TS4.1.2 Regression: Incorrect arity inferred on function returned by util.callbackify if input function has optional or default argument

[whoisbenli]

TypeScript Version: v4.2.0-dev.20201119. Also impacts: 4.1.2. Does not impact: 4.1.0-beta, 4.0.5

Search Terms:
callbackify expected arguments optional default

Code

import util from 'util';

function functionWithDefaultArgReturnsPromise(arg1: number, arg2: string, arg3: boolean = false): Promise<number> {
 return new Promise<number>((resolve, reject) => {
 // do something
 });
}

const functionWithDefaultArgHasCallBack = util.callbackify(functionWithDefaultArgReturnsPromise)

functionWithDefaultArgHasCallBack(1, 'two', true, (err: any, result: any) => {
 // do something

 // this callback function triggers error 
 //
 // "Expected 3 arguments, but got 4.(2554)"
 // 
 // in the v4.2.0-dev.20201119 (nightly at the time in the playground),
 // but not with 4.1.0-beta in the playground, but I do see it on 4.1.2 locally as well as the last release candidate.
});

Expected behavior:
No error, no red squiggly lines

Actual behavior:
Error "Expected 3 arguments, but got 4.(2554)" occurs with red squiggly underlines on the callbackified function.

Playground Link:
4.2.0-dev.20201119 - Error seen
https://www.typescriptlang.org/play?ts=4.2.0-dev.20201119#code/JYWwDg9gTgLgBAVxsANnAZlCI4HImq4DcAUCeggHYDGyElGVtw9A6sDABYAiApugEMEKGAEEoAcwBKvGAiiUAzgAUsIYIt4AKAZICMALjiUEIAEa8oAGji6JAJiOKYUYJQk27AZiNmIEFF4BBgBeDAEUTQBKI1VsDV4AHhNzSwA+OABvEjhcqFl5BkpeAHc4OPVNZNMLKDStLXzFAIA3Xht8gCteWii4EIzs3OG4AHpRuAATCDhmkFk3CRzcgF8o0hWyanpnRho6SnYuPkFhMUkACQFFAGEIlAAhAWoAa37EZBQAOmp7s2eXsB0ABPLQUfYsQ4cHj8IQicTSAoKFRqBJRMjg5hsaEnOHnCRXW73J6vLR6Gy4GAlCC4GwuBDtOBaSzWOBNM59AZZZZjCbTWbYWScRZkYbjOBcDRwX4oFD-V57LEMFzACQSSyKOA88baibDABEAFEAB5gHowXiTOBeWySUy8SgwRQ2MxIOASCDwAAsXy09gArP6vVF9bqtWKJm4JZxeHAWj77F8AAwAWkmvBaX3sSezejzAE4mZRVZwYChgbZ4FxY8h5lErGHXfBKJ64CVoXAfXpkymLDABC63QBJKYzTSxjhweidr7d+xwFAQGXlr4kNZEIA

4.1.2 - Error seen
https://www.typescriptlang.org/play?ts=4.1.2#code/JYWwDg9gTgLgBAVxsANnAZlCI4HImq4DcAUCeggHYDGyElGVtw9A6sDABYAiApugEMEKGAEEoAcwBKvGAiiUAzgAUsIYIt4AKAZICMALjiUEIAEa8oAGji6JAJiOKYUYJQk27AZiNmIEFF4BBgBeDAEUTQBKI1VsDV4AHhNzSwA+OABvEjhcqFl5BkpeAHc4OPVNZNMLKDStLXzFAIA3Xht8gCteWii4EIzs3OG4AHpRuAATCDhmkFk3CRzcgF8o0hWyanpnRho6SnYuPkFhMUkACQFFAGEIlAAhAWoAa37EZBQAOmp7s2eXsB0ABPLQUfYsQ4cHj8IQicTSAoKFRqBJRMjg5hsaEnOHnCRXW73J6vLR6Gy4GAlCC4GwuBDtOBaSzWOBNM59AZZZZjCbTWbYWScRZkYbjOBcDRwX4oFD-V57LEMFzACQSSyKOA88baibDABEAFEAB5gHowXiTOBeWySUy8SgwRQ2MxIOASCDwAAsXy09gArP6vVF9bqtWKJm4JZxeHAWj77F8AAwAWkmvBaX3sSezejzAE4mZRVZwYChgbZ4FxY8h5lErGHXfBKJ64CVoXAfXpkymLDABC63QBJKYzTSxjhweidr7d+xwFAQGXlr4kNZEIA

4.0.5 - Error not seen
https://www.typescriptlang.org/play?ts=4.0.5#code/JYWwDg9gTgLgBAVxsANnAZlCI4HImq4DcAUCeggHYDGyElGVtw9A6sDABYAiApugEMEKGAEEoAcwBKvGAiiUAzgAUsIYIt4AKAZICMALjiUEIAEa8oAGji6JAJiOKYUYJQk27AZiNmIEFF4BBgBeDAEUTQBKI1VsDV4AHhNzSwA+OABvEjhcqFl5BkpeAHc4OPVNZNMLKDStLXzFAIA3Xht8gCteWii4EIzs3OG4AHpRuAATCDhmkFk3CRzcgF8o0hWyanpnRho6SnYuPkFhMUkACQFFAGEIlAAhAWoAa37EZBQAOmp7s2eXsB0ABPLQUfYsQ4cHj8IQicTSAoKFRqBJRMjg5hsaEnOHnCRXW73J6vLR6Gy4GAlCC4GwuBDtOBaSzWOBNM59AZZZZjCbTWbYWScRZkYbjOBcDRwX4oFD-V57LEMFzACQSSyKOA88baibDABEAFEAB5gHowXiTOBeWySUy8SgwRQ2MxIOASCDwAAsXy09gArP6vVF9bqtWKJm4JZxeHAWj77F8AAwAWkmvBaX3sSezejzAE4mZRVZwYChgbZ4FxY8h5lErGHXfBKJ64CVoXAfXpkymLDABC63QBJKYzTSxjhweidr7d+xwFAQGXlr4kNZEIA

Related Issues:
No related issue found.

[orta]

Here's a compiler backed repro:

function functionWithDefaultArgReturnsPromise(arg1: number, arg2: string, arg3: boolean = false): Promise<number> {
 return new Promise<number>((resolve, reject) => {
 // do something
 });
}

const functionWithDefaultArgHasCallBack = callbackify(functionWithDefaultArgReturnsPromise)

functionWithDefaultArgHasCallBack(1, 'two', true, (err, result) => {
 // do something

 // this callback function triggers error 
 //
 // "Expected 3 arguments, but got 4.(2554)"
 // 
 // in the v4.2.0-dev.20201119 (nightly at the time in the playground),
 // but not with 4.1.0-beta in the playground, but I do see it on 4.1.2 locally as well as the last release candidate.
});

// C&P'd infra from node's types below

interface ErrnoException extends Error {
 errno?: number;
 code?: string;
 path?: string;
 syscall?: string;
 stack?: string;
}

function callbackify(fn: () => Promise<void>): (callback: (err: ErrnoException) => void) => void;
function callbackify<TResult>(fn: () => Promise<TResult>): (callback: (err: ErrnoException, result: TResult) => void) => void;
function callbackify<T1>(fn: (arg1: T1) => Promise<void>): (arg1: T1, callback: (err: ErrnoException) => void) => void;
function callbackify<T1, TResult>(fn: (arg1: T1) => Promise<TResult>): (arg1: T1, callback: (err: ErrnoException, result: TResult) => void) => void;
function callbackify<T1, T2>(fn: (arg1: T1, arg2: T2) => Promise<void>): (arg1: T1, arg2: T2, callback: (err: ErrnoException) => void) => void;
function callbackify<T1, T2, TResult>(fn: (arg1: T1, arg2: T2) => Promise<TResult>): (arg1: T1, arg2: T2, callback: (err: ErrnoException | null, result: TResult) => void) => void;
function callbackify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3) => Promise<void>): (arg1: T1, arg2: T2, arg3: T3, callback: (err: ErrnoException) => void) => void;
function callbackify<T1, T2, T3, TResult>(
 fn: (arg1: T1, arg2: T2, arg3: T3) => Promise<TResult>): (arg1: T1, arg2: T2, arg3: T3, callback: (err: ErrnoException | null, result: TResult) => void) => void;
function callbackify<T1, T2, T3, T4>(
 fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: ErrnoException) => void) => void;
function callbackify<T1, T2, T3, T4, TResult>(
 fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<TResult>): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: ErrnoException | null, result: TResult) => void) => void;
function callbackify<T1, T2, T3, T4, T5>(
 fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: ErrnoException) => void) => void;
function callbackify<T1, T2, T3, T4, T5, TResult>(
 fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<TResult>,
): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: ErrnoException | null, result: TResult) => void) => void;
// @ts-ignore
function callbackify<T1, T2, T3, T4, T5, T6>(
 fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, arg6: T6) => Promise<void>,
): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, arg6: T6, callback: (err: ErrnoException) => void) => void;
function callbackify<T1, T2, T3, T4, T5, T6, TResult>(
 fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, arg6: T6) => Promise<TResult>
): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, arg6: T6, callback: (err: ErrnoException | null, result: TResult) => void) => void {
 throw new Error("")
}

Workbench Repro

[typescript-bot]

👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in this issue running against the nightly TypeScript.

---

Comment by Orta Therox (@orta)

❌ Failed: -

• Expected 3 arguments, but got 4.
• Parameter 'err' implicitly has an 'any' type.
• Parameter 'result' implicitly has an 'any' type.

Historical Information

Comment by ben (@whoisbenli)

Version	Reproduction Outputs
4.1.2, Nightly	❌ Failed: - Expected 3 arguments, but got 4. Parameter 'err' implicitly has an 'any' type. Parameter 'result' implicitly has an 'any' type.
3.7.5, 3.8.2, 3.9.2, 4.0.2	👍 Compiled

[ahejlsberg]

This is an effect of #41308. With that PR we made our handling of optional parameters in overload ladders more consistent. For example:

declare function foo(cb: () => void): 0;
declare function foo(cb: (x: number) => void): 1;
declare function foo(cb: (x: number, y: number) => void): 2;

declare function f1(x: number): void;
declare function f2(x: number, y?: number): void;
declare function f3(x: number, y?: any): void;
declare function f4(x: number, y?: unknown): void;

let z1 = foo(f1); // 1
let z2 = foo(f2); // was 2 (pre-4.1), now 1
let z3 = foo(f3); // 1
let z4 = foo(f4); // 1

It has to do with some pretty strange behavior in the subtype relation which we use in the first pass of overload resolution. Previously we didn't consider (x: number, y?: number) => void to be a subtype of (x: number) => void, but strangely we did consider (x: number, y?: any) => void and (x: number, y?: unknown) => void to be a subtypes. We now consider all of them subtypes. It's definitely more consistent, but it ends up subtly changing which overloads we pick in overload ladders when the source has optional parameters.

To put it in context of the OP example above, pre-4.1 we report an error when the function signature is changed to

function functionWithDefaultArgReturnsPromise(arg1: number, arg2: string, arg3: unknown = false): Promise<number>;

i.e. if type unknown is used instead of boolean for the optional argument. That seems very inconsistent. In 4.1 we consistently pick the first overload that matches, which means we consider the optional argument to be omitted.

[ahejlsberg]

BTW, root cause of this issue is the same as #41563.

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.