Ruff should detect unreachable code but reports 'Missing explicit return', fixing it with return None

[bittner]

In the code below Ruff should detect unreachable code, but it reports 'Missing explicit return'.

It tries to --fix the problem appending a return None line even after the unreachable code, which clearly makes no sense.

Example

# FILE: foo.py

def get_rates(data, dataframe_foo):
    """A data science example with data frames."""
    dt_tmp = data.copy()
    rates = (
        dt_tmp.sort_values(dataframe_foo.date_col)
        .groupby([dataframe_foo.id_col, dataframe_foo.bar_col])
        .agg(list)
    )
    rates = rates.reset_index().rename(columns={0: "baz"})
    foobar_rates = rates[["dki_id", "bar", "baz"]]
    return foobar_rates
    rates = rates.reset_index()

After running ruff foo.py --fix you get:

    return foobar_rates
    rates = rates.reset_index()
+   return None

Interestingly, with ruff foo.py --fix --isolated nothing gets changed.

Ruff details

$ ruff --version
ruff 0.0.282

Configuration in pyproject.toml:

[tool.ruff]
extend-exclude = []
extend-select = ["B", "BLE", "C4", "C90", "COM", "DJ", "DTZ", "EM", "G", "I", "N", "PIE", "PL", "PT", "PTH", "R", "RUF", "S", "SIM", "T10", "TID", "W", "YTT"]
extend-ignore = []

[tool.ruff.per-file-ignores]
"tests/**/*.py" = ["S101"]

Maybe related

I found PR #5384, which seems to address the very issue. Interestingly, the configuration rule RUF014 that the PR supposedly implements is not mentioned in any of the recent releases. (I tried to install Ruff from source code to verify the claim of the merged feature not being included, but my system ships a too-old version of rustc, which makes the build fail.)

[zanieb]

#5384 is behind a feature gate and is not available in releases yet.

It seems like we may be able to address this false positive separately.