Add Located::start, Located::end and impl Deref

[MichaReiser]

This is a follow-up to #4192 and is motivated by the discussions in astral-sh#4

The PR adds thestart and end methods to Located that return a node's start or end location. The end method falls back to returning location if end_location is None.

The PR further implements Deref for Located so that the node's fields and methods can be accessed directly: You can write located.field instead of located.node.field

[youknowone]

Thank you!

[MichaReiser]

Thank you!

Thank you for chiming in on the PR, suggesting to upstream these changes and merging them so quickly. It's great fun contributing to RustPython thanks to you :)

[DimitrisJim]

I'd slightly push back on Deref here, docs boldly state it should only be implemented on smart pointer types but we might already be doing it in other places so 😄

[MichaReiser]

I'd slightly push back on Deref here, docs boldly state it should only be implemented on smart pointer types but we might already be doing it in other places so 😄

We can undo the change if you feel strongly about.

The term smart-pointer isn't well defined and there's ongoing discussion to re-phrase or even remove the section rust-lang/rust#91004.

The way I think about it is that Located is a thin-wrapper around Node that adds source locations to it. You could probably even argue that it's, to some extend, similar to an Rc because it stores the inner data and some metadata about it (reference count / source locations)

[DimitrisJim]

I definitely do not feel that strongly!

[youknowone]

Maybe it can be anti-pattern, but we already depends on a lot for Deref for thin wrappers. And it is abused a lot in many projects 😂 . Replacing them to traits will be possible but will be painful. I hope rust have a similar features allows method call for wrappers but disallow * operator to prevent confusion between reference and wrapper.

@MichaReiser Thank you so much for paying attention to keep unified code base. You are most welcome!

[jmaargh]

FYI: Some better guidance on when and when not to Deref is currently in review: rust-lang/rust#110340