Assignable TemplateLiteral of Intersection Type of Primitive and {} to Primitive String

[horita-yuya]

Fixes #60990 (partially)

We can use a technique called branded types by defining a type as primitive & { brand: "branded" }.

This has the benefit of allowing you to handle the target primitive type more constrainedly. For example, with 1 & { brand: "branded" } type, it can only be used in a narrower context than the literal type 1.

The relationship between the types is:

1 & { brand: "branded" } < 1 < number

In other words, 1 & { brand: "branded" } can be assigned to a 1 type, and 1 can be assigned to a number type.

Wouldn't it be more natural to handle Template Literals similarly?

[horita-yuya]

@microsoft-github-policy-service agree