Regression, TS2304: @template-tag no longer works with @type-tag in JSDoc

[Teascade]

🔎 Search Terms

"TS2304", "Cannot find name 'T'."

🕗 Version & Regression Information

• This changed between versions 6.0.3 and 7.0.2
• This changed in commit or PR ??, could not get every-ts to work
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about generic types
• I was unable to test this on prior versions because I wasn't sure what to test on prior versions

⏯ Playground Link

https://www.typescriptlang.org/play/?filetype=js#code/PQKhCgAIUgBAXApgWwA4BsCGTIBUowICeqikA3gBQBuAXHgJSQC8AfHgL4HDgDGA9gDsAzvEgBLACYtINTOgCuiJm0jV5SgNxA

💻 Code

/**
 * @template T
 * @type {(v: T) => T}
 */
const id = (value) => value;

🙁 Actual behavior

On TypeScript 7.0, I get the error TS2304: Cannot find name 'T'.

🙂 Expected behavior

@template-tag should work as expected

Additional information about the issue

No response

[Andarist]

In TS 6 this leaks a type parameter:

/**
 * @template T
 * @type {(v: T) => T}
 */
const id = (value) => value;

// Argument of type 'number' is not assignable to parameter of type 'T'.
//   'T' could be instantiated with an arbitrary type which could be unrelated to 'number'.(2345)
const res = id(42)
//    ^? const res: T

So TS 6 didn't handle this properly at all and it shouldnt be used to claim a regression here. If anything, the TS 7 behavior is much better.

That said, it's a separate question if those 2 tags should be a valid combination or not.

[ahejlsberg]

This was a bug in TS6. The @template tag isn't supposed to affect a @type tag. The proper way to write the example is

/**
 * @type {<T>(v: T) => T}
 */
const id = (value) => value;