Apply uncalled function checks to ternaries

[ssalbdivad]

Search Terms

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.

[RyanCavanaugh]

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

[dragomirtitian]

@RyanCavanaugh Are you taking PRs on this one?

[DanielRosenwasser]

Yes

[DanielRosenwasser]

Just assigning @sandersn so that we can follow up on the PR for 3.9 sooner rather than later.