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102 lines
3.0 KiB
TypeScript
102 lines
3.0 KiB
TypeScript
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
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// This module is browser compatible.
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import { format } from "@std/internal/format";
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import { AssertionError } from "./assertion_error.ts";
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/*!
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* 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
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* licensed as:
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*
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* The MIT License (MIT)
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* Copyright (c) Microsoft Corporation
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
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* associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or substantial
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* portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
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* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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/**
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* Make an assertion that `x` is of type `never`.
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* If not then throw.
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*
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* @experimental **UNSTABLE**: New API, yet to be vetted.
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*
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* @example Exhaustivenss check
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* ```ts
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* import { assertNever } from "@std/assert/unstable-never";
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*
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* type Kinds = "A" | "B";
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*
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* function handleKind(kind: Kinds) {
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* switch (kind) {
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* case "A":
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* doA();
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* break;
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* case "B":
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* doB();
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* break;
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* default:
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* assertNever(kind);
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* }
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* }
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*
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* function doA() {
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* // ...
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* }
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*
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* function doB() {
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* // ...
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* }
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* ```
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*
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* @example Compile-time error when there is a missing case
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* ```ts expect-error ignore
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* import { assertNever } from "@std/assert/unstable-never";
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*
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* type Kinds = "A" | "B" | "C";
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*
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* function handleKind(kind: Kinds) {
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* switch (kind) {
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* case "A":
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* doA();
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* break;
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* case "B":
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* doB();
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* break;
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* default:
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* // Type error since "C" is not handled
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* assertNever(kind);
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* }
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* }
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*
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* function doA() {
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* // ...
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* }
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*
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* function doB() {
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* // ...
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* }
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* ```
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*
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* @param x The value to be checked as never
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* @param msg The optional message to display if the assertion fails.
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* @returns Never returns, always throws.
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* @throws {AssertionError}
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*/
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export function assertNever(x: never, msg?: string): never {
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throw new AssertionError(
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msg ?? `Expect ${format(x)} to be of type never`,
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);
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}
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