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Detect uncalled functions that appear in void expressions #47699
Description
Suggestion
🔍 Search Terms
- uncalled function
- check
- statement
⭐ Suggestion
Today TS can detect uncalled functions that appear in conditionals. I propose also extending this to detect uncalled functions that appear an an expression where the result is unused
📃 Motivating Example
export interface Foo {
doImportantStuff(): void;
}
declare const foo: Foo;
if (foo.doImportantStuff) { // This one is detected
...
}
[foo].forEach(x => foo.doImportantStuff); // Mistake here. The user forgot to call `doImportantStuff`💻 Use Cases
This was inspired by a real world bug in the VS Code codebase. The case with forEach shows the problem we ran into
Off the top of my head, I don't think there would be false positives but may need some more thought to make sure
Activity
RyanCavanaugh commentedon Feb 2, 2022
This specific example isn't detectable in practice. We have a function
isSideEffectFreethat we used in other positions like the comma-sequence operator. It explicitly doesn't considera.bside-effect free because JS getters can and do have side effects, and we don't know from the declaration ofFoothatdoImportantStuffisn't a getter.fatcerberus commentedon Feb 2, 2022
It still does seem a bit inconsistent that
if (a.b) {}is detected as a "forgot-to-call" error, while the similar construction
[ a ].forEach(a => a.b)isn't.
mjbvz commentedon Feb 2, 2022
Yes getters make this difficult to reason about. Just as a code example of the problem:
Famous last words, but the above does seem uncommon though. Would be interesting to see how often it appears in real world code