Analysis: Follow state through a block parameter

[marcoroth]

This pull request teaches the dependency analysis that a block's parameters carry whatever that block iterates, in one template and across a render call, and in all three languages that implement it.

<ul>
  <% @items.each do |item| %>
    <li><%= item.name %></li>
  <% end %>
</ul>

item is @items, one at a time. Matching is by name, so nothing connected the two, and item.name was attributed to nothing.

Ruby learned this within a single template in #2280. This finishes it: the two ports learn the same thing, and the Ruby trace learns it across a render boundary, which is where it was answering a user-facing question incorrectly.

affected_templates and state_flow back herb dependencies and herb actionview flow, and their whole product is the list of templates a piece of state reaches. One shape was missing from it.

traced:

<%= render partial: "posts/card", collection: @posts %>

not traced:

<% @posts.each do |post| %>
  <%= render "posts/card", card: post %>
<% end %>

For the second, affected_templates(entry, "@posts") returned ["index.html.erb"] and omitted _card.html.erb, and state_flow returned a tree with no child. trace_state asks whether a render call's local carries the state, and card: post names a block parameter that nothing tied to the collection that bound it.

The collector now records the blocks open around a render call, with the names each binds, and a local whose value is one of those names carries what its block iterates.

analyze now parses with iteration_nodes, so a block running per item and a block running once are different node types. Without that, form_with model: @post do |f| looks like a collection and f carries @post into every partial rendered inside the form.

Once the trace reaches _card.html.erb, its slots become addressable, and they came back as an identity, which is a client writing one value into every card. A render inside an iterating block is now per item the same way collection: is, and the modes below a block that runs once are left alone.

Follow up on #2279, #2280, #2281, #2282 and #2283.

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☁️ Nx Cloud last updated this comment at 2026-08-18 23:54:02 UTC

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commit: b337dfe