too_few_lines

What it does

Checks for functions with a small amount of lines.

The counter-part to too_many_lines.

It should have a configuration variable too-few-lines-threshold: u64 which should default to 1.

It should be a pedantic lint (presuming a default threshold of 1).

Advantage

• Very small functions may increase lines of code by their usage. Their signature and calls may outweigh the code duplication they remove.

Drawbacks

• Set at anything above very small (e.g 1) it can produce many unreasonable warnings.

Example

fn main() {
    let a = add(1, 2);
}
fn add(rhs: u8, lhs: u8) -> u8 {
    rhs + lhs
}

Could be written as:

fn main() {
    let a = 1 + 2;
}

fn main() {
    let a = line(4, 3, 2, 1);
}
fn line(x: u8, a: u8, b: u8, c: u8) -> u8 {
    add(add(x.pow(a), mul(x, b)), c)
}
fn mul(rhs: u8, lhs: u8) -> u8 {
    rhs * lhs
}
fn add(rhs: u8, lhs: u8) -> u8 {
    rhs + lhs
}

Could be written as:

fn main() {
    let a = 4u8.pow(3) + (4*2) + 1;
}

Start by reading the existing too_many_lines lint linked in the issue and tracing how its threshold configuration and tests are organized. Define the corresponding small-function lint with a default threshold of 1 and pedantic level, then verify that the examples and configuration behavior are covered by tests.