Unexpected compiler error when changing pointer type of self

[jedestep]

Came up with the following program:

struct BarStruct;

impl<'self> BarStruct {
  fn foo(&'self mut self) -> @mut BarStruct { self }
}

Produced this output when compiled:

rust: task failed at 'assertion failed: self.variance.is_some()', /Users/jedestep/rust/rust/src/librustc/middle/typeck/rscope.rs:182
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=1,::rt::backtrace to get further details and report the results to github.com/mozilla/rust/issues
rust: task failed at 'explicit failure', /Users/jedestep/rust/rust/src/librustc/rustc.rc:400
rust: domain main @0x7f8fe900c610 root task failed

[catamorphism]

Reproduced with 26fd428. Nominating for milestone 5, production-ready.

[catamorphism]

Accepted for production-ready

[nikomatsakis]

Should go away when #4846 is fixed

[luqmana]

After a s/'self/'a/ and s/@mut/@/ I can't reproduce the ICE. Instead it fails with a much more reasonable error:

7061.rs:6:42: 6:46 error: mismatched types: expected `@BarStruct` but found `&'a mut BarStruct` (expected @-ptr but found &-ptr)
7061.rs:6     fn foo(&'a mut self) -> @BarStruct { self }
                                                   ^~~~

This is with rustc 0.10-pre (6e7f170 2014-03-03 05:51:38 -0800). Marking as needs-test.