Internal error when docstring end follows double quote

[hugovk]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Take this file:

def thing():
    """Controls vertical alignment of fields
    Arguments:

    valign - vertical alignment, one of "t", "m", or "b" """
    return

(Simplified from https://github.com/jazzband/prettytable/blob/master/prettytable.py)

2. Run Black on it with these arguments: black 1.py
3. See error:

$ black 1.py
error: cannot format 1.py: INTERNAL ERROR: Black produced invalid code: EOL while scanning string literal (<unknown>, line 5). Please report a bug on https://github.com/psf/black/issues.  This invalid output might be helpful: /var/folders/kt/j77sf4_n6fnbx6pg199rbx700000gn/T/blk_vs1w_3yc.log
Oh no! 💥 💔 💥
1 file failed to reformat.

$ cat /var/folders/kt/j77sf4_n6fnbx6pg199rbx700000gn/T/blk_vs1w_3yc.log
  File "/Users/hugo/github/black/src/black/__init__.py", line 6037, in assert_equivalent
    dst_ast = parse_ast(dst)
  File "/Users/hugo/github/black/src/black/__init__.py", line 5948, in parse_ast
    return ast27.parse(src)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/typed_ast/ast27.py", line 50, in parse
    return _ast27.parse(source, filename, mode)
def thing():
    """Controls vertical alignment of fields
    Arguments:

    valign - vertical alignment, one of "t", "m", or "b""""
    return

Expected behavior A clear and concise description of what you expected to happen.

File was formatted.

Environment (please complete the following information):

• Version: master
• OS and Python version: macOS/Python 3.8.3.

Does this bug also happen on master? To answer this, you have two options:

Yes with master. No with latest 19.10b0 release, which does not change the file.

Additional context Add any other context about the problem here.

It's fine with single quotes instead in "t", "m", or "b", or with a newline after "b".

[hugovk]

Git bisect points to a4c11a7 as the first bad commit, from PR #1053, "Re-indent the contents of docstrings".

PR #1417 fixed some other docstring things (#1415) but not this case.

Here's a smaller failing case:

def containing_quotes():
    """No quotes here

    "quotes here" """
    pass

Or:

def containing_quotes():
    """No quotes here

    quote here" """
    pass

[ambv]

Fixed by #1623.