LYR-SEM0139

a 'try' mark over nothing that can throw

warning · spec 06-errors · lint useless-try, group style, warn unless said

A 'try' mark, a 'try?' or 'try!', a 'try' block or a marked loop covers no call that can throw, or marks what an enclosing or earlier mark covers already.

Explanation

A mark says that a call may fail here. Where nothing under it can throw — or a try? inside takes every error first — the mark is wrong, and a try block's catch clauses can never run. A second mark under the first adds nothing. Over a call the compiler refused there is no such warning: what it throws is known once the error is fixed.

Remove the mark; if a call was expected to throw, check that the right function is called.

Wrong

fn safe(): int { return 1; }

fn main(): void {
    let _ = try? safe();
}

Right

fn safe(): int { return 1; }

fn main(): void {
    let _ = safe();
}