Uncalled Function Checks don't check negative condition #34815

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1. Ryan Cavanaugh (RyanCavanaugh)

   added

   Awaiting More FeedbackThis means we'd like to hear from more people who would be helped by this featureThis means we'd like to hear from more people who would be helped by this feature

   SuggestionAn idea for TypeScriptAn idea for TypeScript

   on Oct 30, 2019
2. brandon-leapyear commented on Feb 17, 2021

   

   Brandon Chinn (brandon-leapyear)

   on Feb 17, 2021

   Last edited by brandon-leapyear

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   ✨ This is an old work account. Please reference Brandon Chinn (@brandonchinn178) for all future communication ✨

   ---

   Very much agree with this. In our code, we just got bit by

   if (!nock.isActive) {
     nock.activate()
   }

   In general, I would usually not intentionally want !foo, and if I did want to do something like that, I would do foo === undefined. Even more generally, I would personally disallow coercion from function to boolean completely. Forcing devs to write foo === undefined would make it clear what their intention is, and would force the dev to type foo as Function | undefined, if that's truly what they want.
3. AlexMarkUSDS commented on Jan 21, 2024

   

   Alex Mark (AlexMarkUSDS)

   on Jan 21, 2024

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   This bit me last week in one of the codebases I maintain. I also see that it's bitten a number of others:
   There's relevant info in:

   • Uncalled function checks don't work with negation #43096, which is a duplicate issue
   • TS: no longer seeing an error when not calling function in check vscode#91144
   • One attempted fix at Uncalled function checks don't work with negation #43097, which was almost accepted.

   Daniel Rosenwasser (@DanielRosenwasser), would the TS team accept a contribution for this? I've optimistically opened a PR at #57114
4. RyanCavanaugh commented on Jan 23, 2024

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Jan 23, 2024

   Last edited by RyanCavanaugh

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   There are many, many false positives turned up in that PR. Unless these were ~all good finds, I think this is appropriately left still in "awaiting more feedback" state
5. AlexMarkUSDS commented on Jan 24, 2024

   

   Alex Mark (AlexMarkUSDS)

   on Jan 24, 2024

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   The tool for finding false positives is super neat. It makes sense to me to not merge this -- I followed ~20 links and I think this was the only legitimate bug I found (it should have an await). The rest were all just undefined checks on things that the typings say should always be defined.

   I'm happy to close out that PR (or have you close it). Whatever works for you.