rust-lang/rust-clippy

website: cognitive complexity does insufficiently explain method

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#7,391 opened on Jun 22, 2021

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Description

What it does Checks for methods with high cognitive complexity.

What kind of methology is used in the code is completely missing. Is this method implemented? https://github.com/rust-lang/rust-clippy/issues/3793

Why is this bad Methods of high cognitive complexity tend to be hard to both read and maintain. Also LLVM will tend to optimize small methods > better.

The first statement is unfalsifiable due to missing definition. LLVM and most compilers do graph-based optimisations, so a long switch-case is no problem for LLVM to handle. Which is in contrast to what cognitive complexity applies as method (from my experience).

Known problems Sometimes it’s hard to find a way to reduce the complexity. Search on GitHub

It is not possible to disable unless one annotates it in every file. Many problem domains are inherently complex and splitting the code does not make the problem easier. As it works currently, it does not take into account the code graph of the control structure in a proper way and thus is insufficient.

Example No. You’ll see it when you get the warning.

Configuration This lint has the following configuration variables: cognitive-complexity-threshold: u64: The maximum cognitive complexity a function can have (defaults to 25).

Great, a configuration without understanding how they work.

Contributor guide

Tech stack
rust
Domain
documentation
Issue type
documentation
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Understanding of cognitive complexityRead issue #3793Basic Rust knowledgeFamiliarity with clippy documentation format
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
The issue requests a better explanation of the cognitive complexity methodology used by the clippy lint. Start by reviewing the referenced issue #3793 for background. Then examine the current documentation for the cognitive complexity lint on the clippy website (likely in the clippy book or documentation directory). Look at how other lints explain their implementation details. The goal is to add a clear explanation of the algorithm, possibly with a reference to the original definition of cognitive complexity. Additionally, consider addressing the criticism about LLVM optimization, perhaps by clarifying the lint's intent is about human readability, not compiler optimization.