// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
import { format } from "@std/internal/format";
import { AssertionError } from "./assertion_error.ts";
/*!
* Ported and modified from: https://github.com/microsoft/TypeScript-Website/blob/v2/packages/documentation/copy/en/handbook-v1/Unions%20and%20Intersections.md#union-exhaustiveness-checking
* licensed as:
*
* The MIT License (MIT)
* Copyright (c) Microsoft Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
* associated documentation files (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all copies or substantial
* portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
/**
* Make an assertion that `x` is of type `never`.
* If not then throw.
*
* @experimental **UNSTABLE**: New API, yet to be vetted.
*
* @example Exhaustivenss check
* ```ts
* import { assertNever } from "@std/assert/unstable-never";
*
* type Kinds = "A" | "B";
*
* function handleKind(kind: Kinds) {
* switch (kind) {
* case "A":
* doA();
* break;
* case "B":
* doB();
* break;
* default:
* assertNever(kind);
* }
* }
*
* function doA() {
* // ...
* }
*
* function doB() {
* // ...
* }
* ```
*
* @example Compile-time error when there is a missing case
* ```ts expect-error ignore
* import { assertNever } from "@std/assert/unstable-never";
*
* type Kinds = "A" | "B" | "C";
*
* function handleKind(kind: Kinds) {
* switch (kind) {
* case "A":
* doA();
* break;
* case "B":
* doB();
* break;
* default:
* // Type error since "C" is not handled
* assertNever(kind);
* }
* }
*
* function doA() {
* // ...
* }
*
* function doB() {
* // ...
* }
* ```
*
* @param x The value to be checked as never
* @param msg The optional message to display if the assertion fails.
* @returns Never returns, always throws.
* @throws {AssertionError}
*/
export function assertNever(x: never, msg?: string): never {
throw new AssertionError(
msg ?? `Expect ${format(x)} to be of type never`,
);
}
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