JSDOC generics bug for callbacks when args are present

🔎 Search Terms

"Generics", "JSDOC", "Callback"

🕗 Version & Regression Information

TS 5.7.3
v5.8.0-dev.20250131

⏯ Playground Link

https://www.typescriptlang.org/play/?filetype=js#code/PQKgUGBSDKAiDyBhABAcwKYDt0CcCWAxgM7IBGArqsgGYD2OyBAhgDYulMEDWJA7gBZZkTHKhIj0yAA450RLABcIASUzIFgmrTa1eeTFXQAPJgFspLdABpkAAwAm6avvQAKAJS3kRfrXIt7ZFkFchw1WwA1RAAeaAA+WxsKBWQBIRFUMFtmNg5uL34mcVESPBT7WjlkTFoU2SJtADdJW2gvJkxA4NDMEkiYjoBPBIA6CBBgCFBwZBBkAAEFdHMWJiXkaDBZhakRM2QAb1cMgAYALkPkWlJ5HGacC4BReGQAX3dkAF44jdfGVnYnC4yC2c3muxw+wO8CkCjwtF6fwA2rRYfDegBdEHbebdMIkA5RWJxV6gyagUELBSDKSSA7IYmuaiYC7HUTnS7XW73J7wADcbw+3w2NlRcIRRAA-BcYeLekKfkT4m8yWBqORMAQ5chHM5sK4coDuKK0RKPgctsgrQQJSl6ZgzJI-p8rqbeshJZLDqSrdbbVcbrh7l9quheMhnh5LX7eikiAo1pIXYa8lxXPSuUHcILo0F0CEwqHw1FXPHE+4wKSwNNKYtlhZExtVQRVkQSFFDrnplSaXToH8Jrmy0suyAZr6cRCof3vAn1rnZpMJzbYzhyFr6KW5+hzQvfRo8EQRsOk7PE7nSVXu4te7rDvbHdLZ-gDG8-rL0SRB2AW0USM9vSmYBkAAQVEOwUyBLw9A0YQSmQABaZAYAQFAKjkTAAHI6jkJpJGgMZgGAlCkGXf1GgARguIkhjiatgIAFWgCdfRXeNkEo6iYlIWhtHQDo6LYlJKJDXUXFcNlUBOBV1DXaxLgdUx0AuTDdSYfwFEwnN6NA8DsgBVNoLKXxyBSDISCQki0MqEh6jwjZCOIuBSNY8iACYuOiHi+IEnSmJYmN2MaDzkCJbzLF8oSOLc0SnHEjwvh+BQ5JsB8lJUtSNK094wCAA

💻 Code

In the following example, define() should return VC<S>, but when arg callback has args it does not resolve S and returns VC<any>.

/**
 * @template S
 * @param {(arg0: { observer: EO }) => S} callback 
 * @param {Options} [options] 
 * @returns {VC<S>}
 */
/*
 * @type { <S>(fn: (arg0: { observer: EO; }) => S, options?: Options) => VC<S> }
 */
function define(callback, options) {
    const { name } = options ?? {}
    const observer = new EO()
    const state = callback({ observer })
    return new VC(state)
}

/**
 * @template S
 */
class VC {
    /** @type {S} */
    state
    /**
     * @param {S} state 
     */
    constructor(state) {
        this.state = state
    }
}

/** @typedef {{ name?: string }} Options */

class EO {}

// Arg `callback` with args - JSDOC doesn't resolve S.
// JSDOC    const v1: VC<any>
// TS       const v1: VC<boolean>
const v1 = define((arg0) => true, { name: 'default' })

// Arg `callback` without args - JSDOC does resolve S.
// JSDOC    const v2: VC<boolean>
// TS       const v2: VC<boolean>
const v2 = define(() => true, { name: 'default' })

🙁 Actual behavior

JSDOC doesn't resolve S

🙂 Expected behavior

JSDOC should resolve S in the same way as TS.

Additional information about the issue

No response

Start with the linked TypeScript Playground repro and compare the inferred types of v1 and v2 with the expected TypeScript results. Trace the JSDoc generic callback inference path in the compiler, then add a regression test showing that v1 is inferred as VC when the callback has an argument.