Linter: Add support for as: in actionview-prefer-collection-render

javascript/packages/linter/docs/rules/actionview-prefer-collection-render.md

@@ -14,8 +14,12 @@ The reported message contains the exact replacement tag, built from the loop's r
 <% end %>
 ```
 
-```
-Prefer `<%= render partial: "user", collection: @users %>` over rendering a partial once per iteration. Collection rendering builds the partial once instead of for every item.
+Collection rendering names the local after the partial, so when the loop passes the element under a different name the replacement carries an `as:` to keep the partial working:
+
+```erb
+<% @gems.each do |topic_gem| %>
+  <%= render partial: "gem_card", locals: { topic_gem: topic_gem } %>
+<% end %>
 ```
 
 Rendering an object directly reports the shorthand collection form instead:
@@ -26,15 +30,11 @@ Rendering an object directly reports the shorthand collection form instead:
 <% end %>
 ```
 
-```
-Prefer `<%= render @users %>` over rendering a partial once per iteration. Collection rendering builds the partial once instead of for every item.
-```
-
 ## Rationale
 
 When a partial is rendered inside a loop, Action View looks the template up and sets up a fresh local scope on every iteration. Collection rendering does that work once and then reuses it for every element, so it is meaningfully faster for anything but the shortest collections.
 
-Collection rendering also passes each element as a local named after the partial, and provides a `<partial>_counter` local, which removes the need to thread the loop variable through by hand.
+Collection rendering also passes each element as a local named after the partial, and provides a `<partial>_counter` local, which removes the need to thread the loop variable through by hand. When the loop passes the element under a name that isn't the partial name, the suggestion adds `as:` so the partial keeps receiving the local it expects.
 
 Because the rewrite emits the partial and nothing else, this rule only fires when the loop body is exactly one output `render` and the only local passed is the block argument. Loops that wrap the partial in markup, pass extra locals, or use a block argument the partial doesn't receive are left alone, since collection rendering cannot express them.
 
@@ -46,6 +46,10 @@ Because the rewrite emits the partial and nothing else, this rule only fires whe
 <%= render partial: "user", collection: @users %>
 ```
 
+```erb
+<%= render partial: "gem_card", collection: @gems, as: :topic_gem %>
+```
+
 ```erb
 <%= render @users %>
 ```
@@ -90,6 +94,12 @@ Loops that do more than render a single partial are not flagged, because collect
 <% end %>
 ```
 
+```erb
+<% @gems.each do |topic_gem| %>
+  <%= render partial: "gem_card", locals: { topic_gem: topic_gem } %>
+<% end %>
+```
+
 ## References
 
 - [Action View Partials: Rendering Collections](https://guides.rubyonrails.org/layouts_and_rendering.html#rendering-collections)

javascript/packages/linter/src/rules/actionview-prefer-collection-render.ts

@@ -73,10 +73,21 @@ class PreferCollectionRenderVisitor extends BaseRuleVisitor {
     const locals = keywords.locals ?? []
     if (locals.length !== 1) return null
 
-    const [local] = locals as Array<{ value?: { content?: string } }>
+    const [local] = locals as Array<{ name?: { value?: string }, value?: { content?: string } }>
     if (local.value?.content !== blockArgument) return null
 
-    return `<%= render partial: "${partial}", collection: ${receiver} %>`
+    const localName = local.name?.value
+    if (!localName) return null
+
+    const as = localName === this.collectionLocalNameFor(partial) ? "" : `, as: :${localName}`
+
+    return `<%= render partial: "${partial}", collection: ${receiver}${as} %>`
+  }
+
+  private collectionLocalNameFor(partial: string): string {
+    const name = partial.split("/").pop() ?? partial
+
+    return name.startsWith("_") ? name.slice(1) : name
   }
 }
 

javascript/packages/linter/test/rules/actionview-prefer-collection-render.test.ts

@@ -31,6 +31,54 @@ describe("actionview-prefer-collection-render", () => {
     assertOffenses(html)
   })
 
+  it("suggests `as:` when the local is not named after the partial", () => {
+    const html = dedent`
+      <% @gems.each do |topic_gem| %>
+        <%= render partial: "gem_card", locals: { topic_gem: topic_gem } %>
+      <% end %>
+    `
+
+    expectError('Prefer `<%= render partial: "gem_card", collection: @gems, as: :topic_gem %>` over rendering a partial once per iteration. Collection rendering builds the partial once instead of for every item.')
+
+    assertOffenses(html)
+  })
+
+  it("suggests `as:` when the local is not named after the partial in the shorthand form", () => {
+    const html = dedent`
+      <% @gems.each do |topic_gem| %>
+        <%= render "gem_card", topic_gem: topic_gem %>
+      <% end %>
+    `
+
+    expectError('Prefer `<%= render partial: "gem_card", collection: @gems, as: :topic_gem %>` over rendering a partial once per iteration. Collection rendering builds the partial once instead of for every item.')
+
+    assertOffenses(html)
+  })
+
+  it("does not suggest `as:` when the local matches the partial name in a nested path", () => {
+    const html = dedent`
+      <% @gems.each do |gem_card| %>
+        <%= render partial: "gems/gem_card", locals: { gem_card: gem_card } %>
+      <% end %>
+    `
+
+    expectError('Prefer `<%= render partial: "gems/gem_card", collection: @gems %>` over rendering a partial once per iteration. Collection rendering builds the partial once instead of for every item.')
+
+    assertOffenses(html)
+  })
+
+  it("suggests `as:` when the local does not match the partial name in a nested path", () => {
+    const html = dedent`
+      <% @gems.each do |topic_gem| %>
+        <%= render partial: "gems/gem_card", locals: { topic_gem: topic_gem } %>
+      <% end %>
+    `
+
+    expectError('Prefer `<%= render partial: "gems/gem_card", collection: @gems, as: :topic_gem %>` over rendering a partial once per iteration. Collection rendering builds the partial once instead of for every item.')
+
+    assertOffenses(html)
+  })
+
   it("flags the object shorthand and suggests the shorthand collection form", () => {
     const html = dedent`
       <% @users.each do |user| %>