lent pointer outlives origin for global/threadvar

[nitely]

Description

This compiles even though the returned lent pointer outlives the threadvar value. Same for globals. Try -d:useMalloc for a random output.

type Foo = ref object
  x: seq[int]

var foo {.threadvar.}: seq[Foo]

proc genfoo(): lent Foo =
  foo = @[Foo(x: @[1,2,3])]
  return foo[0]

proc echoFoo() =
  var x = genfoo()
  foo[0] = nil
  foo.setLen 0
  echo x[].x
  echo x[].x.len
echoFoo()

Nim Version

Nim Compiler Version 2.3.1 [Linux: amd64]
Compiled at 2025-01-18
Copyright (c) 2006-2025 by Andreas Rumpf

git hash: 2af9ddc
active boot switches: -d:release

Current Output

@[1, 2, 3]
23859

Expected Output

Compilation error (or it should copy in this case?).

Known Workarounds

No response

Additional Information

No response

[nitely]

it also occurs when returning var Foo