Object destructor not called when reassigning after a try-except block.

[darkestpigeon]

Description

Object destructor not called when reassigning after a try-except block.

Minimal example:

import std/os


type MyObj = object
  data: pointer
  size: int

proc initMyObj(size: int): MyObj =
  assert size > 0
  result.data = allocShared0(size)
  result.size = size
  
  # imitate work
  let p = cast[ptr UncheckedArray[uint8]](result.data)
  for i in 0..<size:
    p[i] = i.uint8

proc `=destroy`(x: MyObj) =
  if not x.data.isNil:
    deallocShared(x.data)

proc `=wasMoved`(x: var MyObj) =
  x.data = nil
  x.size = 0

proc `=copy`(x: var MyObj, y: MyObj) {.error.}


proc main() =
  while true:
    var obj: MyObj
    try:
      obj = initMyObj(10_000_000)
    except:
    # except FloatOverflowError: also causes a leak, although it is never raised
      break

    # discard obj

    obj = MyObj()
    sleep(20)

    echo getOccupiedMem()


main()

Uncommenting the discard obj line removes the issue.

Nim Version

Both on

Nim Compiler Version 2.0.8 [Linux: amd64]
Compiled at 2024-07-03
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: 5935c3bfa9fec6505394867b23510eb5cbab3dbf
active boot switches: -d:release

and

Nim Compiler Version 2.1.99 [Linux: amd64]
Compiled at 2024-09-12
Copyright (c) 2006-2024 by Andreas Rumpf

git hash: 793cee4de1934fd1f6271cf5fed46f01c5abb19b
active boot switches: -d:release

Current Output

10223616                                                                                  
20447232                                                                                  
30670848                                     
40894464                                                                                  
51118080                                                                                                                                                                            
61341696                                                                                  
71565312                                                                                                                                                                            
81788928                                     
92012544                                     
102236160                                                                                                                                                                           
112459776                                                                                 
122683392                                                                                                                                                                           
132907008                                                                                                                                                                           
143130624                                                                                                                                                                           
153354240
...

Expected Output

0                                            
0                                            
0                                                                                                                                                                                   
0                                                                                         
0                                                                                                                                                                                   
0                                                                                                                                                                                   
0                                                                                                                                                                                   
0                                                                                                                                                                                   
0                                                                                         
0                                                                                         
0                                                                                         
0                                                                                         
0                                                                                         
0                                                                                         
0                                                                                         
0    
...

Known Workarounds

In the example above, uncommenting the discard obj line removes the issue.

Additional Information

No response

[forchid]

It's also ok if access obj before try:, such as,

The test source

import std/os


type MyObj = object
  data: pointer
  size: int

proc initMyObj(size: int): MyObj =
  assert size > 0
  result.data = allocShared0(size)
  result.size = size
  
  # imitate work
  let p = cast[ptr UncheckedArray[uint8]](result.data)
  for i in 0..<size:
    p[i] = i.uint8

proc `=destroy`(x: MyObj) =
  if not x.data.isNil:
    deallocShared(x.data)

proc `=wasMoved`(x: var MyObj) =
  x.data = nil
  x.size = 0

proc `=copy`(x: var MyObj, y: MyObj) {.error.}


proc main() =
  while true:
    var obj: MyObj
    discard obj
    try:
      obj = initMyObj(10_000_000)
    except:
    # except FloatOverflowError: also causes a leak, although it is never raised
      break

    # discard obj

    obj = MyObj()
    sleep(20)

    echo getOccupiedMem()


main()

The test result

>except
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

[forchid]

@darkestpigeon I find that this problem doesn't exist in nim-1.6.20 with --mm:orc or --mm:orc, but memory leak 48 bytes
with --mm:refc.

Test test source

import std/os


type MyObj = object
  data: pointer
  size: int

proc initMyObj(size: int): MyObj =
  assert size > 0
  result.data = allocShared0(size)
  result.size = size
  
  # imitate work
  let p = cast[ptr UncheckedArray[uint8]](result.data)
  for i in 0..<size:
    p[i] = i.uint8

proc `=destroy`(x: var MyObj) = # Using `var` in nim-1.6.20
  if not x.data.isNil:
    deallocShared(x.data)

proc `=wasMoved`(x: var MyObj) =
  x.data = nil
  x.size = 0

proc `=copy`(x: var MyObj, y: MyObj) {.error.}


proc main() =
  while true:
    var obj: MyObj
    try:
      obj = initMyObj(10_000_000)
    except:
    # except FloatOverflowError: also causes a leak, although it is never raised
      break

    # discard obj

    obj = MyObj()
    sleep(20)

    echo getOccupiedMem()


main()

The test resul

>except
0
0
0
0
0
0
0
0
0
0
...