Rename either --cfg procmacro2_unstable or --features proc-macro2/unstable

[dtolnay]

These are basically orthogonal flags so it is confusing to give them such similar names. Someone may want to use procmacro2_unstable without proc-macro2/unstable to get the emulation of line and column from #36 on the stable compiler, or may want to use proc-macro2/unstable without procmacro2_unstable to get real spans without the semver-exempt APIs.

[alexcrichton]

How about changing the Cargo feature to nightly or rustc-nightly?

[dtolnay]

👍 for either of those. I might go with --cfg procmacro2_semver_exempt and --features proc-macro2/nightly.

Want me to do proc-macro2 0.2 with a semver-trick to bridge 0.1's unstable feature to 0.2's nightly feature? Or go to 0.2 without a semver-trick? Or just make both changes in 0.1 because ?

[mystor]

Yeah - sorry about the bad naming. I wasn't a big fan of it at the time either :-/.

I called it procmacro2_unstable to match the rayon_unstable cfg flag which rayon uses: https://github.com/rayon-rs/rayon#semver-policy-the-rayon-core-crate-and-unstable-features

[alexcrichton]

@dtolnay I'd personally be ok with just shipping everything in 0.1 (e.g. just commenting that a feature is disabled in Cago.toml), and I'd be fine to rename the --cfg whenever!

[alexcrichton]

(also the names you proposed seemed fine by me, if you're gonna send a PR feel free to decide!)