Remove some feature flag usage from libsyntax

[erickt]

This removes the usage of #[feature(into_cow, slice_patterns, box_syntax, box_patterns, quote, unsafe_destructor)] from being used in libsyntax. My main desire for this is that it brings me one step closer to letting syntex compile with stable rust. Hopefully this doesn't inconvenience rust development.

[rust-highfive]

r? @alexcrichton

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[Manishearth]

@bors-servo: r+

[bors]

📌 Commit c499fee has been approved by Manishearth

[erickt]

Fixed the tidy issue and eliminated a few other feature flags.

[alexcrichton]

In the past we've had some pretty bad code bloat problems by having a totally generic pretty printer, so I'm curious what instigated this change?

[erickt]

I was trying to make it easy to get to the underlying Vec so I could get rid of the reference to TraitObject and the transmute, but I can try a different approach.

[erickt]

@alexcrichton: turned out I could have saved myself a bunch of time trying to get rid of TraitObject by just using a scope and a &mut :)

... I think serde might have gotten me addicted to type parameters...

[alexcrichton]

@bors: r+ 3721bdf

Thanks!

[bors]

☔ The latest upstream changes (presumably #23985) made this pull request unmergeable. Please resolve the merge conflicts.

[erickt]

@bors: r=alexcrichton 51a2935

[bors]

⌛ Testing commit 51a2935 with merge 7805349...

[bors]

💔 Test failed - auto-linux-64-nopt-t

[Manishearth]

/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:838:13: 841:53 error: slice pattern syntax is experimental
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:838 [ast::TtToken(_, token::Ident(name_macro_rules, token::Plain)),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:839 ast::TtToken(_, token::Not),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:840 ast::TtToken(_, token::Ident(name_zip, token::Plain)),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:841 ast::TtDelimited(_, ref macro_delimed)]
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:838:13: 841:53 help: add #![feature(slice_patterns)] to the crate attributes to enable
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:845:21: 847:62 error: slice pattern syntax is experimental
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:845 [ast::TtDelimited(_, ref first_delimed),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:846 ast::TtToken(_, token::FatArrow),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:847 ast::TtDelimited(_, ref second_delimed)]
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:845:21: 847:62 help: add #![feature(slice_patterns)] to the crate attributes to enable
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:850:29: 851:80 error: slice pattern syntax is experimental
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:850 [ast::TtToken(_, token::Dollar),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:851 ast::TtToken(_, token::Ident(name, token::Plain))]
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:850:29: 851:80 help: add #![feature(slice_patterns)] to the crate attributes to enable
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:857:29: 858:80 error: slice pattern syntax is experimental
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:857 [ast::TtToken(_, token::Dollar),
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:858 ast::TtToken(_, token::Ident(name, token::Plain))]
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/parse/mod.rs:857:29: 858:80 help: add #![feature(slice_patterns)] to the crate attributes to enable
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/ext/expand.rs:1966:13: 1966:16 error: slice pattern syntax is experimental
/home/ubuntu/src/rust-buildbot/slave/auto-linux-64-nopt-t/build/src/libsyntax/ext/expand.rs:1966 [b] => b,

[erickt]

@alexcrichton: I included a few more commits that haven't been reviewed. I don't think you've seen the last 4 yet.

[alexcrichton]

Looks good to me! Could this hold off on the last commit for now though? Duplicating that kind of code is a bit unfortunate and there's still other features in use by libsyntax so we can hold off on the duplication as long as possible (hopefully!)

[erickt]

@alexcrichton: Sure no problem. I'll remove that patch for now.

[alexcrichton]

@bors: r+ 19c8d70