Conditional type is ignored and never appears when using never as a parameter of generic type

[whatasoda]

I love TypeScript, I appreciate that you provide us a great development experience.
But I found a strange behavior. I think it's a bug because I remember it worked correctly two years ago.

I want to use never as a type parameter that expects a union type of values of tuple-like array, in order to express that nothing is specified.
So I tried to use conditional type to handle never like:

type MyGeneric<T> = T extends never ? PlaceholderType : OtherTypeTransform<T>;

But it doesn't work correctly. If I set never to the parameter T, the result is always never, not PlaceholderType.

I understand I can use null or undefined instead. But actual values are stored in array and I don't want to use such values in the array. I mean, this issue happens when I assign [].

TypeScript Version: 3.9.2, (also 3.8.3)

Search Terms:

I tried searching whether a similar issue has already raised with these keywords is:issue never type parameter "extends never" conditional "<never>" .

Code

type MyManual0 = never extends never ? true : false; // true 👍
type MyManual1 = unknown extends never ? true : false; // false 👍

type MyGeneric<T> = T extends never ? true : false;

type MyType0 = MyGeneric<never>; // never 🤔
type MyType1 = MyGeneric<unknown>; // false 👍
type MyType2 = MyGeneric<any>; // boolean 👍

Expected behavior:

MyType0 becomes true as well as MyManual0

Actual behavior:

MyType0 becomes never

Playground Link:
https://www.typescriptlang.org/play?#code/C4TwDgpgBAsiMEMB2BXBAbADFAvFJEAbhAE5QQAewESAJgM75GlQD8UwJK0AXFAGYZ6EANxQA9OI5dogXg3AsjsAoUJFjxkadAEZcUFEgDWSAPYB3JOSo0GTYmXaduUPoPTCxkgULlLl4aHAA4jSkAJYAxgA8ACoAfLrRltR0jAR2bNJOLt4iin6qcNH+2HhBISQRkWmksR5S1WSAfBuAKLv5ASBFkDqlIMEEFVH6RmZItRJSrsJQCm1qnRAATLpl-ZXIIGOeAEbGxugQyNPyQA
Related Issues:

[jack-williams]

This is working correctly, but does cause some confusion. It is covered in the FAQ here:

Common bugs that aren't bugs.

The FAQ links through to issue #31751.

[whatasoda]

Sorry, I didn't read the page. 🙇‍♂️ I'll be careful about it in next time.💪

I understand the reason. I agree that it should be resolved to never. 🙂
Also, it seems that the issue you linked helps me to solve my problem.
Thank you so much!