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[`refurb`] Mark `single-item-membership-test` fix as always unsafe (`FURB171`) (#20279) 

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Fixes #20255

Mark single-item-membership-test fixes as always unsafe

- Always set `Applicability::Unsafe` for FURB171 fixes
- Update “Fix safety” docs to reflect always-unsafe behavior
- Expand tests (not in, nested set/frozenset, commented args)

## Test Plan

<!-- How was it tested? -->

I have added new test cases to
`crates/ruff_linter/resources/test/fixtures/refurb/FURB171_0.py` and
`crates/ruff_linter/resources/test/fixtures/refurb/FURB171_1.py`.

---------

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>
This commit is contained in:
Takayuki Maeda 2025-09-19 00:24:15 +09:00 committed by GitHub
parent 1758f26d94
commit 821b2f8b2e
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GPG Key ID: B5690EEEBB952194
5 changed files with 217 additions and 15 deletions
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28
crates/ruff_linter/resources/test/fixtures/refurb/FURB171_0.py vendored
View File

@ -117,3 +117,31 @@ def _():
# After
] and \
0 < 1: ...
# https://github.com/astral-sh/ruff/issues/20255
import math
# NaN behavior differences
if math.nan in [math.nan]:
print("This is True")
if math.nan in (math.nan,):
print("This is True")
if math.nan in {math.nan}:
print("This is True")
# Potential type differences with custom __eq__ methods
class CustomEq:
def __eq__(self, other):
return "custom"
obj = CustomEq()
if obj in [CustomEq()]:
pass
if obj in (CustomEq(),):
pass
if obj in {CustomEq()}:
pass

10
crates/ruff_linter/resources/test/fixtures/refurb/FURB171_1.py vendored
View File

@ -51,3 +51,13 @@ if 1 in set(1,2):
if 1 in set((x for x in range(2))):
pass
# https://github.com/astral-sh/ruff/issues/20255
import math
# set() and frozenset() with NaN
if math.nan in set([math.nan]):
print("This should be marked unsafe")
if math.nan in frozenset([math.nan]):
print("This should be marked unsafe")

25
crates/ruff_linter/src/rules/refurb/rules/single_item_membership_test.rs
View File

@ -6,7 +6,7 @@ use ruff_text_size::Ranged;
use crate::checkers::ast::Checker;
use crate::fix::edits::pad;
use crate::{Applicability, Edit, Fix, FixAvailability, Violation};
use crate::{Edit, Fix, FixAvailability, Violation};
/// ## What it does
/// Checks for membership tests against single-item containers.
@ -27,13 +27,16 @@ use crate::{Applicability, Edit, Fix, FixAvailability, Violation};
/// ```
///
/// ## Fix safety
/// The fix is always marked as unsafe.
///
/// When the right-hand side is a string, the fix is marked as unsafe.
/// This is because `c in "a"` is true both when `c` is `"a"` and when `c` is the empty string,
/// so the fix can change the behavior of your program in these cases.
/// When the right-hand side is a string, this fix can change the behavior of your program.
/// This is because `c in "a"` is true both when `c` is `"a"` and when `c` is the empty string.
///
/// Additionally, if there are comments within the fix's range,
/// it will also be marked as unsafe.
/// Additionally, converting `in`/`not in` against a single-item container to `==`/`!=` can
/// change runtime behavior: `in` may consider identity (e.g., `NaN`) and always
/// yields a `bool`.
///
/// Comments within the replacement range will also be removed.
///
/// ## References
/// - [Python documentation: Comparisons](https://docs.python.org/3/reference/expressions.html#comparisons)
@ -100,14 +103,8 @@ pub(crate) fn single_item_membership_test(
expr.range(),
);
let applicability =
if right.is_string_literal_expr() || checker.comment_ranges().intersects(expr.range()) {
Applicability::Unsafe
} else {
Applicability::Safe
};
let fix = Fix::applicable_edit(edit, applicability);
// All supported cases can change runtime behavior; mark as unsafe.
let fix = Fix::unsafe_edit(edit);
checker
.report_diagnostic(SingleItemMembershipTest { membership_test }, expr.range())

123
crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB171_FURB171_0.py.snap
View File

@ -18,6 +18,7 @@ help: Convert to equality test
4 | print("Single-element tuple")
5 |
6 | if 1 in [1]:
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:6:4
@ -37,6 +38,7 @@ help: Convert to equality test
7 | print("Single-element list")
8 |
9 | if 1 in {1}:
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:9:4
@ -56,6 +58,7 @@ help: Convert to equality test
10 | print("Single-element set")
11 |
12 | if "a" in "a":
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:12:4
@ -95,6 +98,7 @@ help: Convert to inequality test
16 | print("Check `not in` membership test")
17 |
18 | if not 1 in (1,):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:18:8
@ -114,6 +118,7 @@ help: Convert to equality test
19 | print("Check the negated membership test")
20 |
21 | # Non-errors.
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:52:5
@ -344,4 +349,122 @@ help: Convert to inequality test
- ] and \
113 + if foo != bar and \
114 | 0 < 1: ...
115 |
116 | # https://github.com/astral-sh/ruff/issues/20255
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:125:4
|
124 | # NaN behavior differences
125 | if math.nan in [math.nan]:
| ^^^^^^^^^^^^^^^^^^^^^^
126 | print("This is True")
|
help: Convert to equality test
122 | import math
123 |
124 | # NaN behavior differences
- if math.nan in [math.nan]:
125 + if math.nan == math.nan:
126 | print("This is True")
127 |
128 | if math.nan in (math.nan,):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:128:4
|
126 | print("This is True")
127 |
128 | if math.nan in (math.nan,):
| ^^^^^^^^^^^^^^^^^^^^^^^
129 | print("This is True")
|
help: Convert to equality test
125 | if math.nan in [math.nan]:
126 | print("This is True")
127 |
- if math.nan in (math.nan,):
128 + if math.nan == math.nan:
129 | print("This is True")
130 |
131 | if math.nan in {math.nan}:
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:131:4
|
129 | print("This is True")
130 |
131 | if math.nan in {math.nan}:
| ^^^^^^^^^^^^^^^^^^^^^^
132 | print("This is True")
|
help: Convert to equality test
128 | if math.nan in (math.nan,):
129 | print("This is True")
130 |
- if math.nan in {math.nan}:
131 + if math.nan == math.nan:
132 | print("This is True")
133 |
134 | # Potential type differences with custom __eq__ methods
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:140:4
|
139 | obj = CustomEq()
140 | if obj in [CustomEq()]:
| ^^^^^^^^^^^^^^^^^^^
141 | pass
|
help: Convert to equality test
137 | return "custom"
138 |
139 | obj = CustomEq()
- if obj in [CustomEq()]:
140 + if obj == CustomEq():
141 | pass
142 |
143 | if obj in (CustomEq(),):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:143:4
|
141 | pass
142 |
143 | if obj in (CustomEq(),):
| ^^^^^^^^^^^^^^^^^^^^
144 | pass
|
help: Convert to equality test
140 | if obj in [CustomEq()]:
141 | pass
142 |
- if obj in (CustomEq(),):
143 + if obj == CustomEq():
144 | pass
145 |
146 | if obj in {CustomEq()}:
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_0.py:146:4
|
144 | pass
145 |
146 | if obj in {CustomEq()}:
| ^^^^^^^^^^^^^^^^^^^
147 | pass
|
help: Convert to equality test
143 | if obj in (CustomEq(),):
144 | pass
145 |
- if obj in {CustomEq()}:
146 + if obj == CustomEq():
147 | pass
note: This is an unsafe fix and may change runtime behavior

44
crates/ruff_linter/src/rules/refurb/snapshots/ruff_linter__rules__refurb__tests__FURB171_FURB171_1.py.snap
View File

@ -18,6 +18,7 @@ help: Convert to equality test
4 | print("Single-element set")
5 |
6 | if 1 in set((1,)):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:6:4
@ -37,6 +38,7 @@ help: Convert to equality test
7 | print("Single-element set")
8 |
9 | if 1 in set({1}):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:9:4
@ -56,6 +58,7 @@ help: Convert to equality test
10 | print("Single-element set")
11 |
12 | if 1 in frozenset([1]):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:12:4
@ -75,6 +78,7 @@ help: Convert to equality test
13 | print("Single-element set")
14 |
15 | if 1 in frozenset((1,)):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:15:4
@ -94,6 +98,7 @@ help: Convert to equality test
16 | print("Single-element set")
17 |
18 | if 1 in frozenset({1}):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:18:4
@ -113,6 +118,7 @@ help: Convert to equality test
19 | print("Single-element set")
20 |
21 | if 1 in set(set([1])):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:21:4
@ -132,3 +138,41 @@ help: Convert to equality test
22 | print('Recursive solution')
23 |
24 |
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:59:4
|
58 | # set() and frozenset() with NaN
59 | if math.nan in set([math.nan]):
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
60 | print("This should be marked unsafe")
|
help: Convert to equality test
56 | import math
57 |
58 | # set() and frozenset() with NaN
- if math.nan in set([math.nan]):
59 + if math.nan == math.nan:
60 | print("This should be marked unsafe")
61 |
62 | if math.nan in frozenset([math.nan]):
note: This is an unsafe fix and may change runtime behavior
FURB171 [*] Membership test against single-item container
--> FURB171_1.py:62:4
|
60 | print("This should be marked unsafe")
61 |
62 | if math.nan in frozenset([math.nan]):
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
63 | print("This should be marked unsafe")
|
help: Convert to equality test
59 | if math.nan in set([math.nan]):
60 | print("This should be marked unsafe")
61 |
- if math.nan in frozenset([math.nan]):
62 + if math.nan == math.nan:
63 | print("This should be marked unsafe")
note: This is an unsafe fix and may change runtime behavior