Region requires a name

Meaning

Every region block requires an identifier so reports and placement constraints can refer to it.

The name also provides a stable local label in AIF explanations. It does not create a source namespace.

Why it happens

The code used region { ... } as though the name were optional, perhaps following a proposal or another arena language.

Invalid code

fn main() -> Int {
    region { let value = 1 }
    return 0
}

Correct code

fn main() -> Int {
    region work { let value = 1 }
    return 0
}

Common fixes

Add a unique descriptive name immediately after region.

If a byte assertion is needed, place pin(N) after the name: region request pin(4096) { ... }. Region syntax and budget semantics are experimental, so keep compiler-version-sensitive tests.