`option_vec`, a lint that checks for `Option<Vec<T>>`

What it does

Checks for instances of Option<Vec<T>>, and recommends that they be converted to Vec<T>.

Advantage

Option<Vec<T>> holds very little advantage over Vec<T>, as a Vec<T> can already hold zero items.

If the user wishes to enforce that a Vec<T> have some number of values, they can use Rust's type system to enforce this:

pub struct MyAst {
    /// Must have at least one value
    identifiers: Vec<String>,
}
// ...can be rewritten as...
pub struct MyAst {
    first_identifier: String,
    other_identifiers: Vec<String>,
}

(Although this may result in more complex code when consuming structs made this way)

Drawbacks

I do not know of any drawbacks to this lint. If I think of any, I will edit them into this section.

Example

pub struct MyAst {
    identifiers: Option<Vec<String>>,
}

Could be written as:

pub struct MyAst {
    identifiers: Vec<String>,
}

Start in the rust-clippy repository by locating existing lints that inspect Rust type structure, then review their associated tests and documentation patterns. Implement a lint for Option<Vec> that recommends Vec, and verify that the example pattern is detected without unwanted matches.