Make struct-like enum variants experimental

[brson]

Using #9304.

Nominating backcompat.

[catamorphism]

accepted backwards-compatible

[thestinger]

By struct-like enum variants do you mean ones with named fields?

[alexcrichton]

Yeah, this should be experimental:

enum A {
  Variant1 { foo: int }
}

[thestinger]

Would it be marked experimental because we're not sure if we want to commit to supporting it? As far as I know the implementation is shared with structs in adt.rs.

[SiegeLord]

I think struct variants have an important use case for variants with many fields. Consider code like this: https://github.com/brson/rust-sdl/blob/master/src/event.rs#L577 and https://github.com/mozilla/rust/blob/master/src/libsyntax/ast.rs#L227 . In both cases they would benefit greatly from having the variant arguments have explicit names, e.g. consider this code from my library which mirrors the rust-sdl use case: https://github.com/SiegeLord/RustAllegro/blob/master/src/events.rs#L79 and https://github.com/SiegeLord/RustAllegro/blob/master/example.rs#L39 . It seems a lot clearer than the equivalent rust-sdl code: https://github.com/brson/rust-sdl/blob/master/demo/video.rs#L38 .

[sfackler]

I've also found these extremely useful, especially in cases like https://github.com/sfackler/rust-postgres/blob/master/src/message.rs#L73

[brson]

The thinking was that they were broken. Maybe they aren't.