Pattern matching with overlapping matches crash the compiler

[haralkar]

The following code, compiled on Ubuntu 12.04.3 LTS Precise Pangolin - Release i386 (20130820.1) :

fn main() {
    let sl = ~[1,2,3];
    let v : int = match sl.as_slice() {
        [] => 0,
        [a,b,c] => 3,
        [a, ..rest] => a,
        [10,a, ..rest] => 10
    };
}

causes rustc to spew forth:

error: internal compiler error: unexpected failure
This message reflects a bug in the Rust compiler. 
We would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: the compiler hit an unexpected failure path. this is a bug
Ok(task 'rustc' failed at 'called `Option::unwrap()` on a `None` value', /home/haralkar/source/other/rust/src/libstd/option.rs:152
)

stack trace:

#0  0xb7b201f0 in rust_fail () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#1  0xb7b201ca in rt::unwind::Unwinder::begin_unwind::h0fb1c94e84003260fVl::v0.10.pre () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#2  0xb7a5b8fc in rt::unwind::begin_unwind_inner::h773d77f533ab0b7f63l::v0.10.pre () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#3  0xb4d92472 in rt::unwind::begin_unwind::hef0624ac43bd2c30lut::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#4  0xb5115c1d in middle::check_match::is_useful_specialized::h2768080653796199dAv::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#5  0xb511238a in middle::check_match::is_useful::he651c1f6fa4baa58Osv::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#6  0xb510acc3 in middle::check_match::check_expr::h7a2f3f3075653f85L6u::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#7  0xb511be40 in visit::walk_local::h62e699c47b530baa6Nx::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#8  0xb510d091 in middle::check_match::CheckMatchVisitor.Visitor$LT$$LP$$RP$$GT$::visit_local::ha5f445c46fcd4cdeV4u::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#9  0xb510f4b8 in visit::walk_decl::h56fc78a0011a49f22Mx::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#10 0xb510f3a7 in visit::walk_stmt::h5a83bf7c9e1926ddKLx::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#11 0xb510f300 in visit::walk_block::h5fe9aa45b8c870b51Gx::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#12 0xb511c3ea in visit::walk_fn::h2d0a7d76b5928a56TXx::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#13 0xb510d3c1 in middle::check_match::CheckMatchVisitor.Visitor$LT$$LP$$RP$$GT$::visit_fn::h5d86c04b034efca9h5u::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#14 0xb510e166 in visit::walk_item::h2046ebdf6b6a01e8o6z::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#15 0xb510d62c in middle::check_match::check_crate::h743fc3cd5a0af3f1Z5u::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#16 0xb53a124c in driver::driver::phase_3_run_analysis_passes::closure () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#17 0xb5105333 in util::common::time::h03cd35a5f105859447j::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#18 0xb539e988 in driver::driver::phase_3_run_analysis_passes::h3d5ff619b94fc529sZh::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#19 0xb53a41b6 in driver::driver::compile_input::hcf12d2e8a6a52e3f2mi::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#20 0xb53c6f42 in run_compiler::haa0a4958670ee4faueq::v0.10.pre () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#21 0xb53d800c in main_args::closure () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#22 0xb53d6583 in monitor::closure () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#23 0xb53d1c16 in task::TaskBuilder::try::closure () from /usr/local/bin/../lib/librustc-0d83f02f-0.10-pre.so
#24 0xb79bc808 in task::bootstrap_green_task::closure () from /usr/local/bin/../lib/libgreen-80d9e76a-0.10-pre.so
#25 0xb7b19659 in rt::task::Task::run::closure () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#26 0xb7b20134 in rt::unwind::Unwinder::try::try_fn::h7ffff9688f83cea7bUl::v0.10.pre () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#27 0xb7b23573 in rust_try () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#28 0xb7b1951b in rt::task::Task::run::he29d8027dadeaed4wvj::v0.10.pre () from /usr/local/bin/../lib/libstd-966edb7e-0.10-pre.so
#29 0xb79bc6d7 in task::bootstrap_green_task::h24b4ab701c781efax8b::v0.10.pre () from /usr/local/bin/../lib/libgreen-80d9e76a-0.10-pre.so
#30 0x00000000 in ?? ()

[Armavica]

Very similar to #11241.
I managed to get a shorter MCE:

fn main() {
    match ~[] {
        [] => (),
        [2, ..] => (),
        [3, 4, ..] => ()
    };
}

[daimrod]

I think I've encounter the same error with the following code:

fn main() {
    enum List {
        Cons(int, ~List),
        Nil
    }

    let x = ~Cons(1, ~Nil);
    match *x {
        Cons(a, ~ref next) => (),
        Cons(b, ~Nil) => (),
        _ => ()
    }
}

With this build:

$ rustc -v
rustc 0.11-pre-nightly (e415c25 2014-04-07 21:21:47 -0700)
host: x86_64-unknown-linux-gnu

(I couldn't use the shorter MCE because apparently unique vector patterns are no longer supported)

Here is the backtrace:

task 'rustc' failed at 'index out of bounds: the len is 0 but the index is 0', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/librustc/middle/check_match.rs:250
stack backtrace:
   1:     0x7ffff4cf08d0 - rt::backtrace::imp::write::hbf83dfcc05310575AAa::v0.11.pre
   2:     0x7ffff4c52410 - rt::unwind::begin_unwind_inner::h72aa261e64bf1fd83aa::v0.11.pre
   3:     0x7ffff4c52380 - rt::unwind::begin_unwind::h4b893fbf219dd919Daa::v0.11.pre
   4:     0x7ffff4cf04e0 - rt::unwind::begin_unwind_raw::h93661c3a4ab845afc89::v0.11.pre
   5:     0x7ffff4c516b0 - rt::unwind::fail_::h01af7c814d53a60dQ59::v0.11.pre
   6:     0x7ffff4cf0550 - rt::unwind::fail_bounds_check::closure.41280
   7:     0x7ffff4c535e0 - rt::unwind::fail_bounds_check::h4ad50d6b3ee732e1d69::v0.11.pre
   8:     0x7ffff5c7f740 - middle::check_match::is_useful::h50ad727595973596onu::v0.11.pre
   9:     0x7ffff5c86d20 - middle::check_match::is_useful_specialized::h7bf269c0b1d4ff84Itu::v0.11.pre
  10:     0x7ffff5c7f740 - middle::check_match::is_useful::h50ad727595973596onu::v0.11.pre
  11:     0x7ffff5c86d20 - middle::check_match::is_useful_specialized::h7bf269c0b1d4ff84Itu::v0.11.pre
  12:     0x7ffff5c7f740 - middle::check_match::is_useful::h50ad727595973596onu::v0.11.pre
  13:     0x7ffff5c7f740 - middle::check_match::is_useful::h50ad727595973596onu::v0.11.pre
  14:     0x7ffff5c86d20 - middle::check_match::is_useful_specialized::h7bf269c0b1d4ff84Itu::v0.11.pre
  15:     0x7ffff5c7f740 - middle::check_match::is_useful::h50ad727595973596onu::v0.11.pre
  16:     0x7ffff5c79000 - middle::check_match::check_expr::hf7e16ae699ad3b0ai4t::v0.11.pre
  17:     0x7ffff5c7ebd0 - visit::walk_expr_opt::h2b6380fdab1223ffi4t::v0.11.pre
  18:     0x7ffff5c7b9f0 - middle::check_match::check_fn::h732a3f7e2aef6fbbD6u::v0.11.pre
  19:     0x7ffff5c7c5f0 - visit::walk_item::h5b4743caefa33010p4v::v0.11.pre
  20:     0x7ffff5c7bc70 - middle::check_match::check_crate::hf456e2a1e5a27a8eD3t::v0.11.pre
  21:     0x7ffff5c74600 - util::common::time::h7270488e3f9a7dadMug::v0.11.pre
  22:     0x7ffff60a9290 - driver::driver::phase_3_run_analysis_passes::h5bc132a1236cdb1dqje::v0.11.pre
  23:     0x7ffff60afcc0 - driver::driver::compile_input::h5158f3c2b13a0794nIe::v0.11.pre
  24:     0x7ffff60d3540 - run_compiler::h462d0269b5e002b949l::v0.11.pre
  25:     0x7ffff60ea810 - main_args::closure.91855
  26:     0x7ffff60e9140 - monitor::closure.91740
  27:     0x7ffff60e4a70 - task::TaskBuilder::try::closure.91515
  28:     0x7ffff53754d0 - task::spawn_opts::closure.7786
  29:     0x7ffff4cebd60 - rt::task::Task::run::closure.41185
  30:     0x7ffff4cf7310 - rust_try
  31:     0x7ffff4cebba0 - rt::task::Task::run::h2c4ca697d400385cz37::v0.11.pre
  32:     0x7ffff53752a0 - task::spawn_opts::closure.7759
  33:     0x7ffff4cef410 - rt::thread::thread_start::h934e1ab986d86e35gI8::v0.11.pre
  34:     0x7ffff2525fa0 - start_thread
  35:     0x7ffff4926a09 - __clone
  36:                0x0 - <unknown>

[huonw]

@daimrod that's possibly slightly different (at least, the failure message is different, although they're in the same area of code).

Btw, the MCE still works when used without unique vectors:

fn main() {
    match &[] {
        [] => (),
        [2, ..] => (),
        [3, 4, ..] => ()
    }
}

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'called `Option::unwrap()` on a `None` value', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libstd/option.rs:264
stack backtrace:
   1:     0x7fde205896a0 - rt::backtrace::imp::write::h167f38c59baeff8aqRa::v0.11.pre
   2:     0x7fde204eafa0 - rt::unwind::begin_unwind_inner::hc4665026b45f6a5aTra::v0.11.pre
   3:     0x7fde21141f60 - rt::unwind::begin_unwind::ha806566b31ba8340qXp::v0.11.pre
   4:     0x7fde21538520 - middle::check_match::is_useful_specialized::h5bccec681de6c692gAu::v0.11.pre
   5:     0x7fde21530f40 - middle::check_match::is_useful::h5ffe9bbdddc6b96fWtu::v0.11.pre
   6:     0x7fde2152a770 - middle::check_match::check_expr::hd8afce200b8873afQau::v0.11.pre
   7:     0x7fde215303d0 - visit::walk_expr_opt::h85f69636933670ccMku::v0.11.pre
   8:     0x7fde2152d160 - middle::check_match::check_fn::h67f8bdc6ca535dcbbdv::v0.11.pre
   9:     0x7fde2152de10 - visit::walk_item::hd4abe3032d44eb0fQjw::v0.11.pre
  10:     0x7fde2152d3e0 - middle::check_match::check_crate::h945724cd4dbeabc2bau::v0.11.pre
  11:     0x7fde21525c70 - util::common::time::h8ad21ae303e4a453Swg::v0.11.pre
  12:     0x7fde21963e80 - driver::driver::phase_3_run_analysis_passes::h679c7da862d3eab5sje::v0.11.pre
  13:     0x7fde2196a890 - driver::driver::compile_input::h78d619679e701e77nIe::v0.11.pre
  14:     0x7fde2198edf0 - run_compiler::h304797548f90c81exgm::v0.11.pre
  15:     0x7fde219a64f0 - main_args::closure.91891
  16:     0x7fde219a4e20 - monitor::closure.91776
  17:     0x7fde219a0700 - task::TaskBuilder::try::closure.91542
  18:     0x7fde20c1aab0 - task::spawn_opts::closure.7971
  19:     0x7fde205846d0 - rt::task::Task::run::closure.40115
  20:     0x7fde20590230 - rust_try
  21:     0x7fde20584510 - rt::task::Task::run::h5360bb699175a8aefi8::v0.11.pre
  22:     0x7fde20c1a880 - task::spawn_opts::closure.7944
  23:     0x7fde205881e0 - rt::thread::thread_start::h8ec2412a6038d9b80W8::v0.11.pre
  24:     0x7fde1ddbdfa0 - start_thread
  25:     0x7fde201bea09 - __clone
  26:                0x0 - <unknown>

[daimrod]

@huonw Ok, should I open a dedicated issue?

[huonw]

@daimrod it seems to be covered by #12116.