new lint: `vec.drain(..)` instead of `vec.clear()`

[philpax]

What it does

Checks for usage of vec.drain(..) (iterator dropped immediately) which can be replaced with vec.clear()

Lint Name

unnecessary_vec_drain

Category

style

Advantage

• Makes intent clearer
• Marginally more efficient, especially in debug builds

Drawbacks

No response

Example

vec.drain(..);

Could be written as:

vec.clear();

[carloosaf]

@rustbot claim

[koka831]

@rustbot claim

[lana99]

@rustbot claim

[czotomo]

Hi @lana99, are you working on this or is this up for grabs?

[lana99]

I’ve been busy but I will probably push code for the issue this weekend. @czotomo

[bluthej]

Hi @lana99, I don't know if you are still working on this but as I was looking at #9623 I was thinking that the example in the documentation you provided might be improved from this:

let mut vec: Vec<i32> = Vec::new();
vec.drain(..);

to this:

let mut v = vec![0, 1, 2];
v.drain(..);

to make it conform to the examples of the Drain documentation and the Vec documentation.

Sorry if this isn't the place to discuss this, and I don't mean to be nosy, I was just trying to learn from other people's PR how to contribute and yours caught my attention 🙂