Internal compiler error when using a trait with default implementations as a field in a struct

[andymatuschak]

I get this internal compiler error:

rust: task failed at 'option::get none', /Users/andym/Downloads/rust/src/rustc/rustc.rc:1
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug
note: try running with RUST_LOG=rustc=0,::rt::backtrace to get further details and report the results to github.com/mozilla/rust/issues
rust: task failed at 'explicit failure', /Users/andym/Downloads/rust/src/rustc/driver/rustc.rs:275
rust: domain main @0x7fd1e980c210 root task failed
rust: task failed at 'killed', /Users/andym/Downloads/rust/src/libcore/task.rs:663

When I compile this file:

pub trait Something {
    pure fn thing() -> int;
    pure fn what() -> int { 3 }
}

impl int: Something {
    pure fn thing() -> int { 4 }
}

struct AnotherThing {
    something: Something
}

fn main() {
    let at = AnotherThing {something: 4 as Something};
    at.something.what();
}

If Something has only required methods—no provided methods—then the error is not exhibited.

This is manifesting in rustc built from f96a2a2 on Mac OS 10.8.2.

[catamorphism]

Reproduced as of eed2ca6

[catamorphism]

The result is now a type error saying the object doesn't have a what method, rather than an ICE. Nominating for milestone 3, feature-complete (this is part of making default methods work).

[msullivan]

The type error is because we got rid of implicit self, so the test needed to be updated to expose the bug.

Fixed the bug earlier this week, though, but didn't realize that this was the bug for it.

[msullivan]

Marking that this was part of #2794 for tracking purposes.