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[ruff] Detect PLC0207 on chained str.split() calls #23275

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ntBre merged 1 commit into from
Feb 18, 2026
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[ruff] Detect PLC0207 on chained str.split() calls #23275

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7 changes: 6 additions & 1 deletion crates/ruff_linter/resources/test/fixtures/pylint/missing_maxsplit_arg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -54,9 +54,14 @@ class Bar():
Bar.split.rsplit(",")[0] # [missing-maxsplit-arg]
Bar.split.rsplit(",")[-1] # [missing-maxsplit-arg]

## Test unpacked dict literal kwargs
## Test unpacked dict literal kwargs
"1,2,3".split(**{"sep": ","})[0] # [missing-maxsplit-arg]

## Test chained splits
SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]


# OK
## Test not accessing the first or last element
Expand Down
29 changes: 25 additions & 4 deletions crates/ruff_linter/src/rules/pylint/rules/missing_maxsplit_arg.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -133,10 +133,31 @@ pub(crate) fn missing_maxsplit_arg(checker: &Checker, value: &Expr, slice: &Expr
}

let mut target_instance = value;
// a subscripted value could technically be subscripted further ad infinitum, so we
// recurse into the subscript expressions until we find the value being subscripted
while let Expr::Subscript(ExprSubscript { value, .. }) = target_instance.as_ref() {
target_instance = value;
// The value being split on could be the result of a chained split, e.g.
// `s.split('(')[0].split('[')[0]`. We recurse through subscripts and
// split/rsplit calls to find the original string value, since
// `str.split()` returns `list[str]` and subscripting that gives a `str`.
loop {
match target_instance.as_ref() {
Expr::Subscript(ExprSubscript { value, .. }) => {
target_instance = value;
}
Expr::Call(ExprCall { func, .. }) => {
if let Expr::Attribute(ExprAttribute {
attr,
value: call_value,
..
}) = func.as_ref()
{
if matches!(attr.as_str(), "split" | "rsplit") {
target_instance = call_value;
continue;
}
}
break;
}
_ => break,
}
}

// Check the function is called on a string
Expand Down
262 changes: 197 additions & 65 deletions .../pylint/snapshots/ruff_linter__rules__pylint__tests__PLC0207_missing_maxsplit_arg.py.snap
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Expand Up @@ -566,7 +566,7 @@ help: Use `str.split()` and pass `maxsplit=1`
54 + Bar.split.split(",", maxsplit=1)[0] # [missing-maxsplit-arg]
55 | Bar.split.rsplit(",")[-1] # [missing-maxsplit-arg]
56 |
57 | ## Test unpacked dict literal kwargs
57 | ## Test unpacked dict literal kwargs

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:55:1
Expand All @@ -576,7 +576,7 @@ PLC0207 [*] String is split more times than necessary
55 | Bar.split.rsplit(",")[-1] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^
56 |
57 | ## Test unpacked dict literal kwargs
57 | ## Test unpacked dict literal kwargs
|
help: Pass `maxsplit=1` into `str.rsplit()`
52 | Bar.split.split(",")[0] # [missing-maxsplit-arg]
Expand All @@ -585,121 +585,253 @@ help: Pass `maxsplit=1` into `str.rsplit()`
- Bar.split.rsplit(",")[-1] # [missing-maxsplit-arg]
55 + Bar.split.rsplit(",", maxsplit=1)[-1] # [missing-maxsplit-arg]
56 |
57 | ## Test unpacked dict literal kwargs
57 | ## Test unpacked dict literal kwargs
58 | "1,2,3".split(**{"sep": ","})[0] # [missing-maxsplit-arg]

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:58:1
|
57 | ## Test unpacked dict literal kwargs
57 | ## Test unpacked dict literal kwargs
58 | "1,2,3".split(**{"sep": ","})[0] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
59 |
60 | ## Test chained splits
|
help: Pass `maxsplit=1` into `str.split()`
55 | Bar.split.rsplit(",")[-1] # [missing-maxsplit-arg]
56 |
57 | ## Test unpacked dict literal kwargs
57 | ## Test unpacked dict literal kwargs
- "1,2,3".split(**{"sep": ","})[0] # [missing-maxsplit-arg]
58 + "1,2,3".split(maxsplit=1, **{"sep": ","})[0] # [missing-maxsplit-arg]
59 |
60 |
61 | # OK
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
note: This is an unsafe fix and may change runtime behavior

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:179:1
--> missing_maxsplit_arg.py:61:1
|
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
|
help: Pass `maxsplit=1` into `str.split()`
58 | "1,2,3".split(**{"sep": ","})[0] # [missing-maxsplit-arg]
59 |
60 | ## Test chained splits
- SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
61 + SEQ.split("(", maxsplit=1)[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
64 |

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:61:1
|
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
|
help: Pass `maxsplit=1` into `str.split()`
58 | "1,2,3".split(**{"sep": ","})[0] # [missing-maxsplit-arg]
59 |
60 | ## Test chained splits
- SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
61 + SEQ.split("(")[0].split("[", maxsplit=1)[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
64 |

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:62:1
|
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
|
help: Pass `maxsplit=1` into `str.split()`
59 |
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
- SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
62 + SEQ.split("(", maxsplit=1)[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
64 |
65 |

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:62:1
|
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
|
help: Use `str.rsplit()` and pass `maxsplit=1`
59 |
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
- SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
62 + SEQ.split("(")[0].rsplit("[", maxsplit=1)[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
64 |
65 |

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:63:1
|
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^
|
help: Pass `maxsplit=1` into `str.split()`
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
- SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
63 + SEQ.split("(", maxsplit=1)[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
64 |
65 |
66 | # OK

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:63:1
|
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: Pass `maxsplit=1` into `str.split()`
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
- SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
63 + SEQ.split("(")[0].split("[", maxsplit=1)[0].split(".")[-1] # [missing-maxsplit-arg]
64 |
65 |
66 | # OK

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:63:1
|
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
63 | SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: Use `str.rsplit()` and pass `maxsplit=1`
60 | ## Test chained splits
61 | SEQ.split("(")[0].split("[")[0] # [missing-maxsplit-arg]
62 | SEQ.split("(")[0].split("[")[-1] # [missing-maxsplit-arg]
- SEQ.split("(")[0].split("[")[0].split(".")[-1] # [missing-maxsplit-arg]
63 + SEQ.split("(")[0].split("[")[0].rsplit(".", maxsplit=1)[-1] # [missing-maxsplit-arg]
64 |
65 |
66 | # OK

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:184:1
|
177 | # Errors
178 | kwargs_without_maxsplit = {"seq": ","}
179 | "1,2,3".split(**kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
182 | # Errors
183 | kwargs_without_maxsplit = {"seq": ","}
184 | "1,2,3".split(**kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
180 | # OK
181 | kwargs_with_maxsplit = {"maxsplit": 1}
185 | # OK
186 | kwargs_with_maxsplit = {"maxsplit": 1}
|
help: Pass `maxsplit=1` into `str.split()`
176 | ## TODO: These require the ability to resolve a dict variable name to a value
177 | # Errors
178 | kwargs_without_maxsplit = {"seq": ","}
181 | ## TODO: These require the ability to resolve a dict variable name to a value
182 | # Errors
183 | kwargs_without_maxsplit = {"seq": ","}
- "1,2,3".split(**kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
179 + "1,2,3".split(maxsplit=1, **kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
180 | # OK
181 | kwargs_with_maxsplit = {"maxsplit": 1}
182 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
184 + "1,2,3".split(maxsplit=1, **kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
185 | # OK
186 | kwargs_with_maxsplit = {"maxsplit": 1}
187 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
note: This is an unsafe fix and may change runtime behavior

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:182:1
--> missing_maxsplit_arg.py:187:1
|
180 | # OK
181 | kwargs_with_maxsplit = {"maxsplit": 1}
182 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
185 | # OK
186 | kwargs_with_maxsplit = {"maxsplit": 1}
187 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
183 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
184 | "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
188 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
189 | "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
|
help: Pass `maxsplit=1` into `str.split()`
179 | "1,2,3".split(**kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
180 | # OK
181 | kwargs_with_maxsplit = {"maxsplit": 1}
184 | "1,2,3".split(**kwargs_without_maxsplit)[0] # TODO: [missing-maxsplit-arg]
185 | # OK
186 | kwargs_with_maxsplit = {"maxsplit": 1}
- "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
182 + "1,2,3".split(",", maxsplit=1, **kwargs_with_maxsplit)[0] # TODO: false positive
183 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
184 | "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
185 |
187 + "1,2,3".split(",", maxsplit=1, **kwargs_with_maxsplit)[0] # TODO: false positive
188 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
189 | "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
190 |
note: This is an unsafe fix and may change runtime behavior

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:184:1
--> missing_maxsplit_arg.py:189:1
|
182 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
183 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
184 | "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
187 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
188 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
189 | "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: Pass `maxsplit=1` into `str.split()`
181 | kwargs_with_maxsplit = {"maxsplit": 1}
182 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
183 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
186 | kwargs_with_maxsplit = {"maxsplit": 1}
187 | "1,2,3".split(",", **kwargs_with_maxsplit)[0] # TODO: false positive
188 | kwargs_with_maxsplit = {"sep": ",", "maxsplit": 1}
- "1,2,3".split(**kwargs_with_maxsplit)[0] # TODO: false positive
184 + "1,2,3".split(maxsplit=1, **kwargs_with_maxsplit)[0] # TODO: false positive
185 |
186 |
187 | ## Test unpacked list literal args (starred expressions)
189 + "1,2,3".split(maxsplit=1, **kwargs_with_maxsplit)[0] # TODO: false positive
190 |
191 |
192 | ## Test unpacked list literal args (starred expressions)
note: This is an unsafe fix and may change runtime behavior

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:189:1
--> missing_maxsplit_arg.py:194:1
|
187 | ## Test unpacked list literal args (starred expressions)
188 | # Errors
189 | "1,2,3".split(",", *[-1])[0]
192 | ## Test unpacked list literal args (starred expressions)
193 | # Errors
194 | "1,2,3".split(",", *[-1])[0]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
190 |
191 | ## Test unpacked list variable args
195 |
196 | ## Test unpacked list variable args
|
help: Pass `maxsplit=1` into `str.split()`
186 |
187 | ## Test unpacked list literal args (starred expressions)
188 | # Errors
191 |
192 | ## Test unpacked list literal args (starred expressions)
193 | # Errors
- "1,2,3".split(",", *[-1])[0]
189 + "1,2,3".split(",", *[-1], maxsplit=1)[0]
190 |
191 | ## Test unpacked list variable args
192 | # Errors
194 + "1,2,3".split(",", *[-1], maxsplit=1)[0]
195 |
196 | ## Test unpacked list variable args
197 | # Errors
note: This is an unsafe fix and may change runtime behavior

PLC0207 [*] String is split more times than necessary
--> missing_maxsplit_arg.py:194:1
--> missing_maxsplit_arg.py:199:1
|
192 | # Errors
193 | args_list = [-1]
194 | "1,2,3".split(",", *args_list)[0]
197 | # Errors
198 | args_list = [-1]
199 | "1,2,3".split(",", *args_list)[0]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: Pass `maxsplit=1` into `str.split()`
191 | ## Test unpacked list variable args
192 | # Errors
193 | args_list = [-1]
196 | ## Test unpacked list variable args
197 | # Errors
198 | args_list = [-1]
- "1,2,3".split(",", *args_list)[0]
194 + "1,2,3".split(",", *args_list, maxsplit=1)[0]
199 + "1,2,3".split(",", *args_list, maxsplit=1)[0]
note: This is an unsafe fix and may change runtime behavior