls and then processes them. The relevant code is here https://github.com/rails/rails/blob/v5.0.0.beta2/actionview/lib/action_view/dependency_tracker.rb#L118.

I am also going to submit a pull request with a fix for this issue. I believe this issue #21951 is related and is also will be fixed by the pull request.

To reproduce this problem:

1. create a new rails project

2. create a controller with an action (name doesn't matter) and the corresponding view template

3. in the view template add the following erb:

   <script>
     var render = document.getElementById('#render');
     render(data.autokinds);
   </script>
   
   <div id="render" data-auto_kinds="value">
     <h1>hello</h1>
   </div>
   
   <%= render ApplicationHelper::ClassWithPartialPath.new %>
   <%= render ClassWithPartialPath.new %>
   <%= render ApplicationHelper::employee %>

4. run bundle exec rake cache_digests:dependencies TEMPLATE=that_template_name

=> [
  "autokinds/autokind",
  "static/ data-auto_kinds=", # static is the name of the controller I chose
  "ApplicationHelpers/ApplicationHelper",
  "news/new"
]

After the fix, running the cache_digests command on the same template will produce:

=> [
  "employees/employee"
]

This is matching the last render call, the scoped access of a record in the ApplicationHelper. I'm not sure that anyone actually uses that but it is a side-effect fix to prevent the 3rd dependency, "ApplicationHelpers/ApplicationHelper", from showing as a dependency.

[gmcnaughton]

Possibly related: if I use the word "rendered" in an ERB comment, the parser gets confused and makes a dependency on "eds/ed" - rails/cache_digests#17

[byroot]

The HTML part has been fixed by #42458 and subsequent PRs.

For the constant refs, it still not quite fixed but ultimately the dependency tracker is understood as being best effort, so I don't think it's worth keeping this open, but people running into this issue are welcome to open a PR to fix these false positives.