Needless call of to_vec() on temporary Vec

What it does

When to_vec() is called on temporary Vec<_> the lint should warn that to_vec() is not needed and causes extra allocation. (Suggesting removing it.)

Categories

• Kind: performance

What is the advantage of the recommended code over the original code

• One less allocation
• More concise code (the returned value is already a Vec<_>)

Drawbacks

None.

Example

(playground)

fn create_vec() -> Vec<u8> {
    vec![1, 2, 42]
}

fn main() {
    println!("{:?}", create_vec().to_vec());
}

Could be written as:

fn create_vec() -> Vec<u8> {
    vec![1, 2, 42]
}

fn main() {
    println!("{:?}", create_vec());
}

Start with the Rust examples in the issue and inspect Clippy's existing lint and test conventions for method calls. Confirm the temporary Vec case and define tests covering the suggested removal of to_vec(); done means the lint detects the unnecessary allocation without flagging necessary calls.