[exporectomy]

No matter how many new languages we invent, this problem of surprise sub-languages being parsed from strings never goes away. It's almost as if program code should be somehow impossible to confuse with user-visible text. Maybe there's no good solution though :(

[tialaramex]

The appropriate constraint is well known and exists in several languages. The magic format strings mustn't be variables. In Swift there's a type StaticString which matches literals like "This is some text" but is not used for any interpolated strings, or other arbitrary variable values.

Of course just because the constraint is known doesn't mean (as you illustrate) that everybody knows about it or makes use of it in their own programming.

[saagarjha]

This isn't an "appropriate constraint", because dynamically constructing format strings is a thing that normal programs can and do do. StaticString exists due to various limitations on the os_log APIs and it's somewhat amusing that you're trying to spin it into some sort of "known" fact that everyone should follow.