Linter: `erb-no-unused-expressions` conflicts with ViewComponent slot usage

[grantbdev]

ViewComponent has a pattern where a slot can be set including the content for the slot within a <% ... %> tag:

<%= render BlogComponent.new do |component| %>
  <% component.with_header(classes: "title").with_content("My blog") %>
<% end %>

@herb-tools/linter 0.9.4 currently flags these as unused expressions, but they are used.

[marcoroth]

Great catch @grantbdev, thanks! 🙏🏼

Thanks to your bug report I just realized we are not properly detecting render calls with a block. Once we do (I have a PR in the works right now) we could make the erb-no-unused-expressions linter rule ignore the content inside render blocks nodes.

[natematykiewicz]

Is there a way to flag certain methods that are allowed? For example, this is flagging all of my set_meta_tags calls from the meta-tags gem as unused, except they work similar to content_for, where you're defining values that get used by something else.

<% set_meta_tags title: title %>

<%= render MyComponent.new(title:) do %>
<% end %>

[marcoroth]

@natematykiewicz sadly not yet, but I added a note in #1204 (comment)

[natematykiewicz]

I found another one. We using assert_valid_keys to help catch typoes on an array of attribute hashes, and Herb wants that first line to either assign or be deleted. But, assert_valid_keys is designed to either raise or not. Its return value is irrelevant.

<%
  link.assert_valid_keys(:href, :name, :leading_icon, :target)
  href = link.fetch(:href)
  name = link.fetch(:name)
  icon = link[:leading_icon]
  target = link[:target]
%>

[marcoroth]

@natematykiewicz looks like this might be fixed on main:

https://herb-tools.dev/playground/?tab=diagnostics#DwUgUABBA2CWB2BrAdAQwM7oKYCcAuA+gG6pwAmBiWAnugBQBcAFjlgGYA0ED8qAtli4NoWVGQQBzArADGAe3hC8qHBKx4AlJAgt2EALwwEKNuplNGutlqi8BBo0mSm85xnaw2IshQ7hIAbWFRcXgpH3gAXW1lVXU-YyDYtTxokAA+MCA

[natematykiewicz]

I can't seem to get erb-no-unused-expressions to trigger at all on the playground

[marcoroth]

Opened #1587 to fix this

[marcoroth]

I can't seem to get erb-no-unused-expressions to trigger at all on the playground

You are right, I need to check why. I think it has to do with Prism 🤔