Type signature overload is ignored in a place where it makes better sense.

[ackvf]

TypeScript Version: 3.4.0-dev.20190312

Search Terms:
ambient declaration overload

Preface:
I've been using these inline console.debug(val) || val statements for ages, but since recently, void cannot be tested for truthiness. My workaround for typescript projects is to include this in my src/index.tsx file, which works great

declare global {
  interface Console {
    debug(message?: any, ...optionalParams: any[]): false;
  }
}

Enough said, my problem is that this technique does not work in javascript projects.

Code:

// src/global.d.ts

interface Console {
  abc(message?: any, ...optionalParams: any[]): false;
  debug(message?: any, ...optionalParams: any[]): false;
}

// later in src/**/SomeComponent.jsx

[1,2].map((v, ix) => console.debug('v', ix, v) || v) // void cannot be tested for truthiness
[1,2].map((v, ix) => console.abc('v', ix, v) || v) // no error

Expected behavior:
Expected is that the overload that returns false when used in place that test for truthiness is used.
When tested with console.abc, as per the interface, it is correctly picked up as returning false.

Actual behavior:

error: An expression of type 'void' cannot be tested for truthiness ts(1345)

Interestingly, after I have switched to ts@next and thus restarted the TS server, it first picks up my ambient declaration, so the code passes, but then it loads the @types\node\globals.d.ts

[j-oliveras]

Duplicate of #28248 and #26262.

As a workaround, use comma operator:

[1,2].map((v, ix) => (console.debug('v', ix, v), v))
[1,2].map((v, ix) => (console.abc('v', ix, v), v))

[ackvf]

@j-oliveras @DanielRosenwasser
Actually no, I am not upset about void not being tested for truthiness. I am upset about my overload not being applied in a place where the application surroundings require it. If my understanding of overloads is wrong, then I am sorry and I'll be happy to close this issue, but in that case an explanation would be helpful. Thanks in advance.

As you can see, I have seen and commented on that issue that you linked to this one as duplicate:
#26262 (comment) My issue is different.

[typescript-bot]

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

[ackvf]

Wait @typescript-bot why u do dis?!
This issue isn't a duplicate and I have made a recent activity to express that.

[ackvf]

@RyanCavanaugh I believe your bot is malfunctioning, please help!

[RyanCavanaugh]

@ackvf this is a question about how to get your JS file configured to see the global declaration file. I'd recommend StackOverflow as a good support point. Thanks!

[ackvf]

@RyanCavanaugh It does see the global declaration file as demonstrated in the gif, but it chose a different overload even though that overload results in an error.

[RyanCavanaugh]

Overload resolution doesn't work by iterating each overload to see which makes your entire program not-an-error. The first matching overload is chosen; the return type isn't even part of this process.

[ackvf]

Call signature is already considered, but if two return types share one call signature, maybe it should also consider a return type and the surrounding?
Or do you have another advice to force a particular overload or something else to make the compiler not complain?