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[labs/task] Infer the return type of Task.render() #4008

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Merged
justinfagnani merged 3 commits into from
Jul 11, 2023
Merged

[labs/task] Infer the return type of Task.render() #4008

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eb51235
Infer the return type of Task.render()
justinfagnani Jul 10, 2023
4fd43d2
Address feedback
justinfagnani Jul 11, 2023
348ac83
Default task return type to unknown
justinfagnani Jul 11, 2023
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5 changes: 5 additions & 0 deletions .changeset/spicy-mugs-eat.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@lit-labs/task': patch
---

Infer the return type of Task.render()
22 changes: 13 additions & 9 deletions packages/labs/task/src/task.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,7 @@ export interface TaskFunctionOptions {
signal?: AbortSignal;
}

// eslint-disable-next-line @typescript-eslint/no-explicit-any
export type TaskFunction<D extends ReadonlyArray<unknown>, R = any> = (
export type TaskFunction<D extends ReadonlyArray<unknown>, R = unknown> = (
args: D,
options?: TaskFunctionOptions
) => R | typeof initialState | Promise<R | typeof initialState>;
Expand Down Expand Up @@ -327,19 +326,20 @@ export class Task<
return this._error;
}

render(renderer: StatusRenderer<R>) {
render<T extends StatusRenderer<R>>(renderer: T) {
switch (this.status) {
case TaskStatus.INITIAL:
return renderer.initial?.();
return renderer.initial?.() as MaybeReturnType<T['initial']>;
case TaskStatus.PENDING:
return renderer.pending?.();
return renderer.pending?.() as MaybeReturnType<T['pending']>;
case TaskStatus.COMPLETE:
return renderer.complete?.(this.value!);
return renderer.complete?.(this.value!) as MaybeReturnType<
T['complete']
>;
case TaskStatus.ERROR:
return renderer.error?.(this.error);
return renderer.error?.(this.error) as MaybeReturnType<T['error']>;
default:
// exhaustiveness check
this.status as void;
throw new Error(`Unexpected status: ${this.status}`);
}
}

Expand All @@ -351,3 +351,7 @@ export class Task<
: args !== prev;
}
}

type MaybeReturnType<F> = F extends (...args: unknown[]) => infer R
? R
: undefined;
27 changes: 27 additions & 0 deletions packages/labs/task/src/test/task_test.ts
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Expand Up @@ -942,4 +942,31 @@ suite('Task', () => {
assert.equal(el.task.value, secondValue);
assert.notEqual(firstValue, secondValue);
});

test('type-only render return type test', () => {
class TestElement extends ReactiveElement {
task = new Task(this, () => 'abc');
}
customElements.define(generateElementName(), TestElement);
const el = new TestElement();

const accept = <T>(x: T) => x;

accept<number | undefined>(el.task.render({initial: () => 123}));
accept<number | undefined>(el.task.render({complete: () => 123}));
accept<number | undefined>(el.task.render({pending: () => 123}));
accept<number | undefined>(el.task.render({error: () => 123}));
accept<number | undefined>(
el.task.render({initial: () => 123, complete: () => 123})
);

accept<number>(
el.task.render({
initial: () => 123,
complete: () => 123,
pending: () => 123,
error: () => 123,
})
);
});
});