Structural equality on JavaScript backend doesn't work

[Jiří Beneš]

The structural equality on the JavaScript backend seems to be broken.
Although reflexivity (x == x) holds for simple, user-defined types, it doesn't work for Some(x) == Some(x).

type MyType {
  MySingleCase()
}

record EmptyRecord()

def main() = {
  println(MySingleCase() == MySingleCase())   // ~> true
  println(EmptyRecord() == EmptyRecord())     // ~> true

  println(Some(MySingleCase()) == Some(MySingleCase())) // ~> false
  println(Some(EmptyRecord()) == Some(EmptyRecord()))   // ~> false
}

[Jiří Beneš]

effekt/effekt/shared/src/main/scala/effekt/generator/js/Transformer.scala

Lines 52 to 62 in a702e93

 val other = freshName("other") 
 def otherGet(field: JSName): js.Expr = js.Member(js.Variable(other), field) 
 def compare(field: JSName): js.Expr = js"${get(field)} !== ${otherGet(field)}" 
 val noop    = js.Block(Nil) 
 val abort   = js.Return(js"false") 
 val succeed = js.Return(js"true") 
 val otherExists   = js.If(js"!${js.Variable(other)}", abort, noop) 
 val compareTags   = js.If(compare(`tag`), abort, noop) 
 val compareFields = params.map(f => js.If(compare(f), abort, noop)) 
  
 val jsEquals: js.Function = js.Function(`equals`, List(other), otherExists :: compareTags :: compareFields ::: List(succeed)) 

Line 54 is not correct, we should use equals$impl or something similar here in order to recurse.
Currently, we compare:

1. the first "layer" structurally
2. the other layer just based on JavaScript's === equality

[Jiří Beneš]

One should call this:

effekt/libraries/js/effekt_builtins.js

Line 13 in 3e38409

 $effekt.equals = function(obj1, obj2) {