Use local_inner_macros to remove the need to import 'sel_impl' when importing 'sel'

[mehcode]

Fixes #69. As far as I can tell the weird __objc__* macros are needed as the rewrite to $crate:: happens for all crates and there is no opt-out.

[SSheldon]

I need to read up more on the macro changes, but... I'm really surprised that the proper solution is to redefine all of the std macros in every crate!?

[mehcode]

This is if you want to remain compatible with old versions. You can just objc::sel_impl! inside the macros and it'll work but only as of when that's stable.

Note I'm not 100% here but it seems to be what others are doing.

[mehcode]

@SSheldon rust-lang/rust#55268 (comment)

Seems the recommendation is to add a proxy macro on top of your macros that only calls internal macros that then can call std macros freely.

[richard-uk1]

(saw the link in the other issue) I think the idea is that this will only be required transitively - since you can update rust minor versions without breakage using 2015 edition, hopefully everyone will update and the $crate:: solution will be usable in the end.

[SSheldon]

Thank you for your work here and helping me understand the macro changes! :)

At this point my plan is just to publish a version 0.3 of this crate which drops support for Rust 2015. I've merged #76 which switched the macros to use the $crate prefix, and in 39a6d52 the sel_impl! macro is actually removed entirely. So I believe this change is no longer necessary and I'll close out this PR.

[aloucks]

This is still an issue. When exporting a macro that calls send_msg!, the compiler fails to find the sel! macro unless the old style #[macro_use] extern crate objc is used.

[SSheldon]

Thanks for the reminder @aloucks, sorry for any confusion my comment caused. The issue is fixed in master, but I have not yet published a new version. The next version is going to be 0.3, the first breaking change to objc in 3 years, so I'm taking things a little slow to make sure it puts this crate in a good position for another 3 years ;)