gc:arc memory leak when using "return" keyword

[khchen]

I found a memory leak when using system.find(). It seems to be caused by "return" keyword.

Example

type
  Foo = ref object of RootObj
    data: int
    children*: seq[Foo]

proc `=destroy`(self: var type(Foo()[])) =
  echo "destroy foo ", self.data
  for i in self.fields: i.reset

# Just a copy of system.find.
proc systemFind[T, S](a: T, item: S): int {.inline.}=
  for i in items(a):
    if i == item: return
    inc(result)
  result = -1

# Another version without "return" keyword.
proc myFind[T, S](a: T, item: S): int {.inline.}=
  var found = false
  for i in items(a):
    if i == item:
      found = true
      break
    inc(result)

  if not found:
    result = -1

var w1 = Foo(data: 1)
var w2 = Foo(data: 2)
var w3 = Foo(data: 3)

w1.children = @[w2, w3]
discard w1.children.systemFind(w3) # Has memory leak
# discard w1.children.myFind(w3) # No memory leak

Current Output

destroy foo 1
destroy foo 2

Expected Output

destroy foo 1
destroy foo 2
destroy foo 3

$ nim -v
Nim Compiler Version 1.1.1 [Windows: amd64]
Compiled at 2020-03-11

[cooldome]

Works with cpp, so I believe it is goto exceptions related

[cooldome]

Tested: c with setjmp works too

[Araq]

It's caused by the try finally optimization.