Current behaviour 

$ cat foo.py
def foo():
    open('foo', 'wb')


foo()
$ python3.8 -W all::ResourceWarning -X tracemalloc=5 foo.py
foo.py:2: ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>
  open('foo', 'wb')
Object allocated at (most recent call last):
  File "foo.py", lineno 5
    foo()
  File "foo.py", lineno 2
    open('foo', 'wb')
$ python3.8 -W error -X tracemalloc=5 foo.py
Exception ignored in: <_io.FileIO name='foo' mode='wb' closefd=True>
ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>

Expected behaviour

# Pastebin Eu0gvZ5Z
$ cat foo.py
def foo():
    open('foo', 'wb')


foo()
$ python3.8 -W all::ResourceWarning -X tracemalloc=5 foo.py
foo.py:2: ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>
  open('foo', 'wb')
Object allocated at (most recent call last):
  File "foo.py", lineno 5
    foo()
  File "foo.py", lineno 2
    open('foo', 'wb')
$ python3.8 -W error -X tracemalloc=5 foo.py
Exception ignored in: <_io.FileIO name='foo' mode='wb' closefd=True>
ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>
  open('foo', 'wb')
Object allocated at (most recent call last):
  File "foo.py", lineno 5
    foo()
  File "foo.py", lineno 2
    open('foo', 'wb')