list,tuple,sequence: add slice indexing

[davidhewitt]

Follow up to #1825 to add range indexing.

Given that the decision in #1733 was that we are trying to make these APIs feel as much like idiomatic Rust as possible, I opted to make them panic on out of bounds.

This probably closes #1667 ?

[davidhewitt]

Thanks for the great review!

I reworked this to be a macro as suggested. (I threw it in internal_tricks.rs for now, like everything else ends up...)

I also made conditional use of #[track_caller] (on sufficiently new rust versions) so that the panic message points at the user's indexing code rather than internal_tricks.rs

e.g.

thread 'types::sequence::tests::test_seq_index_trait_range_from_panic' panicked at 'range start index 8 out of range for sequence of length 3', src/types/sequence.rs:512:13

[birkenfeld]

I see that the output of get_slice is currently not another PySequence, should we change this? IMO it's similar to expecting a sequence out of repeat etc.

[davidhewitt]

Yeah, I think that's reasonable.

I guess as before, implementations may actually not return a sequence. Then using further sequence APIs will fail, which is ok and sound.

[birkenfeld]

I also made conditional use of #[track_caller] (on sufficiently new rust versions) so that the panic message points at the user's indexing code rather than internal_tricks.rs

Very nice (also that we can do it conditionally)!