Feature Request: Top-level comment for license notice in .rs files

[psandana]

 I want to request/propose an optional feature that will be handy for some projects. Often, projects would like to state their license in the top-level part of every source file. This includes private and public licenses.

It would be handy a formatting option that, if enabled and configured,:

• Checks the presence of a given text as a top-level comment (with // <my comment).
• Introduces the given text as a top-level comment if missing.

Example:

use something;

fn main() {
something::do_sth();
}

to

// Licensed under the MIT License.
use something;

fn main() {
something::do_sth();
}

This could be a single-line, or multi-line comment, acknowledging that some projects may have 2 or more licenses.

[ytmimi]

There was a time when rustfmt did something like this, but we dropped support for it because we felt that rustfmt wasn't the right tool. You can read more at https://github.com/rust-lang/rustfmt/issues/5103