Ruff

The `keep-runtime-typing` setting has been reinstated ([5470](https://github.com/astral-sh/ruff/pull/5470))

The `keep-runtime-typing` setting has been reinstated with revised semantics. This setting was
removed in [4427](https://github.com/astral-sh/ruff/pull/4427), as it was equivalent to ignoring
the `UP006` and `UP007` rules via Ruff's standard `ignore` mechanism.

Taking `UP006` (rewrite `List[int]` to `list[int]`) as an example, the setting now behaves as
follows:

- On Python 3.7 and Python 3.8, setting `keep-runtime-typing = true` will cause Ruff to ignore
`UP006` violations, even if `from __future__ import annotations` is present in the file.
While such annotations are valid in Python 3.7 and Python 3.8 when combined with
`from __future__ import annotations`, they aren't supported by libraries like Pydantic and
FastAPI, which rely on runtime type checking.
- On Python 3.9 and above, the setting has no effect, as `list[int]` is a valid type annotation,
and libraries like Pydantic and FastAPI support it without issue.

In short: `keep-runtime-typing` can be used to ensure that Ruff doesn't introduce type annotations
that are not supported at runtime by the current Python version, which are unsupported by libraries
like Pydantic and FastAPI.

Note that this is not a breaking change, but is included here to complement the previous removal
of `keep-runtime-typing`.

The `keep-runtime-typing` setting has been removed ([4427](https://github.com/astral-sh/ruff/pull/4427))

Enabling the `keep-runtime-typing` option, located under the `pyupgrade` section, is equivalent
to ignoring the `UP006` and `UP007` rules via Ruff's standard `ignore` mechanism. As there's no
need for a dedicated setting to disable these rules, the `keep-runtime-typing` option has been
removed.

`update-check` is no longer a valid configuration option ([4313](https://github.com/astral-sh/ruff/pull/4313))

The `update-check` functionality was deprecated in [2530](https://github.com/astral-sh/ruff/pull/2530),
in that the behavior itself was removed, and Ruff was changed to warn when that option was enabled.

Now, Ruff will throw an error when `update-check` is provided via a configuration file (e.g.,
`update-check = false`) or through the command-line, since it has no effect. Users should remove
this option from their configuration.

`--fix-only` now exits with a zero exit code, unless `--exit-non-zero-on-fix` is specified ([4146](https://github.com/astral-sh/ruff/pull/4146))

Previously, `--fix-only` would exit with a non-zero exit code if any fixes were applied. This
behavior was inconsistent with `--fix`, and further, meant that `--exit-non-zero-on-fix` was
effectively ignored when `--fix-only` was specified.

Now, `--fix-only` will exit with a zero exit code, unless `--exit-non-zero-on-fix` is specified,
in which case it will exit with a non-zero exit code if any fixes were applied.

Fixes are now represented as a list of edits ([3709](https://github.com/astral-sh/ruff/pull/3709))

Previously, Ruff represented each fix as a single edit, which prohibited Ruff from automatically
fixing violations that required multiple edits across a file. As such, Ruff now represents each
fix as a list of edits.

This primarily affects the JSON API. Ruff's JSON representation used to represent the `fix` field as
a single edit, like so:

json
{
"message": "Remove unused import: `sys`",
"content": "",
"location": {"row": 1, "column": 0},
"end_location": {"row": 2, "column": 0}
}


The updated representation instead includes a list of edits:

json
{
"message": "Remove unused import: `sys`",
"edits": [
{
"content": "",
"location": {"row": 1, "column": 0},
"end_location": {"row": 2, "column": 0},
}
]
}

`multiple-statements-on-one-line-def` (`E704`) was removed ([2773](https://github.com/astral-sh/ruff/pull/2773))

This rule was introduced in v0.0.245. However, it turns out that pycodestyle and Flake8 ignore this
rule by default, as it is not part of PEP 8. As such, we've removed it from Ruff.