$ rustc --version
rustc 0.6 (ebba8b4 2013-03-15 22:39:42 -0700)
host: x86_64-unknown-linux-gnu

$ rm -f test.rs && touch test.rs && RUST_LOG=rustc=1,::rt::backtrace rustc test.rs --lib -o ""
warning: missing crate link meta name, using ``as default
warning: missing crate link metavers, using`0.0` as default
rust: task failed at 'assertion failed: !ecx.link_meta.name.is_empty()', /home/lime/src/rust/src/librustc/metadata/encoder.rs:1148
/home/lime/usr/rust/bin/../lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x4b)[0x7f569710b75b]
/home/lime/usr/rust/bin/../lib/librustrt.so(+0x2c039)[0x7f569711c039]
/home/lime/usr/rust/bin/../lib/librustrt.so(upcall_fail+0x190)[0x7f569710d550]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x1064db)[0x7f569a42f4db]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x106482)[0x7f569a42f482]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(_ZN3sys12begin_unwind17_7cd364c41f10422f3_06E+0x71)[0x7f569a37afa1]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(_ZN3sys11fail_assert15_7ab993b54e9a433_06E+0x230)[0x7f569a384550]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x82ebc6)[0x7f569937fbc6]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8ac164)[0x7f56993fd164]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN8metadata7encoder15encode_metadata17_eac9ebefd2dd983c3_06E+0x759)[0x7f5698dfad89]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN6middle5trans4base14write_metadata17_9473cd474ecf143d3_06E+0x8a)[0x7f5698dfa10a]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN6middle5trans4base11trans_crate17_cad9f57a7299f4c43_06E+0x12cc)[0x7f5698dfff9c]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x86ca10)[0x7f56993bda10]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN6driver6driver12compile_rest17_4f584da1f267ffac3_06E+0x417a)[0x7f56993ba8fa]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8ac164)[0x7f56993fd164]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN6driver6driver12compile_upto17_b3a99447756d7d313_06E+0x108)[0x7f56993bdbc8]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8ac164)[0x7f56993fd164]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN6driver6driver13compile_input17_894c3210c26b27423_06E+0xca)[0x7f56993be00a]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN12run_compiler17_3e88db675ebe9e253_06E+0x214a)[0x7f56993edc1a]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8a9aa1)[0x7f56993faaa1]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8a5edb)[0x7f56993f6edb]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8ac164)[0x7f56993fd164]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0xd015e)[0x7f569a3f915e]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x14ffa4)[0x7f569a478fa4]
/home/lime/usr/rust/bin/../lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7f569710bfa4]
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', /home/lime/src/rust/src/librustc/rustc.rc:359
/home/lime/usr/rust/bin/../lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x4b)[0x7f569710b75b]
/home/lime/usr/rust/bin/../lib/librustrt.so(+0x2c039)[0x7f569711c039]
/home/lime/usr/rust/bin/../lib/librustrt.so(upcall_fail+0x190)[0x7f569710d550]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x1064db)[0x7f569a42f4db]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x106482)[0x7f569a42f482]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(_ZN3sys12begin_unwind17_7cd364c41f10422f3_06E+0x71)[0x7f569a37afa1]
/home/lime/usr/rust/bin/../lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x14ffa4)[0x7f569a478fa4]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN7monitor17_c8b32a4d18d0ac153_06E+0x1645)[0x7f56993f02d5]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(+0x8ac164)[0x7f56993fd164]
/home/lime/usr/rust/bin/../lib/librustc-c84825241471686d-0.6.so(_ZN4main16_706f4ee7413ae583_06E+0x7e)[0x7f56993fcd7e]
/home/lime/usr/rust/bin/../lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7f569710bfa4]
rust: domain main @0x15cf3c0 root task failed

It fails because no library name is given anywhere. There should be some user-friendly error message instead of fail_unless!.
(What I actually tried at first is -o . which gives same error.)