rust-extensible

Extensible enums for Rust

This is a plugin form of this RfC.

Basically, if an enum is marked #[extensible], this plugin will prevent its use in a match statement lacking a wildcard. This lets library authors define stable enums whilst keeping the flexibility of extending them later.

```rust

[extensible]

enum Foo { Bar, Baz(u8), Quux } pub use Foo::*;

fn main() { let x = Bar; let mut out = match x { Bar => 1u8, Baz(y) => y, Quux => 0u8, // There is no wildcard here, so it will not compile }; println!("{}", out);

// This is fine
out = match x {
    Bar => 1u8,
    Baz(y) => y,
    _ => 0u8, // THis will compile fine
};
println!("{}", out);

} ```