microsoft / microsoft/TypeScript

Incorrect type inference at function callsite - wrapping type inside of a Tuple

Open
#41,519 2 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Needs Investigation
Dominant language
Go
Stars
111k
Forks
14.3k
Avg merge
2d 4h
Merged PRs (30d)
132

Description

TypeScript Version: 4.0.5
Tested this on v4.1.0-beta, same issue (in playground)
Tested on Nightly (v4.2.0-dev.20201112), same issue (in playground)
Tested on v3.9.7, same issue (in playground)
Tested on v3.8.3, same issue (in playground)
Tested on v3.7.5, same issue (in playground)

Search Terms:
tuple inference
argument not assignable
ts2345

Code

This is inside of a react typescript project, when upgrading react-scripts along with typescript to the latest (v4) versions.

We have a generic custom react hook that is having some tsc errors after upgrading - this one though I haven't been able to work through and it looks like a bug of some kind in how tsc is inferring the type.

import {
	useReducer,
	useRef,
	useLayoutEffect,
	useMemo,
        Reducer,
} from 'react'; //react: ^16.8.6
import _ from 'lodash'; //lodash: ^4.17.20

export interface IOptions {    
	/**
	 * The number of milliseconds to debounce the request. Defaults to no debounce.
	 * When `true`, defaults to 300 milliseconds.
	 */
	debounce?: boolean | number;
}

export interface ICallbacks<T> {
}

export interface IResult<T> {
	isLoading: boolean;
	response?: T;
	error?: any;
}

export interface IReturn<T> extends IResult<T> {
	refetch(): void;
}

type Action<T> =
	| { type: 'REQUEST' }
	| { type: 'SUCCESS'; payload: T }
	| { type: 'FAILURE'; payload: any };

const initialResults: IResult<any> = {
	isLoading: false,
	response: undefined,
	error: undefined,
};

function resultsReducer<T>(
	state: IResult<T>,
	action: Action<T>,
): IResult<T> {
	switch (action.type) {
		case 'REQUEST':
			return { isLoading: true, response: state.response };
		case 'SUCCESS':
			return { isLoading: false, response: action.payload };
		case 'FAILURE':
			return { isLoading: false, error: action.payload };
		default:
			return initialResults;
	}
}

function isCancellable<T = any>(
	fetch: RequestSender<T>,
): fetch is DebouncedRequestSender<T> {
	if ((fetch as any).cancel) return true;

	return false;
}

type DebouncedRequestSender<T = any> = _.DebouncedFunc<
	(
		url: string,
		options: IOptions,
		callbacks: ICallbacks<T>,
		dispatch: DispatchFunc<Action<T>>,
	) => () => void
>;

type RequestSender<T = any> = DebouncedRequestSender<T> | typeof performRequest;

function performRequest<T = any>(
	url: string,
	options: IOptions,
	callbacks: ICallbacks<T>,
	dispatch: React.Dispatch<Action<T>>,
): (() => void) {
	dispatch({ type: 'REQUEST' });

	return () => {};
};

export function useHook<T = any>(
	url: string,
	options: IOptions = {},
	callbacks: ICallbacks<T> = {},
): void {
	const [results, dispatch] = useReducer<
		Reducer<IResult<T>, Action<T>>
	>(resultsReducer, initialResults);

    // Use a ref to hold onto the callbacks. The prevents us from having to
	// include the callbacks in the useEffect dependencies.
	const callbacksRef = useRef(callbacks);
	callbacksRef.current = callbacks;

    // Create a debounced function, if needed. Also, memoize this function so
	// that it doesn't cause unnecessary requests.
	const fetch: RequestSender<T> = useMemo(() => {
		if (options.debounce) {
			// Use a default number of milliseconds if debounce is `true`.
			const wait = options.debounce === true ? 300 : options.debounce;
			return _.debounce(performRequest, wait);
		} else {
			return performRequest;
		}
	}, [options.debounce]);

    useLayoutEffect(() => {
		const cancelFetch: (() => void) | undefined = fetch(
			url,
			options,
			callbacksRef.current,
			dispatch,
		);

		return () => {
			// Cancel the debounced function call, if needed.
			if (isCancellable(fetch)) fetch.cancel();
		};
	}, [url, options, fetch]);

}  

Expected behavior:
I would expect this not to result in a tsc error. I'm not sure where it is inferring this tuple that is wrapping the actual type for the dispatch variable, but based on what intellisense is showing me in VS Code, the dispatch variable's type matches the expected type for the fetch function signature.

Actual behavior:
Argument of type '[Dispatch<Action<T>>]' is not assignable to parameter of type 'Dispatch<Action<T>>'. Type '[Dispatch<Action<T>>]' provides no match for the signature '(value: Action<T>): void'.ts(2345)

Playground Link:
TS Playground link

Related Issues:

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked TypeScript Playground reproduction and inspect the useReducer callsite where dispatch is passed to fetch. Compare the inferred type with the reported tuple-wrapped diagnostic across the listed TypeScript versions. Done means the reproduction type-checks without changing the intended generic hook behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
react, typescript
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.