[`flake8-bugbear`] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (`B006`) by IDrokin117 · Pull Request #20024 · astral-sh/ruff · GitHub

Summary

Resolves #20004

The implementation now supports guaranteed-mutable expressions in the following cases:

Tuple literals with mutable elements (supporting deep nesting)
Generator expressions
Named expressions (walrus operator) containing mutable components

Preserves original formatting for assignment value:

# Test case
def f5(x=([1, ])):
    print(x)

# Fix before
def f5(x=(None)):
    if x is None:
        x = [1]
    print(x)

# Fix after 
def f5(x=None):
    if x is None:
        x = ([1, ])
    print(x)

The expansion of detected expressions and the new fixes gated behind previews.

Test Plan

Added B006_9.py with a bunch of test cases
Generated snapshots

I've added this method to be able to generate an expression with parentheses. I didn't find a way to ensure it is parenthesized. Using expr to generate source code for Tuple, I got

tuple_expr = "([1], 2)"
.expr(tuple_expr) # -> "[1], 2", but expected ([1], 2)

I am not sure about this, would be appreciated for more sophisticated solution.

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

This is great thank you, and sorry for the delay! Can we experiment a bit with the fix?

Also, we should be gating this behind preview - both the expansion of detected expressions and the new fix. If you'd like, you can make these two separate functions in preview.rs since we may stabilize them independently.

@dylwil3 Thanks for your review! I've pushed some changes according to your points:

Added 2 preview flags.
Added annotation expr into fix content if any. It is gated behind preview. There already exists a test, so it might solve the annotation issue.

…ld be simple to support - tuples containing mutable expressions - generator expressions - assignment expressions containing mutable expressions

…unsafe fix

@dylwil3 Could you please review the PR again?

@dylwil3 Could you please review the PR again?

Yes! Sorry for the delay - I will not be able to get to this till the end of the week, but I have not forgotten!

Thank you for your patience and for the great contribution!

* origin/main: [`flake8-bugbear`] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (`B006`) (#20024) [`flake8-comprehensions`] Clarify fix safety documentation (`C413`) (#20640) [ty] improve base conda distinction from child conda (#20675) [`ruff`] Extend FA102 with listed PEP 585-compatible APIs (#20659) [`ruff`] Handle argfile expansion errors gracefully (#20691) [`flynt`] Fix f-string quoting for mixed quote joiners (`FLY002`) (#20662) [ty] Fix file root matching for `/` [ruff,ty] Enable tracing's `log` feature [`flake8-annotations`] Fix return type annotations to handle shadowed builtin symbols (`ANN201`, `ANN202`, `ANN204`, `ANN205`, `ANN206`) (#20612) Bump 0.13.3 (#20685) Update benchmarking CI for cargo-codspeed v4 (#20686) [ty] Support single-starred argument for overload call (#20223) [ty] `~T` should never be assignable to `T` (#20606) [`pylint`] Clarify fix safety to include left-hand hashability (`PLR6201`) (#20518) [ty] No union with `Unknown` for module-global symbols (#20664) [`ty`] Reject renaming files to start with slash in Playground (#20666) [ty] Enums: allow multiple aliases to point to the same member (#20669)

Preview feature: #20024 Rule documentation: https://docs.astral.sh/ruff/rules/mutable-argument-default/

…(`B006`) Preview feature: #20024 Rule documentation: https://docs.astral.sh/ruff/rules/mutable-argument-default/ This is currently stacked on #26950. They were technically separate preview features, but to fix some of the expanded mutable expressions requires the source-preserving fix.

IDrokin117 commented Aug 21, 2025

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dylwil3 self-requested a review August 29, 2025 19:25

dylwil3 added the rule Implementing or modifying a lint rule label Sep 1, 2025

dylwil3 suggested changes Sep 15, 2025

View reviewed changes

Comment thread crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs Outdated

IDrokin117 force-pushed the feat/ruff-20004 branch from 2f34892 to f465a06 Compare September 23, 2025 16:56

IDrokin117 commented Sep 23, 2025

View reviewed changes

Comment thread crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs Outdated

IDrokin117 requested a review from dylwil3 September 23, 2025 17:17

ntBre mentioned this pull request Sep 24, 2025

F821 false positive for __class__ in lambda expression in class definition #20562

Closed

Igor Drokin added 4 commits September 29, 2025 20:51

feat(B006): include certain guaranteed-mutable expressions which shou…

d703128

…ld be simple to support - tuples containing mutable expressions - generator expressions - assignment expressions containing mutable expressions

feat(B006): include certain guaranteed-mutable expressions which shou…

80eab43

…ld be simple to support - tuples containing mutable expressions - generator expressions - assignment expressions containing mutable expressions

feat(B006): added preview for the guaranteed mutable expressions and …

b62aca0

…unsafe fix

fix(B006): commit reviewed snapshots

7c04082

IDrokin117 force-pushed the feat/ruff-20004 branch from 7a6c7c4 to 7c04082 Compare September 29, 2025 17:51

dylwil3 added 3 commits October 3, 2025 09:10

copy source text instead of generate parenthesized expr

07ea2f3

remove expr_parenthesized method

36a0907

update snapshot

9d19c84

dylwil3 approved these changes Oct 3, 2025

View reviewed changes

dylwil3 added fixes Related to suggested fixes for violations preview Related to preview-mode features labels Oct 3, 2025

dylwil3 merged commit 673167a into astral-sh:main Oct 3, 2025
38 checks passed

BrewTestBot mentioned this pull request Oct 7, 2025

ruff 0.14.0 Homebrew/homebrew-core#247299

Merged

ntBre mentioned this pull request Oct 15, 2025

is_mutable_expr causes false negatives in B039, RUF008, RUF012, and RUF024 #20851

Open

This was referenced Jul 17, 2026

[flake8-bugbear] Stabilize source preservation in the fix (B006) #26950

Closed

[flake8-bugbear] Stabilize guaranteed-mutable expression detection (B006) #26952

Closed

ntBre added a commit that referenced this pull request Jul 20, 2026

[flake8-bugbear] Stabilize source preservation in the fix (B006)

cf0f583

Preview feature: #20024 Rule documentation: https://docs.astral.sh/ruff/rules/mutable-argument-default/

ntBre added a commit that referenced this pull request Jul 20, 2026

[flake8-bugbear] Stabilize source preservation in the fix (B006)

a46165e

Preview feature: #20024 Rule documentation: https://docs.astral.sh/ruff/rules/mutable-argument-default/

[`flake8-bugbear`] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (`B006`) by IDrokin117 · Pull Request #20024 · astral-sh/ruff · GitHub

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[flake8-bugbear] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (B006) - #20024

[flake8-bugbear] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (B006)#20024
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IDrokin117:feat/ruff-20004

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+                  pub fn expr_parenthesized(mut self, expr: &Expr) -> String {
+                      self.unparse_expr(expr, precedence::MAX);
+                      self.generate()
+                  }

[`flake8-bugbear`] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (`B006`) by IDrokin117 · Pull Request #20024 · astral-sh/ruff · GitHub

Repository navigation

[flake8-bugbear] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (B006) - #20024

[flake8-bugbear] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (B006)#20024dylwil3 merged 7 commits intoastral-sh:mainastral-sh/ruff:mainfrom IDrokin117:feat/ruff-20004IDrokin117/ruff:feat/ruff-20004Copy head branch name to clipboard

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[flake8-bugbear] Include certain guaranteed-mutable expressions: tuples, generators, and assignment expressions (B006)#20024
dylwil3 merged 7 commits into
astral-sh:mainfrom
IDrokin117:feat/ruff-20004

IDrokin117 commented Aug 21, 2025 •
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