Difference of Type and Interface in constraint behavior.

[val-o]

Bug Report

Generics with type arguments under mapped type constraint (e.g. Record<string, string>) differ when closing the type argument with type declared with type keyword and interface.

Suppose I have a generic type with mapped type constraint:
type A<T extends Record<string, string>> = never;

And I have two types with the same shape

type PersonT = {
    name: string;
}

interface PersonI {
    name: string;
}

But when I try to close type A with PersonI I am getting an error 2345, which I didn't get using PersonT. This may potentially lead to bugs (because there is no check for property existence), because T extends Record<string, any> is a popular pattern, which is used when people who don't know the object keyword try to make an object constraint.

🔎 Search Terms

generic constraint, record constraint

⏯ Playground Link

Playground link with relevant code

💻 Code

🙁 Actual behavior

TS let me pass type created by type keword

🙂 Expected behavior

Same behaviors as interface

[MartinJohns]

Duplicate of #42825. Used search terms: interface extends record unknown

[val-o]

@MartinJohns thanks! closing