Cannot define a matching template literal type to a defined template literal

[EdwardDrapkin]

Bug Report

🔎 Search Terms

string, template, literal, type

🕗 Version & Regression Information

This is the behavior in every version I tried, including Nightly

⏯ Playground Link

Playground link with relevant code

💻 Code

function getCardTitle(title: string): `test-${string}` {
    return `test-${title}`;
}

🙁 Actual behavior

TS infers the type string for the returned string, instead of the templated type.

🙂 Expected behavior

No error!

[EdwardDrapkin]

It appears to happen in any case where there's a literal type, even the most trivial case fails:

const aString: `a${string}` = `a${'string'}`;

[RyanCavanaugh]

as const shouldn't be needed here

[ahejlsberg]

We currently only produce template literal types from template literal expressions in as const contexts. We tried template literal types for all template literal expressions in #41891, but reverted it because it was too breaky. However, a happy medium would be to give template literal types to expressions that are contextually typed by string-like types. I can't imagine that breaking anything and it would solve this and other related issues.