Labeled argument in a call

Built from the repository at commit a8614dc.

Only a constructor takes labels on its arguments: Point(x: 1). A function call, a method call and print take plain arguments in parameter order. A variant takes labels only when it declares them, Shape.Rect(w: 2, h: 3); a variant that declares none, Expr.Num(2), takes plain arguments too.

Why

Labels on the arguments of function calls are planned. Until they arrive, a label there is reported, not ignored, so a program does not rely on a meaning that has not arrived. On a variant, the labels say which payload field each argument fills, so a variant without them has nothing to match a label against. The fix there removes the labels, but as an unsafe fix: a label may name the field you meant to declare.

Broken

fn double(n: i64) -> i64 {
    n * 2
}

fn main() {
    print(double(n: 2))
}

What sisu says

error[E0055]: this call takes no labels on its arguments
 --> E0055.sisu:6:18
  |
6 |     print(double(n: 2))
  |                  ^
  |
  = help: remove the labels: only a constructor, or a variant that declares labels, takes labeled arguments

sisu: 1 error
sisu: for more on a code, run `sisu explain <code>`: E0055

Fixed

fn double(n: i64) -> i64 {
    n * 2
}

fn main() {
    print(double(2))
}