A[] form works, but Array<A> breaks

Bug Report

🔎 Search Terms

site:github.com inurl:/microsoft/TypeScript/issues/ Array [] normalization syntactic sugar

🕗 Version & Regression Information

This works in 3.9.7, broke in 4.0.5, and remains broken in Nightly.

• This changed between versions 3.9.7 and 4.0.5

⏯ Playground Link

Playground link with relevant code

💻 Code

type R<C> = [C, ...R<C>[]] | number;      // works, as expected
type S<C> = [C, ...Array<S<C>>] | number; // fails unexpectedly - should work identically

const r: R<"add"> = ["add", 2, 1];
const s: S<"add"> = ["add", 2, 1];

🙁 Actual behavior

The A[] form in the first line works, but the otherwise-identical Array<…> form on the second line breaks with the warning Type alias 'S' circularly references itself.(2456).

🙂 Expected behavior

Both of these should work, and behave identically, as they are merely syntactic sugar for each other.

リンクされたPlaygroundの例と最小限のRおよびS型エイリアスから始め、TypeScript 3.9.7、4.0.5、Nightlyの間で挙動を比較します。循環型エイリアスのチェックと、Array と T[] の扱いを追跡します。両方の等価な再帰エイリアスが循環参照の診断なしにコンパイルできれば完了です。