Description

David Blass (ssalbdivad)

opened on Jan 7, 2020

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ts2774 ternary condition error function called uncalled

Suggestion

TS2774 (implemented in #32802), i.e. the "This condition will always return true since the function is always defined. Did you mean to call it instead?" error, provides a helpful hint for developers referencing a function in an if statement without calling it. However, the same check doesn't apply to ternaries, which is missing an opportunity to save some debug time and counterintuitive for devs who know about TS2774. I propose reusing TS2774 for developers who forget to call a function in a ternary.

Examples

Now:

const isString = (value: unknown) => typeof value === "string"

// Error (TS2774)
if (isString) {
}
// No error
isString ? true : false

If this suggestion is adopted:

const isString = (value: unknown) => typeof value === "string"

// Error (TS2774)
if (isString) {
}
// Error(TS2774)
isString ? true : false

Checklist

My suggestion meets these guidelines:

• [✔️] This wouldn't be a breaking change in existing TypeScript/JavaScript code
• [✔️] This wouldn't change the runtime behavior of existing JavaScript code
• [✔️] This could be implemented without emitting different JS based on the types of the expressions
• [✔️] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• [✔️] This feature would agree with the rest of TypeScript's Design Goals.

Reacted by SlurpTheo, Diego Stratta and Karol Majewski

Activity

1. Ryan Cavanaugh (RyanCavanaugh)

   added

   Experience EnhancementNoncontroversial enhancementsNoncontroversial enhancements

   SuggestionAn idea for TypeScriptAn idea for TypeScript

   on Jan 7, 2020
2. RyanCavanaugh commented on Jan 7, 2020

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Jan 7, 2020

   Member

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   Seems reasonable; we'd have to assess for breakage but I suspect this would turn out well

   Reacted by David Blass, Christopher Kiss and Titian Cernicova-Dragomir
3. dragomirtitian commented on Jan 21, 2020

   

   Titian Cernicova-Dragomir (dragomirtitian)

   on Jan 21, 2020

   Contributor

   More actions

   Ryan Cavanaugh (@RyanCavanaugh) Are you taking PRs on this one?

   Reacted by Daniel Rosenwasser
4. Daniel Rosenwasser (DanielRosenwasser)

   changed the title [-]Apply TS2774 to ternaries[/-] [+]Apply uncalled function checks to ternaries[/+] on Jan 21, 2020
5. Daniel Rosenwasser (DanielRosenwasser)

   added

   Effort: ModerateRequires experience with the TypeScript codebase, but feasible. Harder than "Effort: Casual".Requires experience with the TypeScript codebase, but feasible. Harder than "Effort: Casual".

   help wanted

   on Jan 21, 2020
6. DanielRosenwasser commented on Jan 21, 2020

   

   Daniel Rosenwasser (DanielRosenwasser)

   on Jan 21, 2020

   Member

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   Yes

   Reacted by Titian Cernicova-Dragomir and David Blass
7. Daniel Rosenwasser (DanielRosenwasser)

   added this to the Backlog milestone on Jan 21, 2020
8. Daniel Rosenwasser (DanielRosenwasser)

   added

   Experimentation NeededSomeone needs to try this out to see what happensSomeone needs to try this out to see what happens

   on Jan 21, 2020
9. Daniel Rosenwasser (DanielRosenwasser)

   modified the milestones: Backlog, TypeScript 3.9.0 on Jan 28, 2020
10. Daniel Rosenwasser (DanielRosenwasser)

    assigned

    Nathan Shively-Sanders (sandersn)

    on Jan 28, 2020
11. DanielRosenwasser commented on Jan 28, 2020

    

    Daniel Rosenwasser (DanielRosenwasser)

    on Jan 28, 2020

    Member

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    Just assigning Nathan Shively-Sanders (@sandersn) so that we can follow up on the PR for 3.9 sooner rather than later.
12. Daniel Rosenwasser (DanielRosenwasser)

    added

    Breaking ChangeWould introduce errors in existing codeWould introduce errors in existing code

    on Feb 20, 2020
13. Nathan Shively-Sanders (sandersn)

    closed this as completedin #36402on Feb 20, 2020
14. Daniel Rosenwasser (DanielRosenwasser)

    added

    Update Docs on Next ReleaseIndicates that this PR affects docsIndicates that this PR affects docs

    and removed

    Experience EnhancementNoncontroversial enhancementsNoncontroversial enhancements

    Experimentation NeededSomeone needs to try this out to see what happensSomeone needs to try this out to see what happens

    on Feb 20, 2020
15. DanielRosenwasser commented on Feb 20, 2020

    

    Daniel Rosenwasser (DanielRosenwasser)

    on Feb 20, 2020

    Member

    More actions

    Thanks Oleksandr Tarasiuk (@a-tarasyuk)!

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