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typescript/no-never

Disallow inferred identifier types of never.

Targeted pattern scope​

⚠️ This rule requires type information to run. Configure type-aware linting (parserOptions.project or projectService) before enabling it.

This rule checks identifier nodes and asks TypeScript for the constrained type at each identifier location.

Explicit type alias declarations of the form type X = never are excluded.

What this rule reports​

This rule uses TypeScript type checking to report identifiers inferred as never.

Why this rule exists​

Unexpected never often indicates unreachable code paths, impossible constraints, or over-narrowed generics.

❌ Incorrect​

const fail = (): never => {
 throw new Error("x");
};

const result = fail();

✅ Correct​

type Never = never;

Behavior and migration notes​

This rule reports only and does not provide an autofix.

Because it is type-driven, enable it only in lint configurations with parser services available.

Options​

This rule has no options.

Additional examples​

function assertNever(_value: never): never {
 throw new Error("unexpected");
}

type NeverAlias = never;
// ✅ alias declaration itself is intentionally excluded

ESLint flat config example​

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/typescript/no-never": "error",
  },
 },
];

When not to use it​

Disable this rule if inferred never identifiers are accepted in your codebase.

Package documentation​

Rule catalog ID: R091

Further reading​

Adoption resources​

  • Start at warning level in CI, then move to error after cleanup.
  • Use focused codemods/autofix batches per package or directory.