Linter Rule: Disallow render calls that infer the partial from an object

Rule: actionview-no-implicit-partial

Description

Detects render calls that pass an object or collection without naming a partial, such as render @products, where Rails derives the template name from the class of each item.

Rationale

render @products renders _product.html.erb once per item, choosing the template from each item's class at runtime. Nothing in the call says so:

<%= render @products %>
Rails derives the partial from `to_partial_path` on `@products` when the template renders, so the template this renders is not named in this `<%= render %>` call. Name it explicitly, with `object:` for a single record or `collection:` for many, and Herb can take you to it, check the locals you pass against its strict locals, and help you rename them. (actionview-no-implicit-partial)

Naming the partial says it:

<%= render partial: "products/product", collection: @products %>

The implicit form is compact and idiomatic, and it costs the same things every unnamed dependency costs. Searching for the templates that render _product.html.erb misses these calls. Changing or subclassing the model changes which template renders, silently.

Naming the partial also turns the call into an edge Herb can follow. Once the template is written down it matches an entry in the partial index, and the language server can jump from the call to the partial and back to every caller, rename a strict local across all of those call sites at once, complete the locals the partial declares as you type them, and report a call that passes a local the partial does not declare or omits one it requires. A derived name matches no entry, which is why the language server says the same thing when you ask it to jump to a partial it cannot resolve.

The implicit form is common Rails, so this reports at info: it is guidance for codebases that want template dependencies written down rather than derived, not a defect report.

Notes

Component renders are not reported

render FlashComponent.new(...) and render Primer::Alpha::Banner.new(...) call render_in on the object rather than looking up a partial, so there is no partial name to write. Any render whose object is built from a constant is left alone, and so is any render whose call chain constructs an object with .new, which covers the factory helpers component libraries use: render component("ui/modal").new(title: t(".title")).

Renders that name a partial, including with a dynamic name, are not reported here. See actionview-no-dynamic-partial-path.

Only output tags are reported. A render in a silent <% %> tag discards its output and is covered by actionview-no-silent-render.

Examples

✅ Good

<%= render partial: "products/product", collection: @products %>

<%= render @products, partial: "product" %>
The partial `product` is looked up relative to the directory of the template rendering it. Moving this template changes which file that resolves to, and renaming the partial means hunting for callers that never spell its full name. Write the full path from the view root so it resolves to the same file from any template, and a search for that path finds every caller. (actionview-prefer-qualified-partial-path)

<%= render partial: "products/product", object: @product %>

🚫 Bad

<%= render @products %>
Rails derives the partial from `to_partial_path` on `@products` when the template renders, so the template this renders is not named in this `<%= render %>` call. Name it explicitly, with `object:` for a single record or `collection:` for many, and Herb can take you to it, check the locals you pass against its strict locals, and help you rename them. (actionview-no-implicit-partial)

<%= render @product %>
Rails derives the partial from `to_partial_path` on `@product` when the template renders, so the template this renders is not named in this `<%= render %>` call. Name it explicitly, with `object:` for a single record or `collection:` for many, and Herb can take you to it, check the locals you pass against its strict locals, and help you rename them. (actionview-no-implicit-partial)

Configuration

Disable it in .herb.yml when the implicit form is the house style:

linter:
  rules:
    actionview-no-implicit-partial:
      enabled: false

References

• Action View - Rendering collections