NoInfer doesn't work in string template types

🔎 Search Terms

NoInfer string template

🕗 Version & Regression Information

This issue exists in every Playground-accessible version that has NoInfer.

⏯ Playground Link

here

💻 Code

function f<A>(a: NoInfer<A>, b: A extends string ? `rel:${A}` : never) {}
f("5", "rel:7"); // error - correct, type of A is "7"

but

function g<A>(a: A, b: A extends string ? `rel:${NoInfer<A>}` : never) {}
g("5", "rel:7"); // no error - surprising - type of A is inferred to be ("5" | "7")

🙁 Actual behavior

no type error on g() above, because the A type is being inferred via the string template in spite of the NoInfer marker.

🙂 Expected behavior

Both of the example calls should be recognized as wrong?

Additional information about the issue

Also tried

function g<A>(a: A, b: A extends string ? NoInfer<`rel:${A}`> : never) {}
function g<A>(a: A, b: NoInfer<A extends string ? `rel:${A}` : never>) {}

no luck.

Start by reproducing the two generic-call examples in the linked TypeScript Playground and compare how NoInfer behaves in the parameter and string-template forms. Trace the type inference behavior for NoInfer inside template literal types; done means the g("5", "rel:7") call is rejected as expected, with coverage for the shown variants.