E3020

Unexpected = in struct expression. The correct syntax for struct expression is { field: expression }.

Erroneous example

struct S {
  a : Int
  b : Int
}

fn main {
  let s : S = { a : 1, b : 2 }
  let ss = { ..s, a = 1 } // Error: Unexpected `=` in struct expression.
  ignore(ss)
}

Suggestion

Change the struct expression to use the correct syntax:

struct S {
  a : Int
  b : Int
}

fn main {
  let s : S = { a : 1, b : 2 }
  let ss = { ..s, a : 1 }
  ignore(ss)
}