ICE: path.segments.len() >= 2

[sp3d]

use std::io::File::open;

fn main()
{
    open();
}

Compiling this program with rustc 0.11.0 (00cdd639a93ec1dcad85cebc52214eeba0441c93 2014-07-07 22:46:41 +0000) on Linux x86_64 gives the backtrace below:

task 'rustc' failed at 'assertion failed: path.segments.len() >= 2', /build/rust-git/src/rust/src/librustc/middle/typeck/check/mod.rs:4161

stack backtrace:
   1:     0x7f2a68a39080 - rt::backtrace::imp::write::h3a9330aff54dee28SMp
   2:     0x7f2a68a3e150 - <unknown>
   3:     0x7f2a6ab58b10 - unwind::begin_unwind_inner::hfe47ee6b84c3939ecZd
   4:     0x7f2a6ab58540 - unwind::begin_unwind_fmt::he04f3e5b01900555FWd
   5:     0x7f2a6b72bc00 - middle::typeck::check::instantiate_path::h1016c26f531c3d957Vh
   6:     0x7f2a6b7de710 - <unknown>
   7:     0x7f2a6b7de710 - <unknown>
   8:     0x7f2a6b7fbbb0 - middle::typeck::check::check_stmt::h79062ff9891ae6cbNmh
   9:     0x7f2a6b7b4680 - <unknown>
  10:     0x7f2a6b7afd60 - <unknown>
  11:     0x7f2a6b7afa90 - <unknown>
  12:     0x7f2a6b7a9d90 - middle::typeck::check::check_item::hf06283fc4609bdb5Efd
  13:     0x7f2a6b7af890 - middle::typeck::check::check_item_types::h9c1f790e4c79589fLHc
  14:     0x7f2a6b921810 - middle::typeck::check_crate::hfc3a3f5789d20299UNC
  15:     0x7f2a6bcda3e0 - driver::driver::phase_3_run_analysis_passes::hfcad747638c229814tq
  16:     0x7f2a6bcd6270 - driver::driver::compile_input::h99a1bc2d7a2f07d6Kgq
  17:     0x7f2a6bd8bc50 - <unknown>
  18:     0x7f2a6bd9fe40 - <unknown>
  19:     0x7f2a6bd9fb10 - <unknown>
  20:     0x7f2a6ae9e900 - <unknown>
  21:     0x7f2a6aba8c50 - rust_try
  22:     0x7f2a6ab556e0 - unwind::try::h24c27a0406a3ae46BNd
  23:     0x7f2a6ab553f0 - task::Task::run::h63d086c1974a8f2aXYc
  24:     0x7f2a6ae9e6d0 - <unknown>
  25:     0x7f2a6ab57940 - <unknown>
  26:     0x7f2a684bc060 - start_thread
  27:     0x7f2a6a827489 - __clone
  28:                0x0 - <unknown>

[edwardw]

The bug here seems not to be the assertion failure itself, but rather that use std::io::File::open; should be rejected. As a matter of fact, such a import is rejected for non-std module:

mod a {
    pub struct Foo;
    impl Foo { pub fn bar() {} }
}

fn main() {
    use a::Foo::bar;    // error: Cannot import from a trait or type implementation
    bar();
}

So it is at least inconsistent that use std::io::File::open; turns out to be legitimate.

[edwardw]

I can confirm that this bug has been fixed as a side effect of #15733. Basically, the assertion assert!(path.segments.len() >= 2); in rustc/middle/typeck/check/mod.rs will always hold now.

[alexcrichton]

Hurray! I think the tests over there suffice for this as well.