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Cannot define a matching template literal type to a defined template literal #43143
Description
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!
Activity
[-]Cannot define a matching template literal type to a template literal in a function declaration[/-][+]Cannot define a matching template literal type to a defined template literal [/+]EdwardDrapkin commentedon Mar 8, 2021
It appears to happen in any case where there's a literal type, even the most trivial case fails:
RyanCavanaugh commentedon Mar 8, 2021
as constshouldn't be needed hereahejlsberg commentedon Mar 24, 2021
We currently only produce template literal types from template literal expressions in
as constcontexts. 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.