docs: clarify C901 examples have same McCabe complexity#25137
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docs: clarify C901 examples have same McCabe complexity#25137algojogacor wants to merge 1 commit into
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The 'bad' and 'good' examples in the C901 (complex-structure) documentation both have the same McCabe complexity of 4, which could be confusing since the 'Use instead' section implies the refactored version reduces complexity. Add a note explaining that the refactored version improves readability through early returns and a flatter structure, and that to meaningfully reduce McCabe complexity, complex logic should be extracted into smaller helper functions. Closes #25028
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Thanks, but we should use an example that reduces complexity or remove the "use instead" alltogether. |
ntBre
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The C901 docstring currently pairs a 3-deep `if/else` example with a guard-clause rewrite under "Use instead". Both versions have McCabe complexity 4, so the rewrite trips (or passes) C901 identically and the docs end up teaching the false equivalence "guard clauses lower McCabe complexity." A reader filed #25028 to flag this. In that thread, MichaReiser said the docs should either use an example that actually reduces complexity or drop the "Use instead" block altogether. A prior attempt (#25137) was closed with the same comment, and a follow-up trying a lookup-table example (#25186) was also closed, which makes me think the safer option is the second one MichaReiser offered. I dropped the "Use instead" block and added a short paragraph naming the techniques that genuinely reduce McCabe complexity (extracting helpers, lookup tables, lower branching factor), with an explicit note that mechanical guard-clause inversion does not. Docstring-only. `cargo dev generate-all` and `uvx prek run --from-ref main` both pass. closes #25028 --------- Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
thejchap
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May 23, 2026
The C901 docstring currently pairs a 3-deep `if/else` example with a guard-clause rewrite under "Use instead". Both versions have McCabe complexity 4, so the rewrite trips (or passes) C901 identically and the docs end up teaching the false equivalence "guard clauses lower McCabe complexity." A reader filed astral-sh#25028 to flag this. In that thread, MichaReiser said the docs should either use an example that actually reduces complexity or drop the "Use instead" block altogether. A prior attempt (astral-sh#25137) was closed with the same comment, and a follow-up trying a lookup-table example (astral-sh#25186) was also closed, which makes me think the safer option is the second one MichaReiser offered. I dropped the "Use instead" block and added a short paragraph naming the techniques that genuinely reduce McCabe complexity (extracting helpers, lookup tables, lower branching factor), with an explicit note that mechanical guard-clause inversion does not. Docstring-only. `cargo dev generate-all` and `uvx prek run --from-ref main` both pass. closes astral-sh#25028 --------- Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
anishgirianish
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May 28, 2026
The C901 docstring currently pairs a 3-deep `if/else` example with a guard-clause rewrite under "Use instead". Both versions have McCabe complexity 4, so the rewrite trips (or passes) C901 identically and the docs end up teaching the false equivalence "guard clauses lower McCabe complexity." A reader filed astral-sh#25028 to flag this. In that thread, MichaReiser said the docs should either use an example that actually reduces complexity or drop the "Use instead" block altogether. A prior attempt (astral-sh#25137) was closed with the same comment, and a follow-up trying a lookup-table example (astral-sh#25186) was also closed, which makes me think the safer option is the second one MichaReiser offered. I dropped the "Use instead" block and added a short paragraph naming the techniques that genuinely reduce McCabe complexity (extracting helpers, lookup tables, lower branching factor), with an explicit note that mechanical guard-clause inversion does not. Docstring-only. `cargo dev generate-all` and `uvx prek run --from-ref main` both pass. closes astral-sh#25028 --------- Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
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Summary
Clarify that the C901 (complex-structure) 'bad' and 'good' documentation examples have the same McCabe complexity.
Root Cause
The current documentation shows two examples — a 'bad' nested-if version and a 'Use instead' early-return version — but both have 4 decision points, giving them the same McCabe complexity of 4. This is confusing because the 'Use instead' section implies complexity reduction when the real improvement is readability.
Fix
Add a note explaining that:
Changes
crates/ruff_linter/src/rules/mccabe/rules/function_is_too_complex.rs: Added clarifying note to the C901 rule documentationTesting
Closes #25028