[DrMeepster]

This can never happen with regular string literals. String literals have the type `&'static str` but formatting returns a `String`.

[pornel]

Perhaps something could be done with compile-time code execution, but the bigger problem is that it wouldn't be backwards-compatible. Currently "{foo}" is a perfectly valid string that doesn't evaluate anything.

[hajile]

In truth, it probably requires something like `f"foo {bar}"`