fix updates_for makes redundant calls

[leastbad]

Type of PR (feature, enhancement, bug fix, etc.)

Bug fix

Description

Modify updates_for element to verify that a page is required before fetching it.

This PR essentially implements the suggestion made in #209, with minor tweaks.

I've done my best to test this new functionality, but I am not a heavy user of updates_for and would appreciate if @julianrubisch could sanity check this. Specifically, my concern is that there could be an unexpected interaction with lazily loaded Turbo Frame content?

I was concerned that filtering out blocks might cause the index-based element selection to point to the wrong element, but so far, I haven't been able to trip it up. I really don't want to break this functionality.

@andrewerlanger I also removed the previous line 117, which was where we performed the shouldUpdate check initially. It seems as though this should no longer be necessary. Is there a good reason to run the check again?

I've tested on a simple User model with enable_updates, as well as name and email attributes:

<%= updates_for current_user, only: :email do %>
  <p><%= current_user.name %></p>
  <p><%= current_user.email %></p>
<% end %>

<%= updates_for current_user, only: :name do %>
  <p><%= current_user.name %></p>
  <p><%= current_user.email %></p>
<% end %>

Seems to work fine when I update either attribute.

Fixes #209

Why should this be added

@andrewerlanger pointed out that we fetch pages from the server before checking if they are used, which is a waste of computing resources and bandwidth.

Checklist

• My code follows the style guidelines of this project
• Checks (StandardRB & Prettier-Standard) are passing
• This is not a documentation update

[julianrubisch]

This looks like a sane approach 👍🏻

I'll see if I can check this against an app of mine.

Would be nice if @andrewerlanger did the same, provided you still use it.

[leastbad]

@julianrubisch @andrewerlanger any feedback so far? I'd love to get this merged if everything looks okay.

[andrewerlanger]

@julianrubisch @leastbad not sure how I missed these messages but only just seeing them now. Sorry for the radio silence and many thanks for pushing ahead with the fix :)