yapf: enable comments inside expression cause infinite hang

[danthedeckie]

Describe the bug

If you have yapf: enable comments inside an expression, you can cause black to hang:

To Reproduce

with file.py as:

def test_func():
    # yapf: disable
    if a:
        return True
    # yapf: enable
    elif b:
        return True

    return False

$ black file.py

It hangs forever.

Expected behavior

It should not hang.

At the very least it should give an error.

Preferably it should ignore those comments and not break anything.

Environment

• Black's version: black, 22.3.0 (compiled: yes)
• OS and Python version: Python 3.8 & 3.10, mac OS 12.3

Also happens on the https://black.vercel.app/

[danthedeckie]

# yapf: disable
if a:
    return True
# yapf: enable
elif b:
    return False

is the smallest I can reduce it to.

It seems that the yapf: disable is needed as well.

[danthedeckie]

And version hunting, it seems (for me) to crop up between:
black==19.10b0 (good - doesn't hang)
and
black==20.8b0 (bad - does hang)

Hopefully that helps narrow it down.

[danthedeckie]

And trying to find the problem w/ git bisect narrows it down to: #1325

892eddacd215d685e136686b7f629ade70adca83 is the first bad commit
commit 892eddacd215d685e136686b7f629ade70adca83
Author: otstrel <otstrel@gmail.com>
Date:   Fri May 8 15:37:17 2020 +0300

    Fix for "# fmt: on" with decorators (#1325)

 black.py                | 49 ++++++++++++++++++++++++++++++++++++++++---------
 tests/data/fmtonoff4.py | 31 +++++++++++++++++++++++++++++++
 tests/test_black.py     |  8 ++++++++
 3 files changed, 79 insertions(+), 9 deletions(-)
 create mode 100644 tests/data/fmtonoff4.py