Uncalled function checks only works with single conditional

TypeScript Version: 3.8.0-dev.20191207

Search Terms:

Code
With strict null checks enabled:

import * as fs from 'fs';

fs.stat('/path/to/file', function(err, stats) {
    if (stats.isFile || stats.isDirectory) {

    }
});

Expected behavior:
Accesses to isFile and isDirectory are reported as errors since these are actually functions

Actual behavior:
No errors.

Errors are only reported when there is a single conditional

Playground Link:

Related Issues:

This is the intended scoping of the check to reduce over-reported errors.

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) I can definitely appreciate the reduction in over-reported errors but do you think not having any error at all seems to defeat the purpose? Could there be a way to mention it once for a particular block of code?

We don't have "Just so you know" warnings and don't intend to add them

I think I may be miscommunicating the scenario or misunderstanding your perspective. I'm hoping to receive the error for the one instance even if there are other conditionals.

For example here we accidentally don't call isDirectory as a function while having some other conditional with it.

import * as fs from 'fs';

fs.stat('/path/to/file', function(err, stats) {
    if (stats.isDirectory && !err) {

    }
});

At the moment if we were to do this the error around stats.isDirectory is not reported at all but if we remove the !err conditional it will report as expected.

Do you think it should still be reported in this scenario?

This is the intended scoping of the check to reduce over-reported errors.

I may have missed any checks for whether this comes up in conditionals, &&, and || - did we see too many problems on those? My hunch is that that'd be nothing but goodness.

We can try expanding the set of things checked and see what comes up.

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

Daniel Rosenwasser (@DanielRosenwasser)

Daniel Rosenwasser (@DanielRosenwasser) How deep do we want to go here? Any sort of arbitrary expression with boolean operators should be ok ? I think the interesting bit is when the condition both checks and uses the function:

interface StatsBase<T> {
    isDirectory(): boolean;
    time: number
}

function A(err: any, stats: StatsBase<any>) {
    if (stats.isDirectory || stats.isDirectory()) { // should be error ?
        
    }
}

function B(err: any, stats: StatsBase<any>) {
    if (stats.isDirectory && stats.isDirectory()) { // should be ok 
    }
}


function C(err: any, stats: StatsBase<any>) {
    if (!stats.isDirectory || stats.isDirectory()) { // should be ok 
    }
}

Playground Link

mshivaku99

Can mshivaku99 and I work on this (we have a class assignment to help fix a bug in an open-source project)

@mykolao-wix yep anything in a milestone (such as Backlog) has been accepted. In this case, Experimentation Needed+Suggestion means that the proposed solution might not be workable, but we want to find out by looking at a real implementation.

Nathan Shively-Sanders (@sandersn)

Nathan Shively-Sanders (@sandersn) is there anyone I can contact to ask src/compiler/checker.ts API questions?

We had a variant of this come up at Google in code like

if (!foo.hasBar) {  // oops, forgot to call the function
  ...
} else {
  // assume foo.hasBar is true
}

I think the broader fix might be something around "expression is always true" when you do a boolean check on a non-optional method.

Playground repro

declare function isFoo(): boolean;

if (isFoo) {
    // expected error, got error
}
if (!isFoo) {
    // expected error, got no error
}

Just opened a pull request (#42835) that attempts to address the two problems mentioned in this thread. Feel free to check it out 🙂

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Uncalled function checks only works with single conditional #35584

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Uncalled function checks only works with single conditional #35584

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RyanCavanaugh commented on Dec 9, 2019

clarkio commented on Dec 9, 2019

RyanCavanaugh commented on Dec 9, 2019

clarkio commented on Dec 9, 2019

DanielRosenwasser commented on Dec 10, 2019

RyanCavanaugh commented on Dec 10, 2019

typescript-bot commented on Dec 13, 2019

dragomirtitian commented on Dec 26, 2019

nityatammana commented on Apr 2, 2020

sandersn commented on Oct 5, 2020

mkloouo commented on Oct 6, 2020

evmar commented on Jan 28, 2021

jonhue commented on Feb 17, 2021

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