borrow sealing doesn't work for borrows within objects

[alaviss]

Example

{.experimental: "views".}
type
  Mint = object
    data: int

  Option = object
    value: lent Mint

proc `=copy`(dst: var Mint, src: Mint) {.error.}

proc some(x: Mint): Option =
  Option(value: x)

proc main() =
  var x = Mint(data: 10)
  let optlent = some(x)

  echo $optlent.value
  x = Mint(data: 12)
  echo $optlent.value

main()

Actual Output

Compiles and run

Expected Output

Error that x cannot be modified because optlent is holding a live borrow.

[saem]

Sorry if this is a silly question, but is var x being treated as var x: var Mint? So it's not really a true/independent location, but it's a view into optLen.x? Also is optLen still a live borrow because of the second echo meaning that optLen still has a read against it?

Did I get all those right?

[alaviss]

Nope, what's happening right now is that the borrow checker is not aware that optlent has borrowed x, so none of the constraints are applied.

[saem]

Nope, what's happening right now is that the borrow checker is not aware that optlent has borrowed x, so none of the constraints are applied.

Sorry, I phrased my line of questioning incorrectly, I meant, "Is this what's meant to be happening ... "

[alaviss]

Then no, for this, x is the "owning" location of Mint, and optlent is a view into x.

Since optlent is referred to by the echo after x = , it's considered to be alive at the point of x = , which meant that the location x should remain sealed from mutations.