Assignment to something that is not a place

Built from the repository at commit a8614dc.

The left side of = or of a compound assignment such as += must be a variable, a field, or an element of an array.

Why

An assignment stores a value in a place. A sum or a call result is a value without a place, so nothing can hold what you assign to it.

Broken

fn main() {
    let mut x = 1
    x + 1 = 3
    print(x)
}

What sisu says

error[E0021]: cannot assign to this expression
 --> E0021.sisu:3:5
  |
3 |     x + 1 = 3
  |     ^^^^^

sisu: 1 error
sisu: for more on a code, run `sisu explain <code>`: E0021

Fixed

fn main() {
    let mut x = 1
    x = 3
    print(x)
}