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

@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.

@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

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

@sandersn
@DanielRosenwasser is it decided if this issue needs to be resolved?

I am doing open-source for this week and would like to help resolve good-first-issue/GraceHopperOSD's issues

@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.

@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 🙂