INTERNAL ERROR: Black produced invalid code: f-string: expecting '}'

[nernst]

Describe the bug

Black reports an internal error with certain long f-strings as it tries to break the line in a syntactically invalid place.

To Reproduce

For example, take this code:

something = []

test_string = f"this is a really string that will be line broken at 120 chars that contains an interpolated join {",".join(something)}"

And run it with these arguments:

$ black file.py -l 120 --target-version py312

The resulting error is:

error: cannot format example.py: INTERNAL ERROR: Black produced invalid code: f-string: expecting '}' (<unknown>, line 4). Please report a bug on https://github.com/psf/black/issues.  This invalid output might be helpful: /tmp/blk_9n5hjqrh.log

Oh no! 💥 💔 💥
1 file failed to reformat.

Expected behavior

The line should not be formatted/line should not be broken in an invalid position

Environment

• Black's version: 24.3.0 (compiled: yes)
• OS and Python version: Linux/CPython 3.12.2

Additional context

A work-around for this case is to change the ",".join(...) to ','.join(...).

[JelleZijlstra]

Duplicate of #3746