internal compiler error trying to match None against Err(_)

[ben0x539]

This is a reduced, invalid code snippet that produces an internal compiler error after diagnosing a type error:

fn f() {
    match None {
            Err(_) => ()
    }
}

Here is the stack traces produced by the RUST_LOG settings suggested by the original error message:

$ RUST_LOG=rustc=0,::rt::backtrace rustc foo.rs
foo.rs:3:12: 3:21 error: mismatched types: expected `core::result::Result<<V2>,<V3>>` but found `core::option::Option<<V1>>` (expected enum core::result::Result but found enum core::option::Option)
foo.rs:3             Err(_) => ()
                     ^~~~~~~~~
rust: task failed at 'index out of bounds: the len is 1 but the index is 1', /home/ben/code/repos/rust/src/rustc/middle/ty.rs:1451
/home/ben/local/lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x5d)[0x7f89a8502e9d]
/home/ben/local/lib/librustrt.so(+0x3377d)[0x7f89a851a77d]
/home/ben/local/lib/librustrt.so(upcall_fail+0x1a8)[0x7f89a8505788]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(_ZN2rt20rt_fail_bounds_check17_e739cc78d15657703_04E+0x1a0)[0x7f89a9b46cd0]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x29f504)[0x7f89a89ea504]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(_ZN6middle2ty5subst17_7a3ff3a9684ad3303_04E+0x2fb)[0x7f89a88e5dbb]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x100521)[0x7f89a884b521]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x3341dd)[0x7f89a8a7f1dd]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x32a8cf)[0x7f89a8a758cf]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x325182)[0x7f89a8a70182]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x3bc990)[0x7f89a8b07990]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x69bcc0)[0x7f89a8de6cc0]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x3326b8)[0x7f89a8a7d6b8]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x69bcc0)[0x7f89a8de6cc0]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x385240)[0x7f89a8ad0240]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x383943)[0x7f89a8ace943]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x38119a)[0x7f89a8acc19a]
/home/ben/local/lib/libsyntax-84efebcb12c867a2-0.4.so(+0xb11cd)[0x7f89a92791cd]
/home/ben/local/lib/libsyntax-84efebcb12c867a2-0.4.so(+0xb1034)[0x7f89a9279034]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(_ZN6middle6typeck11check_crate17_bbe1149ff42c4fc93_04E+0xd49)[0x7f89a8bae5b9]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(_ZN6driver6driver12compile_upto17_25761dc338c52ad63_04E+0x1646)[0x7f89a8dbbeb6]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(+0x69bcc0)[0x7f89a8de6cc0]
/home/ben/local/lib/librustc-c84825241471686d-0.4.so(_ZN6driver6driver13compile_input17_3df932b1ac436bdb3_04E+0xbd)[0x7f89a8dbf1bd]
rustc[0x4091d6]
rustc[0x412534]
rustc[0x40e9b3]
rustc[0x40d66c]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x7985f)[0x7f89a9b7b85f]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0xb9540)[0x7f89a9bbb540]
/home/ben/local/lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7f89a8503644]
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', /home/ben/code/repos/rust/src/rustc/driver/rustc.rs:275
/home/ben/local/lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x5d)[0x7f89a8502e9d]
/home/ben/local/lib/librustrt.so(+0x3377d)[0x7f89a851a77d]
/home/ben/local/lib/librustrt.so(upcall_fail+0x1a8)[0x7f89a8505788]
rustc(_rust_main+0x838)[0x411d48]
rustc[0x412534]
/home/ben/local/lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7f89a8503644]
rust: domain main @0x1779200 root task failed
rust: task failed at 'killed', /home/ben/code/repos/rust/src/libcore/task.rs:663
/home/ben/local/lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x5d)[0x7f89a8502e9d]
/home/ben/local/lib/librustrt.so(+0x3377d)[0x7f89a851a77d]
/home/ben/local/lib/librustrt.so(upcall_fail+0x1a8)[0x7f89a8505788]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(_ZN4task5yield16_9531951b4f79f8b3_04E+0xbd)[0x7f89a9b64e1d]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x946e6)[0x7f89a9b966e6]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(_ZN7private11weaken_task17_16b955f1119438ce3_04E+0xd2)[0x7f89a9b96522]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x9441b)[0x7f89a9b9641b]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0xb9540)[0x7f89a9bbb540]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x93770)[0x7f89a9b95770]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x9310e)[0x7f89a9b9510e]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x92776)[0x7f89a9b94776]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0x7985f)[0x7f89a9b7b85f]
/home/ben/local/lib/libcore-c3ca5d77d81b46c1-0.4.so(+0xb9540)[0x7f89a9bbb540]
/home/ben/local/lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7f89a8503644]

This is with rustc built on incoming at commit f96a2a2.

[catamorphism]

Reproduced as of d2ad028 -- looks like the error isn't fatal enough.

[catamorphism]

I have a fix -- just running tests now.