clippy::excessive_nesting: Checks for blocks which are nested beyond a certain threshold. Note: Even though this lint is warn-by-default, it will only trigger if a maximum nesting level is defined in the clippy.toml file

// lib.rs
pub mod a {
    pub struct X;
    impl X {
        pub fn run(&self) {
            if true {
                // etc...
            }
        }
    }
}

// a.rs
fn private_run(x: &X) {
    if true {
        // etc...
    }
}

pub struct X;
impl X {
    pub fn run(&self) {
        private_run(self);
    }
}

#[allow(clippy::excessive_nesting)]
fn my_function() { /* ... */ }

[lints.clippy]
excessive_nesting = "allow"

cargo clippy -- -A clippy::excessive-nesting

Clippy's own documentation

What it does

Checks for blocks which are nested beyond a certain threshold.

Note: Even though this lint is warn-by-default, it will only trigger if a maximum nesting level is defined in the clippy.toml file.

Why is this bad?

It can severely hinder readability.

Example

An example clippy.toml configuration:

excessive-nesting-threshold = 3

// lib.rs
pub mod a {
    pub struct X;
    impl X {
        pub fn run(&self) {
            if true {
                // etc...
            }
        }
    }
}

Use instead:

// a.rs
fn private_run(x: &X) {
    if true {
        // etc...
    }
}

pub struct X;
impl X {
    pub fn run(&self) {
        private_run(self);
    }
}

// lib.rs
pub mod a;

Configuration

• excessive-nesting-threshold: The maximum amount of nesting a block can reside in

  (default: 0)

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

Related lints

• too_many_argumentsChecks for functions with too many parameters
• clone_on_copyusing `clone` on type `u64` which implements the `Copy` trait
• type_complexityChecks for types used in structs, parameters and let declarations above a certain complexity threshold
• double_comparisonsChecks for double comparisons that could be simplified to a single expression
• double_parensunnecessary parentheses
• duration_subsecChecks for calculation of subsecond microseconds or milliseconds from other Duration methods
• explicit_auto_derefderef which would be done by auto-deref
• explicit_counter_loopChecks for loops over slices with an explicit counter and suggests the use of .enumerate()
• explicit_writeChecks for usage of write!() / writeln()! which can be replaced with (e)print!() / (e)println!()

All 847 Clippy lints · Rust compiler errors · Cargo.toml checker