Internal Compiler Error running cargo doc

[AdamNiederer]

Hey, I'm trying to learn Rust. I have this code. It's not valid Rust, but it causes the compiler to throw an ICE.

struct Square {
    xcoord :i32,
    ycoord :i32,
    len :i32
}

impl Square {
    fn area() {
        len * len
    }
    fn diag() {
        len * 2.sqrt()
    }
    fn quadr() {
        match (xcoord, ycoord) {
            -_ =>
        }
    }
}

fn main() {
    /// Causes a crash
    /// Example usage:
    /// ```
    /// main() #-> Causes crash
    /// ```
    let q = vec!(3, 2, 1);
    let x = 5_000_000_i32;
    let y = &x;
    println!("Hello, world! {}", q.len());
    assert_eq!(q, [3, 2, 2]) // crashes
}

I ran cargo doc on it, and was told to file a bug report. Running cargo build or rustc main.rs does not cause the panic.

[adam@AdamsPC src]$ RUST_BACKTRACE=1 cargo doc
 Documenting kek v0.1.0 (file:///home/adam/kek)
main.rs:16:14: 16:15 error: unexpected token: `_`
main.rs:16             -_ =>
                        ^
main.rs:22:5: 22:37 error: attributes on non-item statements and expressions are experimental. (see issue #15701)
main.rs:22     /// Causes you to crash and shit
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.rs:23:5: 23:23 error: attributes on non-item statements and expressions are experimental. (see issue #15701)
main.rs:23     /// Example usage:
               ^~~~~~~~~~~~~~~~~~
main.rs:24:5: 24:12 error: attributes on non-item statements and expressions are experimental. (see issue #15701)
main.rs:24     /// ```
               ^~~~~~~
main.rs:25:5: 25:32 error: attributes on non-item statements and expressions are experimental. (see issue #15701)
main.rs:25     /// main() #-> Causes crash
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~
main.rs:26:5: 26:12 error: attributes on non-item statements and expressions are experimental. (see issue #15701)
main.rs:26     /// ```
               ^~~~~~~
error: internal compiler error: unexpected panic
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 'phase_2_configure_and_expand aborted in rustdoc!: 5', src/libcore/result.rs:746
stack backtrace:
   1:     0x7efe3d4fa4e0 - std::sys::backtrace::tracing::imp::write::h4c73fcd3363076f5
   2:     0x7efe3d507bdb - std::panicking::default_hook::_$u7b$$u7b$closure$u7d$$u7d$::h0422dbb3077e6747
   3:     0x7efe3d50777c - std::panicking::default_hook::haac48fa641db8fa2
   4:     0x7efe3d4cc70f - std::sys_common::unwind::begin_unwind_inner::h39d40f52add53ef7
   5:     0x7efe3d4ce7f8 - std::sys_common::unwind::begin_unwind_fmt::h64c0ff793199cc1b
   6:     0x7efe3d4f7cf1 - rust_begin_unwind
   7:     0x7efe3d5481af - core::panicking::panic_fmt::h73bf9d7e8e891a73
   8:     0x7efe3da9b42b - core::result::unwrap_failed::h52d645c697d2a555
   9:     0x7efe3da3637d - rustdoc::core::run_core::h5d51993c037675df
  10:     0x7efe3da31c08 - std::sys_common::unwind::try::try_fn::he5d0ca3afe34ca3c
  11:     0x7efe3d4f7c7b - __rust_try
  12:     0x7efe3d4f7c0d - std::sys_common::unwind::inner_try::h9eebd8dc83f388a6
  13:     0x7efe3da338ff - _<F as std..boxed..FnBox<A>>::call_box::h871bc6bfba8a323f
  14:     0x7efe3d505d74 - std::sys::thread::Thread::new::thread_start::h471ad90789353b5b
  15:     0x7efe36288473 - start_thread
  16:     0x7efe3d15d69c - clone
  17:                0x0 - <unknown>

error: Could not document `kek`.

To learn more, run the command again with --verbose.

Here's the rustc version. I pulled it down from the Arch repositories yesterday.

rustc 1.9.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-linux-gnu
release: 1.9.0

[est31]

I've been able to create two minimized examples:

fn main() {
    ///
    match (()) {
        -_ =>
    }
}

And second:

struct Square();

impl Square {
    fn quadr() {
        match (()) {
            -_ =>
        }
    }
}

[kennytm]

@est31 The two minimized examples don't cause ICE in nightly, while OP's does.

And the following ICE on both stable and nightly:

fn a() {
    /// crash
    let q = 1;
}

[adelarsq]

This code also crashes on both stable and nightly:

fn main() {
///
}

[zackmdavis]

This looks like it might be fixed now (ordinary error instead of ICE)?

$ cat src/main.rs 
fn main() {
    /// crash
    println!("{}", "Hello, world!");
}
$ cargo build
   Compiling example_project v0.1.0 (file:///home/ubuntu/example_project)
error: attributes on non-item statements and expressions are experimental. (see issue #15701)
 --> src/main.rs:2:5
  |
2 |     /// crash
  |     ^^^^^^^^^

error: aborting due to previous error

error: Could not compile `example_project`.

To learn more, run the command again with --verbose.
$ cargo doc
 Documenting example_project v0.1.0 (file:///home/ubuntu/example_project)
error: attributes on non-item statements and expressions are experimental. (see issue #15701)
 --> src/main.rs:2:5
  |
2 |     /// crash
  |     ^^^^^^^^^

error: Compilation failed, aborting rustdoc

error: Could not document `example_project`.

To learn more, run the command again with --verbose.
$

[nodakai]

@steveklabnik What does your glacier say about this?

[steveklabnik]

@nodakai it's not currently being tracked in glacier, sounds like it should be!

There's a ton of new ICEs that we haven't moved into glacier.

[Mark-Simulacrum]

This no longer ICEs today. E-needstest.