Conflicting definitions for Set constructor causes unexpected default generic in TS 3.5

TypeScript Version: 3.4.5 vs versions after 3.5

Search Terms: set constructor setconstructor unknown

Code

let s = new Set();

Expected behavior:

In TS 3.4: we expect the default chosen param to give us a Set<{}>.
In TS 3.5: we expect a Set<unknown>.
That change was an intended change in TS 3.5.

Or, if Set has a default generic arg, I expect the same default chosen in 3.4 and 3.5.

Actual behavior:

In TS 3.4, this actually was a Set<any>!

It appears there are multiple overloads of the Set constructor.

lib.es2015.collection.d.ts says:

    new <T = any>(values?: ReadonlyArray<T> | null): Set<T>;

while lib.es2105.iterable.d.ts says:

    new <T>(iterable?: Iterable<T> | null): Set<T>;

Note that one has T = any and the other doesn't.

So somehow TS 3.4 vs TS 3.5 decided to change whether to obey the any default, I think?

まず lib.es2015.collection.d.ts と lib.es2105.iterable.d.ts の Set コンストラクターのオーバーロードを比較し、次に TypeScript 3.4.5 と 3.5 で提供された new Set() の例を再現してください。対象となるバージョン全体で、コンストラクターの宣言とジェネリック推論が意図した動作と一致すれば完了です。