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Weird TS Test Failure
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| // These assertions don't work, from https://github.com/mobxjs/mobx-state-tree/blob/master/__tests__/core/type-system.test.ts. Fails with TS 4.3 and greater. https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-3.html | |
| test("maybe / optional type inference verification", () => { | |
| const T = types.model({ | |
| a: types.string, | |
| b: "test", | |
| c: types.maybe(types.string), | |
| d: types.maybeNull(types.string), | |
| e: types.optional(types.string, "test") | |
| }) | |
| interface ITC extends SnapshotIn<typeof T> {} | |
| interface ITS extends SnapshotOut<typeof T> {} | |
| assert( | |
| _ as ITC, // TS error: Argument of type 'ITC' is not assignable to parameter of type '"❌ Unexpected or missing 'readonly' property"'. | |
| _ as { | |
| [$nonEmptyObject]?: any | |
| a: string | |
| b?: string | |
| c?: string | undefined | |
| d?: string | null | |
| e?: string | |
| } | |
| ) | |
| assert( | |
| _ as ITS, // Argument of type 'ITC' is not assignable to parameter of type '"❌ Unexpected or missing 'readonly' property"'. | |
| _ as { | |
| [$nonEmptyObject]?: any | |
| a: string | |
| b: string | |
| c: string | undefined | |
| d: string | null | |
| e: string | |
| } | |
| ) | |
| }) | |
| // But if we do any kind of modification on them, like omitting a key that doesn't exist, it works | |
| test("maybe / optional type inference verification", () => { | |
| const T = types.model({ | |
| a: types.string, | |
| b: "test", | |
| c: types.maybe(types.string), | |
| d: types.maybeNull(types.string), | |
| e: types.optional(types.string, "test") | |
| }) | |
| interface ITC extends SnapshotIn<typeof T> {} | |
| interface ITS extends SnapshotOut<typeof T> {} | |
| assert( | |
| _ as Omit<ITC, "non-existent-property">, | |
| _ as { | |
| [$nonEmptyObject]?: any | |
| a: string | |
| b?: string | |
| c?: string | undefined | |
| d?: string | null | |
| e?: string | |
| } | |
| ) | |
| assert( | |
| _ as Omit<ITS, "non-existent-property">, | |
| _ as { | |
| [$nonEmptyObject]?: any | |
| a: string | |
| b: string | |
| c: string | undefined | |
| d: string | null | |
| e: string | |
| } | |
| ) | |
| }) |
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