ICE - rustc panic on using let to assign to already initialized array

[impo]

I accidentally used let statements when I was trying to assign to elements of a bytearray instead of just the equals sign. An ICE resulted.

I tried this code:

fn to_size(tag_size: u32) -> [u8; 4] {
    let mut bytes: [u8; 4] = [0; 4];
    assert!(tag_size < 2.pow(28), "to_size: Number too big to convert!");
    let bytes[0] = (tag_size & 0x0FE00000 >> 21) as u8;
    let bytes[1] = (tag_size & 0x001FC000 >> 14) as u8;
    let bytes[2] = (tag_size & 0x00003F80 >> 7) as u8;
    let bytes[3] = (tag_size & 0x0000007F >> 0) as u8;
    bytes
}

fn main() {
    println!("{:?}", to_size(257));
}

I expected the compiler to recognize those lets as errors, but instead it panicked with:

src/main.rs:12:9: 12:14 error: internal compiler error: ident only path should have been covered already
src/main.rs:12     let bytes[0] = (tag_size & 0x0FE00000 >> 21) as u8;
                       ^~~~~
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:130

Meta

rustc --version --verbose:
rustc 1.0.0-beta (9854143 2015-04-02) (built 2015-04-02)
binary: rustc
commit-hash: 9854143
commit-date: 2015-04-02
build-date: 2015-04-02
host: x86_64-unknown-linux-gnu
release: 1.0.0-beta

Backtrace:

stack backtrace:
   1:     0x7fea622273c8 - sys::backtrace::write::h179e141147f9ee14IJC
   2:     0x7fea62252770 - panicking::on_panic::h6aa569d33389f0cfsXI
   3:     0x7fea6218a4a3 - rt::unwind::begin_unwind_inner::h082f07869f4b9731ACI
   4:     0x7fea5f55004d - rt::unwind::begin_unwind::h13428428822164950735
   5:     0x7fea5f54fff3 - diagnostic::SpanHandler::span_bug::he82cb6427e6a50a8jnB
   6:     0x7fea5f57779a - parse::parser::Parser<'a>::parse_pat::ha10816fc85a711f2ADH
   7:     0x7fea5f58c08a - parse::parser::Parser<'a>::parse_local::h7a4b73a54cfe440eUUH
   8:     0x7fea5f58c8af - parse::parser::Parser<'a>::parse_stmt_::hc177f9743625a47b1XH
   9:     0x7fea5f585a5a - parse::parser::Parser<'a>::parse_block_tail::h39c4a68e017bc6c6l8H
  10:     0x7fea5f570e6d - parse::parser::Parser<'a>::parse_inner_attrs_and_block::h11a14d825d017327e7H
  11:     0x7fea5f5996da - parse::parser::Parser<'a>::parse_item_fn::h5e181fed3ab83833pII
  12:     0x7fea5f5902a6 - parse::parser::Parser<'a>::parse_item_::h400393f2ccce4b57jyJ
  13:     0x7fea5f59f3ea - parse::parser::Parser<'a>::parse_mod_items::h9961b2bcefd3983fo4I
  14:     0x7fea5f5a5a75 - parse::parser::Parser<'a>::parse_crate_mod::hb6ea15a6eba26ddd7WJ
  15:     0x7fea5f5ba8f5 - parse::parse_crate_from_file::h4c866de8bdd6168diMQ
  16:     0x7fea628b5a48 - driver::phase_1_parse_input::closure.15614
  17:     0x7fea6288cc63 - driver::phase_1_parse_input::hddfc72484068c586Nqa
  18:     0x7fea62888fa7 - driver::compile_input::h7c62c2870ff901f6Qba
  19:     0x7fea62941a25 - run_compiler::hc815b49ce638c28eV4b
  20:     0x7fea6293f33d - boxed::F.FnBox<A>::call_box::h4290333406520961126
  21:     0x7fea6293e879 - rt::unwind::try::try_fn::h13999576404798567721
  22:     0x7fea622cec68 - rust_try_inner
  23:     0x7fea622cec55 - rust_try
  24:     0x7fea6293eb4b - boxed::F.FnBox<A>::call_box::h14489442628055152240
  25:     0x7fea6223d781 - sys::thread::create::thread_start::h02b7da32b4d7a4aaExH
  26:     0x7fea5c02e373 - start_thread
  27:     0x7fea61dfd27c - __clone
  28:                0x0 - <unknown>

[bombless]

one-line reproduce: http://is.gd/iBkohb

fn a() { let b[] }

EDIT:
but not on my rustc:

$ rustc h.rs
h.rs:1:18: 1:19 error: expected one of `:`, `;`, `=`, or `@`, found `[`
h.rs:1 fn main() { let b[] }

$ rustc -vV
rustc 1.0.0-dev (966d0e466 2015-04-07) (built 2015-04-07)
binary: rustc
commit-hash: 966d0e466536a3715b9d10308e9a2ed999285093
commit-date: 2015-04-07
build-date: 2015-04-07
host: x86_64-pc-windows-gnu
release: 1.0.0-dev

[bombless]

Maybe dup of #22897
But ... my rustc don't ICE this

$ rustc h.rs
h.rs:4:14: 4:15 error: expected one of `:`, `;`, `=`, or `@`, found `[`
h.rs:4     let bytes[0] = (tag_size & 0x0FE00000 >> 21) as u8;

$ rustc -vV
rustc 1.0.0-dev (966d0e466 2015-04-07) (built 2015-04-07)
binary: rustc
commit-hash: 966d0e466536a3715b9d10308e9a2ed999285093
commit-date: 2015-04-07
build-date: 2015-04-07
host: x86_64-pc-windows-gnu
release: 1.0.0-dev

[bombless]

(These ICEs happen on different places, this one is on front-end, so maybe it has been fixed by recent parser rewrite.)