Inconsistent intersections of string literal types and pattern string mapping types

[ahejlsberg]

🔎 Search Terms

Literal type, string mapping type, intersection

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?#code/C4TwDgpgBAYg9nKBeKBvKYBOcwC4oDOwmAlgHYDmUAvgNwBQ9okUAKgAzKwIDaARFhx8AurShQA9BKgB5ANZNw0VgEYu8OP0Fg+UAGRQABmAAkqIqUrUwh0eKmyFzZQCZ1vAdh36jp1ABk4AHcITABjAEMCCAAeC3IKAD5rWzFJaXlFFlYAZndNTyEfQJDwqNj4ykS7dKgAUUxsTAAaKCCI4AB+eiA

💻 Code

type Foo = { prop: string };

type T0 = Foo["prop"]; // string
type T1 = Foo["prop" & `p${string}p`]; // string
type T2 = Foo["prop" & `p${Lowercase<string>}p`]; // string
type T3 = Foo["prop" & Lowercase<string>]; // Error, wat?

🙁 Actual behavior

Error.

🙂 Expected behavior

No error.

Additional information about the issue

See here.