Syntax error when RUF010 autofixes f"{str({})}"

[harupy]

Reproduction

> ruff --version
ruff 0.0.275

> echo 'f"{str({})}"' | ruff --select RUF010 --stdin-filename a.py --fix -

error: Autofix introduced a syntax error. Reverting all changes.

This indicates a bug in `ruff`. If you could open an issue at:

    https://github.com/astral-sh/ruff/issues/new?title=%5BAutofix%20error%5D

...quoting the contents of `a.py`, the rule codes RUF010, along with the `pyproject.toml` settings and executed command, we'd be very appreciative!

f"{str({})}"

[charliermarsh]

Oh boy. Did this trigger on a real project? Just curious how common it is.

[harupy]

Did this trigger on a real project?

Yes, on https://github.com/mlflow/mlflow.

Just curious how common it is.

I think it's uncommon :)

[charliermarsh]

Haha we should still fix it definitely, was just looking for examples :)

[harupy]

The original code looked like this:

"foo bar baz {}".format(str({}))

I first applied UP032:

f"foo bar baz {str({})}"

Then, applied RUF010 to remove str() and hit the error.

[harupy]

f"{{}!s}" is invalid, but f"{{}}" is.

>>> f"{{}}"
'{}'
>>> f"{{}!s}"
  File "<stdin>", line 1
SyntaxError: f-string: single '}' is not allowed

[charliermarsh]

Hmm yeah but they have different meanings, in the first case it's being interpreted as the literal braces whereas in the second it's an expression.

E.g. consider if the original example was: "foo bar baz {}".format(str({"a": 1})). Then f"foo bar baz {{"a": 1}}" would be invalid syntax.