TypeScript Version: 3.0.0-dev.20180712

Search Terms:

Code

// @checkJs: true
// @allowJs: true

// @filename: test.js

/** @type {<T>(param?: T) => T | undefined} */
function typed(param) {
    return param;
}
typed(1);

Expected behavior:

Either param doesn't get it's type from the @type tag or the type parameter T applies to the function.

Actual behavior:

Argument of type '1' is not assignable to parameter of type 'T | undefined'.

Playground Link: not possible

Related Issues: #25525