Linter: Implement erb-no-multiple-statements rule

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

@@ -35,6 +35,7 @@ This page contains documentation for all Herb Linter rules.
 - [`erb-no-instance-variables-in-partials`](./erb-no-instance-variables-in-partials.md) - Disallow instance variables in partials
 - [`erb-no-interpolated-class-names`](./erb-no-interpolated-class-names.md) - Disallow ERB interpolation inside CSS class names
 - [`erb-no-javascript-tag-helper`](./erb-no-javascript-tag-helper.md) - Disallow `javascript_tag` helper
+- [`erb-no-multiple-statements`](./erb-no-multiple-statements.md) - Disallow multiple Ruby statements in a single-line ERB tag
 - [`erb-no-output-control-flow`](./erb-no-output-control-flow.md) - Prevents outputting control flow blocks
 - [`erb-no-output-in-attribute-name`](./erb-no-output-in-attribute-name.md) - Disallow ERB output in attribute names
 - [`erb-no-output-in-attribute-position`](./erb-no-output-in-attribute-position.md) - Disallow ERB output in attribute position

javascript/packages/linter/docs/rules/erb-no-multiple-statements.md

@@ -0,0 +1,51 @@
+# Linter Rule: Disallow multiple Ruby statements in a single-line ERB tag
+
+**Rule:** `erb-no-multiple-statements`
+
+## Description
+
+Disallow multiple Ruby statements separated by semicolons within a single-line ERB tag. Each ERB tag on a single line should contain at most one Ruby statement.
+
+## Rationale
+
+Multiple Ruby statements on a single line in an ERB tag reduce readability and make templates harder to maintain. Splitting statements into separate ERB tags makes each statement easier to understand at a glance.
+
+This rule only applies to single-line ERB tags. Multi-line ERB tags are not checked, as they naturally provide visual separation between statements.
+
+## Examples
+
+### ✅ Good
+
+```erb
+<% user = User.find(1) %>
+<% post = user.posts.first %>
+```
+
+```erb
+<%= user.name %>
+```
+
+```erb
+<%
+  user = User.find(1)
+  post = user.posts.first
+%>
+```
+
+### 🚫 Bad
+
+```erb
+<% user = User.find(1); post = user.posts.first %>
+```
+
+```erb
+<%= user = User.find(1); user.name %>
+```
+
+```erb
+<% a = 1; b = 2; c = 3 %>
+```
+
+## References
+
+- [Ruby Style Guide - Semicolons](https://rubystyle.guide/#no-semicolon)

javascript/packages/linter/src/rules.ts

@@ -25,6 +25,7 @@ import { ERBNoInlineCaseConditionsRule } from "./rules/erb-no-inline-case-condit
 import { ERBNoInstanceVariablesInPartialsRule } from "./rules/erb-no-instance-variables-in-partials.js"
 import { ERBNoInterpolatedClassNamesRule } from "./rules/erb-no-interpolated-class-names.js"
 import { ERBNoJavascriptTagHelperRule } from "./rules/erb-no-javascript-tag-helper.js"
+import { ERBNoMultipleStatementsRule } from "./rules/erb-no-multiple-statements.js"
 import { ERBNoOutputControlFlowRule } from "./rules/erb-no-output-control-flow.js"
 import { ERBNoOutputInAttributeNameRule } from "./rules/erb-no-output-in-attribute-name.js"
 import { ERBNoOutputInAttributePositionRule } from "./rules/erb-no-output-in-attribute-position.js"
@@ -128,6 +129,7 @@ export const rules: RuleClass[] = [
   ERBNoInstanceVariablesInPartialsRule,
   ERBNoInterpolatedClassNamesRule,
   ERBNoJavascriptTagHelperRule,
+  ERBNoMultipleStatementsRule,
   ERBNoOutputControlFlowRule,
   ERBNoOutputInAttributeNameRule,
   ERBNoOutputInAttributePositionRule,

javascript/packages/linter/src/rules/erb-no-multiple-statements.ts

@@ -0,0 +1,86 @@
+import { ParserRule } from "../types.js"
+import { BaseRuleVisitor } from "./rule-utils.js"
+
+import type { UnboundLintOffense, LintContext, FullRuleConfig } from "../types.js"
+import type { ParseResult, ERBContentNode, ParserOptions, PrismNode } from "@herb-tools/core"
+
+function collectStatements(programNode: PrismNode): PrismNode[] {
+  const statements = programNode?.statements?.body
+
+  if (!Array.isArray(statements)) return []
+
+  return statements
+}
+
+class NoMultipleStatementsVisitor extends BaseRuleVisitor {
+  private readonly statements: PrismNode[]
+
+  constructor(ruleName: string, context: Partial<LintContext> | undefined, statements: PrismNode[]) {
+    super(ruleName, context)
+
+    this.statements = statements
+  }
+
+  visitERBContentNode(node: ERBContentNode): void {
+    const startLine = node.location.start.line
+    const endLine = node.location.end.line
+    if (startLine !== endLine) return
+
+    const tagOpening = node.tag_opening?.value
+    if (tagOpening === "<%#") return
+
+    const contentRange = node.content?.range
+    if (!contentRange) return
+
+    const rangeStart = contentRange.start
+    const rangeEnd = contentRange.end
+
+    let statementCount = 0
+
+    for (const statement of this.statements) {
+      const statementOffset = statement.location.startOffset
+
+      if (statementOffset >= rangeStart && statementOffset < rangeEnd) {
+        statementCount++
+      }
+    }
+
+    if (statementCount <= 1) return
+
+    this.addOffense(
+      `Avoid multiple Ruby statements in a single-line ERB tag. Split each statement into its own ERB tag for better readability.`,
+      node.location,
+    )
+  }
+}
+
+export class ERBNoMultipleStatementsRule extends ParserRule {
+  static ruleName = "erb-no-multiple-statements"
+  static introducedIn = this.version("unreleased")
+
+  get defaultConfig(): FullRuleConfig {
+    return {
+      enabled: true,
+      severity: "warning",
+    }
+  }
+
+  get parserOptions(): Partial<ParserOptions> {
+    return {
+      prism_nodes: true,
+      prism_program: true,
+    }
+  }
+
+  check(result: ParseResult, context?: Partial<LintContext>): UnboundLintOffense[] {
+    const documentPrismNode = result.value.prismNode
+    if (!documentPrismNode) return []
+
+    const statements = collectStatements(documentPrismNode)
+    if (statements.length === 0) return []
+
+    const visitor = new NoMultipleStatementsVisitor(this.ruleName, context, statements)
+    visitor.visit(result.value)
+    return visitor.offenses
+  }
+}

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

@@ -28,6 +28,7 @@ export * from "./erb-no-extra-whitespace-inside-tags.js"
 export * from "./erb-no-inline-case-conditions.js"
 export * from "./erb-no-instance-variables-in-partials.js"
 export * from "./erb-no-javascript-tag-helper.js"
+export * from "./erb-no-multiple-statements.js"
 export * from "./erb-no-output-control-flow.js"
 export * from "./erb-no-output-in-attribute-name.js"
 export * from "./erb-no-output-in-attribute-position.js"