Linter: Implement -actionview-strict-locals-partial-only rule

Author: marcoroth

javascript/packages/linter/docs/rules/README.md

@@ -10,6 +10,7 @@ This page contains documentation for all Herb Linter rules.
 - [`actionview-no-silent-render`](./actionview-no-silent-render.md) - Disallow calling `render` without outputting the result
 - [`actionview-no-void-element-content`](./actionview-no-void-element-content.md) - Disallow content arguments for void Action View elements
 - [`actionview-strict-locals-first-line`](./actionview-strict-locals-first-line.md) - Require strict locals on the first line of partials with a blank line after.
+- [`actionview-strict-locals-partial-only`](./actionview-strict-locals-partial-only.md) - Only allow strict local definitions in partial files.
 
 
 #### ERB

javascript/packages/linter/docs/rules/actionview-strict-locals-partial-only.md

@@ -0,0 +1,37 @@
+# Linter Rule: Only allow strict local definitions in partial files
+
+**Rule:** `actionview-strict-locals-partial-only`
+
+## Description
+
+Detects strict locals declarations in files that are not Rails partials. Strict locals are only supported in partials (templates whose filename begins with an underscore), so a declaration in any other template has no effect.
+
+## Rationale
+
+A `<%# locals: (...) %>` comment in a non-partial file (such as a view or layout) is misleading. It looks like it constrains the available local variables, but Rails only processes strict locals in partials. Flagging these declarations prevents confusion and keeps templates honest about their actual contract.
+
+## Examples
+
+### ✅ Good
+
+```erb [app/views/users/_card.html.erb]
+<%# locals: (user:) %>
+
+<div class="user-card">
+  <%= user.name %>
+</div>
+```
+
+### 🚫 Bad
+
+```erb [app/views/users/show.html.erb]
+<%# locals: (user:) %>
+
+<div class="user-card">
+  <%= user.name %>
+</div>
+```
+
+## References
+
+- [Action View - Strict Locals](https://guides.rubyonrails.org/action_view_overview.html#strict-locals)

javascript/packages/linter/src/rules.ts

@@ -4,6 +4,7 @@ import { ActionViewNoSilentHelperRule } from "./rules/actionview-no-silent-helpe
 import { ActionViewNoSilentRenderRule } from "./rules/actionview-no-silent-render.js"
 import { ActionViewNoVoidElementContentRule } from "./rules/actionview-no-void-element-content.js"
 import { ActionViewStrictLocalsFirstLineRule } from "./rules/actionview-strict-locals-first-line.js"
+import { ActionViewStrictLocalsPartialOnlyRule } from "./rules/actionview-strict-locals-partial-only.js"
 
 import { ERBCommentSyntax } from "./rules/erb-comment-syntax.js";
 import { ERBNoCaseNodeChildrenRule } from "./rules/erb-no-case-node-children.js"
@@ -95,6 +96,7 @@ export const rules: RuleClass[] = [
   ActionViewNoSilentRenderRule,
   ActionViewNoVoidElementContentRule,
   ActionViewStrictLocalsFirstLineRule,
+  ActionViewStrictLocalsPartialOnlyRule,
 
   ERBCommentSyntax,
   ERBNoCaseNodeChildrenRule,

javascript/packages/linter/src/rules/actionview-strict-locals-partial-only.ts

@@ -0,0 +1,66 @@
+import { BaseRuleVisitor } from "./rule-utils.js"
+import { ParserRule } from "../types.js"
+
+import { isHTMLTextNode } from "@herb-tools/core"
+import { isPartialFile } from "./file-utils.js"
+
+import type { ParseResult, ERBStrictLocalsNode } from "@herb-tools/core"
+import type { UnboundLintOffense, LintOffense, LintContext, FullRuleConfig } from "../types.js"
+
+class ActionViewStrictLocalsPartialOnlyVisitor extends BaseRuleVisitor {
+  visitERBStrictLocalsNode(node: ERBStrictLocalsNode): void {
+    this.addOffense(
+      "Strict locals declarations are only supported in partials. This file is not a partial.",
+      node.location,
+    )
+  }
+}
+
+export class ActionViewStrictLocalsPartialOnlyRule extends ParserRule {
+  static unsafeAutocorrectable = true
+  static ruleName = "actionview-strict-locals-partial-only"
+  static introducedIn = this.version("unreleased")
+
+  get parserOptions() {
+    return { strict_locals: true }
+  }
+
+  get defaultConfig(): FullRuleConfig {
+    return {
+      enabled: true,
+      severity: "warning",
+    }
+  }
+
+  check(result: ParseResult, context?: Partial<LintContext>): UnboundLintOffense[] {
+    if (isPartialFile(context?.fileName) !== false) return []
+
+    const visitor = new ActionViewStrictLocalsPartialOnlyVisitor(this.ruleName, context)
+    visitor.visit(result.value)
+
+    return visitor.offenses
+  }
+
+  autofix(offense: LintOffense, result: ParseResult): ParseResult | null {
+    const children = result.value.children
+
+    const index = children.findIndex(child =>
+      child.location.start.line === offense.location.start.line &&
+      child.location.start.column === offense.location.start.column
+    )
+
+    if (index === -1) return null
+
+    children.splice(index, 1)
+
+    if (index < children.length) {
+      const next = children[index]
+
+      if (isHTMLTextNode(next) && /^\s*\n/.test(next.content)) {
+        children.splice(index, 1)
+      }
+    }
+
+    return result
+  }
+}

javascript/packages/linter/src/rules/index.ts

@@ -7,6 +7,7 @@ export * from "./actionview-no-silent-helper.js"
 export * from "./actionview-no-silent-render.js"
 export * from "./actionview-no-void-element-content.js"
 export * from "./actionview-strict-locals-first-line.js"
+export * from "./actionview-strict-locals-partial-only.js"
 
 export * from "./erb-comment-syntax.js"
 export * from "./erb-no-case-node-children.js"