Show common iterators as impl Iterator within nested types

[jyn514]

"Common iterators" is intentionally in scare quotes because I don't want to bikeshed exactly what set that should be here. Basically the request is for things like vec![0].into_iter().flat_map(|| ...) to be shown as Iterator<Item = i32> instead of FlatMap<IntoIter<i32>>. As an example, this snippet:

could instead be |...| -> impl Iterator<Item = ConditionalPass>.

[jyn514]

This is similar to #3138, but with a concrete suggestion for iterators rather than "shorten all long types".

[Veykril]

We already do this shortening for hints for bare iterator types coming from std::iter(#6154)

so I suppose you are asking to extend this "shortening" for to also apply if the iterator types are nested inside other types, as for example the closure in your screenshot?

[jyn514]

Oh neat, I didn't realize you did. Yes, it would be great to extend it to nested types :)

[Veykril]

This might be tricky to implement actually as currently we merely have to check if the type implements Iterator and lives in std::iter to replace the inlay hint, otherwise we just display the HIR Type. To get this nested shortening working we would have to change how the formatting works, or maybe replace types with synthetic impl Iterator types? 🤔

[Veykril]

This seems to have been implemented at some point

[HKalbasi]

I still got this (on 09-01-2023):

Or is the issue discussed here is something different?

[Veykril]

Ah, I tested nested iterators where this seems to work i.e impl Iterator<Item = impl Iterator<...>>.