New lint: inspect-then-for_each on iterators should be simplified

[scottmcm]

Inspired by the change made in https://github.com/rust-lang/rust/pull/69022/files#diff-d1ff3aad2daeb77432493d91c41b722bL147

When an inspect is followed by for_each, that's the same as just doing the thing in the inspect at the beginning of the closure in the for_each.

It's possible that this should only be suggested when a brace-bodied closure is already being passed to for_each, like

    .inspect(|x| do_something(x, 2))
    .for_each(|x| {
        do_more(x);
        update_something(x);
    });

which can just be

    .for_each(|x| {
        do_something(x, 2);
        do_more(x);
        update_something(x);
    });

But not for something like .inspect(foo).for_each(bar), where it's not obvious that the closure is better. (It's not bad, but not an obvious improvement.)

[ebroto]

Sure, go ahead!

[nahuakang]

Looking for a new issue. If the original volunteer isn't working on this, I'd like to take a look at this issue this weekend :) @ebroto @flip1995

[flip1995]

Go ahead! :)

[nahuakang]

@flip1995 Off your mind, do you remember a lint with similar logic that I can study a bit? 🙏

(Update: Started researching on Jan 10th, 2021).

[flip1995]

Take a look at the methods module. There is also the infrastructure already implemented, you'll need to implement this lint.

[joao-conde]

Was this not closed by #6577 ?