ICE on pattern matching Option

[pfalabella]

This program does not compile. rustc corerctly identifies my error (writing Ok instead of Some when destructuring an Option). However it also gives an ICE after the error.

fn main() {
    let a = Some(~1);
    match a {
        Ok(a) => println!("{}",a),
        None => fail!()
    }    
}

the ICE:

$ rustc error.rs
error.rs:13:9: 13:14 error: mismatched types: expected `std::option::Option<~<ge
neric integer #0>>` but found `std::result::Result<<generic #11>,<generic #12>>`
 (expected enum std::option::Option but found enum std::result::Result)
error.rs:13         Ok(a) => println!("{}",a),
                    ^~~~~
error: internal compiler error: unexpected failure
This message reflects a bug in the Rust compiler.
We would appreciate a bug report: http://static.rust-lang.org/doc/master/complem
ent-bugreport.html
note: the compiler hit an unexpected failure path. this is a bug
task 'rustc' failed at 'index out of bounds: the len is 0 but the index is 0', D
:\Heather\Contrib\P\rust\src\librustc\middle\typeck\check\vtable.rs:255

version of rustc

$ rustc -v
rustc.exe 0.10-pre (bf9c255 2014-01-23 19:56:35 -0800)
host: i686-pc-mingw32

[isabelmu]

Another way to get there:

enum A { B }
enum C<T> { D(T) }

fn main() {
  match B {
    D(a) => format!("{}", a)
  };
}

From my attempts at reproducing this, there seem to be three necessary ingredients:

• match on value of enum type
• pattern is a variant of a different, generic enum
• use generic part of the pattern in a format_args! invocation

The failure is always at line 255 of vtable.rs.