INTERNAL ERROR: *.pyi file + function + comment + ellipsis

[di]

Seems like a minimal example requires:

• a .pyi file
• a comment after the function declaration
• an ellipsis in the function body

example.pyi:

def f():
    # hi
    ...

$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.14.6
BuildVersion:	18G95

$ python --version
Python 3.7.4

$ python -m black --version
black.py, version 19.3b0

$ cat example.pyi
def f():
    # hi
    ...

$ python -m black example.pyi
error: cannot format example.pyi: INTERNAL ERROR: Black produced invalid code: expected an indented block (<unknown>, line 3). Please report a bug on https://github.com/ambv/black/issues.  This invalid output might be helpful: /var/folders/m_/ffctv9r113lb285667lc7fh800k0_0/T/blk_2fvut1n6.log
All done! 💥 💔 💥
1 file failed to reformat.

$ cat /var/folders/m_/ffctv9r113lb285667lc7fh800k0_0/T/blk_iqek_luy.log
  File "/Users/dustiningram/.pyenv/versions/3.7.4/lib/python3.7/site-packages/black.py", line 3388, in assert_equivalent
    dst_ast = ast.parse(dst)
  File "/Users/dustiningram/.pyenv/versions/3.7.4/lib/python3.7/ast.py", line 35, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
def foobar():  # hi

...

Does also happen on master: Yes

$ python -m black --version
black.py, version 19.3b0+82.gae5588c

$ python -m black example.pyi
error: cannot format example.pyi: INTERNAL ERROR: Black produced invalid code: invalid syntax (<unknown>, line 2). Please report a bug on https://github.com/psf/black/issues.  This invalid output might be helpful: /var/folders/m_/ffctv9r113lb285667lc7fh800k0_0/T/blk_yzbb8_6s.log
Oh no! 💥 💔 💥
1 file failed to reformat.

[di]

Also possibly related, black will remove the comment entirely if the file is formatted a certain way:

$ cat example.pyi
def f(
    ):  # hi
    ...

$ python -m black example.pyi
reformatted example.pyi
All done! ✨ 🍰 ✨
1 file reformatted.

$ cat example.pyi
def f(): ...

[zsol]

Thanks for reporting, I can also repro this

[jdherg-brilliant]

Just ran into this as well. Note that black behaves appropriately when pass is used instead of ..., but that of course contravenes the preferred syntax in PEP 484.

[JelleZijlstra]

Still crashes. The behavior where comments are sometimes removed is tracked separately in #1239.