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Ruff fails to detect nonsensical list index #5082

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dgjustice opened this issue Jun 14, 2023 · 1 comment · Fixed by #5602
Closed

Ruff fails to detect nonsensical list index #5082

dgjustice opened this issue Jun 14, 2023 · 1 comment · Fixed by #5602
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@zanieb
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good first issue Good for newcomers help wanted Contributions especially welcome rule Implementing or modifying a lint rule

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@dgjustice
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ruff is an awesome project! ❤️ I saw this in the wild today on a PR to fix a bug that passed through CI (with ruff check).

Python source code

The developer accidentally deleted the dict variable during a refactor resulting in something structurally identical to this:

foo = ["abc"]["def"]

Ruff check

$ cat foo.py 
foo = ["abc"]["def"]

$ python foo.py 
/home/djustice/tmp/foo.py:1: SyntaxWarning: list indices must be integers or slices, not str; perhaps you missed a comma?
  foo = ["abc"]["def"]
Traceback (most recent call last):
  File "/home/djustice/tmp/foo.py", line 1, in <module>
    foo = ["abc"]["def"]
TypeError: list indices must be integers or slices, not str

$ ruff check foo.py


$ echo $status
0

Ruff version

$ ruff --version
ruff 0.0.264

$
@charliermarsh charliermarsh added question Asking for support or clarification rule Implementing or modifying a lint rule labels Jun 17, 2023
@charliermarsh
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charliermarsh commented Jun 22, 2023 •
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I think this is reasonable but we can probably only support literals (like Python, which raises a syntax warning). This blog post from Adam Johnson is a good explanation of the rule and what we could support: https://adamj.eu/tech/2020/06/21/why-does-python-syntaxwarning-saying-list-indices-must-be-integers-or-slices/.

@charliermarsh charliermarsh added good first issue Good for newcomers help wanted Contributions especially welcome and removed question Asking for support or clarification labels Jun 22, 2023
@zanieb zanieb self-assigned this Jul 7, 2023
@zanieb zanieb mentioned this issue Jul 7, 2023
Merged
zanieb added a commit that referenced this issue Jul 12, 2023
@zanieb
Add RUF016: Detection of invalid index types (#5602)
0666add 
Detects invalid types for tuple, list, bytes, string indices.

For example, the following will raise a `TypeError` at runtime and when
imported Python will display a `SyntaxWarning`

```python
var = [1, 2, 3]["x"]
```

```
example.py:1: SyntaxWarning: list indices must be integers or slices, not str; perhaps you missed a comma?
  var = [1, 2, 3]["x"]
Traceback (most recent call last):
  File "example.py", line 1, in <module>
    var = [1, 2, 3]["x"]
          ~~~~~~~~~^^^^^
TypeError: list indices must be integers or slices, not str
```

Previously, Ruff would not report the invalid syntax but now a violation
will be reported. This does not apply to cases where a variable, call,
or complex expression is used in the index — detection is roughly
limited to static definitions, which matches Python's warnings.

```
❯ ./target/debug/ruff example.py --select RUF015 --show-source --no-cache
example.py:1:17: RUF015 Indexed access to type `list` uses type `str` instead of an integer or slice.
  |
1 | var = [1, 2, 3]["x"]
  |                 ^^^ RUF015
  |
```

Closes #5082
xref
python/cpython@ffff144
konstin pushed a commit that referenced this issue Jul 19, 2023
@zanieb @konstin
Add RUF016: Detection of invalid index types (#5602)
f8800da 
Detects invalid types for tuple, list, bytes, string indices.

For example, the following will raise a `TypeError` at runtime and when
imported Python will display a `SyntaxWarning`

```python
var = [1, 2, 3]["x"]
```

```
example.py:1: SyntaxWarning: list indices must be integers or slices, not str; perhaps you missed a comma?
  var = [1, 2, 3]["x"]
Traceback (most recent call last):
  File "example.py", line 1, in <module>
    var = [1, 2, 3]["x"]
          ~~~~~~~~~^^^^^
TypeError: list indices must be integers or slices, not str
```

Previously, Ruff would not report the invalid syntax but now a violation
will be reported. This does not apply to cases where a variable, call,
or complex expression is used in the index — detection is roughly
limited to static definitions, which matches Python's warnings.

```
❯ ./target/debug/ruff example.py --select RUF015 --show-source --no-cache
example.py:1:17: RUF015 Indexed access to type `list` uses type `str` instead of an integer or slice.
  |
1 | var = [1, 2, 3]["x"]
  |                 ^^^ RUF015
  |
```

Closes #5082
xref
python/cpython@ffff144
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Add RUF016: Detection of invalid index types zanieb/ruff
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@charliermarsh @zanieb @dgjustice