New lint for all/any after mapping to bool.

[duongdominhchau]

What it does

Eliminate map to bool if it is before a call to all/any

Categories (optional)

What is the advantage of the recommended code over the original code

Shorter code.

Drawbacks

If the map operation has side-effect, applying the suggestion will change the meaning of the program.

Example

iter
    .map(|value| value > 0)
    .all(|x| x)

Could be written as:

iter.all(|value| value > 0)

[camsteffen]

In addition to any and all, this may include a large number of transformers: all, any, map, position, flat_map, find, find_map, filter, filter_map, fold.

The lint could be named map_then_identity_tranformer or collapsible_identity_tranformer.

Also this can be generalized further. Not just identity, but any closure where the input variable is referenced only one time in both map and the following transformer. For example:

iter.map(|x| foo(x)).flat_map(|x| bar(x))
// to
iter.flat_map(|x| bar(foo(x)))

This can be called collapsible_map. I think I would prefer to only have this lint and that would cover all cases.

[henrifrancois]

I think I'd like to give this a go. Safe to claim it?

[camsteffen]

Absolutely!

[henrifrancois]

@rustbot claim

[henrifrancois]

Hard time finding time to work on this. Will still be trying to implement this but in the meantime anyone feel free to give this a shot.

[henrifrancois]

@rustbot unclaim

[tamaroning]

@rustbot claim

[tamaroning]

Hi, @camsteffen
Do you know any way to check if a closure param is referenced one time in the closure body?
Just parsing an Expr tree is a little bit tough (￣~￣；)

[camsteffen]

@tamaroning First get the ID of the closure parameter binding which is the HirId in PatKind::Binding. Then use expr_visitor to create a visitor to scan the closure body. In the visitor, use path_to_local_id to check if the current expression matches the binding.

[tamaroning]

@camsteffen
I didn't know that! Thanks!