Clippy lints / Restriction
Clippy lint · Restriction · checked with Clippy 0.1.99
clippy::cognitive_complexity: We used to think it measured how hard a method is to understand
What it meansWe used to think it measured how hard a method is to understand. It is in the restriction group and off by default.
Does it matter?
Ideally, we would like to be able to measure how hard a function is to understand given its context (what we call its Cognitive Complexity). But that’s not what this lint does. See “Known problems”
Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Turn it off, or on
It is off by default. To use it, set it to warn or deny:
Whole crate (Cargo.toml)
[lints.clippy]
cognitive_complexity = "warn"In code
#![warn(clippy::cognitive_complexity)]One run
cargo clippy -- -W clippy::cognitive-complexityThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Settings in clippy.toml
cognitive-complexity-threshold: The maximum cognitive complexity a function can have
Clippy's own documentation
What it does
We used to think it measured how hard a method is to understand.
Why is this bad?
Ideally, we would like to be able to measure how hard a function is to understand given its context (what we call its Cognitive Complexity). But that’s not what this lint does. See “Known problems”
Known problems
The true Cognitive Complexity of a method is not something we can
calculate using modern technology. This lint has been left in
restriction so as to not mislead users into using this lint as a
measurement tool.
For more detailed information, see rust-clippy#3793
Lints to consider instead of this
Past names
- cyclomatic_complexity
Configuration
-
cognitive-complexity-threshold: The maximum cognitive complexity a function can have(default:
25)
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
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- module_name_repetitionsDetects public item names that are prefixed or suffixed by the containing public module’s name
- expect_usedChecks for .expect() or .expect_err() calls on Results and .expect() call on Options
- big_endian_bytesuse of `to_be_bytes`
- cfg_not_testcode is excluded from test builds
- clone_on_ref_ptrChecks for usage of .clone() on a ref-counted pointer, (Rc, Arc, rc::Weak, or sync::Weak), and suggests calling Clone via unified function syntax instead (e.g., Rc::clone(foo))
- create_dircalling `std::fs::create_dir` where there may be a better way
- dbg_macroChecks for usage of the dbg! macro
- decimal_literal_representationWarns if there is a better representation for a numeric literal
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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