Use --edition instead of -Zedition (stabilize edition flag, kind of)

[Manishearth]

Currently, Rust lets you specify the edition via -Zunstable-options -Zedition.

I'd like to stabilize the flag as --edition, such that non-nightly Rust can only pass down --edition=2015, but other versions can specify anything there.

[Manishearth]

@klnusbaum want to work on this? I suspect this would have been better to do before rust-lang/cargo#5214 landed, but I kinda forgot, sorry 😄

You may want to factor it out such that Config or Session has an edition() method that returns the edition, so that code like sess.opts.debugging_options.edition doesn't need to exist.

I'd like this to exist in a week or two, so if you don't have the time lmk and I'll just land it.

[klnusbaum]

Sure! I'd love to work on this. I'll try to take a wack at it sometime this week :)

[klnusbaum]

What are the files that I should be looking at here? librustc/session/mod.rs and librustc/session/config.rs seem like the places I need to start, but the macros in config.rs are a little crazy. Where does the rubber meet the road, i.e. where's the code that says "these options should be mapped to these fields on a struct" or something like that?

[Manishearth]

It uses getopts, I suspect you want to imitate what's done for the pretty option here.

The macros are for codegen/debugging options afaict, and we're moving this option out of there.

[Manishearth]

@klnusbaum btw, you seem to be helping out a bunch with epoch/edition related stuff. You may want to join https://gitter.im/rust-lang/WG-epoch , and let me know if you want more interesting things to work on!

[klnusbaum]

I'm starting to understand this a little more. Hoping to have something by the end of the weekend.

[klnusbaum]

I think we can mark this as done. @Manishearth mentioned that cargo needs to be switched to now use --edition so I'll open another task in the cargo repo for that.

[klnusbaum]

For reference, this was addressed with #50080

[Manishearth]

Fixed by #50080

(For future reference, write "fixes #foo" in the PR body so it gets auto-closed. Or at least mention the issue so it gets cross linked)