no-restricted-syntax

Configuration

rslint.config.ts

import { defineConfig, js } from '@rslint/core';

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-restricted-syntax': 'error',
    },
  },
]);

Rule Details

Disallows specified syntax. This is useful when a project wants to restrict language features such as try-catch, classes, or the in operator.

Restrictions use ESTree node names, such as FunctionDeclaration and WithStatement, or more precise AST selectors. Any node matching a configured selector is reported.

Examples of incorrect code for this rule with ["error", "FunctionExpression", "WithStatement", "BinaryExpression[operator='in']"], parsed as a script:

with (me) {
  dontMess();
}

const doSomething = function () {};

foo in bar;

Examples of correct code for the same configuration:

me.dontMess();

function doSomething() {}

foo instanceof bar;

Options

The rule accepts a list of selector strings:

{
  "no-restricted-syntax": [
    "error",
    "FunctionExpression",
    "WithStatement",
    "BinaryExpression[operator='in']"
  ]
}

Entries can also be objects with a required selector and an optional message:

{
  "no-restricted-syntax": [
    "error",
    {
      "selector": "FunctionExpression",
      "message": "Function expressions are not allowed."
    },
    {
      "selector": "CallExpression[callee.name='setTimeout'][arguments.length!=2]",
      "message": "setTimeout must always be invoked with two arguments."
    }
  ]
}

The custom message replaces the default Using '<selector>' is not allowed. diagnostic. String and object entries can be mixed in one configuration.

Selectors can also target supported TypeScript syntax. For example, TSEnumDeclaration[const=true] selects const enums, while TSEnumDeclaration selects all enums. [const] only checks whether the attribute exists, so it matches ordinary enums as well.

When Not To Use It

Leave this rule disabled if your project has no syntax restrictions.

Differences from upstream

Malformed selectors are ignored instead of rejecting the rule configuration. For example, ["error", "[", "WithStatement"] still restricts WithStatement in rslint; ESLint rejects the malformed [ selector.
TypeScript selectors are limited to the supported AST node mappings. Not every type annotation or type-parameter wrapper is exposed, so broad selectors on type-only syntax can differ from typescript-eslint. Receiver attribute paths also look through TypeScript assertions, such as (console as any).log().
The bare * selector follows the underlying TypeScript AST traversal, starting at the program's children, and does not report additional ESTree wrappers. Named selectors such as ClassBody and ChainExpression, and other broad selectors, can match supported wrappers. Use Program or Program:exit to select the program itself.

#no-restricted-syntax

#Configuration

#Rule Details

#Options

#When Not To Use It

#Differences from upstream