incorrect error message with iso assignment

[SeanTAllen]

Unless there's something about the Stead model that I don't understand, I believe that when we switched to the stead model we ended up with an incorrect error message for this code:

actor Main
  new create(env: Env) =>
    let a: String iso = recover iso "hello".clone() end
    let b: String iso = a

The current error is:

main.pony:4:23: right side must be a subtype of left side
    let b: String iso = a
                      ^
    Info:
    main.pony:3:12: String iso is not a subtype of String iso^: iso is not a subcap of iso^
        let a: String iso = recover iso "hello".clone() end
               ^
    main.pony:3:19: this would be possible if the subcap were more ephemeral. Perhaps you meant to consume a variable here
        let a: String iso = recover iso "hello".clone() end

The previous message was:

right side must be a subtype of left side
    let b: String iso = a
                      ^
    Info:
    <source>:3:12: String iso! is not a subtype of String iso: iso! is not a subcap of iso
        let a: String iso = recover iso "hello".clone() end
               ^
    <source>:3:19: this would be possible if the subcap were more ephemeral
        let a: String iso = recover iso "hello".clone() end
           

[SeanTAllen]

We discussed during sync and decided there is no correct answer here so we are leaving as is. And this might be a change in discussion that came from George's paper.