new lint: find unneccessary Some(x).and_then(|y| Some(y ..))

[matthiaskrgr]

What it does

Catch Some(..).and_then(|..| Some(..)) patterns.

What does this lint do?
Suggest to simplify the statement to Some(do something with x and y)
For example Some(3).and_then(|x| Some(x+4)); could be simplified to Some(3+4)

Categories (optional)

Complexity, maybe pedantic.

What is the advantage of the recommended code over the original code
It's way easier to understand

Drawbacks

None.

Example

Some(3).and_then(|x| Some(x+4));

Could be written as:

Some(3+4)

[alex-700]

@matthiaskrgr
.and_then(|x| Some(..)) perfectly triggers bind_instead_of_map lint. So it seems this lint idea should be about Some(x).map(|x| foo(x)), which should be replaced with Some(foo(x)) for every expression foo.

[matthiaskrgr]

Yes, Some(..).map() could be futher simplified if we know that we will have Some(x..) at the beginning of the statement.

[jonboh]

@rustbot claim