microsoft / microsoft/TypeScript
JSDoc recursive inference not working properly on generic array wrapping
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Description
🔎 Search Terms
"jsdoc", "recursive", "inference", "generic"
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about everything.
⏯ Playground Link
💻 Code
JS with JSDoc typing:
/**
* @template [T = any]
*/
class S {
/**
* @type {Set<T>}
*/
set;
/**
* @param {Set<T>} set
*/
constructor(set) {
this.set = set;
}
array() {
return new S(new Set([...this.set].map(item => [item]))); // returns S<T[][]> but expected S<T[]> !!!
}
}
/**
* @template [T = any]
* @param {Set<T>} set
*/
function sArray(set) {
return new S(new Set([...set].map(item => [item]))); // returns S<T[]> as expected
};
TS version:
class S<T> {
set: Set<T>;
constructor(set: Set<T>) {
this.set = set;
}
array() {
return new S(new Set([...this.set].map(item => [item]))); // returns S<T[]> as expected
}
}
function sArray<T>(set: Set<T>) {
return new S(new Set([...set].map(item => [item]))); // returns S<T[]> as expected
};
🙁 Actual behavior
In JSDoc types when a class with generic type T has a method that returns an instance of the same class but with the generic T[] it's return type will be inferred as T[][]. The same code written in plain TS will return the expected result.
🙂 Expected behavior
It's expected that the JSDoc version of the code has the same output as the TS version for the method that returns an instance of the class with generic wrapped in T[].
Additional information about the issue
No response
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the linked TypeScript Playground reproductions and compare the JSDoc and plain TypeScript versions of class S.array. Investigate generic inference for JSDoc-typed class methods returning a new instance, then verify that the JSDoc method infers S<T[]> rather than S<T[][]> while preserving the existing TypeScript behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript, typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100